Genetic Diversity among Escherichia coli O157:H7 Isolates from Bovines Living on Farms in England and Wales

Abstract

Pulsed-field gel electrophoresis of Escherichia coli O157:H7 isolates (n ‫؍‬ 228) from 122 healthy animals on 11 farms discriminated 57 types. Most clones were found only on individual farms. Numerous clones were found within each farm, with a prevalent clone normally found in several animals. A variety of clones were found within the different phage types.Escherichia coli strains that produce Shiga-like toxins may produce two toxins (Shiga toxin 1 [ST1] and/or ST2) with similar biological activities. A subset of Shiga-toxigenic E. coli strains designated as enterohemorrhagic (EHEC) carry sets of virulence genes (e.g., eaeA) that encode factors for attachment to host cells. Recent studies have revealed the existence of two divergent lineages (EHEC 1 and 2) (25). The EHEC 1 lineage consists solely of a few very closely related and geographically disseminated multilocus genotypes each bearing the O157 phenotype (15). Despite this similarity, pulsed-field gel electrophoresis (PFGE) and other molecular techniques have shown a considerable degree of genetic heterogeneity among O157 isolates in several countries, suggesting large evolutionary distances between strains. PFGE is considered the "gold standard" for fingerprinting of O157 strains and forms the basis of a large surveillance database (PulseNet) (24).Cattle are important reservoirs for this agent. Limited information is available about the genetic diversity of O157:H7 animal strains in the United Kingdom. Several studies have looked at human outbreak isolates, in most cases from Scotland (2,3,16,23). Some studies have described diversity in plasmid profiles in a limited number of animal isolates in comparison with isolates from food and humans (6,8,9). To our knowledge, one recent study (5) was the first to investigate the diversity of genotypes among animal isolates. The aim of the present study was to evaluate the genotypic diversity of O157:H7 isolates on a variety of cattle farms.Bacterial strains. E. coli O157:H7 (666 isolates) was cultured (7) (14) at 100 ng each, 2.5 mM MgCl 2 , and 2 l of bacterial DNA template. The PCR run consisted of 95°C for 10 min (one cycle), followed by 35 cycles of 95°C for 10 s, 65°C for 5 s, and 72°C for 25 s. The nature of the amplicon was determined by melting analysis over a temperature range from 70 to 97°C (0.1°C/s), and the melting temperature (T m ) was 87.5°C. The size of the product (625 bp) was verified by gel electrophoresis.

Comparison of pulsed-field gel electrophoresis patterns of antimicrobial-resistant Escherichia coli and enterococci isolates from the feces of livestock and livestock farmers in Japan

“…Furthermore, our results showed that the most predominant PFGE pattern among E. coli and enterococci strains from animals in each farm was not found. These findings are similar to those of other researchers (Aarestrup, 2000;Donabedian et al, 2003;Hoyle et al, 2006;Liebana et al, 2003;Manson et al, 2004). The demonstration of diversity in the PFGE patterns on the species level will be essential for understanding the molecular ecology of E. coli and enterococci in the intestine of animals and humans.…”

Phage Types and Genotypes of Shiga Toxin-Producing Escherichia coli O157:H7 Isolates from Humans and Animals in Spain: Identification and Characterization of Two Predominating Phage Types (PT2 and PT8)

“…As in previous studies (45,46,47,56,58), our results provide clear evidence for the superior capability of PFGE analysis compared with that of phage typing for the discrimination of unrelated strains. The results of our study also confirm those of earlier investigations about the macrorestriction patterns of epidemiologically unrelated STEC O157:H7 strains with a high degree of similarity due to the relatively limited genetic diversity within this serotype (46).…”

Longitudinal Study of Shiga Toxin-Producing Escherichia coli Shedding in Sheep Feces: Persistence of Specific Clones in Sheep Flocks

“…The ecology and epidemiology of STEC O157 in cattle appear to be very complex, often involving multiple clones on a single farm (14,17). There is some previously published information about the on-farm persistence of specific clones in different cattle production systems (13,15,18,21), including information about persistence in individual animals in a few cases.…”