Epidemiology of resistance to antibiotics - Links between animals and humans

An inevitable side effect of the use of antibiotics is the emergence and di ssemination of resistant bacteria, Most retrospective and prospective studi es show that after the introduction of an antibiotic not only the level of resistance of pathogenic bacteria. but also of commensal bacteria increases . Commensal bacteria constitute a reservior of resistance genes for (potent ially) pathogenic bacteria. Their level of resistance is considered to be a good indicator for selection pressure by antibiotic use and for resistance problems to be expected in pathogens. Resistant commensal bacteria of food animals might contaminate, like zoonotic bacteria, meat (products) and so reach the intestinal tract of humans. Monitoring the prevalence of resistan ce in indicator bacteria such as faecal Escherichia coli and enterococci in different populations, animals, patients and healthy humans, makes it feas ible to compare the prevalence of resistance and to detect transfer of resi stant bacteria or resistance genes from animals to humans and vice versa. O nly in countries that use or used avoparcin (a glycopeptide antibiotic, lik e vancomycin) as antimicrobial growth promoter (AMGP), is vancomycin resist ance common in intestinal enterococci, not only in exposed animals, but als o in the human population outside hospitals. Resistance genes against antib iotics, that are or have only been used in animals, i.e. nourseothricin, ap ramycin etc. were found soon after their introduction, not only in animal b acteria but also in the commensal flora of humans, in zoonotic pathogens li ke salmonellae, but also in strictly human pathogens, like shigellae. This makes it clear that not only clonal spread of resistant strains occurs, but also transfer of resistance genes between human and animal bacteria. Moreo ver, since the EU ban of avoparcin, a significant decrease has been observe d in several European countries in the prevalence of vancomycin resistant e nterococci in meat (products), in faecal samples of food animals and health y humans, which underlines the role of antimicrobial usage in food animals in the selection of bacterial resistance and the transport of these resista nces via the food chain to humans. To safeguard public health, the selectio n and dissemination of resistant bacteria from animals should be controlled . This can only be achieved by reducing the amounts of antibiotics used in animals. Discontinuing the practice of routinely adding AMGP to animal feed s would reduce the amounts of antibiotics used for animals in the EU by a m inimum of 30% and in some member states even by 50%. (C) 2000 Elsevier Scie nce B.V. and international Society of Chemotherapy. All rights reserved.