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

摘要

abstract_textpEnterobacter 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./p/abstract_text