Biotic and Abiotic Effects

Abstract

When enteric bacteria are discharged into the sea, they immediately encounter a wide range of biotic and abiotic stresses in an environment that ismarkedly different to their natural, intestinal habitat. Biotic stresses arise from natural seawater microbiota, which are better scavengers for the limited nutrients available, and may also prey and graze on the enteric newcomers. Abiotic stresses faced by enteric bacteria in seawater include sunlight, temperature, pH, lack of nutrients, salinity, and (possibly) hydrostatic pressure. Although they have few defenses against marine organisms, enteric bacteria have evolved protectivemechanisms against physical stresses. These are designed tomaximize their survival rates, and thus their chances of infecting new hosts via the fecal–oral route. There is ample evidence from epidemiological studies (reviewed by Pruss, 1998) that pathogen survival rates are high enough in sewage-polluted marine waters to constitute a health hazard to bathers (although the proportion of illnesses attributable to bacterial pathogens has not been determined). There is also reasonable epidemiological evidence for the transmission of bacterial pathogens via shellfish, particularly Salmonella spp. (reviewed by Rippey and Verba, 1991). Thus, the extent to which enteric bacteria succumb to, ward off, or recover from the various biotic and abiotic stresses in the alien marine environment is important from a public health perspective. This chapter reviews the principal biotic and abiotic stresses affecting bacterial survival in seawater. However, it should be noted that most of the available information has been derived from studies of bacterial indicators rather than pathogens. Some of this information has also been reviewed in detail elsewhere, including by Harm (1980), Gould and Munro (1981), Gameson and Gould (1985), Jagger (1985), Gameson (1988), Sherr and Sherr (1994), and Rozen and Belkin (2001).