Transduction of stx2a mediated by phage (Φ11-3088) from Escherichia coli O104:H4 in vitro and in situ during sprouting of mung beans br

Escherichia coli O104:H4 strain 11-3088 encoding Stx2a is epidemiologically related to the foodborne outbreak associated with sprouts in Germany, 2011. Sprouting provides suitable conditions for bacterial growth and may lead to transduction of non-pathogenic strains of E. coli with Stx phages. Although transduction of E. coli by Stx phages in food has been documented, data on the phages from E. coli O104:H4 is limited. This study determined the host range of the bacteriophage 011-3088 from E. coli O104:H4 using E. coli O104:H4 dstx2::gfp::ampr and demonstrated phage transduction during sprouting. The 011-3088dstx transduced 5/45 strains, including generic E. coli, pap-positive E. coli O103:H2, ETEC, and S. sonnei. The expression level of 011-3088dstx differed among lysogens upon induction. Of the 3 highly induced lysogens, the lytic cycle was induced in E. coli O104: H4dstx2::gfp::ampr and O103:H2 but not in S. sonnei. E. coli DH5 alpha was the only strain susceptible to lytic infection by 011-3088dstx. To explore the effect of drying and rehydration during seed storage and sprouting on phage induction and transduction, mung beans inoculated with the phage donor E. coli O104:H4dstx2::gfp::ampr (8 log CFU/g) were dried, rehydrated, and incubated with the phage recipient E. coli DH5 alpha (7 log CFU/g) for 96 h. Sprouted seeds harbored about 3 log CFU/g of putative lysogens that acquired ampicillin resistance. At the end of sprouting, 71 % of putative lysogens encoded gfp, confirming phage transduction. Overall, stx transfer by phages may increase the cell counts of STEC during sprouting by converting generic E. coli to STEC.

Automated summary

The study shows that the bacteriophage 011-3088 from Escherichia coli O104:H4 can transduce other strains of E. coli, including pathogenic strains, during sprouting. The expression level of the bacteriophage differs among lysogens upon induction, which may result in infections.