Abstract
Escherichia coli carrying prophage with genes that encode for Shiga toxins are categorized as Shiga toxin-producing E. coli (STEC) pathotype. Illnesses caused by STEC in humans, which are often foodborne, range from mild to bloody diarrhea with life-threatening complications of renal failure and hemolytic uremic syndrome and even death, particularly in children. As many as 158 of the total 187 serogroups of E. coli are known to carry Shiga toxin genes, which makes STEC a major pathotype of E. coli. Seven STEC serogroups, called top-7, which include O26, O45, O103, O111, O121, O145, and O157, are responsible for the majority of the STEC-associated human illnesses. The STEC serogroups, other than the top-7, called “non-top-7” have also been associated with human illnesses, more often as sporadic infections. Ruminants, particularly cattle, are principal reservoirs of STEC and harbor the organisms in the hindgut and shed in the feces, which serves as a major source of food and water contaminations. A number of studies have reported on the fecal prevalence of top-7 STEC in cattle feces. However, there is paucity of data on the prevalence of non-top-7 STEC serogroups in cattle feces, generally because of lack of validated detection methods. The objective of our study was to develop and validate 14 sets of multiplex PCR (mPCR) assays targeting serogroup-specific genes to detect 137 non-top-7 STEC serogroups previously reported to be present in cattle feces. Each assay included 7–12 serogroups and primers were designed to amplify the target genes with distinct amplicon sizes for each serogroup that can be readily identified within each assay. The assays were validated with 460 strains of known serogroups. The multiplex PCR assays designed in our study can be readily adapted by most laboratories for rapid identification of strains belonging to the non-top-7 STEC serogroups associated with cattle.
Highlights
The polysaccharide portion, called the O-antigen, of the lipopolysaccharide layer of the outer membrane of Escherichia coli provides antigenic specificity and is the basis of serogrouping
Of the known 187 serogroups of E. coli, 158 serogroups have been shown to possess genes that encode for Shiga toxin 1, 2 or both
Among the six top-7 non-O157 serogroups, O26, O45, and O103 are the dominant serogroups in cattle feces with prevalence ranging from 40 to 50%
Summary
The polysaccharide portion, called the O-antigen, of the lipopolysaccharide layer of the outer membrane of Escherichia coli provides antigenic specificity and is the basis of serogrouping. Escherichia coli serogroups that cause disease in humans and animals are categorized into several pathotypes. The serogroups that carry Shiga toxin genes on a prophage are categorized as the Shiga toxin-producing E. coli (STEC) pathotype. As many as 158 serogroups of E. coli are known to carry Shiga toxin gene(s), which make STEC the most predominant E. coli pathotype (Table 1). Seven serogroups of STEC, O26, O45, O103, O111, O121, O145, and O157, called “top-7,” are responsible for the majority of human STEC illnesses, including food borne-outbreaks (Brooks et al, 2005; Scallan et al, 2011; Gould et al, 2013; Valilis et al, 2018). STEC serogroups other than the top-7, called “non-top-7” have been reported to cause human illnesses, more often as sporadic infections, a few are known to cause severe infections, such as hemorrhagic colitis and HUS (Hussein and Bollinger, 2005; Bettelheim, 2007; Hussein, 2007; Bettelheim and Goldwater, 2014; Valilis et al, 2018). In a recent systematic review done by Valilis et al (2018), 129 O-serogroups of STEC were identified to be associated with clinical cases of diarrhea in humans
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