38th INTERSCIENCE CONFERENCE ON ANTIMICROBIAL AGENTS AND CHEMOTHERAPY
SEPTEMBER 24-27, 1998, SAN DIEGO CALIFORNIA
CONTACT: JIM SLIWA, [email protected]
Usage of Antimicrobial Growth Promoters in Food Animals Poses a Public Health Threat
E.E. Stobberingh
University Hospital Maastricht
Department of Medical Microbiology
PO Box 5800
6202 AZ Maastricht
The Netherlands
Phone: 31 43 3874644
Paper C-77, Session 71-C
Friday, September 25, 1998 -- 3:00 p.m.
The emerging problem of bacteria resistant against all clinically available antibiotics is strongly correlated with the heavy usage of these drugs. Antibiotics are, however, not only used in human and veterinary medicine, but approximately 50% of the world production is fed to health food animals on a free sale basis to improve nutritional efficiency. This practice causes a high prevalence of resistant bacteria in the fecal flora of animals exposed to these antimicrobial growth promoters (AGP). That the intestinal flora of man and other animals is the largest pool of resistance genes and that resistant bacteria or their genes can cross species barriers, has been illustrated in several studies in which the same resistant bacteria have been found in the instestinal flora of humans in direct or indirect, via the food chain, contact with these animals. Moreover the same resistant genes could also be detected in food poisoning bacteria and strictly human pathogens. Therefore in the EU since 1969 the use of therapeutic antibiotics as AGP in animal feeds is forbidden. As a result antibiotics like tetracycline have been replaced by other molecules with antimicrobial activity, which were at that time not thought suitable or promising enough to be developed further for therapy. Now, however, the pharmaceutical industry in the process of developing new drugs to combat multiresistant bacteria, is using these once rejected molecules as templates for new therapeutic antibiotics. In North European countries with a low vancomycin in humans, that permitted the usage of avoparcin, a glycopeptide like vancomycin. Vancomycin-resistant enterococci (VRE) are not only found in the intestinal flora of animals exposed to the drug, but are alo common in healthy humans. In the USA, where avoparcin has never been licensed, VRE are not isolated outside the hospital setting. Resistance aginst newly developed antibiotics like Synercid and Ziracin is already common before these antibiotics have been used, because large amounts of closely related and cross-resistance-conferring molecules like virginiamycin and avilamycin have been fed to animals. These resistant enterococci are an important cause of infections in immunocompromised patients in hospitals. Another threat is that these bacteria might transfer their resistance genes to other bacteria like the MRSA. These hospital bacteria would then become completely untreatable with the at-the-moment clinically available antibiotics.
The aim of this study was to compare the prevalence of resistance in bacteria from fecal samples of pigs collected at abattoirs in two countries with different antibiotics policies: Sweden, that had banned the use of AGP in 1986 and the Netherlands where AGP are used extensively. In both countries antibiotics for therapeutic and preventive usage in animals require a veterinary prescription.
For all antibiotics tested the resistance in intestinal bacteria was significantly lower in the Swedish samples compared to the Dutch samples. VRE were not found in the Swedish samples at all but were present in 39% of the Dutch samples. Not only was the resistance in Sweden lower against AGP, but also against veterinary prescribed antibiotics.
Higher usage of antibiotics causes more resistance. As avoparcin has also been used on a large scale in Sweden before 1986 the process of resistance emergence seems to be reversible. The unsubstantiated claims that prohibition of AGP would lead to an increased veterinary use of antibiotics to such extent that the prevalence of resistance in the fecal flora would be increased instead of decreased, is not confirmed by this study. The prevalence of resistance against veterinary used antibiotics was also significantly lower in Sweden than the Netherlands. As resistant bacteria of food animals pose a public health risk, a low prevalence of resistance in the fecal flora of these animals should be considered a quality and safety mark for these animals. Abstinence from the use of AGP might be an important first step to reach this goal.
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