Comparable stx2a expression and phage production levels between Shiga toxin-producing Escherichia coli strains from human and bovine origin

Abstract

Shiga toxin-producing Escherichia coli (STEC) can cause diarrhea and severe diseases in humans such as hemolytic uremic syndrome. Shiga toxins (Stx) are encoded in prophages which play an important role in STEC pathogenesis. The pathogenic potential of STEC is considered correlated with the amount of Stx2 produced and, in particular, Stx2a is the subtype most frequently associated with high virulence. The aims of this study were to evaluate stx2a expression levels and Stx2a phage production by qPCR and double-agar-layer method in 29 STEC strains isolated from cattle and humans. Results were also compared to find possible associations with the serotype, origin or some genetic features. Heterogeneous levels of stx2a expression and Stx2a phage production were observed. Statistical comparisons identified a higher stx2a expression in response to mitomycin C in strains isolated from cattle than in those from humans, and a higher increase in phage production under inducing conditions in stx2a strains compared to stx2a/stx2c strains. Notably, most of the strains studied, regardless of serotype and origin, carried inducible Stx2a phages, and evidenced expression of stx2a which showed an increase along with phage production levels under induced conditions, suggesting a high virulence of the strains circulating in Argentina