Micro 8.7 Anaerobic Bacteria

Question 1

1. Obligate anaerobes, facultative anaerobes, and microaerophiles are terms referring to bacteria that require:

A. Increased nitrogen
B. Decreased CO2
C. Increased O2
D. Decreased O2

Answer 1

D. Decreased O2

Question 2

2. Which of the following most affects the oxidation–reduction potential (Eh, or redox potential) of media for anaerobic bacteria?

A. Oxygen
B. Nitrogen
C. pH
D. Glucose

Answer 2

C. pH

Question 3

3. Which of the following is the medium of choice for the selective recovery of gram-negative anaerobes?

A. Kanamycin–vancomycin–anaerobe (KVA) agar
B. Phenylethyl alcohol (PEA) agar
C. Cycloserine cefoxitin fructose agar (CCFA)
D. THIO broth

Answer 3

A. Kanamycin–vancomycin–anaerobe (KVA) agar

Question 4

4. Anaerobic bacteria are routinely isolated from all of the following types of infections except:

A. Lung abscesses
B. Brain abscesses
C. Dental infections
D. Urinary tract infections

Answer 4

D. Urinary tract infections

Question 5

5. Methods other than packaged microsystems used to identify anaerobes include:

A. Antimicrobial susceptibility testing
B. Gas–liquid chromatography (GLC)
C. Special staining
D. Enzyme immunoassay

Answer 5

B. Gas–liquid chromatography (GLC)

Question 6

6. Which broth is used for the cultivation of anaerobic bacteria to detect volatile fatty acids as an aid to identification?

A. Prereduced peptone–yeast extract–glucose (PYG)
B. THIO broth
C. Gram-negative (GN) broth
D. Selenite (SEL) broth

Answer 6

A. Prereduced peptone–yeast extract–glucose (PYG)

Question 7

7. A gram-positive spore-forming bacillus growing on sheep blood agar anaerobically produces a double zone of β-hemolysis and is positive for lecithinase. What is the presumptive identification?

A. Bacteroides ureolyticus
B. Bacteroides fragilis
C. Clostridium perfringens
D. Clostridium difficile

Answer 7

C. Clostridium perfringens

Question 8

8. Egg yolk agar is used to detect which enzyme produced by several Clostridium species?

A. Lecithinase
A. β-Lactamase
C. Catalase
D. Oxidase

Answer 8

A. Lecithinase

Question 9

9. Which of the following organisms will display lipase activity on egg yolk agar?

A. Clostridium botulinum
B. Clostridium sporogenes
C. Clostridium novyi
D. All of these options

Answer 9

D. All of these options

Question 10

10. Which spore type and location is found on Clostridium tetani?

A. Round, terminal spores
B. Round, subterminal spores
C. Ovoid, subterminal spores
D. Ovoid, terminal spores

Answer 10

A. Round, terminal spores

Question 11

11. Gram-positive bacilli recovered from two blood cultures from a 60-year-old patient with diabetes gave the following results:
    Spores seen = Neg
    Hemolysis = + (double zone)
    Motility = Neg
    Lecithinase = +
    Volatile acids by GLC (PYG) = acetic acid (A) and butyric acid (B)
    What is the most likely identification?

A. Clostridium tetani
B. Clostridium perfringens
C. Clostridium novyi
D. Clostridium sporogenes

Answer 11

B. Clostridium perfringens

Question 12

12. Which mechanism is responsible for botulism in infants caused by C. botulinum?

A. Ingestion of spores in food or liquid
B. Ingestion of preformed toxin in food
C. Virulence of the organism
D. Lipase activity of the organism

Answer 12

A. Ingestion of spores in food or liquid

Question 13

13. The classic form of foodborne botulism is characterized by the ingestion of:

A. Spores in food
B. Preformed toxin in food
C. Toxin H
D. All of these options

Answer 13

B. Preformed toxin in food

Question 14

14. Which test is performed to confirm an infection with C. botulinum?

A. Toxin neutralization test
B. Spore-forming test
C. Lipase test
D. Gelatin hydrolysis test

Answer 14

A. Toxin neutralization test

Question 15

15. Which Clostridium spp. causes pseudomembranous colitis or antibiotic-associated colitis?

A. Clostridium ramosum
B. Clostridium difficile
C. Clostridium perfringens
D. Clostridium sporogenes

Answer 15

B. Clostridium difficile

Question 16

16. Identification of C. tetani is usually based on:

A. Gram staining of the wound site
B. Anaerobic culture of the wound site
C. Blood culture results
D. Clinical findings

Answer 16

D. Clinical findings

Question 17

17. Obligate anaerobic gram-negative bacilli that do not form spores, grow well in 20% bile (Bacteroides bile esculin [BBE] agar), and are resistant to penicillin two-unit disks are most likely:

A. Porphyromonas spp.
B. Bacteroides spp.
C. Fusobacterium spp.
D. Prevotella spp.

Answer 17

B. Bacteroides spp.

Question 18

18. Which Bacteroides spp. is noted for “pitting” of the agar and is sensitive to penicillin two-unit disks?

A. Bacteroides vulgatus
B. Bacteroides ovatus
C. Bacteroides thetaiotaomicron
D. Bacteroides ureolyticus

Answer 18

D. Bacteroides ureolyticus

Question 19

19. Which gram-negative bacilli produce brown to black pigment on KVA agar and brick red fluorescence when exposed to an ultraviolet (UV) light source?

A. Porphyromonas spp. and Prevotella spp.
B. Fusobacterium spp. and Actinomyces spp.
C. Bacteroides spp. and Fusobacterium spp.
D. All of these options

Answer 19

A. Porphyromonas spp. and Prevotella spp.

Question 20

20. The following characteristics of an obligate anaerobic gram-negative bacilli best describe which of the listed genera?
    Gram staining = Long, slender rods with pointed ends
    Colonial appearance = Dry bread crumbs or “fried-egg” appearance
    Penicillin two-unit disk test = Susceptible

A. Bacteroides spp.
B. Fusobacterium spp.
C. Prevotella spp.
D. Porphyromonas spp

Answer 20

B. Fusobacterium spp.

Question 21

21. All of the following genera are anaerobic cocci that stain gram positive except:

A. Peptococcus spp.
B. Peptostreptococcus spp.
C. Streptococcus spp.
D. Veillonella spp.

Answer 21

D. Veillonella spp.

Question 22

22. The gram-positive non–spore-forming, anaerobic, short, pleomorphic rods most frequently recovered from blood cultures as a contaminant are:

A. Propionibacterium acnes
B. Clostridium perfringens
C. Staphylococcus intermedius
D. Veillonella parvula

Answer 22

A. Propionibacterium acnes

Question 23

23. Which Clostridium species is most often recovered from a wound infection with gas gangrene?

A. Clostridium sporogenes
B. Clostridium sordellii
C. Clostridium novyi
D. Clostridium perfringens

Answer 23

D. Clostridium perfringens

Question 24

24. Gram staining of a smear taken from the periodontal pockets of a 30-year-old man with poor dental hygiene showed sulfur granules containing gram-positive rods (short diphtheroids and some unbranched filaments) and were non–acid fast. Colonies on blood agar resembled “molar teeth” in formation. The most likely organism is:

A. Actinomyces israelii
B. Propionibacterium acnes
C. Staphylococcus intermedius
D. Peptostreptococcus anaerobius

Answer 24

A. Actinomyces israelii

Question 25

25. Antimicrobial susceptibility testing of Bacteroides and Clostridium spp. anaerobes are done by which of the following methods?

A. Broth microdilution
B. Agar dilution
C. E-Test
D. All of the above

Answer 25

D. All of the above

Question 26

26. An abdominal postoperative wound specimen grew catalase-positive, indole-negative, nonpigmented, nonfluorescent, gram-negative, pleomorphic bacilli (safety pin–shaped) on 20% bile media. The colonies also grew on KVA agar (resistant to kanamycin, vancomycin, and colistin). What is the most likely identification?

A. Fusobacterium nucleatum
B. Bacteroides fragilis
C. Prevotella spp.
D. Porphyromonas spp.

Answer 26

B. Bacteroides fragilis