Isolation, Characterization, and Epidemiological Assessment of Shiga Toxin-Producing Escherichia coli O84 Isolates from New Zealand

Abstract

Shiga toxin-producing Escherichia coli O84 isolates (n ‫؍‬ 22) were examined using culture-and molecularly based methods in order to compare their phenotypic and genotypic characteristics. These analyses directly linked Shiga toxin-producing Escherichia coli O84 isolates from cattle and sheep with human isolates indicating that New Zealand livestock may be a reservoir of infection.The first recorded case in New Zealand of Shiga toxinproducing Escherichia coli (STEC) O157:H7 was in 1993 (3), and since then, STEC strains, including O157, have been isolated from sporadic cases of infection in increasing numbers, reaching a maximum of 91 cases (88 O157 and 3 non-O157) isolates in 2003 (1). Within New Zealand, over 90% of STEC strains detected from human clinical cases are serogroup O157, but whether this is a true reflection of most STEC infections being associated with O157 or whether this is a consequence of screening methods is unknown. Recent investigations detected only non-O157 STEC strains, such as O5, O26, O84, O91, and O128) from New Zealand cattle and sheep

Molecular Subtyping and Genetic Analysis of the Enterohemolysin Gene ( ehxA ) from Shiga Toxin-Producing Escherichia coli and Atypical Enteropathogenic E. coli

“…Most of the bacterial strains used in this study have been described elsewhere (3,11,12,13). Of the strains examined for ehxA, 215 were positive for stx only (99 for stx 1 only, 33 for stx 1 and stx 2 , and 83 for stx 2 only) and 141 were eae positive (115 were positive for eae only, 25 were stx 1 and eae positive, and 1 was stx 2 and eae positive).…”

“…The ehxA gene was more commonly associated with those strains that were eae positive (86.2%) than with those that were stx positive only (51.8%). Previously, ehxA has been used as a marker for identifying specific eae-and ehxApositive STEC serotypes such as O26, O103, O111, O145, and O157, which are more commonly associated with outbreaks of serious human clinical disease, including bloody diarrhea and HUS, than other serotypes (3,5,13,31,32,33,45,46). Indeed, all the eae-positive STEC strains examined in this study (n ϭ 38) were also ehxA positive.…”

“…Other studies using bacterial strains from which pO157 has been removed have failed to provide definitive proof of the importance of the large plasmid or enterohemolysin in STEC pathogenesis (18,43); however, ehxA is found in many STEC serotypes, such as O157:H7, O26:H11, O103:H2, O111:H Ϫ , O113:H21, O5:H Ϫ , and O84:H2/H Ϫ , that are commonly associated with diarrheal disease and HUS, and thus, ehxA has been commonly used as a possible marker for STEC (4,13,24,31,32,33,45,46). Several ehxA-positive serotypes, including O157:H Ϫ (16) and O111:H Ϫ (33), do not exhibit the enterohemolytic phenotype on washed sheep blood agar, indicating that the precise conditions for the regulation and optimum expression of enterohemolysin may remain to be determined.…”

Incidence and prevalence of microbial indicators and pathogens in ovine faeces in New Zealand

“…A prevalence of 0.7% was reported for E. coli O157: H7 for sheep and lambs at slaughter in the UK (Milnes et al 2008), while an Irish study failed to detect any E. coli O157: H7 in the faeces of lambs at slaughter (Lenahan et al 2007). Information on STEC in lambs in NZ is limited, with no E. coli O157: H7 isolated in a survey of sheep (Cookson et al 2006). Cryptosporidium spp.…”

“…Since E. coli O157: H7 was first documented in NZ in 1993 (Baker et al 1999), numerous cases have been reported in clinical isolates and environmental sources, but the incidence in livestock appears to be low. Cookson et al (2006) examined faecal swabs from 46 lambs, but failed to identify any that contained both a Shiga toxin gene (stx1 or stx2) and the E. coli attaching and effacing gene, eae. In the USA, a study targeting E. coli O157 in lambs at slaughter showed a similarly low level of detection of 1.1% (McCluskey et al 1999).…”