Shiga Toxin-Producing Serogroup O91 Escherichia coli Strains Isolated from Food and Environmental Samples

Abstract

Shiga toxin-producing Escherichia coli (STEC) strains of the O91:H21 serotype have caused severe infections, including hemolytic-uremic syndrome. Strains of the O91 serogroup have been isolated from food, animals, and the environment worldwide but are not well characterized. We used a microarray and other molecular assays to examine 49 serogroup O91 strains (environmental, food, and clinical strains) for their virulence potential and phylogenetic relationships. Most of the isolates were identified to be strains of the O91:H21 and O91:H14 serotypes, with a few O91:H10 strains and one O91:H9 strain being identified. None of the strains had the eae gene, which codes for the intimin adherence protein, and many did not have some of the genetic markers that are common in other STEC strains. The genetic profiles of the strains within each serotype were similar but differed greatly between strains of different serotypes. The genetic profiles of the O91:H21 strains that we tested were identical or nearly identical to those of the clinical O91:H21 strains that have caused severe diseases. Multilocus sequence typing and clustered regularly interspaced short palindromic repeat analyses showed that the O91:H21 strains clustered within the STEC 1 clonal group but the other O91 serotype strains were phylogenetically diverse.IMPORTANCE This study showed that food and environmental O91:H21 strains have similar genotypic profiles and Shiga toxin subtypes and are phylogenetically related to the O91:H21 strains that have caused hemolytic-uremic syndrome, suggesting that these strains may also have the potential to cause severe illness.KEYWORDS STEC, O91, virulence, diversity S higa toxin (Stx) is the main virulence factor of Shiga toxin-producing Escherichia coli (STEC). There are two main Stx types, designated Stx1 and Stx2, and each has many subtypes. However, STEC pathogenesis is complex, and Stx alone, without an adherence factor, is deemed to be insufficient to cause severe diseases like hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS) (1, 2). The most common STEC adherence factor is the eae-encoded intimin adhesin, which resides on the locus of enterocyte effacement (LEE) pathogenicity island. However, some STEC strains, such as those of serotypes O91:H21, O113:H21, and others, lack eae but have still caused severe disease (3-5) and so are postulated to have other means for adherence. Genes such as saa, which codes for STEC agglutinating adhesin (6), and sab, which codes for an outer membrane autotransporter protein that enhances biofilm formation (7), have been found in LEE-negative STEC strains and are thought to play a role in adherence.STEC serotype O91:H21 strains are LEE negative but have caused HUS (8, 9). The

ArgO145, a Stx2a prophage of a bovine O145:H- STEC strain, is closely related to phages of virulent human strains

“…Genetic and phylogenetic analyses of STEC strains propose that some strains isolated from bovines and food have the potential to cause severe illness (Feng et al, 2017;Feng et al, 2014;Krüger et al, 2015). In agreement with these observations, previous studies in our laboratory suggest that Stx phages from some bovine strains are able to be induced to similar levels than those from clinical isolates (Krüger et al, 2011;Lenzi et al, 2016).…”

Wild Birds in Live Birds Markets: Potential Reservoirs of Enzootic Avian Influenza Viruses and Antimicrobial Resistant Enterobacteriaceae in Northern Egypt

“…E. coli and Salmonella were recovered from 37.2% and 20.2% of all tested birds, respectively. Serotyping of the isolated E. coli revealed the wide prevalence of certain E. coli serotypes, which are more frequently associated with avian Collibacillosis such as O1 and O78 [32], and Shiga Toxin-Producing serotypes such as O121, O91, and O26 [33,34] were also recovered. Potentially, a higher prevalence of Salmonella spp.…”

Toxins of Locus of Enterocyte Effacement-Negative Shiga Toxin-Producing Escherichia coli

“…In addition, O91 strains have been regularly isolated from patient samples and could be found in different foods [ 7 , 27 , 49 , 51 , 52 ]. Recent studies showed that O91 isolates of various origin (food, environment, and humans) share similar genotypic profiles, are phylogenetically related, could be mainly attributed to cattle as a reservoir for human infections, and, thus, could potentially lead to severe human infections [ 53 , 54 ]. Comparing the infection numbers and distribution in detected serotypes of 2016 to the three previous years, there is an increase in the number of cases, but the overall distribution of LEE-positive and LEE-negative pathogens remained steady throughout those years [ 46 , 55 , 56 , 57 ].…”