Porcine enterotoxigenic E. coli strains differ in their capacity to secrete enterotoxins through varying YghG levels

ABSTRACT

Enterotoxigenic Escherichia coli (ETEC) are an important pathogen for humans and farm animals, like pigs. Porcine ETEC strains induce diarrhea through the production of heat-labile enterotoxin (LT) and/or heat-stable enterotoxins (pSTa/STb). Although LT secretion levels differ between porcine ETEC strains and this has been linked to virulence, it is unclear whether ST secretion levels also differ between porcine ETEC strains. In addition, the molecular mechanism underlying different LT secretion levels has not been elucidated. In this work, multiple porcine ETEC strains were assessed for their capacity to produce and secrete the enterotoxins LT, pSTa and STb. The strains differed greatly in their capacity to secrete LT, pSTa and STb. Remarkably, in some strains periplasmic production did not correlate with their ability to secrete LT, resulting in high periplasmic production and low LT secretion levels. Furthermore, the results indicated that the type two secretion system protein yghG plays a regulatory role in controlling LT secretion levels. These findings highlight yghG as an important mediator for the secretion of heat-labile enterotoxin LT by porcine ETEC strains and provide better insights in ETEC enterotoxin secretion.

Importance Enterotoxigenic E. coli are a major health concern. Enterotoxins secreted by enterotoxigenic E. coli are crucial for diarrhea induction. Enterotoxin secretion levels differ between strains; however, it is currently unclear what drives these differences. The discrepancy in production and secretion capacity of enterotoxins in ETEC is important to clarify their function involved in diarrhea induction. Our results further deepen our understanding of how type II secretion system (T2SS) components of ETEC control enterotoxin secretion levels and may lay the foundation for a better understanding of ETEC molecular pathogenesis.