Characterization of a ViI-like phage specific to Escherichia coli O157:H7.

Elizabeth M Kutter,Hans-Wolfgang Ackermann,Derek Pickard,Hany Anany,Andrew D Brabban,Andrew M Kropinski,Kyobi Skutt-Kakaria,Bob Blasdel,Daniel Bryan,Ayman El-Shibiny,Todd Callaway,Anna Castano,Ana L Toribio,Andre Villegas

doi:10.1186/1743-422x-8-430

Abstract

Phage vB_EcoM_CBA120 (CBA120), isolated against Escherichia coli O157:H7 from a cattle feedlot, is morphologically very similar to the classic phage ViI of Salmonella enterica serovar Typhi. Until recently, little was known genetically or physiologically about the ViI-like phages, and none targeting E. coli have been described in the literature. The genome of CBA120 has been fully sequenced and is highly similar to those of both ViI and the Shigella phage AG3. The core set of structural and replication-related proteins of CBA120 are homologous to those from T-even phages, but generally are more closely related to those from T4-like phages of Vibrio, Aeromonas and cyanobacteria than those of the Enterobacteriaceae. The baseplate and method of adhesion to the host are, however, very different from those of either T4 or the cyanophages. None of the outer baseplate proteins are conserved. Instead of T4's long and short tail fibers, CBA120, like ViI, encodes tail spikes related to those normally seen on podoviruses. The 158 kb genome, like that of T4, is circularly permuted and terminally redundant, but unlike T4 CBA120 does not substitute hmdCyt for cytosine in its DNA. However, in contrast to other coliphages, CBA120 and related coliphages we have isolated cannot incorporate 3H-thymidine (3H-dThd) into their DNA. Protein sequence comparisons cluster the putative "thymidylate synthase" of CBA120, ViI and AG3 much more closely with those of Delftia phage φW-14, Bacillus subtilis phage SPO1, and Pseudomonas phage YuA, all known to produce and incorporate hydroxymethyluracil (hmdUra).

Highlights

In recent years, as concerns about antibiotic resistance and food safety have escalated, researchers have become interested in the use of bacteriophages to detect and combat bacterial contamination of food products [1,2,3,4,5,6]
We have previously described the isolation, characterization, distribution and inter-relationships between E. coli H7 12900 (O157):H7 and phages isolated from sheep and cattle yards that efficiently infect this pathogen [12,13,17,18]
Isolation and Initial Characterization of the CBA Set of Phages Targeting E. coli O157:H7 The systematic isolation and quantitation of E. coli O157:H7 and a group of phages targeting this bacterium from stockyards in the southwest US was described by Callaway et al, [17] and by Oot et al, [18]

Summary

Introduction

As concerns about antibiotic resistance and food safety have escalated, researchers have become interested in the use of bacteriophages to detect and combat bacterial contamination of food products [1,2,3,4,5,6]. A number of different phages targeting E. coli have been isolated and intensely studied but few if any of the well-characterized ones infect serotype O157:H7. We have previously described the isolation, characterization, distribution and inter-relationships between E. coli O157:H7 and phages isolated from sheep and cattle yards that efficiently infect this pathogen [12,13,17,18]. We have found only three types of phages among the many isolated against O157:H7 from sheep and from cattle feedlots: T4-like myoviruses such as CEV1 [13], myoviruses distinct from T4 in morphology and behavior, and T5-like siphoviruses such as CEV2 [12]. We present a detailed characterization of vB_EcoM_CBA120, a phage belonging to the second group

Methods

Results

Discussion

Conclusion