THE SALMONELLA-TYPHIMURIUM AHPC POLYPEPTIDE IS NOT ESSENTIAL FOR VIRULENCE IN BALB C MICE BUT IS RECOGNIZED AS AN ANTIGEN DURING INFECTION/

The OxyR regulon is known to mediate protection against oxidizing agen ts in Salmonella typhimurium. We reported previously that ahp, one of the OxyR-regulated loci, is induced during macrophage interaction (K. P. Francis, P. D. Taylor, C. J. Inchley, and M. P. Gallagher, J. Bacte riol. 179:4046-4038, 1997). We now report on the effects of disrupting ahp or oxyR on virulence in a BALB/c mouse model. Surprisingly, inser tion of a Mudlux derivative within ahpC was found to result in attenua tion, while irreversible inactivation of the locus through insertion o f a cml cassette did not. An SL1344 derivative carrying an oxyR::kan d isruption was also found to be as virulent as the parental strain. Mor eover, both cell-mediated and humoral responses to AhpC were found to develop during the course of infection, probably through T-helper-cell (type I) activation. These results indicate that, although not essent ial for virulence, AhpC is expressed by S. typhimurium during infectio n of BALB/c mice and constitutes a target for the immune system.