Bacillus Anthracis diagnostic
Bacillus anthracis is diagnosed from samples taken inside the nose or a wound. Samples are sent to a laboratory to determine whether they contain bacteria that cause anthrax. The results are normally available approximately two days after taking the samples. Fortunately, many of which were found spores in the nasal passages do not contract anthrax, because the spores did not penetrate the skin and have not been inhaled into the lungs.
To determine whether a person has been exposed to anthrax, you can perform blood tests. If so, antibodies (proteins fighting foreign substances to the body) of the bacteria will have been produced by the immune system of the person and can be detected by laboratory tests.
You can be exposed to anthrax without necessarily getting the disease later. However, if the result of a laboratory test is positive, the person must be careful in case the infection is in its early stages, before symptoms become apparent.
The isolation of a strain of Bacillus can be extremely time consuming when the sample is plurimicrobien. Selective media have been developed for some species (mid-Mossel, allowing enumeration of ¤ Bacillus cereus is the only mid-marketed) and heating for 10 minutes at 70-80 ° C does not always satisfactory results because the heat resistance of spores is variable depending on the environment. In addition, it is necessary to induce germination which often requires a thermal shock with parameters (temperature, time) varies with species.
The diagnosis of type based on morphology, affinity dye (sometimes very difficult to determine because some Gram-positive species appear only in old cultures a few hours), the study of respiratory type and the identification of a spore.
As pointed out Logan and Turnbull, it is essential to establish that the suspect colonies are made ??up of gram-positive bacteria (in case of doubt, a test KOH ** can be useful), sporulated and capable of growing in aerobically.
Sporulation is a central, but sometimes very difficult to obtain in vitro. Should be used sporulation media (often nutrient agar containing sulfate or manganese chloride) and leave old cultures ten days. Microscopic examination phase contrast technique is the best demonstration of spores that appear so bright and due process. A more cumbersome alternative is to seek the presence of spores after staining with green malachite *** .
The species diagnosis is difficult. In practice, it is based on the appearance of the spore which allows to classify the strain in one of three groups defined by Gordon et al. In a second step, use the identification key proposed by Smith et al. allows a presumptive diagnosis of the species may have a medical interest.
- In Group IA,
are VP +, or grow anaerobically at pH 5.7 or in the presence of 7 per percent NaCl, hydrolyze starch and reduce nitrates. These four species have very similar bacteriological characters, for a differential diagnosis, see Table I .
- Bacillus anthracis,
- Bacillus cereus,
- Bacillus thuringiensis and
- Bacillus weihenstephanensis
- In group IB:
- Bacillus licheniformis and Bacillus coagulans grown on agar at pH 6 or anaerobically, but they are VP +, Bacillus licheniformis is gelatinase + and grown in the presence of 7 p. percent NaCl as inverse characters are noted for Bacillus coagulans.
- Bacillus subtilis and Bacillus pumilus grown on agar at pH 6 but not anaerobic, they are VP + but, unlike Bacillus pumilus, Bacillus subtilis reduces nitrate and starch hydrolysis.
Other identification keys have been proposed. Include that of Reva et al. (2001) for mesophilic species, growing aerobically on nutrient agar at pH 7.
The diagnosis of near certainty requires numerical identification techniques (eg joint use of plates or API 50 CH kits and software Biolog identification), or automated identification systems (Bacillus card for the system bioMerieux Vitek) or chemotaxonomic analysis (study of the methyl esters of fatty acids, pyrolysis mass spectrometry after ...).
Also, with the exception of some species, identification of a strain of Bacillus can be performed in a specialized laboratory.
Bacteriological diagnosis is also a problem of interpretation. The Bacillus or their spores are widespread in the environment and are even present on the sampling equipment considered sterile (including the wooden rods swabs) or antiseptic solutions (alcohol 95). With the exception of ¤ Bacillus anthracis, the isolation of a strain of Bacillus must always be a critical interpretation. Thus, the non-sterile gloves, the staff draw blood, the use of alcoholic solutions contaminated ... can lead to the isolation of strains of Bacillus sp. and to conclude wrongly bacteremia. Their responsibility for infection can be established only to the extent they have been isolated in pure culture or in many, many times in the same individual.