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METABOLISM, MICROFLORA EFFECTS, AND GENOTOXICITY IN HALOACETIC ACID-TREATED CULTURES OF RAT CECAL MICROBIOTA
Citation:
Nelson, G M., A E. Swank, L R. Brooks, K C. Bailey, AND S E. George. METABOLISM, MICROFLORA EFFECTS, AND GENOTOXICITY IN HALOACETIC ACID-TREATED CULTURES OF RAT CECAL MICROBIOTA. Klaassen, Curtis (ed.), TOXICOLOGICAL SCIENCES 60(2):232-241, (2000).
Description:
Haloacetic acids are by-products of drinking water disinfection. Several compounds in this class are genotoxic and have been identified as rodent hepatocarcinogens. Enzymes produced by the normal intestinal bacteria can transform some promutagens and procarcinogens to their biologically active forms. The present study was designed to investigate the influence of the cecal microbiota on the mutagenicity of haloacetic acids, and to look at changes in the microbiota populations and enzyme activities associated with exposure to haloacetic acids. PYG medium containing 1 mg/ml monochloroacetic (MCA), momobromoacetic (MBA), dichloroacetic (DCA), dibromoacetic (DBA), trichloroacetic (TCA), tribromoacetic (TBA), or bromochloroacetic (BCA) acid was inoculated with rate cecal homogenate and incubated anaerobically at 37degrees C. Growth curves were performed with enumeration of the microflora populations on selective media. Mutagenicity in a Salmonella microsuspension bioassay was determined after incubation, enzyme assays determined the activities for B-glucuronidase, B-galactosidase, B-glucosidase, azoreductase, nitroreductase, dechlorinase, and dehydrochlorinase. The haloacetic acids, with the exception of BCA, were toxic to the cecal microbiota, and especially to the enterococci. DBA, TBA, and BCA were mutagenic in the microsuspension assay, but the presence of the intestinal flora did not significantly alter the mutagenicity. BCA increased the activities of several enzymes, and therefore has the potential to affect the biotransformation of co-exposed compounds.
Key Words: disinfection by-products, mutagenicity, Salmonella microsuspension assay, biotransformation, intestinal flora, enzymes.