Prevalence of Shiga toxin-producing Escherichia coli in pasture-based dairy herds

Abstract

Shiga toxin‐producing Escherichia coli strains (STEC) are food‐borne pathogens. While E. coli O157:H7 is commonly associated with cattle, less is known about the prevalence of non‐O157 STEC serogroups in bovines. This study evaluated the prevalence and virulence status of O157:H7 and six E. coli O‐serogroups (O26, O103, O45, O145, O121, O111) in New Zealand dairy farms using molecular as well as culture‐based methods. Fresh farm dairy effluent (FDE) (n = 36) and composite calf faeces (n = 12) were collected over three samplings from 12 dairy farms. All seven target serogroups were detected through molecular techniques. Of the 202 isolates which were serologically confirmed following traditional culturing and immunomagnetic separation (IMS), O103, O26, O45 and O121 were the most common serogroups, being found in 81, 47, 42 and 32% of the FDE and in 17, 33, 25 and 9% of the calf faeces respectively. The majority (157/202) of the isolates were negative for stx and eae virulence genes. The prevalence of the seven target STEC was low, and only nine O26 isolates (4%) were recovered from four of the farms. The study has highlighted the need for improving the isolation of Top 7 STEC from the stx‐negative populations present in fresh dairy effluent and calf faeces. Significance and Impact of the Study Shiga toxin‐producing Escherichia coli (STEC) are important food‐borne pathogens that can cause severe illness in humans. Cattle are asymptomatic reservoirs for STEC, and transmission to humans can be by consumption of food products or water contaminated with cattle faeces. Our study investigated the prevalence of O157:H7 and six E. coli serogroups of STEC (O26, O103, O45, O145, O121, O111) over time in the dairy reservoir and increases the knowledge and understanding of these pathogens on pasture‐based farms. Such information is required to develop risk‐assessment models aiming at limiting transmission of these STEC to human.

Prevalence and Epidemiology of Non-O157 Escherichia coli Serogroups O26, O103, O111, and O145 and Shiga Toxin Gene Carriage in Scottish Cattle, 2014–2015

“…Strain isolation confirmed 76.7% of the O26 PCR-positive farms, with those herds not confirmed having a significantly higher minimum C t value than that of herds yielding strains. This isolation rate compares favorably with that reported for clinical isolation ( 26 ) and other livestock studies ( 46 , 47 , 51 , 71 ). A number of practical reasons may account for failed isolation, including the low number of colony picks screened per pat, repeated freeze-thaw before reculture compromising viability, low bacterial concentration, and IMS bead efficacy ( 73 , 74 ).…”

“…The high prevalence of O103 positivity was unexpected, but is corroborated by other studies, with O103 found to be a predominant non-O157 serogroup in dairy cattle in New Zealand (46) and Ireland (47), and in beef cattle in the US (48,49), Canada (50), and Australia (44). Despite high serogroup prevalence, recovered O103 isolates from cattle appear to carry stx genes relatively infrequently (44,46,47,49,51) as also observed in the previous Scottish survey (33).…”

“…Overall, the distribution of stx subtypes in the O26 STEC shedding herds was very similar to that observed in clinical strains across the same time period (60). Isolates from six out of the fifteen O26 STEC shedding herds met the criteria for JEMRA level 1 (13), whilst the This isolation rate compares favourably with that reported for clinical isolation (26) and other livestock studies (46,47,51,71). A number of practical reasons may account for failed isolation, including the low number of colony picks screened per pat, repeated freeze-thaw before re-culture compromising viability, low bacterial concentration and IMS bead efficacy (73,74).…”

Evaluation of Cattle for Naturally Colonized Shiga Toxin-Producing Escherichia coli Requires Combinatorial Strategies

“…For instance, thirty calves from a closed herd in Canada were found to harbor at least one of the seven major STEC serogroups with the predominant being O103 (75.8%) and O157 (70%) [73]. Analysis of composite calf feces collected from 12 dairy farms in New Zealand identified STEC O26 (33%) to be the most prevalent serogroup, followed by O45 (25%), O103 (17%), and O121(9%) [79]. STEC O103 is also being increasingly associated with outbreaks in the US; after the venison-related O103 outbreak in 2010, three recent multistate outbreaks were associated with O103 contaminated ground beef, ground bison meat, and clover sprouts following investigations by the Centers for Disease Control and Prevention and USDA-FSIS [80][81][82][83].…”

Phylogenetic context of Shiga toxin-producing Escherichia coli serotype O26:H11 in England

“…STEC O26:H11 colonize the gut of ruminants, such as cattle, sheep and goats, and other animals including small mammals, birds and domestic pets may act as transient vectors [15,16]. Transmission to humans occurs following the consumption of contaminated food or water, and direct contact with animals or their environment [17][18][19]. There is evidence of personto-person spread in households and institutional settings, and the infectious dose is likely to be similar to that of STEC O157:H7 (10-100 organisms) [20,21].…”