ENDOSPORE-FORMING GRAM-POSITIVE RODS AND COCCI

A General Introduction has been added to each disease chapter in an attempt to give a brief updated overview of the taxonomic, biological and other characteristics of the virus family or group of bacteria /protozoa that cause disease in livestock and, where relevant, involve wildlife. As the text of the three-volume book Infectious Diseases of Livestock is currently under revision the Editors are aware that there are inconsistencies between the updated introductions to chapters and the content of the chapters themselves. Once the chapters have been updated – a process that is currently underway – these inconsistencies will be removed.

The genera included in this group have diverse characteristics and are only grouped together for convenience because of their ability to form endospores.⁴ Of the six genera contained within the group, only species in the genera Bacillus and Clostridium are of veterinary importance. The characteristics of these two genera and the species contained within them are dealt with in the introductory sections preceding or within the relevant chapters dealing with them. The endospores that are characteristic for the members of this group are round or oval and form within the bacterial cells. These spores are highly resistant to the lethal effects of heat, desiccation and disinfectants, which allows them to survive in nature for prolonged periods, sometimes for decades — a factor that is important in the persistence of the bacteria in the environment and in the epidemiology of the diseases caused by them. Taxonomically, the genera Bacillus and Clostridium belong to a major and diverse group of bacteria known as the Bacillus/Clostridium group (low guanine and cytosine Gram-positive bacteria), that includes Listeria, Staphylococcus, Streptococcus and the mollicutes.³ Clostridium is then placed in the family Clostridiaceae and Bacillus in the family Bacilliceae.³

Species of bacteria within the two relevant genera in this group cause some of the oldest and most destructive diseases known.

Bacillus anthracis, which causes anthrax, a highly fatal and contagious disease of humans and animals, is the only species of the genus that is an important pathogen, although some of the others, such as Bacillus cereus, may be opportunistic pathogens. Numerous clostridial species, on the other hand, are causes of disease, their pathogenicity being mainly dependent on their ability to produce a range of toxins that have diverse effects, including histotoxicity, haemolysis and neurotoxicity. These toxins are elaborated in and absorbed either from the lumen of the intestinal tract of an animal, resulting in an enterotoxaemia (e.g. pulpy kidney disease), or foci of necrotic tissue (e.g. tetanus and gas gangrene), or they are produced in feed or decomposing matter of animal or vegetable origin (e.g. botulism, which is a form of food poisoning). Clostridium piliforme (formerly Bacillus piliformis), the agent of Tyzzer’s disease (see Tyzzer’s disease); is included in the genus Clostridium based on phylogenetic studies on the 16S RNA.^{1, 2} It is phenotypically similar to other clostridia in that it is a large rod, is motile and produces subterminal spores. Unlike other clostridia it possesses a Gram-negative cell wall and is an obligate intracellular pathogen.

References

1. COLLINS, M.D., LAWSON, P.A., WILLEM, A., CARDOBA, J.J., FERANDEZGARAZABAL, J., GARCIA, P., HIPPE, H. & FARROW, J.A.E., 1994. The phylogeny of the genus Clostridium: Proposal of five new generea and eleven new species combinations. International Journal of Systematic Bacteriology, 44, 812–826.
2. DUNCAN, A.J., CARMAN, R.J., OLSEN, G.J. & WILSON, K.H., 1993. Assignment of the agent of piliform Tyzzer’s disease to Clostridium comb. nov. on the basis of 16S RNA sequence analysis. International Journal of Systematic Bacteriology, 43, 314–318.
3. GARRITY, GT. M. & HOLT, J.G., 2001. Taxonomic outline of the Archaea and Bacteria. In: BOONE, D.R. & CASTENHOLZ, R.W., (eds). Bergey’s Manual of Systematic Bacteriology, 2nd ed. Vol. 1. (The Archaea and the Deeply Branching and Phototrophic Bacteria). New York: Springer-Verlag
4. SNEATH, P.H.A., 1986. Endospore-forming Gram-positive rods and cocci. In: SNEATH, P.H.A., MAIR, N.S., SHARPE, M.E. & HOLT, J.G., (eds). Bergey’s Manual of Systematic Bacteriology. Baltimore: Williams & Wilkins.