A 66-kilodalton heat shock protein of Salmonella typhimurium is responsible for binding of the bacterium to intestinal mucus.

Salmonella typhimurium infections have increased during the last few years. However, the interplay of virulence factors in S. typhimurium pathogenesis is still poorly understood, particularly with regard to the mechanisms and components of the bacterium which are involved in its interaction with the intestinal mucus. We have observed that S. typhimurium is aggregated by incubation with colonic mucus (guinea pig model). To quantify this phenomenon, an aggregation assay was established. By using this assay, it was found that the aggregation profile of S. typhimurium strains freshly isolated from patients (age 9 and older) with salmonellosis correlated with the severity of the disease. An isolate with high aggregation behavior was chosen for characterization of the bacterial component involved in binding to colonic mucus material. The component of S. typhimurium responsible for aggregation was purified and characterized as a 66-kDa protein which was able to completely inhibit mucus-mediated bacterial aggregation. This protein was recognized by monoclonal antibodies against the 65-kDa heat shock protein (HSP) of Mycobacterium leprae. The 66-kDa protein of S. typhimurium was inducible by incubating the bacteria at 50 degrees C and was secreted into the supernatant, from which it could be isolated in both dimeric and polymeric forms. The monoclonal anti-HSP 65, as well as a polyclonal antibody against the 66-kDa protein of S. typhimurium, caused dose-dependent inhibition of the aggregation of S. typhimurium by crude mucus preparations. This is the first report showing that a bacterial HSP is involved in mucus-mediated interaction of pathogens with the host.