Heterogeneity in Induction Level, Infection Ability, and Morphology of Shiga Toxin-Encoding Phages (Stx Phages) from Dairy and Human Shiga Toxin-Producing Escherichia coli O26:H11 Isolates

Abstract

e Shiga toxin (Stx)-producing Escherichia coli (STEC) bacteria are foodborne pathogens responsible for diarrhea and hemolyticuremic syndrome (HUS). Shiga toxin, the main STEC virulence factor, is encoded by the stx gene located in the genome of a bacteriophage inserted into the bacterial chromosome. The O26:H11 serotype is considered to be the second-most-significant HUScausing serotype worldwide after O157:H7. STEC O26:H11 bacteria and their stx-negative counterparts have been detected in dairy products. They may convert from the one form to the other by loss or acquisition of Stx phages, potentially confounding food microbiological diagnostic methods based on stx gene detection. Here we investigated the diversity and mobility of Stx phages from human and dairy STEC O26:H11 strains. Evaluation of their rate of in vitro induction, occurring either spontaneously or in the presence of mitomycin C, showed that the Stx2 phages were more inducible overall than Stx1 phages. However, no correlation was found between the Stx phage levels produced and the origin of the strains tested or the phage insertion sites. Morphological analysis by electron microscopy showed that Stx phages from STEC O26:H11 displayed various shapes that were unrelated to Stx1 or Stx2 types. Finally, the levels of sensitivity of stx-negative E. coli O26:H11 to six Stx phages differed among the 17 strains tested and our attempts to convert them into STEC were unsuccessful, indicating that their lysogenization was a rare event.

Shigatoxin encoding Bacteriophage ϕ24B modulates bacterial metabolism to raise antimicrobial tolerance

“…This heterogeneity is further supported by Bonanno et al 12. who identified multiple Stx-phage morphologies not previously reported12. Stx-phages are closely related to bacteriophage lambda, with a comparable genome organisation.…”

“…used a multi-loci PCR typing approach to demonstrate that no two Stx phage isolates had the same genotype11. This heterogeneity is further supported by Bonanno et al 12. who identified multiple Stx-phage morphologies not previously reported12.…”

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

“…The present study detected highly heterogeneous stx 2a expression and also diverse amounts of phage particles among strains. The levels were in the order of reported magnitudes (Bonanno, Petit, Loukiadis, Michel, & Auvray, ; Muniesa, Blanco, et al, ; Neupane et al, ; Olavesen, Lindstedt, Løbersli, & Brandal, ; de Sablet et al, ). Features that determine variability in these levels among STEC have not yet been elucidated; therefore, some bacterial and phage traits were studied to assess possible relationships with differences in stx 2a expression and phage production.…”

A Rapid Immunoassay for Detection of Shiga Toxin-Producing Escherichia coli Directly from Human Fecal Samples and Its Performance in Detection of Toxin Subtypes

“…Interestingly, this specimen was Stx2 positive only when tested directly, even though both Stx1 and Stx2 were detected when the sample was cultured. It is possible that Stx1 production was not stimulated in vivo whereas Stx2 production was stimulated (50). In addition to antibiotics, other agents present in the gut, such as bacteriocins, and neutrophil products, such as peroxides, can induce toxin production (51, 52).…”