Mutagenicity testing with Salmonella typhimurium strains. I. Unusual phenotypes of the tester strains.

Some of the Salmonella typhimurium strains in mutagenesis testing are atypical. Unlike the wild S. typhimurium these do not produce H-2-S, are not agglutinated by S. typhimurium typing sera and on fermentation of carbohydrates they do not produce gas. Thus these tester strains cannot readily be identified as S. typhimurium by standard laboratory procedures. This may cause a problem in the differentiation of tester strains from bacterial contaminants. The possibility exits that these phenotypic traits may affect the response of the strains to mutagens.