Exam #2 - (CH 16) Aerobic gram-positive bacilli Review Questions

Question 1

Points to Remember

■ C. diphtheriae causes serious disease in populations of countries where the diphtheria vaccine is not available.
■ Nondiphtheria Corynebacterium species can be opportunistic pathogens.
■ L. monocytogenes can be differentiated from streptococci and enterococci on the basis of Gram stain morphology, catalase reaction, and motility.
■ E. rhusiopathiae differs from L. monocytogenes in catalase reaction, hydrogen sulfide production, and lack of ability to grow at 4 ° C.

Answer 1

■ A. haemolyticum can be differentiated from other non– spore-forming gram-positive bacilli and β-hemolytic streptococci by Gram stain morphology, catalase activity, and the CAMP inhibition reaction or reverse CAMP test.
■ G. vaginalis is part of the normal biota of the urogenital tract but might play a role in BV. It is weakly β-hemolytic on HBT agar and stains as a gram-variable rod. ■ Aerobic actinomycetes are generally soil inhabitants. They are weak pathogens sometimes associated with wounds after traumatic implantation into subcutaneous tissue.

Question 2

Points to Remember

■ Nocardia spp. are gram-positive, filamentous organisms that can grow on nutritionally simple media and are partially acid fast.
■ To provide accurate identification and speciation of actinomycetes, 16S rRNA gene sequencing is often required; however, this is unavailable in most laboratories.
■ Members of the genus Bacillus are aerobic, gram-positive, catalase-positive, rod-shaped organisms that form endospores.
■ Many aerobic gram-positive spore-forming bacilli are rarely associated with human infections. The most important pathogen in this group is B. anthracis.

Answer 2

■ B. anthracis is generally susceptible to penicillin and is nonmotile and nonhemolytic on SBA, features important to differentiate the organism from B. cereus.
■ B. cereus is a common cause of food poisoning and opportunistic infections. Food poisoning caused by B. cereus and occurs in two forms: diarrheal and emetic.

Question 3

Based on 16S rRNA sequencing, corynebacteria are closely related to
A. Escherichia.
B. Proteus.
C. Nocardia.
D. Vibrio.

Answer 3

C. Nocardia.

Question 4

Corynebacterium diphtheriae appears microscopically as a
A. palisading gram-positive bacillus.
B. gram-positive cocci in chains.
C. curved gram-positive coccobacillus.
D. large, straight, filamentous, gram-positive bacillus.

Answer 4

A. palisading gram-positive bacillus.

Question 5

Corynebacterium diphtheriae is differentiated from C. ulcerans and C. pseudotuberculosis by
A. formation of the Tinsdale halo.
B. Christie, Atkins, Munch-Peterson (CAMP) reaction.
C. nitrate reduction.
D. lack of urease production.

Answer 5

D. lack of urease production.

Question 6

Corynebacterium urealyticum is most commonly associated with
A. wound infections.
B. dandruff.
C. upper respiratory tract infections.
D. urinary tract infections.

Answer 6

D. urinary tract infections.

Question 7

Neonatal fatality rates for Listeria monocytogenes approach
A. 5%.
B. 20%.
C. 50%.
D. 75%.

Answer 7

C. 50%.

Question 8

The incubation period of Erysipelothrix rhusiopathiae is
A. 12 to 18 hours.
B. 24 to 36 hours.
C. 2 to 7 days.
D. 9 to 12 days.

Answer 8

C. 2 to 7 days.

Question 9

The _____blank_______ for Gram-stained vaginal smears is a more accurate means of diagnosing bacterial vaginosis than culture.
A. Q score
B. Nugent scoring system
C. Bridgemate scoring system
D. POCA scoring system

Answer 9

B. Nugent scoring system

Question 10

Which organism is the most common cause of actinomycotic mycetoma?
A. Nocardia brasiliensis
B. Nocardia farcinica
C. Franciscella tularensis
D. Actinomyces israelii

Answer 10

A. Nocardia brasiliensis

Question 11

Diagnosis of Tropheryma whipplei is best made by microscopic examination of a(n)
A. early morning expectorated sputum sample.
B. catheter tip.
C. endoscopic duodenal biopsy.
D. preserved stool sample.

Answer 11

C. endoscopic duodenal biopsy.

Question 12

When Bacillus anthracis spores are inhaled into the pulmonary parenchyma, the patient may develop
A. cutaneous anthrax.
B. tuberculosis.
C. Rocky Mountain spotted fever.
D. Woolsorter’s disease.

Answer 12

D. Woolsorter’s disease.

Question 13

Food poisoning due to contaminated fried rice is most frequently associated with
A. Bacillus subtilis.
B. Bacillus cereus.
C. Bacillus circulans.
D. Lysinibacillus sphaericus.

Answer 13

B. Bacillus cereus.

Question 14

Most members of the genus Bacillus are
A. gram-positive, catalase-positive, rod-shaped, spore-formers.
B. gram-positive, catalase-positive, curved, non-spore-formers.
C. gram-positive, catalase-negative, pleomorphic, spore-formers.
D. gram-positive, catalase-negative, rod-shaped, non-spore-formers.

Answer 14

A. gram-positive, catalase-positive, rod-shaped, spore-formers.

Question 15

An isolate with the appropriate colony and microscopic morphology may be suspected to be Bacillus anthracis if it is:
a. β-Hemolytic on SBA
b. Nonmotile
c. Catalase negative
d. Gram negative, non– spore forming

Answer 15

b. Nonmotile

Question 16

An aerobic, gram-positive, spore-forming bacillus was isolated from raw vegetables that were associated with an outbreak of gastroenteritis. The organism produced β-hemolysis, was catalase positive, and was motile. The most likely organism is:
a. Bacillus anthracis
b. Nocardia nova
c. Bacillus cereus
d. Tsukamurella spp.

Answer 16

c. Bacillus cereus

Question 17

Bacillus cereus is most noted for causing:
a. Food poisoning
b. Meningitis
c. Sexually transmitted disease
d. UTIs

Answer 17

a. Food poisoning

Question 18

Which forms of infection are caused by Bacillus anthracis?
a. Injectional
b. Inhalation
c. Gastrointestinal
d. Cutaneous
e. All of the above

Answer 18

e. All of the above

Question 19

The functionality of lethal factor requires the presence of what other protein from Bacillus anthracis to form an active toxin?
a. Cyclic adenosine monophosphate (cAMP)
b. Edema factor
c. D-Glutamic acid
d. Protective antigen

Answer 19

d. Protective antigen

Question 20

Describe the appearance of spore-forming bacteria seen with the spore stain.

Answer 20

In the spore stain, vegetative cells are red, and the spores stain green.

Question 21

Corynebacterium species often appear as _____blank_________ on Gram staining.
a. Pleomorphic, gram-positive, club-shaped bacilli that appear in palisades or in “V” and “L” formations
b. Branching gram-positive bacilli that appear as fine, intertwining, delicate filaments
c. Short, thin gram-positive bacilli that appear in chains
d. Large square-ended, gram-positive or gram-variable bacilli in chains where the ends of the single cells fit snugly together

Answer 21

a. Pleomorphic, gram-positive, club-shaped bacilli that appear in palisades or in “V” and “L” formations

Question 22

The biochemical tests performed on a gram-positive bacillus were consistent with Corynebacterium diphtheriae. As a definitive test, the laboratory scientist should now:
a. Perform Gram staining of the isolate and observe this for its pleomorphic morphology
b. Prepare a methylene blue stain and examine it for metachromatic granules
c. Perform an Elek test to determine whether the organism produces exotoxin
d. Subculture the organism to cystine-tellurite blood agar and examine this for black colonies

Answer 22

c. Perform an Elek test to determine whether the organism produces exotoxin

Question 23

Diphtheria is uncommon in the United States because:
a. The insect vector has been eliminated
b. Of vaccination of the animal reservoir
c. Of routine use of an effective human vaccine
d. Aggressive antimicrobial therapy has nearly eliminated the bacteria

Answer 23

c. Of routine use of an effective human vaccine

Question 24

True infections with nondiphtheria Corynebacterium spp., such as C. jeikeium or C. striatum, are often in immunocompromised patients or patients who have had: a. Insertion of hardware or prosthetic devices
b. Coronary artery bypass surgery
c. Vitamin B12 deficiency
d. A lengthy hospital stay

Answer 24

a. Insertion of hardware or prosthetic devices

Question 25

A( n) __blank_______ test can help to differentiate which clinically significant Corynebacterium spp. recovered from urine samples? a. Gelatin hydrolysis; C. ulcerans b. Reverse CAMP; C. pseudotuberculosis c. Alkaline phosphatase; C. amycolatum d. Urease; C. urealyticum

Answer 25

d. Urease; C. urealyticum

Question 26

A newborn female becomes febrile and will not feed for about an hour after birth. A gram-positive rod is recovered from blood cultures from the newborn. The isolate has the characteristics listed below: What is the most likely identity of the isolate? Weakly β-hemolytic on SBA Gram-positive bacilli, no spores observed Catalase positive Hydrogen sulfide negative Motile at room temperature a. Erysipelothrix rhusiopathiae b. Listeria monocytogenes c. Corynebacterium ureilyticum d. Gardnerella vaginalis

Answer 26

b. Listeria monocytogenes

Question 27

A commercial fisherman with red sores on his hands was seen by his physician. Biopsy and culture of one of the lesions grew an organism with the characteristics listed below: What is the most likely identification? Nonhemolytic on SBA Gram-positive bacilli, no spores observed Catalase negative Hydrogen sulfide production positive Growth in gelatin resembled a test-tube brush a. Rhodococcus equi b. Listeria monocytogenes c. Lactobacillus acidophilus d. Erysipelothrix rhusiopathiae

Answer 27

d. Erysipelothrix rhusiopathiae

Question 28

A 42-year-old man from Guatemala cuts his bare feet on thorns while walking. A subcutaneous abscess develops, and when the patient is seen by a physician, his foot is swollen. When the wound is pressed by the physician, purulence is expressed along with some soft, white granules. A filamentous organism that is partially acid fast is recovered from the granules. This is most likely an ___(blank)_______ mycetoma caused by ____(blank)________. a. Actinomycotic; Pseudallescheria boydii b. Actinomycotic; Nocardia brasiliensis c. Eumycotic; Madurella mycetomatis d. Eumycotic; Gordonia bronchialis

Answer 28

b. Actinomycotic; Nocardia brasiliensis

Question 29

What other organisms can give similar clinical and laboratory findings as those for Listeria monocytogenes? How are these organisms differentiated from L. monocytogenes?

Answer 29

Streptococcus agalactiae (group B Streptococcus) and Enterococcus spp. can produce clinical laboratory findings similar to those for L. monocytogenes. Initial differentiation between L. monocytogenes and similar microorganisms can be made by the Gram stain, catalase test, and esculin hydrolysis.

Question 30

A 17-year-old male presented to an emergency department with a history of multiple episodes of febrile pharyngitis followed in 10 to 14 days by extensive desquamation of his hands and feet. The reoccurrences have followed several courses of antimicrobial therapy, including amoxicillin and cephalosporins. Rapid group A streptococci screens and cultures have been consistently negative for Streptococcus pyogenes. A specimen with a request for an alternative agent is submitted to a reference laboratory, and the results listed below are observe: The patient was subsequently treated with erythromycin, and he recovered. What was the etiologic agent? SBA: small, slightly hemolytic colony, which at 48 hours is a dark spot sunken in the agar Catalase negative Nitrate negative Reverse CAMP test positive a. Corynebacterium diphtheriae b. Arcanobacterium haemolyticum c. Listeria monocytogenes d. Rhodococcus equi

Answer 30

b. Arcanobacterium haemolyticum

Question 31

A sample from a female patient suspected to have bacterial vaginosis is sent to the laboratory. Which of the following would be an appropriate medium for this specimen? a. Loeffler medium b. HBT agar c. CTBA d. BCYE agar

Answer 31

b. HBT agar

Question 32

A 57-year-old man from New York City presents to the emergency department with diarrhea, arthralgia, abdominal pain, malabsorption, and weight loss of 10 lb (4.5 kg) over the last month. A duodenal biopsy is performed, but no infectious agent is recovered on culture media. However, on Gram staining, a gram-positive rod is observed in macrophages in the biopsy tissue. The organism is identified by 16S rRNA gene sequencing. What is the most likely identity of this organism? a. Bacillus anthracis b. Nocardia asteroides c. Tropheryma whipplei d. Erysipelothrix rhusiopathiae

Answer 32

c. Tropheryma whipplei