Comparative study of the invasiveness of Salmonella serotypes Typhimurium, Choleraesuis and Dublin for Caco-2 cells, HEp-2 cells and rabbit ileal epithelia

Abstract

Patterns of invasiveness of Salmonella serotypes Typhimurium, Choleraesuis and Dublin in Caco-2 cells (without centrifugation) were compared with previously published studies of the rabbit ileal invasion assay (RIIA) and (where relevant) a HEp-2 cell invasion assay. Optimal conditions for the use of Caco-2 cell monolayers in bacterial invasion assays were defined. Centrifuge-assisted attachment of bacteria to cells was not used routinely as this increased the invasiveness of known hypo-invasive strains and detachment of Caco-2 cells. Inocula with too high bacterial numbers resulted in rapid acidification of media and detachment of the monolayers. The invasiveness of Typhimurium strains TML, WAKE, WII8, LT7, SL1027 and M206 in Caco-2 cells reflected that seen in the RIIA. The invasiveness of Choleraesuis strain A50 was similar to that in the RIIA except that bacteria grown at 37°C and used without storage at 4°C were slightly more invasive than those grown at 37°C and stored at 4°C before use. Dublin strain 3246 showed no apparent temperature-regulated invasiveness in Caco-2 cells, in contrast to the results observed in the RIIA. Dublin strain 3246 did not cleave tight junctions in the Caco-2 cell monolayer as it did in rabbit ileal epithelia both in vitro and in vivo . Three Tn phoA insertion LPS mutants of Typhimurium TML were uniformly hypo-invasive in both Caco-2 cells and the RIIA; in contrast, they were differentially invasive in HEp-2 cells. Three smooth Tn phoA insertion mutants of Typhimurium TML ( invH, invG and pagC ) were hypo-invasive in both the Caco-2 and HEp-2 cell invasion assays but not in the RIIA.