A number of antibacterial drugs are routinely included on a continuous basis in the feed of animals used for the production of food. These drugs, most of which are also utilized in human medicine, are added to animal feed for therapeutic, prophylactic, and various production purposes. The agricultural applications of medically important drugs have been questioned because of the direct selegctive effects of the drugs favoring an increased occurrence of drug resistance in pathogens of animal origin. Furthermore, because of the transmissibility of resistance in gram-negative enteric organisms, resistant enteric organisms normally considered nonpathogenic may provide a reservoir of resistance for both human and animal pathogens.Reports have documented the prevalence of resistance among specific members of the Enterobacteriaceae obtained from farm animals fed various antibacterial drugs (3,5,7,8,(10)(11)(12)(13)(14)(15)

Fenbendazole (FBZ) was administered intravenously (1 mg/kg) and orally (5 mg/kg) to catheterized, confined channel catfish. Blood samples were collected for 72 h, and resulting FBZ plasma concentrations were pharmacokinetically modelled. Following intravenous administration t 1/2 alpha was 0.51 h, t 1/2 beta was 16.8 h, body clearance (C1B) was 0.0598 L/kg/h, and Vd (area) was 1.45 L/kg. After oral administration the t 1/2 (abs) was 1.47 h, the t 1/2 beta was 20.1 h, and the tlag was 0.1 h. Following oral administration of 5 mg FBZ/kg body weight, the following tissues and body fluids were sampled for concentrations of FBZ, oxfendazole (FBZ-SO), sulphone metabolite (FBZ-SO2) and hydroxy metabolite (FBZ-OH): liver, posterior kidney, fat, muscle, bowel contents and urine. Fenbendazole was detected in the highest concentrations in abdominal fat, whereas oxfendazole was found primarily in the kidney, liver and abdominal fat. The sulphone metabolite was detected only in urine and bowel contents, while the hydroxy metabolite was found most often in the liver and abdominal fat samples.

Fecal samples were collected from five groups of people differing in the manner of their exposure to antibacterial drugs. The groups included: (i) people working on farms who were continuously in contact with the predominantly resistant florae of farm animals receiving rations containing antibacterial drugs, (ii) people residing on the same farms with no direct exposure to the farm animals, (iii) people treated with antibacterial drugs, (iv) untreated people residing with treated individuals, and (v) untreated people with no exposure to farm animals or treated individuals. The samples were examined by quantitative plating for proportions of antibiotic-resistant, gram-negative enteric organisms. Individual isolates were also examined for their susceptibility to 11 different antibacterial drugs. The results indicate that enteric florae unexposed directly to the selective effects of antibacterial drugs may be affected by contact with predominantly resistant florae directly exposed to antibacterial drugs.Antibacterial drugs are widely used for production purposes on livestock and poultry farms. This practice has been questioned because it might create conditions detrimental to animal and human health. It has been established that the enteric florae of farm animals are largely composed of drug-resistant organisms as a result of the continuous exposure to antibacterial agents (5, 7-10). Due to the transmissible nature of drug resistance in gramnegative enteric organisms, it has been postulated that the resident animal flora may comprise a reservoir of resistance for animal and human pathogens.A central question to an objective assessment of the possible danger to public health posed by the agricultural use of antibacterial drugs is whether or not organisms and/or R factors originating on the farm can become established in the florae of human beings who have consumed food of animal origin. An investigation relating to this question was conducted to determine whether or not enteric florae continuously exposed to antibacterial drugs and composed largely of antibiotic-resistant organisms influenced epidemiologically associated enteric florae unexposed to antibacterial drugs. A previous paper reported the high proportions of antibiotic-resistant, gram-negative enteric organisms in fecal samples from Illinois farm animals given feeds containing antibacterial drugs (7). This paper reports the proportions of resist- ' (BBL) was used for all broth cultures. Nutrient agar (Difco) slants were used for isolate storage.Antibiotics. The following concentrations of antibacterial drugs in MacConkey agar were used: nalidixic acid, 40 ,ug/ml; oxytetracycline, 20 tg/ml; dihydrostreptomycin, 25 ug/ml; and ampicillin, 50 jug/ml. Concentrations of oxytetracycline, dihydrostreptomycin, and ampicillin were selected to provide the best possible correlations between KirbyBauer disk susceptibility tests and growth on agar.Fecal samples. Ten-to 20-g fecal samples were collected into 40-ml -quantities of sterile, pH 7.2, buffered-glycerol-s...

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