Bacullis Anthracis/ Anthrax

Bacullis Anthracis/ Anthrax

Introduction

Bacillus anthracis is related to Bacillus cereus, Bacillus mycoides, Bacillus pseudomycoides, Bacillus thuringiensis and Bacillus weihenstephanensis. These six species have strong genetic similarities (homologies DNA - DNA sequence homologies of 16S and 23S rRNA, sequence homologies of the 16S rDNA intergenic spacer-23S rDNA) and are often combined within a single group called the "Bacillus cereus group".

Some authors have proposed to bring this entire Bacillus within a single species (Bacillus cereus) and assign them a status of subspecies. If such proposals were validated, the result of confusion and important practical consequences because some species, such as Bacillus anthracis and Bacillus cereus, have a medical interest and other, such as Bacillus thuringiensis, have great economic importance (Sinclair A, 2011).

Bacteriological Characters

Bacillus anthracis is a Gram positive, with square ends, 1.0 to 1.2 m m diameter by 3 m to 5 m in length, motionless, sporulated, encapsulated, synthesizing a layer S. In pathological specimens, Bacillus anthracis is present in isolated form or in short chains, but in culture, it frequently formed longer chains giving it an appearance in "bamboo". Bacillus anthracis is nitrate reductase positive, urease negative, TP +, it acidifies glucose but not mannitol or xylose, it liquefies gelatine very slowly and phosphatase activities and lécithinasique is nil or negligible. Bacillus anthracis is aerobic-anaerobic and grows in 24 hours on ordinary media, incubated under normal atmosphere, giving colonies of 3 to 5 mm in diameter that look R, "the head of Medusa". On blood agar, the germ is not hemolytic in 24 hours but, by extending the incubation, it develops a slight zone of hemolysis incomplete. After culturing on agar enriched serum and / or bicarbonate and incubated at 37 ° C in an atmosphere containing 5 p. percent CO 2, the bacterium synthesizes its capsule and colonies have a smooth and shiny.

The spore, ovoid and non-deforming, occupies a central position. It survives in the soil for long periods (survival of the spores is about a hundred years but, spores whose age was estimated at 200 years have leveraged the vegetative form) . Persistence in soil is favored by a neutral or slightly alkaline (pH between 6 and 8.5). This resistance explains the persistence of the disease in some regions ("cursed fields") or its resurgence when spores buried up to the surface thanks to major works. The possibility of germination followed by a multiplication of the vegetative form in the soil cannot be totally excluded (theory of Van Ness).

Sporulation requires a temperature of between 15 and 42 ° C, a humid atmosphere and the presence of oxygen. The latter requirement leads to prohibit the autopsy of dead coal (except in specially equipped) and block the natural orifices of corpses to prevent the exposure of bacilli to the oxygen in the air, sporulation and the spread of spores. By cons, in the absence of dissection, the putrefactive germs cause any sporulation inhibiting anaerobic and leading to death of bacteria. Thus, experimentally, it is no longer possible ...