Bacteria and Antibiotic Resistance Essay Example | Topics and Well Written Essays - 1500 words

Bacteria and Antibiotic Resistance - Essay Example "Virulence" and "pathogenicity" refer to the ability of bacteria to cause disease. "Bacteria are complex (while viruses must "live" in a "host" (us), bacteria can live independently) and so are easier to kill" (Antibiotics, Bacteria and (usually not) Viruses 2007). The traditional criteria for establishing that a bacterium is responsible for a disease have been Koch's postulates, which were developed in 1882. Although serving well for many years, these postulates have limitations: (1) not all bacteria can be cultured, (2) not all members of a species are equally virulent, and (3) adequate animal hosts are not always available. Host susceptibility is an important virulence factor for bacteria. The first important step in bacterial pathogenesis is adherence to a host cell. This occurs by means of pili, which consist of long rods that extend out from the bacterial surface. The tips of the pili contain proteins that attach to host cell receptors. In some cases, "pilin, the protein subuni ts of the pilus shaft, attach to the host cell's receptors. In addition to pili, bacterial surface proteins called adhesins attach firmly to the host cells" (Walsh 2003, p. 34). Sometimes the host makes antibodies against pili or adhesin proteins, and this induces the bacteria to make different types of adhesins. Only Gramnegative bacteria make adhesins; the mechanism of how Gram-positive bacteria attach to a host cell is not known (Walsh 2003). The virulence of many bacterial pathogens is due to the toxins they produce, which disrupt normal cell functions and cause cell death. Scholar and Pratt (2000) explain that "exotoxins are proteins that are excreted by dividing bacteria. Exotoxins that attack a variety of cell types are called cytotoxins" (p. 76); those that attack a particular cell type or tissue have specific names, such as neurotoxin, leukotoxin, hepatotoxin, or cardiotoxin. Exotoxins can be associated with a specific bacterial disease. In addition to toxic proteins, pathogenic bacteria also produce hydrolytic enzymes that degrade host tissues and disseminate bacteria within the host. Heat-shock proteins produced by bacteria stimulate autoimmune responses so that host antibodies and T-cells attack healthy host cells (Scholar and Pratt 2000). The essential property that differentiates antibiotics from antiseptics is that they are sufficiently selective to allow their use within the body, rather than just on the surface. This selective toxicity is not absolute but it is quantifiable as we shall see in chapter 6. There is, therefore, always room for improvements and developing drug licensing regulations seek improvements in the comparative safety of antibiotics. "Antibiotics work by destroying either the proteins that build a bacterium's cell wall or the protein-producing ribosomes" (Greene 2000, p. 23). The drug must inhibit the target bacteria at lower concentrations, usually much lower, than those concentrations that produce toxic effects in humans. Some antibiotics can be given in very high doses without toxic effects, e.g. penicillins, but others may produce serious toxicity at levels that are not much above those required for treatment of infection. Many alterations to antibiotics have been made to improve this select ivity; though with some antibiotics this is virtually impossible to achieve. The most selective antibiotics tend to be those that inhibit a process in bacteria that does