Abstract
BackgroundEnteroaggregative (EAEC) and Shiga-toxin producing Escherichia coli (STEC) are a major cause of diarrhea worldwide. E. coli carrying both virulence factors characteristic for EAEC and STEC and producing extended-spectrum beta-lactamase caused severe and protracted disease during an outbreak of E. coli O104:H4 in Europe in 2011. We assessed the opportunities for E. coli carrying the aggR and stx genes to emerge in ‘backyard’ farms in south-east Asia.ResultsFaecal samples collected from 204 chicken farms; 204 farmers and 306 age- and gender-matched individuals not exposed to poultry farming were plated on MacConkey agar plates with and without antimicrobials being supplemented. Sweep samples obtained from MacConkey agar plates without supplemented antimicrobials were screened by multiplex PCR for the detection of the stx1, stx2 and aggR genes. One chicken farm sample each (0.5 %) contained the stx1 and the aggR gene. Eleven (2.4 %) human faecal samples contained the stx1 gene, 2 samples (0.4 %) contained stx2 gene, and 31 (6.8 %) contained the aggR gene. From 46 PCR-positive samples, 205 E. coli isolates were tested for the presence of stx1, stx2, aggR, wzxO104 and fliCH4 genes. None of the isolates simultaneously contained the four genetic markers associated with E. coli O104:H4 epidemic strain (aggR, stx2, wzxO104 and fliCH4). Of 34 EAEC, 64.7 % were resistant to 3rd-generation cephalosporins.ConclusionThese results indicate that in southern Vietnam, the human population is a more likely reservoir of aggR and stx gene carrying E. coli than the chicken population. However, conditions for transmission of isolates and/or genes between human and animal reservoirs resulting in the emergence of highly virulent E. coli strains are still favorable, given the nature of‘backyard’ farms in Vietnam.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0827-z) contains supplementary material, which is available to authorized users.
Highlights
Enteroaggregative (EAEC) and Shiga-toxin producing Escherichia coli (STEC) are a major cause of diarrhea worldwide
An example of the emergence of highly virulent pathogenic E. coli strains is the Enterohaemorrhagic E. coli (EHEC) O104:H4, responsible for the large and devastating outbreak of hemorrhagic colitis in Europe in 2011 [2]. This outbreak strain was found to carry an unusual combination of the pathogenic features of enteroaggregative E. coli (EAEC) and Shiga toxin (Stx)-producing E. coli (STEC)
Further investigation of the distribution of genes encoding for virulence factors aggR, stx1 and stx2 in environmental, animal and human reservoirs is required to better understand the potential for the emergence of E. coli carrying this unusual combination of virulence genes
Summary
Enteroaggregative (EAEC) and Shiga-toxin producing Escherichia coli (STEC) are a major cause of diarrhea worldwide. Some E. coli strains may become capable of causing disease in humans and some animal species by expression of one or multiple virulence factors, such as adhesins and toxins [1]. An example of the emergence of highly virulent pathogenic E. coli strains is the Enterohaemorrhagic E. coli (EHEC) O104:H4, responsible for the large and devastating outbreak of hemorrhagic colitis in Europe in 2011 [2] This outbreak strain was found to carry an unusual combination of the pathogenic features of enteroaggregative E. coli (EAEC) and Shiga toxin (Stx)-producing E. coli (STEC). STEC has been found in contaminated food, water [8] and the farm environment [9,10,11] Given these differences between reservoirs, it is striking that Stx-producing EAEC has emerged to cause outbreaks in humans [12]. Further investigation of the distribution of genes encoding for virulence factors aggR, stx and stx in environmental, animal and human reservoirs is required to better understand the potential for the emergence of E. coli carrying this unusual combination of virulence genes
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