Anthrax laboratory tests

Overview
Other than Gram stain of specimens, there are no specific direct identification techniques for identification of Bacillus species in clinical material. These organisms are Gram-positive but with age can be Gram-variable to Gram-negative. A specific feature of Bacillus species that makes it unique from other aerobic microorganisms is its ability to produce spores. Although spores are not always evident on a Gram stain of this organism, the presence of spores confirms that the organism is of the genus Bacillus.

All Bacillus species grow well on 5% Sheep blood agar and other routine culture media. PLET (polymyxin-lysozyme-EDTA-thallous acetate) can be used to isolate B.anthracis from contaminated specimens, and bicarbonate agar is used as an identification method to induce capsule formation.

Bacillus sp. will usually grow within 24 hours of incubation at 35 degrees C, in ambient air (room temperature) or in 5% CO2. If bicarbonate agar is used for identification then the media must be incubated in 5% CO2.

B.anthracis appears as medium-large, gray, flat, irregular with swirling projections, often referred to as "medusa head" appearance, and is non-hemolytic on 5% sheep blood agar. It is non-motile, is susceptible to penicillin and produces a wide zone of lecithinase on egg yolk agar. Confirmatory testing to identify B.anthracis includes gamma bacteriophage testing, indirect hemagglutination and enzyme linked immunosorbent assay to detect antibodies. Anthrax is also a Biphasic disease