seems, however, that there is no current report that proves that antibiotic contamination of the aquatic environment has caused human bacterial pathogens to become resistant (MacMillan, 2001). Food-borne or zoonotic disease associated with aquacultural products including aquaponics, seems to be rare; for this reason it is assumed that that food-borne bacterial pathogens that are also resistant to antibiotics in these products are even more rare. As noted earlier in this report, most food-borne illnesses associated with fish in the USA were caused by non-bacterial conditions such as ciguatera and scombroid poisonings, but in none of these situations was an aquacultural product involved (MacMillan, 2001). In aquaculture, there are several natural barriers to the transfer of resistance factors and the occurrence of enteric bacteria that infect humans. These barriers include temperature, itinerant (transitory) microbial flora, and important physiological and evolutionary differences. Various physical factors may also decrease the probability of the transfer of resistance. Likely the most obvious natural barrier is that of body temperature. Farmed aquatic species are all poikilothermic, with a labile body temperature that is dependent on environmental temperature. Generally, the body temperature of poikilotherms is too low to be considered optimal for the proliferation of most enteric bacteria likely to infect humans. Most human food-borne pathogens prefer the comparatively warm temperatures of homeotherms (creatures like humans that have a relatively stable temperature that is independent of the ambient temperature; warm-blooded) (Inglis et al, 1993; MacMillan, 2001). The usual enteric bacteria of concern in debates on public policy are
E.coli, Campylobacter jejuni, C. coli, Shigella and Salmonella spp, Vibrio cholerae, V. paratyphi, Staphylococcus aureus, Listeria monocytogenes and Yersinia enterocolitica (Inglis et al, 1993; MacMillan, 2001). Of these species, only L. monocytogenes is known to be capable of reproducing at low temperatures – in fact, usual refrigerator temperatures (4oC) are ideal for the proliferation of these organisms, and are often used to encourage their growth in
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