Serologic evidence for effective production of cytolysin A in Salmonella enterica serovars typhi and paratyphi A during human infection

Abstract

ClyASTy and ClyASPaA are closely related pore-forming cytolysins of Salmonella enterica serovars Typhi and Paratyphi A whose expression is strongly repressed under standard in vitro growth conditions. We show here that human infections by these pathogens cause a specific antibody response to ClyA, indicating effective toxin production during infection.

FIG. 1.

Western blot analysis of human serum samples for the presence of ClyA-reactive antibodies. The sera tested here were drawn from individuals showing the following conditions: lanes 1 to 5, patients with active or recently contracted typhoid fever caused by the Salmonella serovar Typhi (S. Typhi) strains ST2757A/01, ST423/03, ST1989/03, ST4457/03, and ST1617/05, respectively; lanes 6 and 7, patients with active paratyphoid fever caused by the Salmonella serovar Paratyphi A (S. Paratyphi A) strains ST4042B/03 and ST463/05, respectively; lane 8, patient with active enteric fever caused by double infection with serovar Typhi strain ST2116A/03 and serovar Paratyphi A strain ST2116B/03; lane 9, chronic carrier of Salmonella serovar Typhi strain ST6941/01; lane 10, individual with recent infection by Salmonella serovar Typhimurium (S. Typhimurium); lane 11, healthy blood donor (typical result); lane 12, healthy blood donor showing very weak ClyA reactivity (false-positive result; rare). To test the sera for ClyA reactivity, polyvinylidene difluoride membrane strips carrying identical amounts (5 to 10 ng) of purified and electrophoretically separated ClyA_K-12 were incubated overnight with the different serum samples. ClyA-bound antibodies were subsequently detected on the membrane by using HRP-conjugated anti-human IgG/IgA/IgM secondary antibodies.