A microbiologist is looking at a sheep blood agar (SBA) plate from a patient who might have been exposed to a biological agent.The colonies that are growing on the plate are nonhemolytic, large, have a ground-glass appearance, and look like a Medusa's head.On Gram stain, the colonies are large gram-positive rods that seem to have central spores.What is the most probable organism?
A)Bacillus anthracis
B)Brucella mallei
C)Burkholderia cepacia
D)Yersinia pestis

Question

Quizplus · Accepted Answer

In aerobic culture, B.anthracis will yield large (2- to 5-mm), nonhemolytic colonies on 5% SBA.Colony growth can be rapid, as little as 8 hours.Mature colonies have a ground-glass appearance; cells are characteristically large gram-positive bacilli, possibly showing endospore formation.The spores are central or subterminal and do not cause the bacterial cell to swell.The colony margins often have feathery projections coming from the margin, referred to as "Medusa-head" colonies.

A Microbiologist Is Looking at a Sheep Blood Agar (SBA)