Abstract
Most source attribution studies for Campylobacter use subtyping data based on single isolates from foods and environmental sources in an attempt to draw epidemiological inferences. It has been suggested that subtyping only one Campylobacter isolate per chicken carcass incurs a risk of failing to recognise the presence of clinically relevant, but numerically infrequent, subtypes. To investigate this, between 21 and 25 Campylobacter jejuni isolates from each of ten retail chicken carcasses were subtyped by pulsed-field gel electrophoresis (PFGE) using the two restriction enzymes SmaI and KpnI. Among the 227 isolates, thirteen subtypes were identified, the most frequently occurring subtype being isolated from three carcasses. Six carcasses carried a single subtype, three carcasses carried two subtypes each and one carcass carried three subtypes. Some subtypes carried by an individual carcass were shown to be potentially clonally related. Comparison of C. jejuni subtypes from chickens with isolate subtypes from human clinical cases (n = 1248) revealed seven of the thirteen chicken subtypes were indistinguishable from human cases. None of the numerically minor chicken subtypes were identified in the human data. Therefore, typing only one Campylobacter isolate from individual chicken carcasses may be adequate to inform Campylobacter source attribution.
Highlights
In 2006, New Zealand (NZ) had the highest reported rates of Campylobacteriosis in the developed world at approximately 385 per 100,000 of population [1]
To address whether identification of minor subtypes in poultry increases the likelihood of identifying C. jejuni subtypes relevant to the human etiology of campylobacteriosis, we determined the diversity of subtypes on fresh chicken carcasses
227 isolates were characterized by SmaI pulsed-field gel electrophoresis (PFGE) to identify subtypes of C. jejuni
Summary
In 2006, New Zealand (NZ) had the highest reported rates of Campylobacteriosis in the developed world at approximately 385 per 100,000 of population [1]. Studies of E. coli subtypes in human faeces discussed the importance of multiple isolations from a single stool sample to identify both dominant and minor subtypes [23]. Studies of E. coli clonal diversity in individual samples have used a binomial formula to determine the number of randomly selected colonies required to achieve a 90% probability of identifying a minor clone:. 1 − (1 − p)n, where p is the frequency of the minor clone and n is the number of colonies tested [23] This current study presents subtyping data for multiple C. jejuni colonies isolated from individual chicken carcasses using an enrichment method. The recognition of clonally related subtypes from the same sample and/or human case was recognised as potentially significant for the epidemiological tracking of outbreak sources
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