Question 1

Induction of capsule formation by B.anthracis can be accomplished with&#10;A)5% sheep blood agar.&#10;B)PLET agar.&#10;C)bicarbonate agar.&#10;D)urea agar.&#10;E)All of the above are correct.

Accepted Answer

As a means of identification, bicarbonate agar is used to induce B. anthracis capsule formation.

Question 2

Media that can be used for isolation of Bacillus anthracis include&#10;A)Thayer-Martin agar.&#10;B)5% sheep blood agar.&#10;C)MacConkey agar.&#10;D)CNA blood agar.

Accepted Answer

All Bacillus and related genera grow well on 5% sheep blood agar, chocolate agar, routine blood culture media, and commonly used nutrient broths. They will not grow on MacConkey agar, and those that are susceptible to nalidixic acid will not grow on CNA (Columbia agar with nalidixic acid and colistin). Two special media are used for isolation and identification of B. anthracis. PLET (polymyxin-lysozyme-EDTA-thallous acetate) can be used for selection and isolation of this species from contaminated specimens. As a means of identification, bicarbonate agar is used to induce B. anthracis capsule formation.

Question 3

Suspect spore-forming gram-positive bacilli that are nonhemolytic, nonmotile, and penicillin-susceptible, and that produce a wide zone of lecithinase on egg yolk agar can be identified as&#10;A)Corynebacterium diphtheriae.&#10;B)Bacillus anthracis.&#10;C)Bacillus cereus.&#10;D)Corynebacterium jeikeium.

Accepted Answer

B. anthracis should be suspected if typical nonhemolytic "Medusa head" colonies are observed on 5% sheep blood agar and if the organism is subsequently found to be nonmotile and lecithinase-positive.

Question 4

Suspect spore-forming gram-positive bacilli that are hemolytic, motile, and penicillin-resistant and that produce a wide zone of lecithinase on egg yolk agar can be identified as&#10;A)Corynebacterium diphtheriae.&#10;B)Bacillus anthracis.&#10;C)Bacillus cereus.&#10;D)Corynebacterium jeikeium.

Accepted Answer

B. cereus is another important species to identify. It is penicillin-resistant, beta-hemolytic, and motile and it produces a wide zone of lecithinase on egg yolk agar.

Question 5

Induction of sporulation by Bacillus sp.can be accomplished with&#10;A)5% sheep blood agar.&#10;B)PLET agar.&#10;C)bicarbonate agar.&#10;D)urea agar.&#10;E)All of the above are correct.

Accepted Answer

To induce sporulation, organisms can be grown on triple sugar iron agar (TSI), urea agar, or nutrient agar containing 5 mg/L of manganese sulfate. On Gram-stained smears, spores appear clear because they do not retain the crystal violet or safranin. However, spores will stain with specific dyes such as malachite green, which is forced into the spore using heat; the vegetative cell is then counterstained with safranin.

Deck 15: Bacillus and Similar Organisms