Isolation of a Lysogenic Bacteriophage Carrying the stx _{1 OX3} Gene, Which Is Closely Associated with Shiga Toxin-Producing Escherichia coli Strains from Sheep and Humans

Abstract

A specific PCR for the detection of a variant of the gene encoding Shiga toxin 1 (stx 1 ) called stx 1 OX3 (GenBank accession no. Z36901) was developed. The PCR was used to investigate 148 Stx 1 -producing Escherichia coli strains from human patients (n ‫؍‬ 72), cattle (n ‫؍‬ 27), sheep (n ‫؍‬ 48), and a goat (n ‫؍‬ 1) for the presence of the stx 1 OX3 gene. The stx 1 OX3 gene was present in 38 Shiga toxin-producing E. coli (STEC) strains from sheep belonging to serogroups O5, O125, O128, O146, and OX3 but was absent from Stx 1 -positive ovine STEC O91 strains. The stx 1 OX3 gene was also detected in 22 STEC strains from humans with nonbloody diarrhea and from asymptomatic excreters. Serotypes O146:H21 and O128:H2 were most frequently associated with stx 1 OX3 -carrying STEC from sheep and humans. In contrast, Stx 1 -producing STEC strains from cattle and goats and 50 STEC strains from humans were all negative for the stx 1 OX3 gene. The stx 1 OX3 -negative strains belonged to 13 serotypes which were different from those of the stx 1 OX3 -positive STEC strains. Moreover, the stx 1 OX3 gene was not associated with STEC belonging to enterohemorrhagic E. coli (EHEC) serogroups O26, O103, O111, O118, O145, and O157. A bacteriophage carrying the stx 1 OX3 gene (phage 6220) was isolated from a human STEC O146:H21 strain. The phage was able to lysogenize laboratory E. coli K-12 strain C600. Phage 6220 shared a similar morphology and a high degree of DNA homology with Stx 2 -encoding phage 933W, which originates from EHEC O157. In contrast, few similarities were found between phage 6220 and Stx 1 -encoding bacteriophage H-19B from EHEC O26.The production of Shiga toxins (verocytotoxins) Stx1 and Stx2 is associated with certain strains of Escherichia coli. Ruminant animals such as cattle, sheep, and goats are naturally colonized with Shiga-toxin-producing strains of E. coli (STEC) and shed these organisms with their feces into the environment. Humans can be infected with STEC by contaminated food and by direct transmission of bacteria, and some STEC types pathogenic for humans cause diarrhea, hemorrhagic colitis, and hemolytic-uremic syndrome (16). Over 200 serotypes of E. coli are known to be associated with the production of Shiga toxins (16). Analysis of the genes encoding Stx1 and Stx2 revealed the existence of various stx subtypes which show differences in their nucleotide sequences. In some strains, the stx genes were found to be carried by temperate bacteriophages, such as stx 1 in STEC O26 and stx 1 and stx 2 in STEC O157 (12,18,20,32,34). A variant of the stx gene of Shigella sonnei and a variant of the stx 2e gene, which is present in porcine STEC strains, were recently found to be carried by bacteriophages (7,15). On the other hand, the stx gene of Shigella dysenteriae type 1 and some other variants of stx 1 and stx 2 present in E. coli were not associated with viable bacteriophages (11,23,35).Paton et al. have described four variants of the stx 1 gene in STEC strains isolated from humans and animals (22, 24)....

Diversity of stx 2 converting bacteriophages induced from Shiga-toxin-producing Escherichia coli strains isolated from cattle

“…Moreover, phages carrying one of the stx 2 variants which have also been described in phages induced from strains of animal origin (Muniesa et al, 2000;Schmidt et al, 2000;Koch et al, 2001) were also detected. However, the results may in fact underestimate the real number of inducible stx-phages, as we have only been able to consider those phages detectable by the methods used here or those that were able to infect the host strains used.…”

Serotypes and Virulence Profiles of Non-O157 Shiga Toxin-Producing Escherichia coli Isolates from Bovine Farms

“…STEC strains harboring stx 1c or stx 1d are more commonly associated with ovine sources (41) and are rarely recovered from patients suffering from HC or HUS (23,24).…”

Diet influences the ecology of lactic acid bacteria and Escherichia coli along the digestive tract of cattle: neural networks and 16S rDNA

“…Lastly, it is also important to note that management of E. coli in cattle faeces is not simply a question of understanding dietary interactions. There are other factors that influence prevalence in cattle such as bacteriophages (Koch et al, 2001;O'Brien et al, 2001) that may be related to the bursts of pathogen often seen in feedlot cattle (Midgley et al, 1999). In addition, environmental contamination from sources such as drinking water (LeJeune et al, 2001) and cross contamination between animals (Midgley & Desmarchelier, 2001) should be taken into account.…”