THYMINE AUXOTROPHY AS AN ATTENUATING MARKER IN VIBRIO-CHOLERAE

Vibrio cholerae CVD102 is a thymine-dependent auxotroph of CVD101, a c holera toxin A(-)B(+) candidate live oral cholera vaccine. Previous cl inical experience with these strains suggested that, by restricting in testinal growth, thymine auxotrophy is attenuating for V. cholerae. St udies in the infant mouse cholera model cast doubt upon this conclusio n however. Stable thyA mutants selected from each of three pathogenic strains showed unimpaired gut colonization in mixed-infection competit ion experiments. Similar results were obtained using thyA mutants sele cted from two atoxigenic strains, including CVD101. Further studies wi th CVD102 showed that the reduced colonization potential of this strai n could not be compensated by the provision of a functional thyA(+) ge ne in trans. CVD102 shows reduced synthesis of toxin-coregulated pill (TCP) during in vitro growth, suggesting the presence of a second, und efined mutation in this strain. Given the critical role of TCP in inte stinal colonization, it seems probable that this previously unrecogniz ed mutation is responsible for the poor in vivo performance of CVD102. (C) 1995 Academic Press Limited