Anthrax is an infectious disease caused by spores of the bacterium Bacillus anthracis.
In human anthrax, the bacillus is usually demonstrable in material from a malignant pustule, sometimes in sputum from pulmonary anthrax and also in the blood in the septicemic stage of all forms of the infections. Man is relatively resistant to anthrax and laboratory workers are rarely infected. However great care should be taken to avoid escape of the long surviving spores into laboratory environment and all the procedures should be carried out in safety cabinet. Anthrax cannot spread directly from human to human but anthrax spores can be transported by human clothings, shoes etc. In humans, anthrax is caused by exposure to dead infected animals, consumptions of infected animal tissue or exposure to light density anthrax spores from animal wool, fur, hide, etc.
PLET Agar Base originally formulated by Knisley (1) is the best selective medium for cultivation of B.anthracis (2, 3, 4) from suspected environmental specimens, animal products or clinical specimens, inhibiting Bacillus cereus.
Beef heart infusion from solids and tryptose provide the carbonaceous and nitrogenous compounds necessary for growth whereas sodium chloride provides the osmotic equilibrium. Thallous acetate and Polymyxin (FD185) are inhibitory agents allowing growth of B.anthracis while inhibiting contaminants. Lysozyme (FD185) specifically suppresses the growth of gram-negative contaminants. The suspected specimen may be used directly for streaking or heat-treated or alcohol-treated specimens can be used for streaking. On incubation at 37°C for 24 hours colonies develop from 30-100% of the B.anthracis spores that would grow on non-selective Heart Infusion Agar (M169), being smaller and smoother than on the later medium. PLET Agar Base inhibits growth of most strains of B.cereus, B.subtilis , other Bacillus species, Enterobacteriaceae and Pseudomonas species. Some strains of B. cereus from soil form colonies but they are smaller than those of B. anthracis, minute after 24 hours and moderately sized after 48 hours. Colonies of B.anthracis appear in 36-40 hours after incubation at 37°C. Roughly circular, creamy- white colonies with a ground-glass texture are further subcultured on blood agar plates for identification. Capsule production can be seen directly or on blood agar plates (4).
Directions: Suspend 40.34 grams in 990 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to 50°C. Aseptically add rehydrated contents of 1 vial of Anthracis Selective Supplement (FD185). Mix well and dispense as desired.