PCR-Based Detection and Molecular Characterization of Shiga Toxin-Producing Escherichia coli Strains in a Routine Microbiology Laboratory over 16 years

Abstract

dShiga toxin-producing Escherichia coli (STEC) is a heterogeneous group of bacteria causing disease ranging from asymptomatic carriage and mild infection to hemolytic uremic syndrome (HUS). Here, we describe patients with STEC infection and characterize the STEC strains detected in our laboratory by use of PCR for stx 1 , stx 2 , and eae from 1996 through 2011. Patient information was collected from referral forms and from the Norwegian Surveillance System for Communicable Diseases. STEC isolates were characterized with respect to serogroup or serotype, selected potential virulence genes, and multilocus variable-number tandemrepeat analysis (MLVA) genotype. STEC strains were isolated from 138 (1.09%) of 12,651 patients tested. STEC strains of serogroups O26, O103, O121, O145, and O157 were the most frequent. These serogroups, except non-sorbitol-fermenting O157, were also the most frequent among the 11 patients (all <5 years old) who developed HUS. Twenty-four STEC strains were classified as being HUS associated based on an epidemiological link to a HUS case, including an MLVA genotype identical to that of the STEC strain. The age of the patient (<5 years) and the genes eae and stx 2a were significantly associated with HUS-associated STEC (P < 0.05 for each parameter), while stx 1 was associated with non-HUS-associated STEC (P < 0.05). All of the potential virulence genes analyzed, except ehxA, were significantly more frequent among HUS-associated than non-HUS-associated strains (P < 0.05 for each gene). However, these genes were also present in some non-HUS-associated STEC strains and could therefore not reliably differentiate between HUS-associated and non-HUS-associated STEC strains.

Molecular Profiling of Escherichia coli O157:H7 and Non-O157 Strains Isolated from Humans and Cattle in Alberta, Canada

“…Our data support that HUS development is dependent on ageassociated factors as shown in previous studies (25). Our findings correlate with those of a recent study showing that the age of the patient (Ͻ5 years) and the presence of eae and stx 2a genes in STEC showed significant associations with the development of HUS (P Ͻ 0.05 for each parameter), while stx 1 -positive STEC was associated with non-HUS cases (P Ͻ 0.05) (24). Nonetheless, age is not the sole determining factor for disease progression, and additional investigation is needed to identify the genetic determinants of HUS.…”

“…Strains belonging to seropathotype A contained almost all of the virulence genes tested (stx 2 , espY1, espY3, eae-gamma, nleD-2, espX2, espO1-1, lpfA, espY4-2, espX6, and etpD). The presence of genes espK, eae, espG, terE, ureD, espV, espN, espX7, ecs1763, ecs1822, espM1, nleF, nleG, nleH1-2, espJ, espM2, espW, efa1, efa2, ent, nleB, and nleE can be used to differentiate strains belonging to seropathotypes B from those belonging to seropathotypes D and E. These data corroborate a recent study showing that these potential virulence genes were significantly more frequent among HUSassociated than non-HUS-associated strains (24). Interestingly, five clinical non-O157 isolates lacking the eae gene were associated with human disease; four isolates also lacked stx 2 and three lacked most of the virulence genes tested.…”

Assessing the Public Health Risk of Shiga Toxin-Producing Escherichia coli by Use of a Rapid Diagnostic Screening Algorithm

“…Furthermore, VF that play an important role in toxin production and attachment to host cells were highly associated with PT groups I ϩ II or PT group I alone, while other VF were associated with PT group III. Previous studies also reported that the number of VF present in STEC isolates increases the pathogenic potential of STEC and the strong association of certain accessory VF with severe illness and outbreaks (12,17,22,27,33,34,36,44). Interestingly, the accessory virulence gene content of the stx 2f -positive STEC isolates that clustered in a distinct branch with two stx-negative EPEC isolates was lower than the other STEC isolates categorized in PT group II.…”

“…While the stx subtypes stx2a and stx2c and the LEEpositive strains are associated with a high risk of more serious illness (9,(22)(23)(24), other virulence gene combinations (even in E. coli strains that lack the stx genes) may also be associated with severe disease, including HC and HUS (12,(25)(26)(27). Furthermore, patient characteristics and infectious doses also determine the outcome of disease (28).…”

Prevalence of E. coli and detection of virulent genes by multiplex PCR in meat products

“…Characterize STEC detected by use of PCR for detection of stx1, stx2 and eae genes from 996 through 2011. STEC isolates were characterized with respect to serogroup or serotype, (Haugum et al, 2014).…”