THE EFFECT OF BAMBERMYCIN, CARBADOX, CHLORTETRACYCLINE AND OLAQUINDOX ON ANTIBIOTIC-RESISTANCE IN INTESTINAL COLIFORMS - A NEW ANIMAL-MODEL

Groups of germ-free mice kept in isolators and associated with fecal microflora from piglets were continuously given water or a solution of 1 of the following: chlortetracycline (20 .mu.g/ml), carbadox (50 .mu.g/ml), olaquindox (50 .mu.g/ml), bambermycin (flavomycin) (5 .mu.g/ml) or mixtures of these groups. The proportions of lactose-fermenting bacteria in their feces which were resistant to chlortetracycline, carbadox or olaquindox were measured by a comparative plate-counting procedure. Compared to occurrence in control mice, the occurrence of antimicrobial drug-resistant bacteria was higher in mice receiving chlortetracycline (P < 0.001) and lower in mice receiving bambermycins (P < 0.005). Olaquindox and carbadox did not change the proportion of resistant coliforms in mice feces. A control experiment was conducted with 5 groups of germ-free mice given the same flora and kept without drugs in separate isolators. No difference in the occurrence of resistant coliforms was found between these groups. The germ-free mouse associated with fecal microflora from a conventional animal seems to be a suitable model for determining in vivo the effect of low doses of antimicrobial drugs on drug resistance in lactose-fermenting enteric flora.