|KHALIL, ROWAIDA - Alexandria University Of Egypt|
Submitted to: Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2016
Publication Date: 4/23/2016
Publication URL: https://handle.nal.usda.gov/10113/5801838
Citation: Khalil, R., Skinner, C.B., Patfield, S.A., He, X. 2016. Phage-mediated Shiga toxin (Stx) horizontal gene transfer and expression in non-Shiga toxigenic Enterobacter and Escherichia coli strains. Pathogens and Disease. 74(5):1-11. doi: 10.1093/femspd/ftw037.
Interpretive Summary: Enterobacter cloacae M12X01451 is a new strain recently isolated from a human clinical specimen of a patient with a mild diarrheal illness. It produces a new subtype of Stx1, named as Stx1e, of prophage origin. The clinical relevance and the role of this strain in human pathogenicity have not yet been addressed. This is the first study of transducing non-toxigenic/laboratory strains with a stx1e-encoding phage induced from the M12X01451 strain, in comparison with a stx1a-phage from a foodborne pathogenic E. coli O157:H7 strain, RM8530. The results obtained are of clinical importance, and demonstrate the potential of horizontal gene transfer (HGT) between clinical strains carrying the stx prophages and bacteria from different genera under conditions resembling the human gastrointestinal tract. Consequences of this HGT over extended periods of time may result in the conversion of commensal bacterial hosts to pathogens and addition of more virulence to pathogenic strains, which could have serious impacts on human health.
Technical Abstract: M12X01451, an Enterobacter cloacae strain recently identified from a clinical specimen, produces a new Stx1e that was not neutralized by existing anti-Stx1 monoclonal antibodies. Acquisition of stx by Ent. cloacae is rare and information regarding the origin and stability of the stx1e in M12X01451 is not known. In this study, the presence of phages encoding stx1a and stx1e was analyzed in RM8530 (an E. coli O157 strain) and M12X01451. Their ability to infect E. coli DH5a, E. coli 465-97 and Ent. cloacae 13047 strains was confirmed by spot and bacterial growth tests. In strains lysogenized by stx1e-phage, stx1e was detected in 97.5% and 72.5% of progenies subcultured for 10 (T10) and 20 (T20) times. However, stx1a was detected in 65% and 17.5% of T10 and T20 progenies of stx1a-phage lysogenized hosts. Infection of M12X01451 and RM8530 with each other’s phages led to the formation of lysogens carrying both stx1a- and stx1e-phages. The acquired stx1a was lost after T10, whereas the stx1e was maintained even after T20 in M12X01451 lysogens. In RM8530 lysogens, the acquired stx1e was retained, but 20% of stx1a was lost after T20. The stx1e in T20 RM8530 lysogens was stable and no mutations were observed. ELISA and western blot analyses demonstrated that Stx1e was produced in all strains lysogenized by stx1e-phage, but no Stx1a was detected in any strains lysogenized by the stx1a-phage. Results obtained in this study could help us to understand the potential risk of emerging new Stx-producing strains and design control measures to prevent phage-mediated stx gene transfer.