Pathogenic organisms

Before the connection between disease and sewage-carried pathogens was recognized in the mid-18th century, disastrous epidemics were common. For example, typhoid fever and cholera killed 

TABLE 8.6. Infectious agents present in polluted wastewater 

Nevertheless, in many parts of the world—and largely because of poor sanitation regarding water and sewage—a significant portion of the world s population is chronically infected. More than 250 million new cases of water-borne disease are reported each year, about 10 million of which result in death (about 50% of these are children under five). 

For example, the average density of fecal coliforms in human excreta is 1.3 x 107/g. The US EPA has set a standard of no detectable coliforms per 100 mL in drinking water. In contrast, the Clean Water Act indicates 200 fecal coliforms/100 mL for wastewater discharges. 

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Disinfection destroys pathogenic organisms. This procedure can render an object safe for use. Disinfectants include solutions of hypochlorites, tinctures of iodine or iodophores, phenoHc derivatives, quaternary ammonium salts, ethyl alcohol, formaldehyde, glutaraldehyde, and hydrogen peroxide (see Disinfectants AND antiseptics). Effective use of disinfected materials must be judged by properly trained personnel. 

Pathogenic organisms Bacteria, viruses or cysts which cause disease (typhoid, cholera, dysentery) in a host (such as a person). There are many types of bacteria (non-pathogenic) which do NOT cause disease. Many beneficial bacteria are found in wastewater treatment processes actively cleaning up organic wastes. 

The macrolides are effective against a wide variety of pathogenic organisms, particularly infections of die respiratory and genital tract. 

Both vaccines and toxoids are administered to stimulate the immune response within the body to specific antigens or toxins. These agents must be administered before exposure to the pathogenic organism. The initiation of the immune response, in turn, produces resistance to a specific infectious disease. The immunity produced in this manner is active immunity. Display 54-5 gives examples of indications for use of toxoids and vaccines. 

The development of vaccines based on S-layer technologies has focused on two strategies (1) exploiting S-layers present on pathogenic organisms, and (2) use of S-layer lattices as carrier/adjuvants for vaccination and immunotherapy [100,101]. 

Studies on S-layers present on the cell envelopes of a great variety of pathogenic organisms [100] revealed that these crystalhne arrays can represent important virulence factors. Most detailed studies have been performed on the fish pathogenic bacteria Aeromonas salmonicida and Aeromonas hydrophila [102] and the human pathogen Campylobacter fetus uh p. fetus [103] and Bacillus anthracis [104]. For example, whole-cell preparations or partially purified cell products are currently used as attenuated vaccines against various fish pathogens [102,105]. 

In some infections the pathogenic organisms are located intracellularly within phagocytic cells and, therefore, remain relatively protected from drugs which penetrate cells poorly, such as the penicillins and cephalosporins. In contrast, erythromycin, rifampicin and chloramphenicol readily penetrate phagocytic cells. Legionnaires disease is an example of an intracellular infection and is treated with rifampicin and/or erythromycin. 

Pathogenic organisms possess certain properties which enable them to overcome these primary defences. They produce metabolic substances, often enzymic in nature, which facilitate the invasion of the body. The following are examples of these. 

The hazard of the transfer of microorganisms from humans to pharmaceutical preparations may be reduced by comprehensive training in personal hygiene coupled with regular medical checks to prevent carriers of pathogenic organisms from coming in contact with any product. 

The indigenous microbial population is quite different in the home and in hospitals. Pathogenic organisms are found much more frequently in the latter and consequently are isolated more often from medicines used in hospital. Usually, there are fewer opportunities for contamination in the home, as patients are generally issued with individual supplies in small quantities. 

Mutans streptococci are the major pathogenic organisms of dental caries in humans. The pathogenicity is closely related to production of extracellular, water-insoluble glucans from sucrose by glucosyltransferase and acid release from various fermentable sugars. Poly(catechin) obtained by HRP catalyst in a phosphate buffer (pH 6) markedly inhibited glucosyltransferase from Streptococcus sorbrinus 6715, whereas the inhibitory effect of catechin for this enzyme was very low. 

Toxoid A toxin of a pathogenic organism treated to destroy its toxicity but leave it capable of inducing antibody formation upon injection. 

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