Effect of chlorination on antibiotic resistance profiles of sewage-related bacteria.

A total of 1,900 lactose-fermenting bacteria were isolated from raw sewage influent and chlorinated sewage effluent from a sewage treatment plant, as well as from chlorinated and neutralized dilute sewage, before and after a 24-h regrowth period in the laboratory. Of these isolates, 84% were resistant to one or more antibiotics. Chlorination of influent resulted in an increase in the proportion of bacteria resistant to ampicillin and cephalothin, the increase being most marked after regrowth occurred following chlorination. Of the other nine antibiotics tested, chlorination resulted in an increased proportion of bacteria resistant to some, but a decrease in the proportion resistant to the remainder. Multiple resistance was found for up to nine antibiotics, especially in regrowth populations. Identification of about 5% of the isolates showed that the highest proportion of Escherichia coli fell in untreated sewage. Some rare and potentially pathogenic species were isolated from chlorinated and regrowth samples, including Yersinia enterocolitica, Yersinia pestis, Pasteurella multocida, and Hafnia alvei. Our results indicate that chlorination, while initially lowering the total number of bacteria in sewage, may substantially increase the proportions of antibiotic-resistant, potentially pathogenic organisms.

Mutagenicity screening of foods I. Results with beverages.

Following a number of recent reports on the presence of mutagens in certain foods, a general survey of the mutagenic potential of a wide variety of food products has been initiated. Here, results for samples of 28 widely consumed beverages from 13 general categories are reported. Each sample was concentrated and fractionated by polarity and solubility to give up to seven fractions, each of which was assayed for mutagenic potential with Salmonella typhimurium TA98 and TA100 +/- fortified liver homogenate. Fractions showing evidence of either mutagenicity or toxicity were retested at the same and lower concentrations. The utility of the fractionation procedure and the sensitivity of the screening strategy were established by assaying six beverages spiked with known mutagens prior to fractionation. Statistical analysis of the data resulted in positive findings for seven beverages, although confirmation of these results through analysis of a second sample was obtained only for red wine, grape juice, and instant coffee. The remaining 21 beverages showed no strong evidence of mutagenic activity. For those foods for which the variation among replicate plates was largest, the false-positive rate for the two-stage screening procedure employed was estimated to be less than 1% while the false-negative rate for a beverage inducing a threefold increase in the background mutation rate was conservatively estimated to be limited to 14%.

Chronic toxicity of methylmercury in the rat.

Groups of 50 male and 50 female Wistar rats were fed diets containing methylmercuric chloride to provide daily doses of 0, 0.002, 0.010, 0.050 and 0.250 mg Hg/kg/day for up to 26 months. Food consumption, and body weight measurements were monitored weekly on all rats. Hematological examinations were done at 0, 6, 12, 15 and 17 months of treatment. Histopathologic examination and analysis for total mercury levels were performed terminally. Male rats receiving 0.25 mg Hg/kg/day had decreased body weights, decreased hematocrit and hemoglobin values, overt clinical signs of neurotoxicity and increased mortality compared to controls. Female rats receiving 0.25 mg Hg/kg/day had decreased body weights and minimal clinical signs of neurtoxicity. Histopathological examination revealed demyelination of the dorsal nerve roots and peripheral nerves, severe kidney damage and decreased basophilia of hepatocytes in male rats receiving 0.25 mg Hg/kg/day. Male rats receiving 0.05 mg Hg/kg/day had minimal renal damage. Female rats receiving 0.25 mg Hg/kg/day had demyelination of the dorsal nerve roots and peripheral nerves and minimal renal damage. No histopathological lesions were observed in the female rats receiving 0.05 mg Hg/kg/day and in male and female rats in the other dose groups.