Invasive ability of C. jejuni/coli isolates from children with diarrhea and the effect of iron-regulated proteins.

The invasive ability of C. jejuni/coli strains isolated from children with diarrhea was studied using an in vitro HEp-2 cell invasion assay. The ratio between the number of intracellular bacteria and the number of bacteria in the inoculum was determined (invasion index). It was found that under anaerobic conditions, there was a significant decrease in the invasion index as compared to standard conditions (5% CO2). Of 11 strains tested, seven were determined as invasive on the basis of invasion indexes within the range of 0.0002-0.01. In a previous study [D. Schwartz et al., Zbl. Bakt. 280, 338-347 (1994)], it was found, that most of the C. jejuni/coli isolates tested produced an outer membrane protein when grown under conditions of iron depletion (IRP). The IRP were detected in eight of the nine strains tested in the present study (five invasive and three non-invasive strains). In one non-invasive strain, IRP was not detected. When kept under conditions of iron depletion, one of the invasive strains exhibited a significant increase in invasive capacity. The results suggest that iron depletion seems to stimulate the invasion capacity of C. jejuni/coli in vitro.

Anaerobiosis, type 1 fimbriae, and growth phase are factors that affect invasion of HEp-2 cells by Salmonella typhimurium.

The invasion of HEp-2 cells by Salmonella typhimurium was studied under various conditions. Anaerobiosis was shown to markedly affect the internalization of bacterial cells by HEp-2 cells. Anaerobically grown bacteria incubated with HEp-2 cells under anaerobic conditions markedly stimulated the rate of invasion. Anaerobiosis may therefore be a controlling factor in the invasion process. Cells obtained during the logarithmic phase of growth invaded at much higher rates than cells obtained during the stationary phase of growth. The presence of mannose-sensitive type 1 fimbriae on the bacterial surface also promoted invasion, and these fimbriae appear to play a role as an accessory virulence factor.