Question 1

A 28-year-old woman suspected of having sepsis caused by Gardnerella vaginalis has multiple blood cultures drawn; however, all sets were negative.Which one of the following statements explains this discrepancy?

A) The lot of blood culture media is most likely defective.
B) The blood culture bottles should be incubated anaerobically to enhance the growth of the organism.
C) Gardnerella vaginalis is inhibited by sodium polyanethol sulfonate (SPS) in the blood culture.
D) No discrepancy is present. Gardnerella vaginalis remains localized and does not cause sepsis.

C
Gardnerella is inhibited by SPS, which currently is used as an anticoagulant in most commercial blood culture media.An SPS-free medium or a medium with SPS that is supplemented with gelatin should be used when G.vaginalis sepsis is suspected.

Accepted Answer

Gardnerella is inhibited by SPS, which currently is used as an anticoagulant in most commercial blood culture media.An SPS-free medium or a medium with SPS that is supplemented with gelatin should be used when G.vaginalis sepsis is suspected.

Question 2

To test the validity of TSI media, quality control should be performed using which two organisms?&#10;A) Gardnerella and Lactobacillus&#10;B) Erysipelothrix and Gardnerella&#10;C) Propionibacterium and Lactobacillus&#10;D) Actinomyces and Arcanobacterium

Accepted Answer

Only Erysipelothrix produces H₂S in TSI agar.All other organisms are negative; therefore the only positive and negative organisms used for quality control purposes are Erysipelothrix and Gardnerella.

Question 3

A catalase-negative, non-spore-forming, nonbranching, gram-positive rod that produces hydrogen sulfide when inoculated into triple sugar iron (TSI)agar is most likely:&#10;A) Corynebacterium.&#10;B) Bacillus.&#10;C) Actinomyces.&#10;D) Erysipelothrix.

Accepted Answer

Erysipelothrix is the only catalase-negative, gram-positive, non-spore-forming rod that produces hydrogen sulfide (H₂S)when inoculated into TSI agar.Some Bacillus spp.also blackens the butt of TSI, but it is catalase-positive and produces spores.

Question 4

A farmer has a localized, painful skin infection.Cultures are set up, and alpha-hemolytic, catalase-negative, and gram-positive bacilli are isolated.Based on this information, which of the following biochemical results are expected-urease, H₂S production in TSI, and nitrate reduction?

A) Positive urease, positive TSI, and positive nitrate
B) Positive urease, negative TSI, and negative nitrate
C) Negative urease, positive TSI, and negative nitrate
D) Negative urease, negative TSI, and negative nitrate

Accepted Answer

The organism is Erysipelothrix, which is negative for urease and nitrate but produces H₂S in a TSI slant.

Question 5

A gram-positive bacillus identified as Lactobacillus is isolated in large quantities from the urine of a 16-year-old female.Based on this information, the patient should receive which antibiotic?&#10;A) Penicillin&#10;B) Tetracycline&#10;C) Vancomycin&#10;D) No antibiotics should be administered.

Accepted Answer

Since Lactobacillus is normal vaginal flora, its presence in urine is usually insignificant and considered a contaminant; therefore antibiotic therapy is not administered.

Question 6

Which organism is nonhemolytic on 5% sheep blood agar but hemolytic on human blood?&#10;A) Weissella confusa&#10;B) Arcanobacterium haemolyticum&#10;C) Lactobacillus spp.&#10;D) Gardnerella vaginalis

Accepted Answer

G.vaginalis is beta-hemolytic on human blood Tween (HBT)bilayer agar but nonhemolytic on 5% sheep blood agar

Question 7

A catalase-negative, non-spore-forming, gram-positive rod that is not acid-fast could possibly belong to which group of bacteria?&#10;A) Corynebacterium&#10;B) Bacillus&#10;C) Actinomyces&#10;D) Erysipelothrix

Accepted Answer

The genera described in this chapter are all catalase-negative, non-spore-forming, and gram-positive rods; some may exhibit rudimentary branching.

Question 8

Clue cells are associated with which gram-positive bacilli?&#10;A) Gardnerella vaginalis&#10;B) Lactobacillus&#10;C) Erysipelothrix rhusiopathiae&#10;D) Arcanobacterium haemolyticum

Accepted Answer

The presence of clue cells is characteristic of bacterial vaginosis caused by Gardnerella vaginalis.Clue cells typically are present, and large numbers of gram-positive rods (e.g., lactobacilli)representing normal vaginal flora are absent or few in number.

Question 9

The wet mount and Gram stain of vaginal secretions from a patient who has bacterial vaginosis caused by Gardnerella vaginalis will reveal large:&#10;A) squamous epithelial cells with numerous attached pleomorphic gram-variable or gram-negative coccobacilli and rods.&#10;B) numbers of large gram-positive rods.&#10;C) numbers of polymorphonuclear leukocytes.&#10;D) pleomorphic gram-negative rods with many leukocytes.

Accepted Answer

Gardnerella are small pleomorphic gram-variable or gram-negative coccobacilli and have short rods.The wet mount and Gram stain of vaginal secretions are key tests for diagnosing bacterial vaginosis caused by G.vaginalis.A wet mount prepared in saline solution reveals the characteristic "clue cells," which are large, squamous epithelial cells with numerous attached small rods.A Gram-stained smear of the discharge shows the attached organisms to be gram-variable coccobacilli.Clue cells typically are present, and large numbers of gram-positive rods (e.g., lactobacilli)representing normal vaginal flora are absent or few in number.

Question 10

The reverse Christie, Atkins, Munch-Petersen (CAMP)test is positive for these curved gram-positive bacilli.Which beta-hemolytic organism is used in conjunction with this organism in the reverse CAMP test?

A) Streptococcus pyogenes
B) S. agalactiae
C) S. saprophyticus
D) S. aureus

Accepted Answer

In a reverse CAMP test, Arcanobacterium haemolyticum is streaked on a blood agar plate.S.aureus is then streaked perpendicular to the Arcanobacterium.An arrow pointing to the S.aureus indicates a reverse CAMP-positive test.

Deck 17: Erysipelothrix Lactobacillus and Similar Organisms