Iron influences the expression of colonization factor CS6 of enterotoxigenic Escherichia coli

Abstract

Enterotoxigenic Escherichia coli (ETEC) is a major pathogen of acute watery diarrhoea. The pathogenicity of ETEC is linked to adherence to the small intestine by colonization factors (CFs) and secretion of heat-labile enterotoxin (LT) and/or heat-stable enterotoxin (ST). CS6 is one of the most common CFs in our region and worldwide. Iron availability functions as an environmental cue for enteropathogenic bacteria, signalling arrival within the human host. Therefore, iron could modify the expression of CS6 in the intestine. The objective of this study was to determine the effect of iron availability on CS6 expression in ETEC. This would help in understanding the importance of iron during ETEC pathogenesis. ETEC strain harbouring CS6 was cultured under increasing concentrations of iron salt to assess the effect on CS6 RNA expression by quantitative RT-PCR, protein expression by ELISA, promoter activity by β-galactosidase activity, and epithelial adhesion on HT-29 cells. RNA expression of CS6 was maximum in presence of 0.2 mM iron (II) salt. The expression increased by 50-fold, which also reduced under iron-chelation conditions and an increased iron concentration of 0.4 mM or more. The surface expression of CS6 also increased by 60-fold in presence of 0.2 mM iron. The upregulation of CS6 promoter activity by 25-fold under this experimental condition was in accordance with the induction of CS6 RNA and protein. This increased CS6 expression was independent of ETEC strains. Bacterial adhesion to HT-29 epithelial cells was also enhanced by five-fold in the presence of 0.2 mM iron salt. These findings suggest that CS6 expression is dependent on iron concentration. However, with further increases in iron concentration beyond 0.2 mM CS6 expression is decreased, suggesting that there might be a strong regulatory mechanism for CS6 expression under different iron concentrations.

The Biology and the Evolutionary Dynamics of Diarrheagenic Escherichia coli Pathotypes

“…Other plasmid-encoded genetic factors that have been reported to play a significant role in the pathogenesis of ETEC include a class I SPATE (serine protease autotransporters of the Enterobacteriaceae) EatA that digests EtpA secreted by ETEC, thereby promoting the adhesion of flagella to the host receptor [30,31]. ETEC can invade the host cell with two chromosomally encoded genes tia and tibA.…”

Perspectives on Metals in Microbiology

“…Decreases in extracellular and, in turn, intracellular metal availability often signal potentially hostile environments, such as the presence of microbial competitors or a host. For example, Bhakat and co-workers describe how enterotoxigenic Escherichia coli use the environmental cue of iron-limitation to induce expression of the host colonization factor CS6 [8]. In response to infection, host organisms can suppress metal availability and starve invading microbes in a process known as ‘nutritional immunity’.…”