Zoonotic approach to Shiga toxin-producing Escherichia coli: integrated analysis of virulence and antimicrobial resistance in ruminants and humans.

B Oporto,M Ocejo,M Montes,J M Marimón,A Hurtado,M Alkorta

doi:10.1017/s0950268819000566

Abstract

In 2014-2016, we conducted a cross-sectional survey in 115 sheep, 104 beef and 82 dairy cattle herds to estimate Shiga toxin-producing Escherichia coli (STEC) prevalence, and collected data on human clinical cases of infection. Isolates were characterised (stx1, stx2, eae, ehxA) and serogroups O157 and O111 identified by PCR, and their antimicrobial resistance (AMR) profiles were determined by broth microdilution. STEC were more frequently isolated from beef cattle herds (63.5%) and sheep flocks (56.5%) than from dairy cattle herds (30.5%) (P < 0.001). A similar but non-significant trend was observed for O157:H7 STEC. In humans, mean annual incidence rate was 1.7 cases/100 000 inhabitants for O157 STEC and 4.7 for non-O157 STEC, but cases concentrated among younger patients. Distribution of virulence genes in STEC strains from ruminants differed from those from human clinical cases. Thus, stx2 was significantly associated with animal STEC isolates (O157 and non-O157), ehxA to ruminant O157 STEC (P = 0.004) and eae to human non-O157 STEC isolates (P < 0.001). Resistance was detected in 21.9% of human and 5.2% of animal O157 STEC isolates, whereas all non-O157 isolates were fully susceptible. In conclusion, STEC were widespread in ruminants, but only some carried virulence genes associated with severe disease in humans; AMR in ruminants was low but profiles were similar to those found in human isolates.

Highlights

Shiga toxin-producing Escherichia coli (STEC) are important human pathogens that can cause a variety of clinical manifestations, from self-limited diarrhoea to more severe illness such as haemorrhagic colitis or haemolytic uremic syndrome (HUS) [1]
STEC were more frequently isolated from beef cattle herds (63.5%) and sheep flocks (56.5%) than from dairy cattle herds (30.5%) (P < 0.001)
STEC were more frequently isolated from beef cattle (63.5% of herds) and sheep (56.5% of flocks) than from dairy cattle (30.5% of herds) (χ2 = 13.07, P < 0.001 and χ2 = 19.95, P < 0.001, respectively)

Summary

Introduction

Shiga toxin-producing Escherichia coli (STEC) are important human pathogens that can cause a variety of clinical manifestations, from self-limited diarrhoea to more severe illness such as haemorrhagic colitis or haemolytic uremic syndrome (HUS) [1]. STEC is the most common infectious agent causing HUS, a syndrome characterised by progressive renal failure. HUS is associated to high morbidity and mortality during the acute phase and to long-term renal and extrarenal complications, in children [2]. Cattle in particular, are considered the primary reservoir of STEC, and the main source of human infection [3]. Faecal shedding of STEC by infected animals can contaminate the environment of the farm, where STEC may survive for long periods of time [4]. Contaminated manure used as fertiliser or effluents from farmland containing STEC can contaminate fresh produce [5]

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