Characterization of a halo-acid-tolerant variant of Clostridium botulinum B-aphis

Clostridium botulinum B-aphis spores plated on medium containing 4% salt at pH 6.0 yielded colonies at a frequency of ca. 1 in 10(6). A subculture of one of these colonies, designated strain Ba410, was compared with the parent strain, B-aphis, for a variety of traits. After 7 days of incubation at 37 degrees C, strain Ba410 grew in medium containing 7% NaCl, whereas strain B-aphis could not grow in salt concentrations greater than 5%. The strains also differed in cellular and colonial morphology. After exponential growth in the basal medium was completed, lysis of both strains was pH dependent; in media containing salt, lysis of Ba410 cells was pH independent. Strain Ba410 was more proteolytic than strain B-aphis in conditions of low pH and high salt, so that its toxin could be detected by the mouse assay. In a medium containing alanine and cysteine, the germination rate of B-aphis was 0.77% min-1, whereas that of Ba410 was 0.14% min-1; 2% salt inhibited the germination of Ba410 but not B-aphis.