The isolation and genotypic characterisation of campylobacter jejuni from environmental matrices

Abstract

Infection by Campylobacter is the most notified gastrointestinal disease in New Zealand. Reliable recovery and identification of campylobacters is challenging. Improved and validated methods are needed to increase the power of subtyping and epidemiological studies to trace the sources and transmission routes of Campylobacter. An enrichment-PCR method for the isolation and detection of C. jejuni and C. coli was developed and sensitivity levels determined in 13 environmental matrices, including animal faeces, food and water. Less than ten cells per sample of either C. jejuni or C. coli could be detected, except for rabbit faeces where the minimum number of cells detected per sample was greater than ten cells for C. coli (range 3-32 cells). The sensitivity of the method was comparable to that determined for the conventional methods in the same matrices. Application of the method to retail chicken carcasses (n =204) determined a prevalence of 27.5% C. jejuni and 1% C. coli. River water assays (n = 293) found 55.3% of samples to contain C. jejuni and 4.1% C. coli. Furthermore, the enrichment-PCR assay was shown to identify up to three subtypes in individual water samples. It was proposed that the identification of non-dominant subtypes carried by a chicken carcass may aid the identification of subtypes implicated in human cases of campylobacteriosis. An average of twenty-three C. jejuni isolates from each of ten retail chicken carcass were subtyped by PFGE using the two restriction enzymes SmaI and KpnI. Fifteen subtypes, in total, were identified from the ten carcasses. One subtype was identified on three carcasses. Five carcasses carried a single subtype, three carcasses carried two subtypes each and two carcasses carried three subtypes each. Some of the subtypes carried by an individual carcass were shown to be clonally related raising the question of in vivo recombination events during host passage. Comparison of C. jejuni subtypes from chickens with those isolated from human clinical cases revealed three of the fifteen subtypes correlated with those from human cases. None of the minority subtypes were identified in human case isolate data, suggesting that the lack of identification of non-dominant subtypes from chicken carcasses may not hinder the investigation of campylobacteriosis outbreaks.