| Summary: | A polyphasic study of the population diversity in a collection of Campylobacter jejuni isolates involved in human disease and from animal and environmental sources was undertaken. Isolates were characterised by phenotype, using heat stable antigen serotype, bacteriophage type and biotyping methods. Isolates were also genotyped by restriction fragment length polymorphism analysis of genomic DNA, using a 16S rRNA gene probe, a random-cloned DNA sequence probe, and of the flagellin A gene following amplification by the potymerase chain reaction. A diverse range of polyphasic strain profiles was seen amongst a population of C. jejuni isolates examined from sporadic human infections in the UK over a seven-month period. Associations between gene polymorphisms identified a number of prevalent genotypes and a cluster analysis of RFLP profiles identified a strong relationship between three of these prevalent genotypes. The association of these three genotypes with serogroup and phage-group markers was highly suggestive of clonality within this C. jejuni population. Three hunian pathogenic C. jejuni strains identified by this analysis could be recognised by association with specific Preston phage-groups. A retrospective survey indicated that these phage-groups were responsible for approximately 27% of sporadic cases of C. jejuni infection in the UK. The population diversity amongst sporadic human C. jejuni isolates remained consistent over a seven year period and these three phagegroups were a consistent feature of sporadic C. jejuni infections during this period. Each phage-group demonstrated a distinctly different seasonal distñbution suggesting that the epidemiology of these strains could be different. C. jejuni isolates from poultry samples were also diverse and a significant proportion of these isolates were indistinguishable from human C. jejuni isolates using the same polyphasic strain characteristics. Pathogenic human strains were found in contaminated environments but environmental populations largely contained stains which had not been seen amongst human isolates in this study. One of the strains identified in this study (R4:C8:11S4:flaA-26:PG55: BT6000) was demonstrated to have a global distribution and appears to have a host preference for cattle. In addition this strain was responsible for at least four milkborne outbreaks of (Ljejuni enteritis. Data from this study indicates that this strain may be responsible for up to 5 % of sporadic cases of human enteritis in the United Kingdom each year and that milking cows may be a reservoir for the organism.
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