Deck 15: 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

A middle-aged women presented to the emergency room complaining of cramping and gastrointestinal discomfort.She had recently attended a family reunion the past weekend.The event was a picnic where potato salad,hamburgers,deviled eggs,hot dogs and chips were served.A feces culture was requested resulting in no growth.What would be the next recommended follow-up testing?

A)Serologic testing for IgM and IgG
B)No follow-up testing required
C)Collect an additional specimen and attempt to cultivate on specialized media
D)Treat the patient with ampicillin

Answer 2

D
A follow-up specimen is highly likely to not result in the isolation of a potential pathogen without an increase or change in symptoms at this time.The patient's condition may resolve independently if the isolate is a pathogen such as Staphylococcus aureus that may have been transmitted in the potato salad or deviled eggs.The other potential sources of infection include the hamburger,Escherichia coli or the hot dogs for L.monocytogenes.E.coli is not indicated unless there is evidence of undercooked hamburger.

Question 3

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
B)C.diphtheria and Streptococcus pneumoniae
C)C.ulcerans and Corynebacterium pseudotuberculosis
D)C.glucuronolyticum and C.ulcerans

Answer 3

A
The only organisms that are positive and negative for urea are C.ulcerans and C.diphtheria.The other organisms are either both positive or both negative for urea.

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

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

Question 6

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)food-borne listeriosis.
B)staphylococcal food poisoning.
C)gastric gangrene.
D)Salmonella infection.

Question 7

A 13-year-old girl presented to her physician complaining of being tired,having a mild sore throat and fever.She appears to have a grey coating on her tonsils when examined by the physician.The most logical etiologic agent associated with the patient's illness is:

A)Streptococcal pharyngitis.
B)diphtheriae.
C)scarlet fever.
D)Tonsillitis.

Question 8

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 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)L.monocytogenes.
B)Corynebacterium diphtheriae.
C)Bacillus anthracis.
D)Bacillus cereus group

Question 10

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.
B)Corynebacterium glucuronolyticum.
C)Corynebacterium xerosis.
D)Corynebacterium ulcerans.

Question 11

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

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

Question 12

A cerebrospinal fluid (CSF)culture was performed on a newborn in distress.After overnight incubation,small gram-positive bacilli with a soft zone of b-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