Combined Use of Two Genetic Fingerprinting Methods, Pulsed-Field Gel Electrophoresis and Ribotyping, for Characterization of Escherichia coli O157 Isolates from Food Animals, Retail Meats, and Cases of Human Disease

Abstract

Two genetic fingerprinting techniques, pulsed-field gel electrophoresis (PFGE) and ribotyping, were used to characterize 207 Escherichia coli O157 isolates from food animals, foods of animal origin, and cases of human disease (206 of the isolates were from the United Kingdom). In addition, 164 of these isolates were also phage typed. The isolates were divided into two general groups: (i) unrelated isolates not known to be epidemiologically linked (n ‫؍‬ 154) and originating from food animals, foods and the environment, or humans and (ii) epidemiologically related isolates (n ‫؍‬ 53) comprised of four related groups (RGs) originating either from one farm plus the abattoir where cattle from that farm were slaughtered or from one of three different English abattoirs. PFGE was conducted with the restriction endonuclease XbaI, while for ribotyping, two restriction endonucleases (PstI and SphI) were combined to digest genomic DNAs simultaneously. The 207 E. coli O157 isolates produced 97 PFGE profiles and 51 ribotypes. The two genetic fingerprinting methods had similar powers to discriminate the 154 epidemiologically unrelated E. coli O157 isolates in the study (Simpson's index of diversity [D] ‫؍‬ 0.98 and 0.94 for PFGE typing and ribotyping, respectively). There was no correlation between the source of an isolate (healthy meat or milk animals, retail meats, or cases of human infection) and either particular PFGE or ribotype profiles or clusters. Combination of the results of both genetic fingerprinting methods produced 146 types, significantly more than when either of the two methods was used individually. Consequently, the superior discriminatory performance of the PFGE-ribotyping combination was proven in two ways: (i) by demonstrating that the majority of the E. coli O157 isolates with unrelated histories were indeed distinguishable types and (ii) by identifying some clonal groups among two of the four RGs of E. coli O157 isolates (comprising PFGE types different by just one or two bands), the relatedness of which would have remained unconfirmed otherwise.

Genetic Diversity among Escherichia coli O157:H7 Isolates and Identification of Genes Linked to Human Infections

“…The E. coli O157 test strains used in this work were from the VLA collection and were used in a previous study (3). All strains were confirmed as E. coli with an API 20E kit (bioMerieux) and as serotype O157 with a latex agglutination kit (Oxoid) The H7 type was established by PCR following the methods of Wang et al (37).…”

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

“…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.…”

“…Preparation and XbaI digestion of DNA for PFGE and analysis of results were conducted as described previously (5).…”

Use of Pulsed-Field Gel Electrophoresis of Conserved XbaI Fragments for Identification of Swine Salmonella Serotypes

“…Many laboratories have used PFGE to determine strain relatedness, confirm an outbreak of a bacterial disease, and identify the source of a strain or outbreak (1)(2)(3)(4). Consequently, PFGE has become a very important tool in epidemiology (14).…”