1. What is the primary distinguishing characteristic of Enterobacteriaceae?

a. They are Gram-positive cocci.

b. They are oxidase-positive bacteria.
c. They are facultative anaerobic, Gram-negative rods.
d. They are obligate intracellular bacteria.

2. Which member of the Enterobacteriaceae family is known for its swarming motility?
a. Escherichia coli
b. Proteus mirabilis
c. Klebsiella pneumoniae
d. Shigella dysenteriae

3. Which Enterobacteriaceae species is the most common cause of community-acquired urinary

tract infections (UTIs)?
a. Proteus mirabilis
b. Enterobacter cloacae
c. Escherichia coli
d. Klebsiella pneumoniae

4. Which of the following is a characteristic of Shigella species?

a. Ferments lactose
b. Motile at body temperature
c. Produces Shiga toxin
d. Forms swarming colonies

5. What is the primary mode of transmission of Salmonella Typhi?

a. Airborne droplets
b. Contaminated food and water
c. Direct skin contact
d. Insect bites

6. Which biochemical test is used to differentiate Klebsiella pneumoniae from Escherichia coli?
a. Indole test
b. Coagulase test
c. Catalase test
d. Oxidase test

7. What is the primary virulence factor of Enterotoxigenic Escherichia coli (ETEC)?

a. Endotoxin
b. Shiga toxin
c. Heat-labile and heat-stable enterotoxins
d. Coagulase
8. Which Enterobacteriaceae species is known for its ability to form red pigment when grown at
room temperature?
a. Salmonella enterica
b. Klebsiella oxytoca
c. Serratia marcescens
d. Providencia stuartii

9. Which of the following species is a lactose-fermenting member of Enterobacteriaceae?

a. Shigella sonnei
b. Proteus vulgaris
c. Escherichia coli
d. Salmonella enterica

10. What is the selective and differential medium used to isolate Salmonella and Shigella?
a. MacConkey agar
b. Hektoen Enteric agar
c. Blood agar
d. Mannitol Salt agar

11. Which Yersinia species is the causative agent of plague?

a. Yersinia pseudotuberculosis
b. Yersinia enterocolitica
c. Yersinia pestis
d. Yersinia ruckeri

12. What is the major virulence factor of Klebsiella pneumoniae that allows it to evade
phagocytosis?
a. Lipopolysaccharide
b. Capsule
c. Flagella
d. Hemolysin

13. The Weil-Felix test is used to detect antibodies against which Enterobacteriaceae-related
infection?
a. Salmonella enterica
b. Proteus mirabilis
c. Escherichia coli
d. Yersinia enterocolitica

14. What staining technique is primarily used to identify Mycobacterium tuberculosis?

a. Gram stain
b. India ink stain
c. Ziehl-Neelsen stain
d. Giemsa stain
15. Which feature of Mycobacterium tuberculosis contributes to its slow growth?
a. Lack of a cell wall
b. High lipid content in the cell wall
c. Absence of peptidoglycan
d. Limited nutrient uptake capability

16. What is the main site of initial infection for Mycobacterium tuberculosis?
a. Liver
b. Gastrointestinal tract
c. Lungs
d. Skin

17. A bacterial isolate was inoculated into a Triple Sugar Iron (TSI) agar slant and incubated at
37°C for 24 hours. The following results were observed:
Slant: Red
Butt: Yellow
Gas production: None
H₂S production: None
Which carbohydrate(s) were fermented, and what do these results indicate about the
organism's metabolism?
a. Only glucose was fermented; the organism is a non-lactose fermenter
b. Glucose and lactose were fermented; the organism is a lactose fermenter
c. Only lactose was fermented; the organism lacks glucose metabolism
d. No sugars were fermented; the organism is obligately aerobic

18. Which Mycobacterium species is known to cause Hansen’s disease (leprosy)?

a. Mycobacterium tuberculosis
b. Mycobacterium kansasii
c. Mycobacterium avium
d. Mycobacterium leprae

19. A 5-year-old child presents with fever, sore throat, and a grayish membrane covering the
tonsils and pharynx. The physician suspects Corynebacterium diphtheriae infection. Which of
the following culture media is most appropriate for isolating and identifying the organism?
a. MacConkey Agar
b. Blood Agar
c. Tellurite Agar
d. Thiosulfate Citrate Bile Salts Sucrose (TCBS) Agar
e. Lowenstein-Jensen (LJ) Medium

20. Haemophilus influenzae requires which two growth factors?

a. X and Z factors
b. Y and V factors
c. X and V factors
d. H and J factors

21. Which Bordetella species is the primary causative agent of whooping cough?
a. Bordetella parapertussis
b. Bordetella bronchiseptica
c. Bordetella holmesii
d. Bordetella pertussis

22. A bacterial isolate was inoculated into a Simmons Citrate agar slant. After 24 hours of
incubation, the slant turned blue. What enzyme does this test for, and what metabolic process
is indicated by the color change?
a. Urease; breakdown of urea into ammonia
b. Citrate lyase; utilization of citrate as a sole carbon source
c. Tryptophanase; conversion of tryptophan into indole
d. Phenylalanine deaminase; removal of an amine group from phenylalanine

23. The primary mode of transmission of Legionella pneumophila is through:

a. Inhalation of contaminated aerosols
b. Direct contact with infected individuals
c. Consumption of contaminated food
d. Insect bites

24. Which Vibrio species is associated with necrotizing wound infections and sepsis, particularly
in immunocompromised individuals?
a. Vibrio cholerae
b. Vibrio vulnificus
c. Vibrio parahaemolyticus
d. Vibrio alginolyticus

25. Which of the following is the primary virulence factor of Vibrio cholerae?
a. Exfoliative toxin
b. Cholera toxin
c. Enterotoxin A
d. Hemolysin

26. A microbiologist inoculated a stool sample onto Hektoen Enteric (HE) agar to differentiate
between Salmonella and Shigella. The colonies appeared as blue-green with black centers.
What metabolic property is responsible for the black coloration, and which chemical in the
medium detects it?
a. Lactose fermentation; neutral red
b. Hydrogen sulfide (H₂S) production; sodium thiosulfate and ferric ammonium citrate
c. Indole production; Kovac’s reagent
d. Urease activity; phenol red
27. Which of the following best describes Pseudomonas aeruginosa infections?
a. They primarily affect immunocompetent individuals.
b. They are commonly associated with nosocomial infections.
c. They cause primarily upper respiratory tract infections.
d. They are strictly anaerobic infections.

28. Which of the following Clostridium species is the primary cause of antibiotic-associated
pseudomembranous colitis?
a. Clostridium tetani
b. Clostridium perfringens
c. Clostridium difficile
d. Clostridium botulinum

29. What is the characteristic appearance of Clostridium tetani under the microscope?
a. "Medusa head" colonies
b. "Boxcar-shaped" rods
c. "Drumstick" or "tennis racket" shape
d. "Safety pin" appearance

30. Which bacterium is associated with gas gangrene?

a. Clostridium tetani
b. Clostridium botulinum
c. Clostridium perfringens
d. Clostridium difficile

31. Which Treponema species causes syphilis?

a. Treponema pallidum
b. Treponema carateum
c. Treponema denticola
d. Treponema pertenue

32. The primary mode of transmission of Leptospira interrogans is:

a. Aerosol inhalation
b. Ingestion of contaminated food
c. Direct contact with infected animals or contaminated water
d. Sexual contact

33. Which medium is used to culture Neisseria gonorrhoeae?

a. MacConkey agar
b. Blood agar
c. Thayer-Martin agar
d. Chocolate agar without antibiotics
34. A laboratory is testing an unknown gram-negative coccobacillus isolated from a case of
acute epiglottitis. Growth is observed only on chocolate agar but not on sheep blood agar.
Further testing reveals that the organism grows around a Staphylococcus streak on blood agar.
Which of the following is the most likely biochemical characteristic of this organism?
a. Requires X factor only
b. Requires V factor only
c. Requires both X and V factors
d. Requires neither X nor V factors
e. Can grow on MacConkey agar without additional factors

35. A stool sample from a patient with bloody diarrhea and fever is sent to the laboratory for
bacterial culture. The suspected pathogen is Campylobacter jejuni. Which of the following
conditions is required for optimal isolation of this organism?
a. Incubation at 35°C in ambient air
b. Growth on MacConkey agar under aerobic conditions
c. Incubation at 42°C under microaerophilic conditions
d. Culture on Thiosulfate-Citrate-Bile-Salts-Sucrose (TCBS) agar
e. Growth on Lowenstein-Jensen (LJ) medium at 37°C

36. Which Enterobacteriaceae species is urease-positive, phenylalanine deaminase-positive, and

known for its swarming motility?
a. Escherichia coli
b. Salmonella enterica
c. Proteus mirabilis
d. Klebsiella pneumoniae

37. A bacterium isolated from a stool sample grows on Hektoen Enteric (HE) agar, producing
blue-green colonies with black centers. It is also H2S-positive on Triple Sugar Iron (TSI) agar,
lysine decarboxylase-positive, and motile. What is the most likely identification?
a. Escherichia coli
b. Salmonella enterica
c. Shigella flexneri
d. Klebsiella pneumoniae
Answer: b. Salmonella enterica

38. A lactose-fermenting bacterium was isolated from a urine sample. It formed pink colonies
on MacConkey agar and exhibited the following biochemical test results:
Indole test: Positive
Urease test: Negative
Citrate test: Negative

TSI slant: Acid/Acid (A/A) with gas, no H₂S

What is the most likely organism?

a. Enterobacter cloacae
b. Escherichia coli
c. Klebsiella pneumoniae
d. Proteus mirabilis
Answer: b. Escherichia coli

39. Which biochemical test differentiates Escherichia coli from Enterobacter cloacae?
a. Citrate utilization
b. Oxidase test
c. Catalase test
d. TSI agar slant reaction

40. A Gram-negative rod was isolated from a urinary tract infection. It produced a red pigment
at room temperature, was indole-negative, and citrate-positive. Which organism is most likely
responsible?
a. Escherichia coli
b. Serratia marcescens
c. Proteus vulgaris
d. Morganella morganii