Comparable stx_2a 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 diarrhoea and severe diseases in humans, such as haemolytic uraemic syndrome. STEC virulence is considered to correlate with the amount of Shiga toxins (Stx) produced, especially Stx2, whose subtype Stx2a is most frequently associated with high virulence. Stx are encoded in prophages, which play an important role in STEC pathogenesis. The aim of this study was to evaluate stx2a expression levels and Stx2a phage production using qPCR and the double‐agar‐layer method in 29 STEC strains, corresponding to serotypes O26:H11 (6), O91:H21 (1), O145:H‐ (11) and O157:H7 (11), isolated from cattle and humans. Results were then tested for possible associations with serotype, origin or some genetic features. We observed heterogeneous levels of stx2a expression and Stx2a phage production. However, statistical comparisons identified a higher stx2a expression in response to mitomycin C in strains isolated from cattle than in those from humans. At the same time, compared to stx2a/stx2c strains, stx2a strains showed a higher increase in phage production under induced conditions. Notably, most of the strains studied, regardless of serotype and origin, carried inducible Stx2a phages and evidenced expression of stx2a that increased along with phage production levels under induced conditions.

Characterization of the flanking region of the Shiga toxin operon in Stx2a bacteriophages reveals a diversity of the NanS-p sialate O-acetylesterase gene

“…The conserved genome localization of nan S-p suggests that its transcription is regulated by Q protein and prompted us to evaluate its expression under basal and mitomycin C-induced conditions in a set of stx 2a -positive STEC strains of our collection. The assays showed that all cultures, except one, increased nan S-p expression under induced conditions similar to that obtained for stx 2a in a previous study [37] . Furthermore, the exception was a strain that did not show nan S-p expression but had not demonstrated stx 2a expression either.…”

“…Previous studies have identified Q gene variants, of which Q 933 , Q 21 and Q O111:H- are the best characterized [48] . However, associations between each Q allele and levels of Stx2 production are still not clear [37] , [49] – [51] . The present study detected stx 2a genes mainly linked to genes encoding proteins Q933 and QO111:H-, and none with Q21, similar to a previous study [50] .…”

“…Expression of nan S-p was quantified in mitomycin-C-induced STEC cultures relative to uninduced cultures using real-time qPCR. Bacterial growth conditions, total RNA extraction and cDNA synthesis were previously described for stx 2a -expression of the same strains [37] .…”