Microbiology MCQ 0% 8 Created by clinicalsci Microbiology MCQ Welcome to the Clinical Microbiology Multiple Choice Questions test. You have 30 minutes to answer 30 questions. Lets begin, Good Luck!! 1 / 30 In the CAMP test, a single streak of a beta-hemolytic Streptococcus is placed perpendicular to a streak of beta-lysin-producing Staphylococcus aureus. After incubation, a zone of increased lysis in the shape of an arrowhead is noted; this indicates the presumptive identification of: S. equinus S. agalactiae S. equinus S. bovis Streptococcus agalactiae isolates can be presumptively identified by the demonstration of a positive CAMP reaction. CAMP is an acronym for the scientists (Christie, Atkins, Munch, Petersen) who discovered this phenomenon!. Group B streptococci elaborate the CAMP factor, which acts to enhance the zone of hemolysis produced by beta-lysin-producing strains of Staphylococcus aureus. Incubation of test plates should be earned out in ambient air, because increased CO, and anaerobic incubation increase the rate of false-positive CAMP reactions by group A streptococci. 2 / 30 In suspected cases of brucellosis, the optimal specimen to be collected for the isolation of the etiologic agent is: Urine Blood Cerebrospinal fluid Nasopharyngeal exudates The etiologic agents of brucellosis are the brucellae, which are small, nonmotile, gram-negative coccobacilli that are facultative intracellular parasites. Isolation of these organisms is difficult. In suspected cases, which are generally job related, multiple blood cultures are recommended for optimal recovery of the agent. Bone marrow cultures have been found to be positive when cultures of blood failed to recover the organism. 3 / 30 The K antigen of the family Enterobacteriaceae is: The somatic antigen Heat labile The antigen used to group Shigella Located on the flagellum The K (capsule) antigen surrounds the bacterial cell and masks the somatic antigens of the cell wall, which are used to group members of the Enterobacteriaceae. These heat-labile antigens can be removed by heating a suspension of the culture at 100°C for 10-30 minutes. Antisera that contain K antibody can be used to demonstrate the presence of the capsular antigens. 4 / 30 Which of the following is causative of melioidosis ? Moraxella catarrhalis Burkholderia cepacia Burkholderia pseudomallei Stenotrophomonas maltophilia Burkholderia pseudomallei is the causative agent of melioidosis. The bacterium is found in soil and water in subtropical areas of Southeast Asia and Australia. Melioidosis exhibits several forms, from skin abscesses to abscess formation in internal organs. 5 / 30 Which of the following is catalase negative? Corynebacterium Bacillus Listeria Leuconostoc Of the genera listed, only Leuconostoc is catalase negative. Leuconostoc is vancomycin resistant and associated with infections in hospitalized patients. It has also been linked to septicemias in neonates. 6 / 30 Enterotoxin produced by Staphylococcus aureus is responsible for causing Carbuncles Scalded skin syndrome Enterocolitis Impetigo Staphylococcal enterocolitis food poisoning cases result from the ingestion of contaminated foods containing preformed thermostable enterotoxin. This form of intoxication causes a perfuse and watery diarrhea due to the loss of electrolytes and fluids into the lumen. In many cases, the causative agent may never be recovered from patient specimens. 7 / 30 The causative agent of "malignant pustule" is: Bacillus anthracis Listeria monocytogenes Erysipelothrix rhusiopathiae Corynebacterium ulcerans Bacillus anthracis infects humans by three routes: respiratory, gastrointestinal, and cutaneous. Malignant pustule is the name given to lesions seen in cutaneous anthrax in humans. The lesion is, however, neither malignant nor a pustule. The disease produces a localized abscess on the skin, which forms a characteristic black eschar surrounded by a red raised ring. 8 / 30 The beta-hemolysis produced by group A Streptococcus seen on the surface of a sheep blood agar plate is primarily the result of wchich streptolysin? M S H O Streptolysin S is primarily responsible for the beta-hemolysis seen on the surface of a sheep blood agar plate inoculated with a group A streptococcus. Of the two hemolysins secreted by beta-hemolytic group A streptococcus, Streptolysin S is stable in the presence of atmospheric oxygen. Streptolysin O is inactivated in the presence of oxygen, and it is best demonstrated when the agar has been stabbed and subsurface hemolysis is revealed. 9 / 30 Some strains of Serratia marcescens produce a red-colored pigment. Pigment production is enhanced by: Growth on typtic soy agar without blood Incubation at 42°C Growth on sheep blood agar Incubation at 22°C Serratia marcescens is a chromogenic member of the family Enterobacteriaceae. S. marcescens is the most clinically significant of the genus and is frequently involved in nosocomial infection. The red pigment produced is not water soluble and is demonstrated more readily by incubation at room temperature than at 35°C. 10 / 30 Which of the following lack motility ? Serratia Enterobacter Salmonella Klebsiella Klebsiella spp. are all nonmotile, which aids in their identification. Klebsiella spp. produce a capsule resulting in mucoid colonies. Shigella, another genus in the family Enterobacteriaceae, is also nonmotile. 11 / 30 Rust-colored sputum in cases of lobar pneumonia is characteristic of which of the following possible etiologic agents? Staphylococcus aureus Streptococcus pneumoniae Corynebacterium jeikeium Streptococcus pyogenes Streptococcus pneumoniae is most commonly associated with cases of lobar pneumonia. Patients characteristically produce blood-tinged, rust-colored sputum in which the characteristic gram-positive lanceolate diplococci can be found. S. pneumoniae forms alpha-hemolytic colonies when grown on sheep blood agar. 12 / 30 The majority of clinical isolates of Klebsiella are K. aerogenes K. oxytoca K. pneumoniae K. ozaenae Klebsiella pneumoniae is the species most frequently recovered from the vast majority of clinical cases. Members of the genus Klebsiella have a capsule and appear mucoid on cultures. This highly encapsulated organism can cause severe pneumonia, nosocomial infections of several types, infantile enteritis, and other extraintestinal infections. 13 / 30 One of the most common etiologic agents of community-acquired uncomplicated cases of cystitis is: Enterobacter aerogenes Escherichia coli Proteus vulgaris Klebsiella pneumoniae Escherichia coli is frequently the etiologic agent of community-acquired cystitis. This agent can be easily recognized by its fermentation of lactose, negative citrate reaction, and positive indole test. On eosin methylene blue agar, Escherichia coli produces characteristic dark colonies with a metallic sheen. 14 / 30 Edwardsiella tarda is occasionally isolated in stool specimens and can biochemically be confused with ? Vibrio cholerae Salmonella Yersinia enterocolitica Enterohemorraghic E. coli Edwardsiella tarda is a motile member of the family Enterobacteriaceae and as such is characteristically peritrichously flagellated. These organisms are infrequently isolated in the clinical laboratory. Biochemically they may initially resemble Salmonella in many ways, such as hydrogen sulfide production and the inability to ferment lactose. 15 / 30 The pulmonary form of anthrax is known as: Woolsorters disease Valley fever Farmers' lung Walking pneumonia Bacillus anthracis is the causative agent of woolsorters disease or the pulmonary form of anthrax. The mode of infection is the inhalation of spores by the patient, usually during the performance of his/her occupation (sheep shearing or processing of animal hair). Prompt diagnosis and treatment of this disease is needed because it is known to progress rapidly to a fatal form of septicemia. 16 / 30 Swimmer's ear, a form of external otitis is commonly caused by : Pseudomonas aeruginosa Acinetobacter baurnannii Bordetella bronchiseptica Haemophilus influenzae Swimmer's ear is a form of external otitis common to persons who swim and fail to completely dry their ear canals when they get out of the water. The organism most commonly associated with this condition is Pseudomonas aeruginosa. It is an organism known to be an opportunistic pathogen and one that favors a watery environment. 17 / 30 Campylobacter spp. are associated most frequently with cases of: Gastroenteritis Appendicitis Osteomyelitis Endocarditis Campylobacter jejuni rivals Salmonella as the most common bacterial cause of diarrheal disease in humans. Campylobacter enterocolitis is characterized by fever, bloody diarrhea, and abdominal pain. Special selective culture media and incubation under a microaerophilic atmosphere at 42°C are required for the recovery of this organism from clinical samples. 18 / 30 The most common etiologic agent of infections associated with the surgical insertion of prosthetic devices such as artificial heart valves and cerebrospinal fluid shunts is: Streptococcus mutans Staphylococcus capitis Corynebacterium urealyticum Staphylococcus epidermidis Staphylococcus epidermidis is a saprophytic microorganism found on the skin and mucous membranes of humans. This coagulase-negative Staphylococcus is seen frequently as a contaminant in blood cultures when proper venipuncture technique has not been used. S epidermidis has been implicated in serious human infections associated with the surgical insertion of prosthetic devices. 19 / 30 Which of the following organism is oxidase-positive and glucose nonfermenting ? Klebsiella pneumoniae Escherichia coli Pseudomonas aeruginosa Aeromonas hydrophila Pseudomonas aeruginosa is the most commonly encountered gram-negative non-fermenter of glucose and oxidase positive species that is not a member of the family Enterobacteriaceae. It is ubiquitous in nature and is found in homes and hospitals. It is an opportunistic pathogen responsible for nosocomial infections. 20 / 30 Staphylococcus aureus, when present, could most likely be recovered from a stool sample if the primary plating medium included: Bismuth sulfite Thiosulfate citrate bile salts sucrose Phenylethyl alcohol Xylose-lysine-desoxycholate Phenylethyl alcohol agar (PEA) is a selective medium for the isolation of gram-positive cocci. Blood agar medium is supplemented with 0.15% phenylethyl alcohol, which is inhibitory to most gram-negative aerobic bacilli. This medium is particularly helpful when a specimen containing gram-positive cocci is contaminated with a Proteus spp. due to the inhibition of swarming by PEA. 21 / 30 Haemophilus ducreyi is the causative agent of: Lymphogranuloma venereum Trachoma Whooping cough Chancroid Haemophilus ducreyi is the causative agent of chancroid, a serious sexually transmitted disease. The disease is more prevalent in the tropics than in temperate parts of the world. The bacteria produce buboes in the groin and can cause a septicemia. 22 / 30 Streptococcus sanguis, a viridans streptococcus, is most commonly associated with which of the following clinical conditions? Pharyngitis Relapsing fever Subacute bacterial endocarditis Otitis media Subacute bacterial endocarditis is an inflammation of the lining membrane of the heart, which most often is caused by a member of the viridans group of streptococci. Streptococcus sanguis is one of several species that may lodge in an abnormal heart or on valves damaged by previous infection. Viridans streptococci are normal inhabitants of the human upper respiratory tract. 23 / 30 Precipitates of diphtheria toxin and antitoxin formed in agar gels are an in vitro means for detecting toxigenic strains of Corynebacterium diphtheriae. The name of this test procedure is the: Hodge test D-test Elek test Nagler test The Elek immunodiffusion test is recommended for detecting toxigenic strains of Corynebacterium diphtheriae. In the test, diphtheria antitoxin is impregnated on a sterile filter paper strip, which is pressed onto the surface of an Elek agar plate. Test and control strains are then inoculated perpendicular to the strip on both sides and without touching the strip. A positive reaction by toxigenic strains produces a precipitin line at a 45-degree angle to the inoculum streak. 24 / 30 Which is the causative agent of the form of conjunctivitis known as pinkeye ? Chlamydia trachomatis Haemophilus aegyptius Moraxella lacunata Klebsiella ozaenae Haemophilus aegyptius is the causative agent of "pinkeye." This form of conjunctivitis is highly contagious and is frequently seen in children attending daycare centers. The agent is an aerobic gram-negative bacillus that is nonmotile and requires both hemin (X factor) and nicotine adenine dinucleotide (NAD, V factor) for growth. 25 / 30 Severe disseminated intravascular coagulation often complicates cases of septicemia is caused by: Moraxella sp. Neisseria meningitidis Neisseria gonorrhoeae Acinetobacter sp. The Waterhouse-Friderichsen syndrome of disseminated intravascular coagulation occurs in cases of fulminant meningococcemia—Neisseria meningitidis septicemia. Invasion of the circulatory system by N. meningitidis may produce only a transient bacteremia or meningitis or may go on to cause a rapidly fatal infection. In cases of meningococcemia with intravascular coagulation, acute adrenal insufficiency due to hemorrhage into the adrenal gland may result. 26 / 30 Acinetobacter baumannii is characteristically: Able to grow on MacConkey agar Motile Oxidase positive Sensitive to penicillin Acinetobacter baumannii is not able to reduce nitrate. This species will oxidize but not ferment glucose. Acinetobacter spp. are able to grow on MacConkey agar, and they are oxidase negative, nonmotile, and characteristically resistant to penicillin. 27 / 30 Which enzyme cannot be synthesized by streptococci? Lipase Hyaluronidase Catalase Kinase Organisms that synthesize the enzyme catalase are able to protect themselves from the killing effects of H2O2 by converting it to H2O and O2. Streptococci are unable to synthesize the heme prosthetic group for this enzyme and are catalase negative. Therefore, they grow better on blood-containing media because of the catalase like activity of hemoglobin. 28 / 30 Fecal cultures are inoculated on thiosulfate-citrate-bile salts-sucrose agar specifically for the isolation of: Campylobacter Vibrio Shigella Salmonella A highly selective medium, thiosulfate-citrate- bile salt-sucrose (TCBS) is used for the isolation of Vibrio spp. Species able to ferment sucrose, such as V. cholerae, produce yellow colonies. Non-sucrose-fermenting organisms produce green colonies. 29 / 30 The species of Mycobacterium that would be most commonly associated with contamination of the hot water system in large institutions such as hospitals is: M. xenopi M. avium M. marinum M. bovis The optimal growth temperature of Mycobacterium xenopi is 42°C, which enables its survival and replication as an environmental contaminant in hot water systems. Human infections caused by M. xenopi are rare. The majority of clinically significant Mycobacterium spp., those not known to cause cutaneous infections, have an optimal growth temperature of 37°C. 30 / 30 A test for the hydrolysis of esculin in the presence of bile is especially useful in identifying species of the genus: Abiotrophia Corynebacterium Staphylococcus Enterococcus Enterococcus and other group D streptococci can be presumptively identified based on their ability to hydrolyze esculin in the presence of 1-4% bile salts. The medium is made selective for enterococci by the addition of either sodium azide or 4% bile salts. Organisms able to grow on this medium and hydrolyze esculin produce esculetin, which reacts with an iron salt to form a black color in the agar. Please enter your Name and Email to to view your results and answers. NameEmail Your score is The average score is 48%Share your score ! Facebook Twitter 0% Restart quiz