Is lack of susceptible recipients in the intestinal environment the limiting factor for transduction of Shiga toxin-encoding phages?

Abstract

To determine whether a Shiga toxin 2 (Stx2)-encoding phage from Escherichia coli O157:H7 could be transmitted to commensal E. coli in a ruminant host without adding a specific recipient strain. Sheep were inoculated with an E. coli O157:H7 strain containing an Stx2-encoding bacteriophage (Phi3538) in which a chloramphenicol-resistant gene, cat, is inserted into stx(2). A total of 149 faecal samples were sampled and analysed for detection and quantification of E. coli O157:H7 and presumptive transductants. Phage Phi3538 (Deltastx(2)::cat) was demonstrated to be transduced to an ovine E. coli O175:H16 at one occasion. The study demonstrates an in vivo transduction in sheep from an E. coli O157:H7 strain to an ovine E. coli O175:H16. A functional Stx2-encoding phage was incorporated into the host's DNA. This is the first in vivo stx phage transduction study reported in which a recipient strain was not fed to the test animals. We suggest that the access to susceptible hosts is one main limiting factor for transduction to occur in the intestine.