Introduction to Microbiology, Zoonoses and Antibiotics

Abstract

Microorganisms are biological entities (organisms) which are so small they cannot be visualised without the aid of some type of microscope. There are six groups that make up the microorganisms – archaea, bacteria, protozoa, fungi, algae and viruses. Despite their small size, it is clear that microorganisms have a profound influence on human and animal life and indeed on all aspects of the biosphere. Prokaryotes come in a variety of shapes and sizes. Probably the most frequently encountered are cocci (coccus – singular) (round or oval cells), bacilli (bacillus singular) (rod-shaped) and vibrios (curved). Algae are photosynthetic eukaryotes with the cells containing chloroplasts. Algae are autotrophic primary producers and do not cause infections; they are thus of limited importance in the veterinary field. The fungi are an important and diverse group of eukaryotes; although formerly considered to be plants, they are now known to be more closely related to animal cells. Protozoa, otherwise known as protists, are also a very varied group. Protozoa are nearly all chemoheterotrophs ranging from free-living cells to obligate parasites. Viruses are infectious particles which lack a cellular structure. Since viruses do not possess the mechanisms needed to produce energy and the ribosomes required to synthesise proteins, they are incapable of independent metabolism, replication or movement. As a result, viruses are completely dependent on the host cells, which they effectively hijack, to produce new virus particles. For survival microbes require sources of energy, carbon and several other elements including nitrogen, oxygen, phosphorus, sulphur, potassium, sodium, calcium, magnesium and iron. Trace elements are also needed but in relatively small amounts. All these elements are required for the maintenance of life processes and the synthesis of new biomass. Animals are host to large numbers of microbes, many of which contribute to the health of their host. However, the majority of these microbes have the ability to cause disease. Many of these microbes may only be able to infect a single species, but others are able to cross the species barrier to infect other species, including humans. Diseases that can be passed between vertebrate animals and humans are known as zoonotic diseases, or zoonoses.