MEDICAL BACTERIOLOGY (MBMM3311) - MCQs | MCQ Quiz | OmpathStudy Kenya

Question 1

A gram-positive coccus isolated from a wound shows golden-yellow colonies on blood agar but is coagulase negative. The most likely organism is

Accepted Answer

Staphylococcus saprophyticus — S. saprophyticus can produce yellow pigment but is coagulase negative, unlike S. aureus which is coagulase positive. This organism is commonly associated with urinary tract infections in young women.

Question 2

Which organism can grow at refrigeration temperature (4°C)?

Accepted Answer

Listeria monocytogenes — Listeria is psychrophilic and can multiply at refrigeration temperatures (4°C), making it a significant food safety concern in refrigerated ready-to-eat foods. This unique ability distinguishes it from most other pathogenic bacteria.

Question 3

A 25-year-old sexually active female presents with urinary tract infection. The organism that is coagulase-negative and novobiocin resistant is

Accepted Answer

Staphylococcus saprophyticus — S. saprophyticus is novobiocin resistant and causes UTI in young sexually active women, being the second most common cause of UTI after E. coli. S. epidermidis is novobiocin sensitive, which helps differentiate these two coagulase-negative staphylococci.

Question 4

A burn patient develops green-blue pus with a fruity odor. The organism is

Accepted Answer

Pseudomonas aeruginosa — Pseudomonas produces pyocyanin (blue-green pigment) and pyoverdine giving green-blue pus with a characteristic grape-like or fruity odor. This organism is a common opportunistic pathogen in burn wounds.

Question 5

Which organism produces black colonies on bismuth sulfite agar?

Accepted Answer

Salmonella typhi — S. typhi produces hydrogen sulfide (H2S) which reacts with bismuth sulfite to form black bismuth sulfide, producing characteristic black colonies with metallic sheen. This is used for selective isolation of S. typhi.

Question 6

"Swarming" motility on blood agar is characteristic of

Accepted Answer

Proteus species — Proteus shows swarming motility creating concentric waves or ripples on agar due to highly active flagella and differentiation into elongated swarmer cells. This can be inhibited by increasing agar concentration or adding bile salts.

Question 7

"Elek test" is used to detect toxigenicity of

Accepted Answer

Corynebacterium diphtheriae — Elek immunoprecipitation test detects diphtheria toxin production by C. diphtheriae strains. Lines of precipitation form between toxin-producing colonies and antitoxin-soaked filter paper strips on agar.

Question 8

The most common cause of acute bacterial meningitis in adults is

Accepted Answer

Streptococcus pneumoniae — S. pneumoniae (pneumococcus) is the leading cause of bacterial meningitis in adults and elderly, accounting for approximately 50% of cases. It also causes pneumonia, otitis media, and sinusitis.

Question 9

A stool sample shows gram-negative curved rods with "gull wing" or "S" shape. The organism is

Accepted Answer

Campylobacter jejuni — Campylobacter has characteristic S-shaped, gull wing, or spiral morphology and shows rapid darting corkscrew motility. It is a leading cause of bacterial gastroenteritis worldwide, transmitted through contaminated poultry.

Question 10

A patient with infective endocarditis has blood culture showing catalase negative, gram-positive cocci resistant to optochin and not lysed by bile. The organism is

Accepted Answer

Enterococcus faecalis — Enterococcus is optochin resistant, bile insoluble, and catalase negative, distinguishing it from S. pneumoniae (optochin sensitive, bile soluble). Enterococci are common causes of subacute endocarditis and UTIs.

Question 11

"Quellung reaction" is used to identify capsule of

Accepted Answer

All of the above — Quellung reaction (capsular swelling test) can identify capsules of any encapsulated bacteria when mixed with specific anticapsular antisera. The capsule appears to swell under microscopy, allowing serotype identification.

Question 12

A comma-shaped gram-negative rod showing "shooting star" motility in hanging drop is

Accepted Answer

Vibrio cholerae — V. cholerae shows characteristic rapid darting or shooting star motility in hanging drop preparation due to its single polar flagellum. This distinctive motility pattern aids in presumptive identification.

Question 13

"Widal test" detects antibodies against

Accepted Answer

Salmonella typhi — Widal test detects agglutinating antibodies against O (somatic) and H (flagellar) antigens of Salmonella typhi in typhoid fever. A four-fold rise in titer is significant, though the test has limitations in endemic areas.

Question 14

Which organism produces "currant jelly" sputum?

Accepted Answer

Klebsiella pneumoniae — Klebsiella pneumonia produces thick, bloody, mucoid sputum resembling currant jelly due to extensive tissue necrosis and the organism's large polysaccharide capsule. This destructive pneumonia often affects alcoholics and diabetics.

Question 15

"McFadyean reaction" showing pink-staining capsule is diagnostic for

Accepted Answer

Bacillus anthracis — McFadyean polychrome methylene blue staining shows characteristic pink/purple capsule around blue B. anthracis bacilli in blood or tissue smears. This is used for rapid diagnosis of anthrax in animals.

Question 16

Which organism shows "tumbling motility" at 25°C but not at 37°C?

Accepted Answer

Listeria monocytogenes — Listeria exhibits characteristic tumbling or end-over-end motility at room temperature (20-25°C) due to peritrichous flagella expression. Motility is reduced or absent at 37°C, which helps distinguish it from other motile gram-positive rods.

Question 17

"Satellite phenomenon" on blood agar indicates

Accepted Answer

Staphylococcus aureus providing factors for Haemophilus — Haemophilus influenzae grows as small satellite colonies around S. aureus colonies on blood agar. S. aureus provides V factor (NAD) through hemolysis and heating of blood, while Haemophilus requires both X (hemin) and V factors.

Question 18

A patient with facial nerve palsy, meningitis, and rash has CSF showing gram-negative diplococci. The organism is

Accepted Answer

Neisseria meningitidis — N. meningitidis causes meningococcemia with petechial/purpuric rash, meningitis, and can affect cranial nerves including the facial nerve. The organism appears as gram-negative kidney bean-shaped diplococci in CSF.

Question 19

A diabetic patient develops malignant external otitis. The organism is

Accepted Answer

Pseudomonas aeruginosa — P. aeruginosa causes severe, invasive external otitis in diabetic and elderly immunocompromised patients. The infection extends from ear canal to temporal bone (osteomyelitis) and can involve cranial nerves with high morbidity.

Question 20

"Leonine facies" (lion-like face) is associated with

Accepted Answer

Lepromatous leprosy — Lepromatous leprosy causes progressive facial skin thickening, nodule formation, and loss of eyebrows creating a characteristic lion-like appearance (leonine facies). This is caused by Mycobacterium leprae, though the question relates to bacterial morphology concepts.

Question 21

A food handler with boils transmits food poisoning with rapid onset vomiting. The organism is

Accepted Answer

Staphylococcus aureus — S. aureus produces heat-stable enterotoxin in contaminated food causing rapid onset (2-6 hours) food poisoning characterized by severe nausea, vomiting, and abdominal cramps. The toxin is preformed and not destroyed by reheating.

Question 22

"Kanagawa phenomenon" (beta-hemolysis on Wagatsuma agar) is positive for pathogenic strains of

Accepted Answer

Vibrio parahaemolyticus — Kanagawa test differentiates pathogenic (hemolytic, toxin-producing) from non-pathogenic V. parahaemolyticus strains. Pathogenic strains produce thermostable direct hemolysin (TDH) causing beta-hemolysis on special Wagatsuma blood agar.

Question 23

Which organism ferments lactose slowly (late lactose fermenter)?

Accepted Answer

Citrobacter freundii — Citrobacter is a late lactose fermenter, taking more than 24 hours to ferment lactose on MacConkey agar. It initially appears as colorless (non-lactose fermenting) colonies that gradually turn pink, unlike E. coli which ferments lactose rapidly.

Question 24

A patient with chronic gastritis and peptic ulcer has a urease-positive curved rod. The organism is

Accepted Answer

Helicobacter pylori — H. pylori produces abundant urease enzyme creating an alkaline microenvironment that neutralizes gastric acid, allowing colonization of gastric mucosa. It causes chronic gastritis, peptic ulcers, and is associated with gastric cancer.

Question 25

"Strawberry tongue" and "sandpaper rash" are features of infection with

Accepted Answer

Streptococcus pyogenes — Scarlet fever, caused by erythrogenic toxin-producing Group A Streptococcus (S. pyogenes), presents with strawberry tongue (red with prominent papillae), circumoral pallor, and fine sandpaper-like rash that blanches on pressure.

Question 26

Which organism shows "school of fish" arrangement in tissue sections?

Accepted Answer

Fusobacterium necrophorum — Fusobacterium, a fusiform anaerobic gram-negative bacillus, shows characteristic school of fish arrangement with spindle-shaped cells having tapered ends aligned parallel in one direction. It causes Lemierre's syndrome and necrotizing infections.

Question 27

Which organism produces "draughtboard" or "pavement stone" colonies?

Accepted Answer

Neisseria gonorrhoeae — N. gonorrhoeae produces distinctive colony morphology types (T1-T5) on chocolate agar, with virulent forms showing small, raised colonies creating a draughtboard or pavement stone pattern. Colony type correlates with pilus expression and virulence.

Question 28

"Sulfur granules" in pus are characteristic of

Accepted Answer

Actinomyces israelii — Actinomyces forms yellow "sulfur granules" (actually microcolonies with radiating filaments, not containing actual sulfur) in draining sinuses of cervicofacial actinomycosis. These granules contain gram-positive branching filaments with peripheral clubs.

Question 29

A patient with cystic fibrosis has recurrent pulmonary infections with mucoid colonies. The organism is

Accepted Answer

Pseudomonas aeruginosa — P. aeruginosa forms mucoid biofilm due to overproduction of alginate polysaccharide in CF patients' lungs, causing chronic infection. The mucoid phenotype is characteristic of CF-associated P. aeruginosa and indicates poor prognosis with difficult eradication. END OF MCQs

MEDICAL BACTERIOLOGY (MBMM3311) - MCQs | MCQ Quiz | OmpathStudy Kenya

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