Phage-mediated Shiga toxin (Stx) horizontal gene transfer and expression in non-Shiga toxigenic Enterobacter and Escherichia coli strains

摘要

Enterobacter cloacae M12X01451 strain recently identified from a clinical specimen produces a new Stx1 subtype (Stx1e) that was not neutralized by existing anti-Stx1 monoclonal antibodies. Acquisition of stx by Ent. cloacae is rare and origin/stability of stx(1e) in M12X01451 is not known. In this study, we confirmed the ability of Stx1a- and Stx1e-converting phages from an Escherichia coli O157:H7 strain RM8530 and M12X01451 respectively to infect several E. coli and Ent. cloacae strains. stx(1e) was detected in 97.5% and 72.5% of progenies of strains lysogenized by stx(1e) phage after 10 (T-10) and 20 (T-20) subcultures, versus 65% and 17.5% for stx(1a) gene. Infection of M12X01451 and RM8530 with each other's phages generated double lysogens containing both phages. stx(1a) was lost after T-10, whereas the stx(1e) was maintained even after T-20 in M12X01451 lysogens. In RM8530 lysogens, the acquired stx(1e) was retained with no mutations, but 20% of stx(1a) was lost after T-20. ELISA and western blot analyses demonstrated that Stx1e was produced in all strains lysogenized by stx(1e) phage; however, Stx1a was not detected in any lysogenized strain. The study results highlight the potential risks of emerging Stx-producing strains via bacteriophages either in the human gastrointestinal tract or in food production environments, which are matters of great concern and may have serious impacts on human health.