Bacteriology

Bacteria, along with blue-green algae, are prokaryotic cells. That is, in contrast to eukaryotic cells, they have no nucleus; rather the genetic material is restricted to an area of the cytoplasm called the nucleoid. Prokaryotic cells also do not have cytoplasmic compartment such as mitochondria and lysosomes that are found in eukaryotes. However, a structure that is found in prokaryotes but not in eukaryotic animal cells is the cell wall which allows bacteria to resist osmotic stress. These cell walls differ in complexity and bacteria are usually divided into two major groups, the gram-positive and gram-negative organisms, which reflect their cell wall structure.  The possession of this cell wall, which is not a constituent of animal cells, gives rise to the different antibiotic sensitivities of prokaryotic and eukaryotic cells.  Prokaryotes and eukaryotes also differ in some important metabolic pathways, particularly in their energy metabolism and many bacterial species can adopt an anaerobic existence.

In this section, we shall look at the structure of typical bacterial cells and the ways in which they liberate energy from complex organic molecules. Various aspects of bacterial structure and metabolism are the basis of bacterial identification and taxonomy. Bacteria are constantly accumulating mutational changes and their environment imposes a strong selective pressure on them. Thus, they constantly  and rapidly evolve. In addition, they exchange genetic information, usually between members of the same species but occasionally between members of different species. We shall see how this occurs. 

Bacteria have parasites, the viruses called bacteriophages which are obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery. Eventually, these lyze the infected bacterial cell liberating new infection phage particles. The interrelationships of bacteria and the pages will be investigated.

Finally, we shall look at general aspects of bacterial pathogenesis, that is how bacteria damage the host organism, before surveying a variety of human diseases that are caused by bacteria.