Safety Of Antimicrobials

Not long after the antibiotics were discovered and accepted into feeding programs for livestock and poultry, questions were raised relative to their safety. Many of those concerns continue today. The most pressing concern is whether the widespread usage of antibiotics in animal feeds contributes to a reservoir of drug-resistant enteric bacteria that are capable of transferring their resistance to pathogenic bacteria, thereby causing a potential public health hazard.[11,12]

Although transfer of antibiotic-resistant plasmids (R-plasmids) occurs rapidly in vitro, the extent to which it occurs in the animal, and between animal bacteria and human bacteria, is not well documented. Animal bacteria do not colonize very effectively in humans unless extremely large doses are consumed, and even then they

are transient.[13]

In 1988, the National Academy of Science's Institute of Medicine was asked by the FDA to conduct an independent review of the human health consequences and make a quantitative risk assessment associated with the use of penicillin and tetracyclines at subtherapeutic levels in animal feeds. The committee was unable to find a substantive body of direct evidence that established the existence of a definite health hazard in humans that could be associated with the use of subtherapeutic concentrations of these antibiotics in animal feeds.[14] Other groups of scientists have extensively reviewed the published data and concluded that there is no evidence of human health being compromised by subtherapeutic antimicrobial usage in animals.[4,15]

The question of whether antimicrobial resistance constitutes a significant threat to human health will likely continue to be debated in the scientific community as well as in the political arena. Antibiotics for growth promotion have already been banned in several countries in Europe, and a ban on certain, if not all, antibiotics for growth promotion has been proposed for the United States. Even a complete ban would likely have little effect on antibiotic resistance levels or patterns, according to some long-term, antibiotic withdrawal studies.[10] Three years after the European ban on growth-promoting antibiotics, there was little effect on resistance levels in humans, whereas the health of pigs and chickens markedly deteriorated.[16]

Monitoring and surveillance of microbial resistance in animals and humans has continued for many years with no animal-to-human infection path being clearly delineated. While the incidence of antimicrobial resistance in the human population is high, the amounts and patterns of resistance have not changed substantially.1-17-1 Many would argue that the high incidence of antimicrobial resistance in humans is mainly a result of antibiotics that are prescribed directly for human use, because well over half of the antibiotics produced in the United States are used in human medicine.[15]

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