Abstract
Enterotoxigenic Escherichia coli (ETEC) strains are important pathogens for humans and farm animals such as 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 II secretion system (T2SS) protein YghG plays a regulatory role in controlling LT secretion levels. These findings highlight YghG as an important mediator of the secretion of the heat-labile enterotoxin LT by porcine ETEC strains and provide better insights into ETEC enterotoxin secretion.IMPORTANCE Enterotoxigenic E. coli strains 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 the production and secretion capacities 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.