Molecular characterisation and epidemiology of Scottish Escherichia coli O157 isolates of animal origin
Escherichia coli O157 is a major cause of HUS in Scotland, primarily as the result of consumption of contaminated foodstuffs, mainly bovine in origin. The genetic diversity of 801 E. coli O157 isolated from Scottish cattle and other farm animals was tested together with 134 human isolates tested for antibiotic susceptibility and six in 16S rDNA sequencing. PFGE was the technique of choice for elucidation of genetic variability in strains of E. coli O157. Using two endonucleases enabled maximum discrimination identifying microvariation which ribotyping, 16S rRNA and eaeA gene sequencing and ITS typing failed to detect. AFLP was the second most discriminatory technique and the results displayed a significant level of congruence with PFGE data. ERIC-PCR gave anomalous results and a low index of discrimination. Phage typing did not generate genetic data and was not as discriminatory as PFGE. Combination of phage type and PFGE data gave more discrimination than either method used in isolation. This was also true of verotoxin typing, especially verotoxin 2 typing. Antimicrobial resistance to various antimicrobial agents, whether plasmid-borne or chromosomally, must be considered an emerging problem. Several clonal types of E. coli O157 displayed resistance. The use of MIC values using the E-test is promising as a highly discriminatory typing technique. Ciprofloxacin and BAY 12087 were enhancers of release and/or production of verotoxins by E. coli O157 cells while fosfomycin and clarithromycin were inhibitory. Although E. coli O157 isolates displayed considerable variability, most were assigned to two major clusters, A and B, having a cut-off value at 69% Dice similarity. Several possible indications for a higher recombination tendency than previously assigned were apparent. Certain isolates circulated within the animal population for prolonged periods of up to four years and were more common in Scotland. The majority of E. coli O157 isolate subtypes, however, displayed a less stable genotype being isolated on a single occasion from Scotland. Moreover, a measurable genetic drift is occurring within the E. coli O157 population in cattle with the constant isolation of newly emergent subtypes.