Deck 16: Listeria Corynebacterium and Similar Organisms

Question 1

Bacteria described as being coryneform have which of the following morphologic features?

A) Squared rods with squared ends arranged in pairs
B) Short gram-positive cocci in branching chains
C) Resemble and are often referred to as Chinese letters
D) Long branching gram-positive bacilli

Answer 1

C
Most of the genera in this chapter (except Listeria, Rothia, and Oerskovia)are classified as coryneform bacteria, that is, they are gram-positive and have short or slightly curved rods with rounded ends; some have rudimentary branching.Cells are arranged singly in "palisades" of parallel cells or in pairs that remain connected after cell division to form V or L shapes.Groups of these morphologic characteristics observed together resemble, and are often referred to as, Chinese letters.

Question 2

After 48 hours of incubation, black colonies with a dark brown halo are observed on Tinsdale agar.What type of toxin does this organism produce?

A) Emetic toxin
B) Exotoxin
C) Enterotoxin
D) Endotoxin

Answer 2

B
C.diphtheriae produces black colonies with a dark brown halo on Tinsdale agar and is also a potent exotoxin.

Question 3

Patients who are immunocompromised and women who are pregnant should avoid eating soft cheeses such as Mexican-style, feta, Brie, Camembert, and blue-veined cheeses to prevent:

A) foodborne listeriosis.
B) staphylococcal food poisoning.
C) gastric gangrene.
D) Salmonella infection.

Answer 3

A
Patients who are immunocompromised may prevent foodborne listeriosis by avoiding soft cheeses such as Mexican-style, feta, Brie, Camembert, and blue-veined cheeses.In addition, leftover or ready-to-eat foods such as hot dogs or cold cuts should be thoroughly heated before consuming them.

Question 4

A pharyngeal specimen is inoculated on cystine-tellurite blood agar, modified Tinsdale agar, and MacConkey agar.After 48 hours of incubation, black colonies with a brown halo are observed on the Tinsdale agar and gray colonies are isolated from the cystine-tellurite agar.However, no growth is observed on the MacConkey agar.Which one of the following statements explains this discrepancy?

A) The MacConkey agar is most likely expired.
B) The MacConkey agar should be incubated an additional 24 hours to observe growth.
C) The pH of the media may be altered, causing an environment that is too acidic for the organism to grow.
D) No discrepancy is present; this organism does not grow on MacConkey agar.

Question 5

A catalase-positive, gram-positive bacillus that is not acid-fast, does not branch, and does not form spores could possibly belong to which group of bacteria?

A) Corynebacterium
B) Bacillus
C) Actinomyces
D) Mycobacterium

Question 6

A gram-positive bacillus, which grew on Tinsdale agar, is esculin hydrolysis-negative, urease-positive, and nonlipophilic.The organism can be identified as:

A) C. diphtheria (subsp. gravis).
B) C. imitans.
C) C. xerosis.
D) C. ulcerans.

Question 7

A cerebrospinal fluid (CSF)culture was performed on a newborn in distress.After overnight incubation, small gram-positive bacilli with a soft zone of beta hemolysis grew on sheep blood agar.Based on this information, what results would be expected on the following tests: hippurate; Christie, Atkins, Munch-Petersen (CAMP); and motility?

A) Negative hippurate, positive CAMP, and negative motility
B) Positive hippurate, negative CAMP, and positive motility
C) Positive hippurate, positive CAMP, and positive motility
D) Negative hippurate, negative CAMP, and negative motility

Question 8

The isolation of a small gram-positive, catalase-positive rod with a narrow zone of beta hemolysis isolated from blood or CSF should be used as strong presumptive evidence for:

A) listeriosis.
B) diphtheria.
C) pertussis.
D) tetanus.

Question 9

The organism that exhibits characteristic end-over-end tumbling motility when incubated in nutrient broth at room temperature for 1 to 2 hours is:

A) Listeria monocytogenes.
B) Corynebacterium diphtheriae.
C) Bacillus anthracis.
D) Bacillus cereus.

Question 10

Quality control is set up on urea media.Which two organisms should be used to determine the validity of the media?

A) C. ulcerans and C. diphtheria (subsp. mitis)
B) C. diphtheria (subsp. gravis) and C. diphtheria (subsp. intermedius)
C) C. ulcerans and C. pseudotuberculosis
D) C. diphtheria (subsp. belfanti) and C. diphtheria (subsp. gravis)