Genetic Features Differentiating Bovine, Food, and Human Isolates of Shiga Toxin-Producing Escherichia coli O157 in The Netherlands

Abstract

The frequency of Escherichia coli O157 genotypes among bovine, food, and human clinical isolates from The Netherlands was studied. Genotyping included the lineage-specific polymorphism assay (LSPA6), the Shiga-toxin-encoding bacteriophage insertion site assay (SBI), and PCR detection and/or subtyping of virulence factors and markers [stx1, stx 2a /stx 2c , q21/Q933, tir(A255T), and rhsA(C3468G)]. LSPA6 lineage II dominated among bovine isolates (63%), followed by lineage I/II (35.6%) and lineage I (1.4%). In contrast, the majority of the human isolates were typed as lineage I/II (77.6%), followed by lineage I (14.1%) and lineage II (8.2%). Multivariate analysis revealed that the tir(A255T) SNP and the stx 2a /stx 2c gene variants were the genetic features most differentiating human from bovine isolates. Bovine and food isolates were dominated by stx 2c (86.4% and 65.5%, respectively). Among human isolates, the frequency of stx 2c was 36.5%, while the frequencies of stx 2a and stx 2a plus stx 2c were 41.2% and 22.4%, respectively. Bovine isolates showed equal distribution of tir(255A) (54.8%) and tir(255T) (45.2%), while human isolates were dominated by the tir(255T) genotype (92.9%). LSPA6 lineage I isolates were all genotype stx 2c and tir(255T), while LSPA6 lineage II was dominated by tir(255A) (86.4%) and stx 2c (90.9%). LSPA6 lineage I/II isolates were all genotype tir(255T) but showed more variation in stx 2 types. The results support the hypothesis that in The Netherlands, the genotypes primarily associated with human disease form a minor subpopulation in the bovine reservoir. Comparison with published data revealed that the distribution of LSPA6 lineages among bovine and human clinical isolates differs considerably between The Netherlands and North America. Shiga toxin-producing Escherichia coli (STEC) O157 is considered a serious pathogen due to its low infectious dose, the severe clinical symptoms (especially among children), and the potential for food-and waterborne outbreaks (7,22,35). STEC O157 can be transmitted to humans by direct contact with the ruminant reservoir or indirectly via ingestion of contaminated food or water (33). STEC O157 has several virulence genes that play a crucial role in the development of clinical symptoms. These include the Shiga toxin genes 1 and 2 (stx 1 and stx 2 ), several genes located on the chromosomal locus of enterocyte effacement (LEE), which codes for a specialized epithelium attachment system responsible for the characteristic attaching and effacing (A/E) phenotype, and (putative) virulence factors encoded on various genomic pathogenicity islands (20,25).In The Netherlands, the prevalences of STEC O157 at the herd level are on average 8% for dairy herds and 13% for veal herds (2), with seasonal peaks from 30% to 70% during the summer months (12,19). The notification rates of STEC O157 disease cases in The Netherlands (including outbreaks) for 2007, 2008, and 2009 were 0.50, 0.27, and 0.34 cases per 100,000 inhabitants per year, respectively (14). It can be cons...

Genetic diversity of Shiga toxin-producing Escherichia coli O157 : H7 recovered from human and food sources

“…Characterization of lineage types among E. coli O157 : H7 strains in Belgium revealed higher prevalence of lineage I/II among E. coli O157 : H7 strains analysed (70.6 %). This finding is consistent with previous studies that reported the higher frequency of distribution of this lineage among tested E. coli O157 : H7 strains from the Netherlands (55.1 %), Argentina (90 %) and Australia (88 %) (Franz et al, 2012;Mellor et al, 2012). This lineage has been shown to share characteristics of both lineage I and lineage II, but has been presented to cause human illness at frequencies similar to those of lineage I strain and includes a hyper-virulent isolate of which multistate 'spinach' outbreak strains are representative Ziebell et al, 2008).…”

“…Molecular typing and microbial genomics have facilitated the characterization and comparison of E. coli O157 : H7 strains recovered from different isolation sources demonstrating non-random distribution of genotypes among clinical and non-clinical strains (Besser et al, 2008;Franz et al, 2012;Hartzell et al, 2011;Lee et al, 2011;Whitworth et al, 2010;Yang et al, 2004;Yokoyama et al, 2011;Zhang et al, 2010;Ziebell et al, 2008). In addition, several epidemiological studies supported the growing evidence of substantial variability in the virulence of E. coli O157 : H7 genotypes implicated in different outbreaks and variation in patient symptoms (Besser et al, 2008;Grant et al, 2008;Manning et al, 2008).…”

“…This gene encodes a translocated intimin receptor that mediates adhesion to mammalian cells and the formation of attaching and effacing (A/E) lesions through binding to intimin (Kaper et al, 2004). Some investigators previously suggested that tir (255T) harbouring strains are more virulent in humans than tir (255A) harbouring strains Franz et al, 2012;Mellor et al, 2013). Shiga toxin bacteriophage insertion (SBI) site analysis relies on amplification of the stx toxin genes (stx 1 and stx 2 ) and the insertion site junctions of their encoding bacteriophages that can be used as a valuable genotyping technique to distinguish E. coli O157 : H7 strains, based on their distribution, gene expression and virulence potential (Besser et al, 2008;Shaikh & Tarr, 2003).…”

Veterinary Public Health Approach to Managing Pathogenic Verocytotoxigenic Escherichia coli in the Agri-Food Chain

“…Whereas >90% of E. coli O157 isolates recovered from the beef chain in Ireland possessed vt and eae in combination, <10% of non-O157 VTEC serogroups fell into this category (38). In a Belgian study on O26, O103, O145, and O111 in cattle feces, about 6% of samples were positive and about 50% of isolates had key human virulence genes (47,48). A further study showed that for E. coli O157 genotypes associated with human illness a minor subpopulation was in the bovine reservoir.…”

“…A further study showed that for E. coli O157 genotypes associated with human illness a minor subpopulation was in the bovine reservoir. (47,48) This shows that while VTEC isolates in beef play a role in human illness, a risk assessment of their virulence potential is essential.…”