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The infectious diseases department of a hospital admitted a patient with nausea, liquid stool with mucus and blood streaks, fever, weakness. Dysentery was suspected. What method of laboratory diagnostics should be applied to confirm the diagnosis?
The laboratory diagnosis of infectious diseases involves two main approaches: one is the bacteriologic approach in which the organism is identified by staining and culturing the organism and the other is the immunologic approach in which the organism is identified by detection of antibodies against the organism in the patient’s serum. When cultures are negative (i.e bacteriologic method), then immunologic testing is commonly used.
Tuberculin (Mantoux) skin test: this test is done by intradermal injection of tuberculoprotein (tuberculin), purified protein derivative (PPD).
Type IV hypersensitivity reaction.
Immunization against tuberculosis is induced by injection of attenuated strains of bovine type of tubercle bacilli, Bacilli Calmette Guerin (BCG).
Stool culture test revealed in a 6-month-old bottle-fed baby the strain of intestinal rod-shaped bacteria of antigen structure 0-111. What diagnosis can be made?
Colienteritis - Antigen structure 0-111
The causative agents of colienteritis in children are O-groups -25; -26; -44; -55; -86; -91; -111; -114; -119; -125; -126; -127; -128; -141; -146 and others (they cause diseases in infants of the first month of life and in older infants). Most widely spread serotype is O-111:K58:H2
Pseudomonas produces blue green pigment; Yellow-green and red-brown pigments. Escherichia, proteas, Klebsiella, Azotobacter do not produce pigments.
Diphtheria bacteria (Corynebacterium diphtheria) is Gram positive, pleomorphic, often club-shaped rods and are arranged in palisades or in V (at an angle) or L-shaped formations. Media used for isolation are Tellurite agar & Lὄffler medium.
Lὄffler nutrient medium consists of coagulated serum & nutrient broth. Selective indicator medium containing tellurite are used in selective culturing. K tellurite is used to inhibit the accompanying flora.
A patient has been hospitalised with provisional diagnosis of botulism. What serological reaction should be used to reveal botulinum toxin?
Serological reactions or tests are carried out on a sample of blood serum which is used to detect serum antibodies or antibody-like substances that appear specifically in association with certain diseases. Types:
* Neutralization reaction: depend on capacity of antibody to neutralize infectious properties of infectious organisms. If the antibody is present to botulinum toxin, it confirms the diagnosis. It shows that the body has developed antibodies against the antigen (botulinum toxin). A patient who is not infected will not have the antibody.
* Precipitation reaction: takes place when the antibody and specifically prepared antigens are mixed together.
* Bordet-Gengou: specific for Bordetella pertussis.
In a village, a case of anthrax had been registered. Medical services began epidemiologically indicated specific prophylaxis of population against anthrax. What preparation was used for this purpose?
A 55-year-old patient with a characteristic rash, fever, dizziness has been admitted to a hospital. He has been provisionally diagnosed with typhus. No similar cases have been reported. In his youth (15 years old) the patient suffered typhus in a boarding school. What disease is it?
Epidemic typhus (human body louse) – Rickettsia prowazekii, can remain latent and reactivate months or years in an infected patient, with symptoms similar to or even identical to the original attack of typhus, including a rash that starts centrally and spreads out, sparing palms and soles. This delayed relapse of epidemic typhus – Brill’s disease.
In one of Polessye regions there was an outbreak of helminthiasis manifested by cramps and facial edmata. The developed preventive measures in particular included ban for eating infested pork even after heat processing. What helminthiasis was the case?
A patient who has recently arrived from an endemic area presents with elevated body temperature, headache, chills, malaise, that is with the symptoms which are typical for a common cold. What laboratory tests are necessary to prove or to disprove the diagnosis of malaria?
For malaria diagnosis, microscopy of blood smears, utilizing blood films; it is the most economic, preferred and reliable diagnosis of malaria because each of the 4 major parasite species has distinguishing characteristics (Plasmodium vivax, ovale, falciparum and malariae).
An outbreak of an intestinal infection occurred in a kindergarten on the eve of New Year holidays. Bacteriological examination of patients’ faeces didn’t reveal any pathogenic bacteria. Electron microscopy revealed roundish structures with clear outer edges and a thick core resembling a wheel. Specify the most likely causative agent of this infection:
Rotavirus is the most important global cause of infantile gastroenteritis, is a segmented dsRNA virus (a reovirus). Major cause of acute diarrhea during winter, especially in day care centers, kindergartens. ‘Roundish structure like a wheel’
Adenovirus causes febrile pharyngitis (sore throat), acute hemorrhagic cystitis, pneumonia, conjunctivitis (pink eye).
Coxsackievirus (hand-foot-mouth disease): oval-shaped vesicles on palms and soles; vesicles and ulcers in oral mucosa.
E. coli and Proteus vulgaris are bacteria; from the question, bacteriological examination of patient’s faeces didn’t reveal any pathogenic bacteria.
A smear of streptobacillus preparation stained by Ozheshko method has been studied microscopically with oil immersion. What structural feature of the bacteria has been studied?
At a bacteriological laboratory animal skins are analyzed by means of Ascoli precipitation test. What is detected if the reaction is positive?
Ascoli’s test or reaction is for detection of Anthrax antigens. Positive Ascoli’s test confirms the diagnosis, using an anthrax antiserum.
A 12-year-old boy has been hospitalized for suspected food poisoning. The fecal samples were inoculated on the Endo agar, which resulted in growth of a large number of colorless colonies. What microorganism is most likely to be EXCLUDED from the list of possible causative agents of the disease?
Bacteriological examination of purulent discharges from the urethra revealed some gram-negative bean- shaped bacteria located in the leukocytes. They can be identified as the causative agent of the following disease:
Gonorrhea is caused by Neisseria gonorrhoeae. Its often intracellular (within neutrophils), gram-negative diplococci. It is sexually or perinatally transmitted.
Syphillis is caused by Treponema pallidum(spirochetes); Chancroid is caused by Haemophilus ducreyi; Trichonomoniasis is caused by trichomonas vaginalis; Veneral lymphogrnaulomatosis is caused by Chlamydia trachomatis (L1-L3). They are all sexually transmitted.
Specific identification of the gonococcus can be made either by its fermentation of glucose (but not maltose) or by fluorescent-antibody staining.
A hospitalized patient bitten by a rabid animal has an avulsive wound of shin. What kind of vaccine must be given to prevent rabies?
A smear of sputum from the patient with suspected lobar pneumonia was stained with the use of the following stains and reagents: solution of gentian violet, Lugol’s solution, 96o alcohol, water magenta. What staining method was applied in this case?
A patient has severe catarrhal symptoms. Material growth on Bordet-Gengou agar showed mercury-drop-like colonies. Examination of the blood smears revealed some small ovoid gram-positive bacilli sized 1-3 microns. What microorganisms were isolated?
Bordet-Gengou agar and Regan-Lowe medium: media for isolation of Bordetella pertussis.
Tellurite agar/Lὄffler medium – corynebacterium diphtheria
Lὄwenstein-Jensen agar – M.tuberculosis; Eaton agar – M. pneumonia
Thayer-Martin agar – Neisseria meningitides/gonorrhoeae
Brucella agar – Brucella
The laboratory for especially dangerous infections conducts microscopic examination of pathological material from a patient with suspected plague. The sample was stained by Burri-Gins technique. What property of the causative agent can be identified by this technique?
Burri-Gins technique – capsule formation
Ozheshko – spores
Hepatitis B virus (HBV): incubation period 30-180days; it’s a DNA virus. Transmission: sexual, blood, vertical transmission via pregnancy and breast feeding. Primarily spread by blood, accidental needle sticks. HBV diagnosis is accomplished by testing for a series of serological markers of HBV. Nucleic acid testing for HBV-DNA is increasingly being used to quantify HBV viral load and measure the effectiveness of therapeutic agents.
A miner consulted a physician about the appearance of body rash followed by a loss of appetite, bloating, duodenal pain, frequent bowel movements, dizziness. Ovoscopic probes of feces and duodenal contents revealed some eggs covered with a transparent membrane through which 4-8 germinal cells could be seen. What disease is likely to have occurred in the patient?
Ancylostomiasis also known as Miner’s anemia is caused by Ancylostoma (hookworm). Larvae penetrate the body and produces an intestinal infection causing anemia by sucking blood from intestinal walls. Findngs: intestinal bleeding, abdominal pains, anemia, severe diarrhea and malnutrition. This is consistent with the symptoms in the question.
In the surgical ward, the dressing material was undergoing sterilization in an autoclave. Through an oversight of a nurse the mode of sterilization was changed and the temperature in the autoclave reached only 100oC instead of the due 120oC . What microorganisms can stay viable under these conditions?
Some bacteria can form spores at the end of the stationary phase when nutrients are limited. Spores are highly resistant to heat and chemicals. Spores have diplocinic acid in their core; have no metabolic activity. To kill spores, we must autoclave (as is done to surgical instruments) by steaming at 121oc for 15 minutes. Examples of species that form spores and disease caused is Clostridum botulinum – Botulism; Bacillus anthracis – Anthrax; Clostridium tetani – Tetanus; Coxiella burnetti – Q fever. Amongst the two groups of spore forming microorganisms, Clostridium is more heat resistant than Bacillus. Temperatures of 110oc will kill most Bacillus spores within a short time. In the case of Clostridium, temperatures of up to 121o c are needed to kill the spores within a relatively short time.
Typical manifestations of food poisoning caused by C. botulinum are double vision, abnormal functioning of the swallowing and breathing. These symptoms develop as a result of:
Clostridium botulinum is a gram positive rod (bacillus). They secrete botulinum toxin (an exotoxin).
Findings: flaccid paralysis, floppy baby; toxin prevents release of stimulatory (acetylcholine) signals at neuromuscular junctions → flaccid paralysis. Exotoxin is secreted from certain species of gram positive and gram negative bacteria. Its toxoids are used as vaccines. Inhibition of the release of stimulatory neurotransmitters can lead to the symptoms listed in the question.
A patient consulted a physician about chest pain, cough, fever. Roentgenography of lungs revealed eosinophilic infiltrates which were found to contain the larvae. What kind of helminthiasis are these presentations typical for?
Ascaris lumbricoides (giant roundworm) is the causative agent of Ascariasis. Transmission: fecal-oral; eggs are visible in faeces under microscope. Some patients may have pulmonary symptoms or neurological disorders during migration of the larvae. A bolus of worms may obstruct the intestine; migrating larvae may cause pneumonitis and eosinophilia.
A patient consulted a dentist about limited mouth opening (trismus). He has a history of a stab wound of the lower extremity. What infection may cause these symptoms?
Tetanus is caused by Clostridium tetani that secretes a toxin called tetanospasmin. Findings: spasticity, risus sardonicus (raised eyebrows and open grin) and lockjaw (trismus); toxin prevents release of inhibitory (GABA and glycine) neurotransmitters from Renshaw cells in spinal cord. It can be prevented with tetanus vaccine.
A female patient consulted a physician about digestive disorder, extended abdominal pain. Examination revealed drastic decrease in hemoglobin concentration. It is known from the anamnesis that while living in the Far East the patient used to eat freshly-salted caviar. Some relatives living with her had the similar condition. What is the most likely diagnosis?
· Diphyllobothrium latum causes diphyllobothriasis. A fish tapeworm. In contrast to the other cestodes, which have suckers , the scolex of D. latum has two elongated sucking grooves by which the worm attaches to the intestinal wall. Infection by D. latum causes little damage in the small intestine. In some individuals, megaloblastic anemia occurs as a result of vitamin B12 deficiency caused by preferential uptake of the vitamin by the worm. Transmission: ingestion of larvae from raw freshwater fish. Caviar is prepared from fish.
· Echinococcus granulosus causes Echinococcosis. It is composed of a scolex and only 3 proglottids, making it one of the smallest tapeworms. The scolex has a circle of hooks and 4 suckers similar to Taenia solium. Dogs are the most important definitive hosts. The intermediate hosts are usually sheep. Humans are almost always dead-end intermediate hosts. Transmission: ingestion of eggs from dog faeces. Disease – hydatid cysts in liver causing anaphylaxis if antigens released.
· Taeniasis: there are two important human pathogens in the genus Taenia: T. solium (pork tapeworm) and T. saginata (beef tapeworm)
· Trichiniasis (Trichinosis) is caused by Trichinella spiralis (nematode- roundworm). Transmission: fecal-oral; undercooked meat (especially pork). A few days after eating undercooked meat, usually pork, the patient experiences diarrhea followed by 1-2weeks later by fever, muscle pain, periorbital edema and eosinophilia.
· Ascaridiasis (Ascariasis) caused by Ascaris lumbricoides (giant roundworm). The major damage occurs during larval immigration rather than from the presence of the adult worm in the intestines. The principal sites of tissue reaction are the lungs, where inflammation with an eosinophilic exudates occurs in response to larval antigens. Ascaris pneumonia with fever, cough and eosinophilia can occur with a heavy larval burden.
There are two medically important genera of gram positive cocci: staphylococcus and streptococcus. Microscopically, staphylococci appear in grape-like clusters, whereas streptococci are in chains or pairs. Streptococcus pneumonia causes pneumonia, bacteremia, meningitis and infections of the upper respiratory tract. Pneumococci are gram positive lancet-shaped cocci arranged in pairs (diplococci) or short chains.
The term “lancet-shaped” means that the diplococci are oval with somewhat pointed ends rather than being round).
Klebsiella and the Neisseria genus are gram negative.
The contents of vesicles that appeared on the mucous membrane of a patient with variola was sent to a virological laboratory. Which of the listed changes were revealed during the smear microscopy?
The pox virus family includes 3 viruses of medical importance: smallpox virus, vaccinia virus and molluscum contagiosum virus (MCV). Poxviruses are the largest and most complex viruses. The smallpox virus is also called variola virus. It is the agent of smallpox, the only disease that has been eradicated from the face of the earth. Eradication is due to the vaccine.
Smallpox virus is transmitted via respiratory aerosol or by direct contact with virus either in the skin lesions or on fomites such as bedding. The virus replicates in the cytoplasm which form inclusion bodies (paschen) stainable in the cytoplasm of infected cells.
Negri bodies are inclusion bodies in Rabies; Guanieri bodies are inclusion bodies in vaccinia, variola (Note: vaccinia virus is nonpathogenic for humans); but paschen bodies is specific and pathognomonic for variola or smallpox.
Serological diagnostics of infectious diseases is based upon specific interaction with antigens. Specify the serological reaction that underlies adhesion of microorganisms when they are affected by specific antibodies in presence of an electrolyte:
1. Agglutination is commonly used as a method of identifying specific bacterial antigens and in turn the identity of such bacteria. Because the clumping reaction occurs quickly and is easy to produce, agglutination is an important technique in diagnosis. It is the clumping of cells such as bacteria or red blood cells in the presence of an antibody or complement. The antibody or other molecule binds multiple particles and joins them creating a large complex. The antibody (agglutinin) and antigen (agglutinogen) take part in the agglutination reaction. Their interaction takes place in definite quantitative proportions and in the presence of an electrolyte (0.85% NaCl solution). In mechanism and outer manifestation, the agglutination reaction is similar to the precipitin reaction. Both reactions are accompanied by the production of visible precipitates of antigen with the difference that in the agglutination reaction microbial bodies serve as the antigen, whereas in the precipitin reaction (precipitation reaction) the antigen is the product of the breakdown of microbial bodies, very minute particles of dissolved antigens requiring a large amount of antibodies for complete interaction.
In order to determine toxigenicity of diphtheria bacilli a strip of filter paper impregnated with antitoxic diphtherial serum was put on the dense nutrient medium. There were also inoculated a microbial culture under examination and a strain that is known to be toxigenic. If the microbial culture under examination produces exotoxin, this will result in formation of:
1. The presence of the antitoxic diphtheria serum (antibody) and the exotoxin (antigen) cause an interaction between them leading to the production of antigen-antibody complexes producing precipitates (precipitin lines) on the strip of filter paper. We will have a precipitin ring if a tube were to be used instead of a filter paper.
A patient underwent esophagogastroduodenoscopy. Analysis of the biopsy material enabled doctors to diagnose him with helicobacteriosis. What property of the bacteria found in this patient had to be obligatory taken into account during their cultivation?
Helicobacter pylori causes gastritis and peptic ulcers. Infection with H. pylori is a risk factor for gastric carcinoma and is linked to mucosal-associated lymphoid tissue (MALT) lymphoma.
It is a gram negative, flexibacteria, oxidase positive, microaerophilic, motile and the only species in the Helicobacter genus to have multiple unipolar – sheathed flagella. Microaerophiles need O2 because they cannot ferment or respire anaerobically. However, they are poisoned by high concentrations of O2. They gather in the upper part of the test tube but not the very top. CO2 is essential for initial growth of H. pylori in liquid media (microaerophilic property). They produce urease, so it’s a diagnostic tool and not a necessary consideration for cultivation (culture medium).
There was a record of some anthrax cases among animals in a countryside. The spread of disease can be prevented by means of immunization. What kind of vaccine should be used?
A bacteriological laboratory received sputum sample of a patient suffering from tuberculosis. Bacterioscopic examination of smears and detection of tuberculosis bacillus can be realized by one of enrichment methods that involves processing of sputum only with solution of caustic soda. What is this method called?
Vibrio cholera is the cause of cholera. It is curved, comma-shaped, gram negative rods.
It is transmitted by fecal contamination of water and food, primarily from human sources. Clinically, watery diarrhea in large volumes is the hallmark of cholera. There are no red blood cells or white blood cells in the stool. Rice-water stool is the term often applied to the non-bloody effluent. Grows in an alkaline media. Dark-field and phase contrast microscopy have been used for screening fecal specimens for the presence of V. cholera. With these techniques, liquid stools are microscopically examined for the presence of organisms with typical darting (“shooting star”) mobility [analogous to ‘hanging drop’].
During examination of a patient a dentist revealed a lot of \"white spots zones of enamel demineralization. What microorganisms take part in the development of this process?
Streptococcus mutans are gram positive cocci shaped bacteria. They are facultative anaerobes and a major contributor of tooth decay. It’s a cariogenic microorganism that breaks down sugar for energy and produces an acidic environment which demineralizes the superficial structure of the tooth. The result of the conversion disintegrates the coating of the tooth then later dissolves the calcium molecule creating a hole. Transmission of S. mutans can be found in people of all ages although it is more common for infants and children. Since every human has bacteria in their mouth, the only prevention is to lessen the impact of acid fermentation by practicing adequate oral hygiene.
A 4 year old child presents with general weakness, sore throat and deglutitive problem. After his examination a doctor suspected diphtheria and sent the material to the bacteriological laboratory. In order to determine the diphtheria causative agent the material should be inoculated into the following differential diagnostic medium:
Diphtheria bacteria (Corynebacterium diphtheria) is Gram positive, pleomorphic, often club-shaped rods and are arranged in palisades or in V (at an angle) or L-shaped formations. Media used for isolation are Tellurite agar & Lὄffler medium. Lὄffler nutrient medium consists of coagulated serum & nutrient broth. Selective indicator medium containing tellurite are used in selective culturing. K tellurite is used to inhibit the accompanying flora.
Sanitary bacteriological research on water by the membrane filter method revealed two red colonies on a membrane filter (Endo agar) through which 500 ml of analyzed water were passed. Calculate the coli index and coli titer of the analyzed water:
1. 4 and 250
Coli titer is the smallest amount of water where 1 E.coli is present.
Coli index is the amount of E. coli in 1 liter of water.
2 E.coli - 500ml
1 E.coli - ?
? = 250
Therefore, Coli titer = 250
1 liter of water = 1000ml
2 E. coli - 500ml
? - 1000ml (1L)
? = 4
Therefore, Coli index = 4
Coliform index (Coli index) and Coli titer are used to rate the purity of water, soil and air based on the count of fecal bacteria by testing for coliforms especially the well known Escherichia coli (E. coli).
A 55-year-old male patient was hospitalised to a surgical clinic for suspected septicemia. What material should be taken for analysis?
1. Septicemia is a clinical form of sepsis that indicates bacteria in the blood. In cases of septicemia, blood is inoculated into glucose broth (sugar broth) and the isolated pure culture is tested for its hemolytic properties. Glucose is a sugar that some bacteria can use because of an enzyme that begins the breakdown of this compound.
A man died from an acute infectious disease accompanied by fever, jaundice, haemorrhagic rash on the skin and mucous membranes as well as by acute renal insufficiency. Histological examination of renal tissue (stained by Romanovsky-Giemsa method) revealed some convoluted bacteria looking like C and S letters. What bacteria were revealed?
Three genera of spirochetes cause human infection:
·Treponema: causes syphilis and the nonveneral treponematoses. Morphology – thin, tight spirals
· Borrelia: causes lyme disease and relapsing fever. Morphology – large and loosely coiled
·Leptospira: causes leptospirosis. Morphology – thin, tight spirals
A culture of monkey cells (Vero) and a group of mouse sucklings were infected with an inoculum taken from a child with provisional diagnosis \"enterovirus infection\". There was no cytopathic effect on the cell culture but mouse sucklings died. What enteric viruses might have caused disease of this child?
1. Picornaviruses are small nonenveloped viruses composed of an icosahedral nucleocapsid and a single-stranded RNA genome (ssRNA). Picornavirus family ncludes two groups of medical importance: the enteroviruses and rhinoviruses. Among the major enteroviruses are the poliovirus, coxsackieviruses, echoviruses and hepatitis A virus.
Coxsackieviruses are named for the town of Coxsackie, NY, where they were first isolated. Coxsackievirus cause a variety of diseases. Coxsackieviruses are divided into group A and group B viruses based on early observations of their pathogenicity in newborn mice (mouse sucklings). Group A causes flaccid paralysis while group B causes spastic paralysis. Coxsackie A virus causes paralysis and death of the mice; coxsackie B causes less severe infection in the mice.
Microscopic examination of a gram- stained scrape from a patient’s tongue revealed oval, round, elongated chains of dark-violet gemmating cells. What disease can be caused by this causative agent?
1. There are two types of fungi: yeasts and molds. Yeasts grow as single cells that reproduce by asexual budding (gemmating). Molds grow as long filaments (hyphae) and form a mat (mycelium). Candida albicans is an oval yeast with a single bud. It is part of the normal flora of mouth (oral cavity), mucous membranes of upper respiratory, gastrointestinal and female genital tracts. In tissues it may appear as yeast or as pseudohyphae. Pseudohyphae are elongated yeasts (elongated chains) that visually resemble hyphae but are not true hyphae. Candida albicans causes thrush, vaginitis, esophagitis and chronic mucocutaneous candidiasis.
1. Balantidium coli causes balantidiasis. It is the only ciliated protozoan that causes human disease i.e. diarrhea. Domestic animals, especially pigs are the main reservoir for the organism and humans are infected after ingesting the cysts in food or water contaminated with animal or human faeces. Diagnosis is made by finding large ciliated trophozoites or large cysts with a characteristic V-shaped nucleus in the stool. The trophozoites excyst in the small intestine, travel to the colon (large intestine) and by burrowing into the wall cause an ulcer similar to that of Entamoeba histolytica.
A male patient has been diagnosed with gastric ulcer. Bacteriological examination of biopsy material from the affected part of stomach revealed small colonies of gram-negative, oxide reductase-positive flexibacteria that grew on the chocolate agar on the fifth day. Which of the following microorganisms is the most likely causative agent?
1. Some bacteria can form spores at the end of the stationary phase when nutrients are limited. Spores are highly resistant to heat and chemicals. Have dipicolinic acid in their core and they have no metabolic activity. Examples of species that form spores and the disease they cause:
Gas gangrene/Food poisoning
A pregnant woman was registered in an antenatal clinic and underwent complex examination for a number of infections. Blood serum contained IgM to the rubella virus. What is this result indicative of?
ARVI – Acute respiratory viral infection. High IgM level usually indicate an acute or primary infection because, it is the first antibody to appear in response to initial exposure to an antigen. Secondary or reinfection show an increase in IgG. IgM antibodies appear early in the course of an infection, this makes it useful in the diagnosis of infectious diseases. Demonstrating IgM antibodies in a patient’s serum indicates recent infection or in a neonate’s serum, it indicates intrauterine infection.
After inoculation of the material obtained from the pharynx of an angina patient onto the blood-tellurite agar, grey colonies could be observed. They were 4-5 mm in diameter, radially striated (in form of rosettes). Microscopical examination revealed gram-positive bacilli with clavate swollen ends arranged in form of wide-spread fingers. Identify these microorganisms:
Examination of a patient with pustular skin lesions allowed to isolate a causative agent that forms in the blood agar roundish yellow middle-sized colonies surrounded by haemolysis zone. Smears from the colonies contain irregular- shaped clusters of gram-positive cocci. The culture is oxidase- and catalase-positive, ferments mannitol and synthesizes plasmocoagulase. What causative agent was isolated?
Staphylococcus aureus is a gram positive cocci that appear in clusters. It causes:
· Inflammatory disease like skin infections, organ abscesses
· Toxin mediated disease like the toxic shock syndrome (TSST-1)
· MRSA (methicillin-resistant Staphylococcus aureus) infection.
Staphylococcus aureus is a β-hemolytic bacteria i.e. they form a clear zone of hemolysis on blood agar.
They are catalase and coagulase (plasmocoagulase) positive.
The diagnosis of localized infections depends on gram staining and culture of the discharge which is then viewed under the microscope. In men, the finding of gram negative diplococci within polymorphonuclear leukocytes in a urethral discharge specimen is sufficient for diagnosis. But in women, the use of gram stain alone can be difficult to interpret, therefore cultures should be done. The specimen is cultured on Thayer-Martin medium. Gram stains on cervical specimens can be falsely positive because of the presence of gram negative diplococci in the normal flora and can be falsely negative because of the inability to see small number of gonococci when using the oil immersion lens (in oil immersion microscope).
Enterobius vermicularis causes pinworm infection (enterobiasis).
The life cycle is confined to humans. The infection is acquired by ingesting the worm eggs. Perianal pruritus is the most prominent symptom. Pruritus is thought to be an allergic reaction to the presence of either the adult female or the eggs. Scratching predisposes to secondary bacterial infection. In Laboratory diagnosis, the eggs are recovered from perianal skin by using the scotch tape technique and can be observed microscopically. Unlike those of other intestinal nematodes, these eggs are not found in the stools. There are no means of prevention. It is treated with mebendazole.
Researchers of a bacteriological laboratory examine tinned meat for botulinic toxin. For this purpose a group of mice was injected with an extract of the material under examination and antitoxic antibotulinic serum of A, B, E types. A control group of mice was injected with the same extract but without antibotulinic serum. What serological reaction was applied?
During the repeated Widal’s agglutination test it was noticed that the ratio of antibody titers and O-antigens S.typhi in the patient’s serum had increased from 1:100 to 1:400. How would you interpret these results?
In many tests in which antibodies are detected in the patient’s serum, an acute and convalescent serum sample is obtained and at least a fourfold increase in titer (1:100 – 1:400) between the acute and convalescent samples must be found for a diagnosis to be made. The reason these criteria are used is that the presence of antibodies in a single sample could be from a prior infection, so a significant (fourfold or greater) increase in titer is used to indicate that this is a current infection. IgM antibody can also be used as an indicator of current infection.
A patient has acne on his face. Microspcopic examination of scrapings from the affected areas revealed living porrect vermiform arthropoda 0,2-0,5 mm large with four pairs of short extremities in the front part of their bodies. What is the laboratory diagnosis?
Demodex folliculorum and Demodex brevis: they are species of face mite. When large numbers of D. folliculorum are found in humans, the infestation is known as Demodicosis. D. folliculorum is semi-transparent elongated organism consisting of a head, neck, body and tail. As an adult, it can measure 0.1-0.4mm in length and possess 4 pairs of short legs near its head and neck region. In the course of time, because of chronic progradient course, pathologic process results in formation of inflammatory nodes, infiltrates and persistent vascular dilatation. Hyperemia of facial skin and eruptions are also seen.
Among junior children of an orphanage an outbreak of intestinal infection with signs of colienteritis was registered. In order to identify isolated causative agent it is necessary to:
Considering the options, the most specific for diagnosis is study antigenic properties of the causative agent because; Reactions of antigens and antibodies are highly specific. An antigen will react only with antibodies elicited by itself or by a closely related antigen. Because of the great specificity, reactions between antigens and antibodies are suitable for identifying one (either the antibody or antigen) by using the other. To identify isolated causative agent, it is necessary to detect antigen in the patient’s specimen. Use known antibody to detect presence of antigens of the organisms.
Immunofluorescence (fluorescent antibody): fluorescent dyes e.g. fluorescein and rhodamine, can be covalently attached to antibody molecules and made visible by UV light in the fluorescence microscope. The immunofluorescence reaction is DIRECT when known labeled antibody interacts directly with unknown antigen and INDIRECT when a two-stage process is used e.g. known antigen is attached to a slide, the patient’s serum (unlabelled) is added and the preparation is washed; if the patient’s serum contains antibody against the antigen, it will remain fixed to it on the slide and can be detected on addition of a fluorescent dye-labelled antibody to human IgG and examination by UV microscopy. The indirect test is often more sensitive than direct immunofluorescence, because more labeled antibody adheres per antigenic site. Immunofluorescence staining of cells obtained from the patient or of cells infected in culture can provide a rapid and specific diagnosis.
A 7 year old child often suffers from streptococci angina. Doctor suspected development of rheumatism and administered serological examination. The provisional diagnosis will be most probably confirmed by presence of antibodies to the following streptococci antigen:
Group A streptococci produce 5 important toxins and hemolysins as follows:
· Erythrogenic toxin: causes the rash of scarlet fever.
· Streptolysin O is a hemolysin that is inactivated by oxidation (oxygen-labile). It is antigenic, and antibody to it (ASO – antistreptolysin O) develops after group A streptococcal infections. The titer of ASO antibody can be important in the diagnosis of rheumatic fever.
· Streptolysin S is a hemolysin that is not inactivated by oxygen (oxygen-stable). It is not antigenic.
· Pyogenic exotoxin A is the toxin responsible for most cases of streptococcal toxic shock syndrome.
· Exotoxin B is a protease that rapidly destroys tissue and is produced in large amounts by the strains of S. pyogenes, the so-called “flesh eating” streptococci that cause necrotizing fascitis.
Bordetella pertussis causes whooping cough (pertussis). B. pertussis is a gram negative bacillus (rod). It is a pathogen only for humans, transmitted by airborne droplets produced during the severe coughing episodes. In lab diagnosis, the organism can be isolated from nasopharyngeal swabs taken during the paroxysmal stage. Bordet-Gengou medium used for this purpose contains a high percentage of blood (20-30%) to inactivate inhibitors in the agar.
Microscopical examination of a microbial culture revealed fusiform spore-forming microorganisms that get violet-blue Gram’s stain. What microorganisms were revealed?
There are four medically important clostridium species: Clostriidum tetani (causes tetanus), Clostridium botulinum (causes botulism), Clostridium perfringes (causes either gas gangrene or food poisoning) and Clostridium difficile. All Clostridia are anaerobic, spore-forming, gram positive rods (violet-blue gram’s stain).
Material taken from a patient with provisional diagnosis \"influenza\" was referred to a laboratory. For virological examination the hemadsorption reaction was applied. This reaction can be applied for detection of the following viruses:
Hemadsorption i.e. attachment of erythrocytes to the surface of virus-infected cells. This technique is limited to viruses with a hemagglutinin protein on their envelope such as mumps, parainfluenza and influenza viruses.
Bacteriological examination of purulent discharges from the urethra revealed gram-negative bacteria looking like coffee beans. They were localized in the leukocytes and could decompose glucose and maltose to acid. These are the causative agents of the following disease:
Study of bacteriological sputum specimens stained by the Ziel-Neelsen method revealed some bright-red acid-resistant bacilli that were found in groups or singularly. When inoculated onto the nutrient media, the signs of their growth show up on the 10-15 day. These bacteria relate to the following family:
A bacteriological laboratory has received smears from the sputum of a patient with a chronic pulmonary disease. Microscopical examination of the smears stained by the Ziehl-Neelsen technique revealed red bacilli. What property of the tuberculosis bacillus has shown itself?
A woman delivered a dead child with multiple developmental defects. What protozoan disease might have caused the intrauterine death?
ToRCHeS infections: Toxoplasma gondii; Rubella; Cytomegalovirus; HIV; Herpes simplex virus-2; Syphilis. These are microbes that may pass from mother to fetus. Transmission is transplacental in most cases or via delivery. Toxoplasma gondii causes toxoplasmosis. It is transmitted from cat faeces or ingestion of undercooked meat. Congenital infection of the fetus occurs only when the mother is infected during pregnancy. Congenital infection can result in abortion, stillbirth or neonatal disease with encephalitis, chorioretinitis and hepatosplenomegaly.
Retrospective diagnostics of bacterial dysentery involved serological analysis of blood serum intended for determination of Shigella antibody titre. Which of the following reactions should be applied for this purpose?
Hemagglutination tests: many viruses clump red blood cells from one species or another (active hemagglutination). This can be inhibited by antibody specifically directed against the virus (hemagglutination inhibition) and can be used to measure the titer of such antibody. Red blood cells (RBCs) also can absorb many antigens and when mixed with matching antibodies, they will clump (this is known as passive hemagglutination, because the Red cells are passive carriers of the antigen).
During the regular sanitary-epidemiological inspection of a pharmacy, the bacteriological analysis of air was performed. The air was found to have bacilli, yeast fungi, hemolytic streptococci, micrococci. Which of the detected microorganisms indicate the direct epidemic danger?
Group A β-hemolytic streptococci (Streptococcus pyogenes) are one of the most important human pathogens. They are the most frequent bacterial cause of pharyngitis and a very common cause of skin infections. They adhere to pharyngeal epithelium via pili covered with lipoteichoic acid and M protein. The mode of spread of the hemolytic streptococcus is complex and dependent on a number of interrelated factors such as the presence of carriers, droplets, droplet nuclei and dust; viability, infectivity and virulence of airborne streptococci; ventilation; ultraviolet radiation; and population density and susceptibility. In general, group A streptococci are spread by contact. Such contact may be direct as the transfer of Streptococci from the nose to the hands to the surgical wound or airborne. Studies have shown that they produce direct epidemic danger.
A 65-year-old man has purulent abscess on his neck. Analyses revealed a culture of gram-positive cocci with plasmocoagulase activity. This culture relates most likely to:
Staphylococcus aureus is a gram positive cocci that appear in clusters. It causes:
Staphylococcus aureus is a β-hemolytic bacteria i.e. they form a clear zone of hemolysis on blood agar. They are catalase and coagulase (plasmocoagulase) positive.
Blood of a patient with presumable sepsis was inoculated into sugar broth. There appeared bottom sediment. Repeated inoculation into blood agar caused growth of small transparent round colonies surrounded by hemolysis zone. Examination of a smear from the sediment revealed gram-positive cocci in form of long chains. What microorganisms are present in blood of this patient?
1. There are two medically important genera of gram positive cocci: Staphylococcus and Streptococcus. They are nonmotile and do not form spores. Microscopically, staphylococci appear in grape-like clusters and produce catalase (i.e. catalase positive), whereas streptococci are in chains and do not produce catalase (i.e. catalase negative). One of the most important characteristics for identification of streptococci is the type of hemolysis they manifest (alpha-hemolytic and beta hemolytic). Alpha-hemolytic (α-hemolytic) streptococci form a green zone around their colonies as a result of incomplete lysis of RBCs in the agar. Beta-hemolytic (β-hemolytic) streptococci form a clear zone around their colonies because complete lysis of the RBCs occurs. Β-hemolysis is due to the production of enzymes (hemolysins) called streptolysin O and streptolysin S. Some streptococci are non-hemolytic (gamma-hemolysis).
In order to estimate toxigenity of diphtheria agents obtained from patients the cultures were inoculated on Petri dish with nutrient agar on either side of a filter paper strip that was put into the centre and moistened with antidiphtheric anti-toxic serum. After incubation of inoculations in agar the strip-like areas of medium turbidity were found between separate cultures and the strip of filter paper. What immunological reaction was conducted?
1. Precipitation in agar(Precipitation gel reaction): antibody is incorporated into agar and antigen is inoculated i.e. antibody is the antidiphtheric antitoxic serum and the antigen is the diphtheria agent, inoculated in the nutrient agar. Antigen and antibody are placed in different wells in agar and allowed to diffuse and form concentration gradients. Where optimal proportions occur, lines of precipitate form. This method indicates whether antigens are identical, related but not identical or not related.
Areas of medium turbidity indicate where the antibody specific for the antigen have cross-linked.
A patient with clinical signs of encephalitis was delivered to the infectious diseases hospital. Anamnesis registers a tick bite. Hemagglutination-inhibition reaction helped to reveal antibodies to the causative agent of tick-borne encephalitis in the dilution 1:20 which is not diagnostic. What actions should the doctor take after he had got such result?
Tick-borne encephalitis is a disease caused by a flavivirus that affects the central nervous system. It is transmitted through the bite of an infected tick. A serum sample is obtained as soon as a viral etiology is suspected (acute phase) and a second sample is obtained 10-14days later (convalescent phase). If the antibody titer in the convalescent phase serum sample is at least fourfold higher than the titer in the acute phase serum sample, the patient is considered to be infected. For example, if the titer in the acute phase serum sample is ¼ and the titer in the convalescent phase serum sample is 1/16 or greater, the patient has had a significant rise in antibody titer and has been recently infected. If however, the titer in the convalescent phase serum is 1/8, this is not a significant rise (not diagnostic) and should not be interpreted as a sign of recent infection, but a second sample is obtained 10-14days later.
A 40 year old man noticed a reddening and an edema of skin in the area of his neck that later developed into a small abscess. The incised focus is dense, yellowish-green. The pus contains white granules. Histological examination revealed drusen of a fungus, plasmatic and xanthome cells, macrophages. What type of mycosis is the most probable?
Actinomycetes are true bacteria (related to Corynebacteria and Mycobacteria), but they form long, branching filaments that resemble the hyphae of fungi. They are gram positive but some (such as Nocardia asteroids) are also weakly acid-fast. There are two medically important organisms, Actinomyces israelii and Nocardia asteroids. Actinomyces israelii causes Actinomycosis (abscess with draining sinuses). Strictly anaerobic; it forms part of the normal flora of the oral cavity. Actinomycosis appears as a hard, nontender swelling that develops slowly and eventually drains pus through sinus tracts. In about 50% of cases, the initial lesion involves the face and neck.
Skin of a man who died from cardiac insufficiency has an eruption in form of spots and specks. There are also bedsores in the area of sacrum and spinous vertebral processes. Microscopical examination of CNS, skin, adrenal glands revealed in the vessels of microcirculatory bed and in small arteries destructive-proliferative endothrombovasculitis with Popov’s granulomas; interstitial myocarditis. What diagnosis corresponds with the described picture?
Rickettsiae are obligate intracellular parasites because they are unable to produce sufficient energy to replicate extracellularly. They are the agents of typhus, spotted fevers and Q fever. The typical lesion caused by the rickettsiae is a vasculitis (endothrombovasculitis), particularly in the endothelial lining of the vessel wall where the organism is found. Damage to the vessels of the skin results in the characteristic rash and in edema, and hemorrhage caused by increased capillary permeability. Rickettsia rickettsii causes Rocky Mountain spotted fever. In rickettsioses, especially in louseborne typhus, which is caused by Rickettsia prowazekii and in Rocky Mountain spotted fever, which is caused by R. rickettsii, the formation of typhus nodules in the small vessels results in a proliferative destructive thrombovasculitis with formation of perivascular granulomas (popov’s granulomas) consisting of macrophages, lymphocytes and plasma cells.
A man was admitted to the hospital on the 5th day of disease that manifested itself by jaundice, muscle aching, chill, nose bleedings. In course of laboratory diagnostics a bacteriologist performed dark-field microscopy of the patient’s blood drop. Name a causative agent of this disease:
1. Three genera of spirochetes cause human infection:
· Treponema: causes syphilis and the nonveneral treponematoses. Morphology – thin, tight spirals
· Borrelia: causes lyme disease and relapsing fever. Morphology – large and loosely coiled
· Leptospira: causes leptospirosis. Morphology – thin, tight spirals
Examination of a child revealed some whitish spots looking like coagulated milk on the mucous membrane of his cheeks and tongue. Analysis of smears revealed gram-positive oval yeast-like cells. What causative agents are they?
Bacteriological examination of a patient with food poisoning required inoculation of a pure culture of bacteria with the following properties: gram-negative movable bacillus that grows in the Endo’s medium in form of colourless colonies. A representative of which species caused this disease?
Positive result of immune-enzyme assay with HIV antigens is an evidence of a current HIV infection.
Reaction of passive hemagglutination conducted with erythrocytic typhoid Vi-diagnosticum helped to reveal some antibodies in the dilution of the patient’s serum at a ratio of 1:80 that exceeds the diagnostic titer. Such result witnesses of:
When the dilution of the patient’s serum exceeds the diagnostic titer, the patient is a potential carrier of the infectious agent. If less than the diagnostic titer, the examination is carried out again in 10 – 14days after the first examination. A dilution of the patient’s serum that gives the diagnostic titer indicates an acute or current infection.
A patient has symptoms of inflammation of urogenital tracts. Examination of a vaginal smear revealed big monocellular, pear-shaped organisms with the pointed spike at the posterior end of body, big nucleus and undulating membrane. What protozoa were found in the smear?
In the urogenital tract, the flagellate protozoa, Trichomonas vaginalis is the important pathogen. Trichomonas vaginalis causes trichomoniasis. It is a pear-shaped organism with a central nucleus and four anterior flagella. It has an undulating membrane that extends about two-thirds of its length. It exists only as a trophozoite; there is no cyst form. The organism is transmitted by sexual contact and the primary locations of the organism are the vagina and the prostate. In women, a watery, foul-smelling, greenish vaginal discharge accompanied by itching and burning occurs.
Slime, blood and protozoa 30-200 microns long have been revealed in a man’s feces. The body is covered with cilias and has correct oval form with a little bit narrowed anterior and wide round shaped posterior end. At the anterior end a mouth is visible. In cytoplasm there are two nuclei and two short vacuoles. What are the described features typical for?
Balantidium coli causes balantidiasis. It is the only ciliated protozoan that causes human disease i.e. diarrhea. Domestic animals, especially pigs are the main reservoir for the organism and humans are infected after ingesting the cysts in food or water contaminated with animal or human faeces. Diagnosis is made by finding large ciliated trophozoites or large cysts with a characteristic V-shaped nucleus in the stool. The trophozoites excyst in the small intestine, travel to the colon (large intestine) and by burrowing into the wall cause an ulcer similar to that of Entamoeba histolytica.
From the nasopharynx of a 5-year-old child it was excreted a microorganism which is identical to Corynebacterium diphtheriae dose according to morphological and biochemical signs. But this microorganism does not produce exotoxin. As a result of what process can this microorganism become toxigenic?
A man who was bitten by the unknown dog applied to the surgeon. Wide ragged wounds were localized on the face. What curative-prophylactic aid should be given to prevent rabies?
A patient who came to the doctor because of his infertility was administered to make tests for toxoplasmosis and chronic gonorrhoea. Which reaction should be performed to reveal latent toxoplasmosis and chronic gonorrhoea of the patient?
Precipitation (precipitin): in this test, the antigen is in solution. The antibody cross-links antigen molecules in variable proportions and aggregates (precipitates) form. Precipitin test can be done in solution or in semisolid medium (agar). This reaction can be made quantitative i.e. antigen or antibody can be measured in terms of micrograms of nitrogen present. It is used primarily in research.
Hepatitis serologic markers:
· Anti-HAV (IgM): IgM antibody to HAV; best test to detect acute hepatitis A
· Anti-HAV (IgG): IgG antibody indicates prior HAV infection and/or prior vaccination. This antibody protects against reinfection.
· HBsAg: Antigen found on surface of HBV; indicates hepatitis B infection.
· Anti-HBs: Antibody to HBsAg; indicates immunity to hepatitis B.
· HBcAg: Antigen associated with core of HBV.
· Anti-HBc: Antibody to HBcAg
· HBeAg: A second different antigenic determinant in the HBV core. HBeAg indicates active viral replication and therefore high transmissibility.
· Anti-HBc: Antibody to HBeAg; indicates low transmissibility.
Hepatitis A virus (HAV); Hepatitis B surface antigen (HBsAg); Hepatitis B core antigen (HBcAg); Hepatitis B e antigen (HBeAg).
Favus is caused by anthropophilic fungus Trychophyton schoenleini which affects glabrous skin and scalp. Favus is a form of tinea capitis in which crusts are seen on the scalp. Typical (scutular) form: the main element is a scutula being a pure fungus culture in the epidermis. Affected hair is lusterless, atrophic, brittle, lifeless, very much like hair of old uncared wigs.
Parents with an ill child consulted an infectionist. They had been working in one of Asian countries for a long time. The child has sallow skin, loss of appetite, laxity, enlarged liver, spleen, peripheral lymph nodes. What protozoal illness can be suspected?
The genus Leishmania includes 4 major pathogens: Leishmania donovani; L. tropica; L. Mexicana and L. braziliensis. Leishmania donovani is the cause of kala-azar (visceral leishmaniasis). In visceral leishmaniasis, the organs of the reticuloendothelial system (liver, spleen and bone marrow) are the most severely affected. It occurs in the Middle East, southern Russia, China, India and Sub-saharan Africa. The lifecycle involves the sandfly as the vector and a variety of mammals such as dogs, foxes and rodents as reservoirs.
Agglutinin – antibody; agglutinogen – antigen
Agglutination: in this test, the antigen is particulate (e.g. bacteria and red blood cells) or is an inert particle (latex beads) coated with an antigen. Because the antibody (agglutinin) is divalent or multivalent, it cross-links the antigenically multivalent particles and forms a latticework; then clumping (agglutination) can be seen. This reaction can be done in a small cup or tube or with a drop on a slide.