Identification, Shiga toxin subtypes and prevalence of minor serogroups of Shiga toxin-producing Escherichia coli in feedlot cattle feces

Abstract

Shiga toxin-producing Escherichia coli (STEC) are foodborne pathogens that cause illnesses in humans ranging from mild to hemorrhagic enteritis with complications of hemolytic uremic syndrome and even death. Cattle are a major reservoir of STEC, which reside in the hindgut and are shed in the feces, a major source of food and water contaminations. Seven serogroups, O26, O45, O103, O111, O121, O145 and O157, called ‘top-7’, are responsible for the majority of human STEC infections in North America. Additionally, 151 serogroups of E. coli are known to carry Shiga toxin genes (stx). Not much is known about fecal shedding and prevalence and virulence potential of STEC other than the top-7. Our primary objectives were to identify serogroups of STEC strains, other than the top-7, isolated from cattle feces and subtype stx genes to assess their virulence potential. Additional objective was to develop and validate a novel multiplex PCR assay to detect and determine prevalence of six serogroups, O2, O74, O109, O131, O168, and O171, in cattle feces. A total of 351 strains, positive for stx gene and negative for the top-7 serogroups, isolated from feedlot cattle feces were used in the study. Of the 351 strains, 291 belonged to 16 serogroups and 60 could not be serogrouped. Among the 351 strains, 63 (17.9%) carried stx1 gene and 300 (82.1%) carried stx2, including 12 strains positive for both. The majority of the stx1 and stx2 were of stx1a (47/63; 74.6%) and stx2a subtypes (234/300; 78%), respectively, which are often associated with human infections. A novel multiplex PCR assay developed and validated to detect six serogroups, O2, O74, O109, O131, O168, and O171, which accounted for 86.9% of the STEC strains identified, was utilized to determine their prevalence in fecal samples (n = 576) collected from a commercial feedlot. Four serogroups, O2, O109, O168, and O171 were identified as the dominant serogroups prevalent in cattle feces. In conclusion, cattle shed in the feces a number of STEC serogroups, other than the top-7, and the majority of the strains isolated possessed stx2, particularly of the subtype 2a, suggesting their potential risk to cause human infections.

Inconsistent PCR detection of Shiga toxin-producing Escherichia coli: Insights from whole genome sequence analyses

“…Immunomagnetic separation was used to overcome some of the difficulties in isolating STEC in the present study. However, it is worth mentioning that as IMS is serogroup-based, it has a small spectrum of detection due to the large number of existing STEC serogroups [1)] Also, some cross reactions among serogroups have occurred, decreasing the discriminatory power of IMS [40,41]. Other challenges in isolation of STEC were addressed by our group in previous studies [42,43].…”

“…1 STEC confirmed by WGS. Fifteen isolates(CAP 9,12,13,21,24,27,28,29,31,36,37,38,40,41,and 43) did not have sequences attributable to stx-encoding phage in their genome. CAP 19 was STEC as determined by WGS but did not show any stx-encoding phage.…”

Development of Single Nucleotide Polymorphism (SNP)-Based Triplex PCR Marker for Serotype-specific Escherichia coli Detection

“…Thus, various polymorphisms can be used to detect very similar strains from different sources [2,3]. In addition, SNPs could be used as an accurate and convenient method to detect disease outbreaks, for the surveillance of food-borne pathogens [13,26] and their source detection [28,34], to develop risk models for outbreaks, and even to map the phylogenetic and evolutionary relationships between similar strains [49].…”

“…Shiga toxin-producing E. coli (STEC), E. coli O157 has been a major food-borne pathogen since the early 1980s; however, early and accurate diagnosis presents preventive measures to minimize the risk of food-borne pathogens and their outbreaks [32,33]. E. coli O157:H7 has been reported in several outbreaks worldwide, in both developing and developed countries, including in the USA [34], Canada [35], and Europe [36]. Currently, there several molecular techniques are commonly used for food-borne disease surveillance and the subtyping of E. coli, such as the PulseNet [37,38], Multilocus Sequence Typing [39], and Multilocus Variable-Number Tandem-Repeat Analysis [40] techniques.…”

The Biology and the Evolutionary Dynamics of Diarrheagenic Escherichia coli Pathotypes

“…Escherichia coli inhabits and adapts to different hosts, a quest that resulted in the acquisition and loss of genes, which further drive diversity in this bacterium and contribute to the evolution of harmless strains to pathogenic lifestyles [1]. While E. coli is an integral part of the microbiota of different hosts, it can also cause severe infections in humans and animals [2,3]. A subgroup of E. coli that are pathogenic can cause a broad range of human diseases due to evolution that resulted in the development of patho-features enabling it to adapt and survive in different environments.…”