Characterization of a stx2a prophage present in STEC O145:H- isolated from cattle

Abstract

Introduction Phages that carry Shiga toxin genes (stx phages) regulate Stx production and also the dissemination of stx genes. Furthermore, the emergence of STEC strains probably occurs in the gastrointestinal tract of ruminants. The aims of this study was to determine the whole genome sequence of the stx2a prophage present in a STEC strain representing the first described stx2-positive O145:H- isolation from a cow in Argentina, and afterwards perform a comparative analysis against complete stx-phage sequences available in databases. Methods Genomic DNA from FB5 strain was prepared using the Ultraclean Microbial DNA isolation kit (MoBio). Paired-end and mate-paired libraries were generated and sequenced on the Illumina Miseq platform. Combined reads were de novo assembled using CLC Genomics Workbench and the contig of interest was detected by BLAST using the stx2a sequence from the phage 933W. The sequence of the stx2a phage was identified and annotated using PHAST and RAST. Comparative analyses were performed using BLAST programs. Results and Discussion The complete sequence of the stx2a phage (66,618 bp) was detected in a contig of 279,109 bp length. The phage was termed ArgO145. Sequence annotation revealed the presence of 95 predicted coding sequences, most of them previously detected in other stx phages. Whole genome comparison of ArgO145 with stx phages collected in databases revealed high similarities with those identified in STEC from other countries. Particularly, ArgO145 showed 99% identity (90% query cover) with VT2phi-272, a stx phage from an O157:H7 strain, and 98% identity (86-88% cover) with stx phages from human O104:H4 strains.ImplicationsTo our knowledge, this is the first report describing the genome of a stx2a phage from a bovine strain. Since stx phages are considered highly diverse, it is remarkably that ArgO145 showed similarity with stx phages present in strains isolated from patients and belonging to other serotypes.