Rifaximin-induced alteration of virulence of diarrhoea-producing Escherichia coli and Shigella sonnei.

Rifaximin shortens the duration of travellers' diarrhoea without important alteration of colonic flora. This study investigated the expression of virulence factors [heat-stable (ST) and heat-labile (LT) enterotoxins, surface adhesion factors (CS2/CS3, CS6) and matrix metalloproteinase-9 (MMP-9)] as well as the interleukin (IL)-8 induction potential of diarrhoeagenic Escherichia coli and Shigella sonnei strains exposed to rifaximin (8, 32 and 64mg/L) for 4, 8, 18 and 24h. Following exposure to rifaximin, enterotoxigenic E. coli (ETEC) isolates did not express ST/LT, CS2/CS3 or CS6, whereas enteroaggregative E. coli (EAEC) and S. sonnei isolates did not produce detectable amounts of MMP-9. Moreover, induction of IL-8 was undetectable. At subinhibitory concentrations, rifaximin alters the virulence of ETEC, EAEC and S. sonnei isolates. These findings help explain the efficacy of rifaximin despite minimal alteration of colonic flora.