Microbiology MCQ 0% 36 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 Fecal cultures are inoculated on thiosulfate-citrate-bile salts-sucrose agar specifically for the isolation of: Shigella Vibrio Campylobacter 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. 2 / 30 Campylobacter spp. are associated most frequently with cases of: Osteomyelitis Endocarditis Gastroenteritis Appendicitis 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. 3 / 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? S M 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. 4 / 30 In suspected cases of brucellosis, the optimal specimen to be collected for the isolation of the etiologic agent is: Blood Cerebrospinal fluid Nasopharyngeal exudates Urine 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. 5 / 30 Which of the following lack motility ? Enterobacter Klebsiella Salmonella Serratia 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. 6 / 30 Which of the following organism is oxidase-positive and glucose nonfermenting ? Aeromonas hydrophila Klebsiella pneumoniae Pseudomonas aeruginosa Escherichia coli 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. 7 / 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: D-test Hodge test Nagler test Elek 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. 8 / 30 Which organism produces violet-colored colonies ? Pseudomonas aeruginosa Chryseobacterium meningosepticum Chromobacterium violaceum Serratia marcescens Chromobacterium violaceum is a motile, gram-negative bacillus found in soil and water that can be pathogenic for humans. The production of a non-water-soluble violet pigment by these organisms aids in their identification. Chromobacterium is catalase and oxidase positive and generally attacks carbohydrates fermentatively. 9 / 30 The organism associated with a disease characterized by the presence of a pseudomembrane in the throat and the production of an exotoxin that is absorbed into the bloodstream with a lethal effect is: Streptococcus pyogenes Corynebacterium diphtheriae Staphylococcus aureus Arcanobacterium haemolyticum Strains of Corynebacterium diphtheriae infected by a lysogenic bacteriophage produce an extremely potent exotoxin. Absorption of the toxin may cause a rapidly fatal hypertoxic disease characterized by myocarditis and neuritis. This disease most commonly affects children aged 1 to 10 years. Transmission is by contact with a human carrier or with contaminated fomites. 10 / 30 Which of the following is not true of Shigella sonnei? Large numbers of organisms must be ingested to produce disease. The organism produces an inflamma- tory condition in the large intestine with bloody diarrhea. The organism is a late lactose fermenter. The organism produces disease most commonly in the pediatric population. Shigella has a low infecting dose and has been reported to cause outbreaks in daycare centers and can be spread to family members. These organisms are found in humans only at the time of infection; they are not part of the normal flora. Transmission is by the fecal-oral route, typically by ingestion of contaminated foods or water. 11 / 30 The pulmonary form of anthrax is known as: Farmers' lung Woolsorters disease Valley fever 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. 12 / 30 Which is the causative agent of the form of conjunctivitis known as pinkeye ? Chlamydia trachomatis Moraxella lacunata Haemophilus aegyptius 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. 13 / 30 Which of the following is causative of melioidosis ? Burkholderia pseudomallei Burkholderia cepacia Moraxella catarrhalis 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. 14 / 30 Rust-colored sputum in cases of lobar pneumonia is characteristic of which of the following possible etiologic agents? Streptococcus pyogenes Corynebacterium jeikeium Streptococcus pneumoniae Staphylococcus aureus 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. 15 / 30 Streptococcus sanguis, a viridans streptococcus, is most commonly associated with which of the following clinical conditions? Otitis media Subacute bacterial endocarditis Relapsing fever Pharyngitis 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. 16 / 30 Hemolytic uremic syndrome is a consequence of a bacterial infection with: Yersinia enterocolitica Vibrio cholerae O1 Salmonella Typhi E. coli O157:H7 E. coli O157:H7 produces a toxin similar to Shiga toxin produced by Shigella dysenteriae. It is most commonly transmitted by ingestion of undercooked ground beef or raw milk. Hemorrhagic colitis is characteristic of infection, but infection can also lead to hemolytic uremic syndrome resulting from toxin-mediated kidney damage. 17 / 30 Swimmer's ear, a form of external otitis is commonly caused by : Bordetella bronchiseptica Acinetobacter baurnannii Haemophilus influenzae Pseudomonas aeruginosa 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. 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: Staphylococcus capitis Corynebacterium urealyticum Staphylococcus epidermidis Streptococcus mutans 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 Severe disseminated intravascular coagulation often complicates cases of septicemia is caused by: Acinetobacter sp. Moraxella sp. Neisseria gonorrhoeae Neisseria meningitidis 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. 20 / 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. bovis M. avium M. xenopi M. marinum 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. 21 / 30 The causative agent of "malignant pustule" is: Bacillus anthracis Corynebacterium ulcerans Listeria monocytogenes Erysipelothrix rhusiopathiae 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. 22 / 30 Enterotoxin produced by Staphylococcus aureus is responsible for causing Impetigo Scalded skin syndrome Carbuncles Enterocolitis 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. 23 / 30 The majority of clinical isolates of Klebsiella are K. ozaenae K. pneumoniae K. oxytoca K. aerogenes 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. 24 / 30 Haemophilus ducreyi is the causative agent of: Lymphogranuloma venereum Chancroid Whooping cough Trachoma 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. 25 / 30 One of the most common etiologic agents of community-acquired uncomplicated cases of cystitis is: Enterobacter aerogenes Escherichia coli Klebsiella pneumoniae Proteus vulgaris 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. 26 / 30 The K antigen of the family Enterobacteriaceae is: The antigen used to group Shigella The somatic antigen Heat labile 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. 27 / 30 Which enzyme cannot be synthesized by streptococci? Lipase Kinase Hyaluronidase Catalase 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 Acinetobacter baumannii is characteristically: Sensitive to penicillin Able to grow on MacConkey agar Oxidase positive Motile 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. 29 / 30 Enterococcus faecium is characteristically: PYR negative Inhibited by the presence of bile in culture media Beta-hemolytic Able to grow in the presence of high concentrations of salt Enterococcus faecium is an important agent of human infection. Their differentiation from other enterococcal strains is of importance because of their resistance to most clinically useful antimicrobial agents, including vancomycin. The ability to tolerate a high concentration of salt is characteristic of the clinically significant species of Enterococcus. E. faecium is PYR positive and is usually nonhemolytic. 30 / 30 A test for the hydrolysis of esculin in the presence of bile is especially useful in identifying species of the genus: Enterococcus Staphylococcus Abiotrophia Corynebacterium 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 52%Share your score ! Facebook Twitter 0% Restart quiz