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Eighty‐seven different mineral waters available for purchase in the Federal Republic of Germany were tested for the presence of heterotrophic bacteria and, specifically, antibiotic‐resistant Pseudomonas species. Waters lacking carbon dioxide and Heilwasser (waters often prescribed for a variety of ailments) tended to show the highest numbers of bacteria. Eighty‐one isolates of Pseudomonas were obtained from 39 samples of mineral water. Of the 9 species found, P. cepacia and P. maltophilia, most commonly associated with nosocomial infections, made up 13. 6% of the isolates. These 2 species also showed the highest resistance to the ten antibiotics used in the study. A comparison of antibiotic resistance patterns between mineral water and clinical isolates from the Medizinische Hochschule, Hannover, shows a higher similarity than that between mineral water and Massachusetts General Hospital (Boston) isolates. With the exception of P. pseudoalcaligenes, all mineral water isolates showed basically 100% resistance to cefoxitin and were highly resistant to ampicillin. Only 1 of 81 isolates (1. 2%) was resistant to tobramycin, although 2 isolates of P. cepacia showed intermediate resistance to this drug. Though no P. aeruginosa were found in any of the samples, the presence of species associated with nosocomial infections and highly resistant to commonly used antibiotics suggests that careful thought be given to the routine ingestion of mineral water by compromised individuals and those with underlying disease.

The addition of carbaryl (100μg/ml) to a model estuarine ecosystem did not affect the number of bacteria in the sediment, but reduced the diversity (as measured by the rarefaction technique) of the microbial community as compared with a control model ecosystem. Two carbaryltolerant strains of bacteria were isolated from the carbaryl-treated system, but none were isolated from the control system. Bacterial growth and filter paper decomposition in mixed cultures was prevented by 100μg/ml carbaryl, but this amount had no effect on the extracellular cellulase of an estuarine isolate. Increasing the amount of organic matter in the medium attenuated the toxicity of carbaryl to pure cultures of an estuarine isolate. The addition of 1, 10, or 100μg/ml carbaryl to field plots had no effect on bacterial numbers, diversity, or filter paper decomposition. The amount of carbaryl in sediments exposed to 100μg/ml fell below the limit of detection by thin-layer chromatography within 12 hours. In sterile and nonsterile model systems, carbaryl rapidly adsorbed to sediment, and hydrolyzed to 1-naphthol in both sediment and water. Although carbaryl may be toxic to bacteria under some conditions, the amounts that might enter and persist in an estuary are insufficient to have a significant impact on the sediment microbial community.

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