VTEC screening to detect a prophage sequence reported in O157 subpopulations from human patients

Abstract

Introduction Certain VTEC are associated with severe human infections, while others seem to be restricted to cattle. Thereby, a distinct subpopulation might have evolved to be either more virulent or adapted to survive in the food chain. Verocytotoxins (VTs) are bacteriophage-encoded and their expression is associated with the lytic cycle. The region between gam and cII genes encodes factors that control lytic and lysogenic states of the phage and the expression of late genes, included vtx. Tozzoli et al. (2014) developed primers amplifying a DNA sequence internal to this region (cro-cI) and determined that this cro-cI sequence was more frequent in O157 strains from human disease than from bovine. Methods Eighty-six VTEC strains (belonging to O157 and no-O157 serogroups) isolated from human patients, cattle and meat products, and carrying different vtx subtypes, were analyzed by PCR to detect the specific variant of cro-cI region described by Tozzoli et al. (IAI 82: 3023-3032, 2014). Also, a BLAST search (Primer-BLAST) was performed to identify the sequence among E. coli genomes deposited in GenBank. Results and Discussion The target sequence was detected in 26 of the analyzed strains (from human, bovine or meat origin). Most of the positive strains are O157:H7 and carry vtx2c, alone or in combination with other vtx subtype. Interestingly, the particular cro-cI region was also present in one O171:H2 strain and the vtx2c reference strain. Furthermore, most of the sequences detected in the GenBank were associated with vtx2c. Implications Phages harboring a cro-cI illness in other countries) are present among VTEC strains isolated from cattle and patients in Argentina and are not restricted to O157:H7 strains. Particularly, they seem to be associated mostly to strains that carry vtx2c.