MUTATION OF INVH, BUT NOT STN, REDUCES SALMONELLA-INDUCED ENTERITIS IN CATTLE

The induction of secretory and inflammatory responses in calves by Sal monella typhimurium and Salmonella dublin strains was compared, and th e effects of mutations in the invH and stn genes were assessed, S. typ himurium induced greater secretory and inflammatory responses than S. dublin in bovine ileal loops, despite the fact that these serotypes we re recovered from bovine ileal mucosa in comparable numbers (P. R. Wat son, S. M. Paulin, A. P. Bland, P. W. Jones, and T. S. Wallis, Infect. Immun, 63:2743-2754, 1995), These results implicate serotype-specific factors other than, or in addition to, intestinal invasion in the ind uction of enteritis, The secretory and inflammatory responses induced by S. typhimurium and S. dublin in bovine ligated ileal loops were not significantly altered by mutation of stn, which suggests that stn doe s not have a major role in Salmonella-induced enteritis, The invH muta tion significantly reduced the secretory and inflammatory responses in duced in bovine ileal loops, and this correlated with a reduction in t he severity of enteritis following oral inoculation of calves, The att enuation associated with the invH mutation did not appear to be due to an increased susceptibility to the innate host defense mechanisms, be cause the resistance of S. typhimurium to the bactericidal action of e ither bovine polymorphonuclear leukocytes or bovine serum was not sign ificantly altered, However, lysis of macrophages following infection w ith S. typhimurium was significantly reduced by the invH mutation, The invH mutation prevented the normal secretion of several proteins, inc luding SipC, by S. typhimurium, indicating that the function of the in v-spa-encoded type III protein secretion system was disrupted, Taken t ogether, these observations implicate inv-spa-dependent effecters in m ediation of Salmonella-induced enteritis in cattle, Clearly, however, other undefined serotype-specific virulence factors are also involved in Salmonella-induced enteritis.