Sensitivity of Direct Culture, Enrichment and PCR for Detection of Campylobacter jejuni and C.coli in Broiler Flocks at Slaughter.

Abstract

Broiler chicken flocks are a significant source of Campylobacter jejuni and Campylobacter coli that result in the major public health problem of campylobacteriosis. Accurate estimates of the prevalence of both C.coli and C.jejuni in flocks would enhance epidemiological understanding, risk assessment and control options. This study combined results from a panel of 10 detection tests (direct culture, enrichment and PCR) on caecal samples from flocks at slaughter. A parallel interpretation approach was used to determine the presence of Campylobacter spp. and for C.jejuni and C.coli individually. The sample was considered positive if at least one method detected the target and this interpretation was taken to represent a 'proxy gold standard' for detection in the absence of a gold standard reference test. The sensitivity of each individual method to detect Campylobacter spp., C.jejuni and C.coli was then estimated relative to the proxy gold standard. Enrichment in adapted Exeter broth (deficient in polymyxin B) with a resuscitation step was 100% sensitive, whilst direct culture on modified charcoal cefoperazone deoxycholate agar (mCCDA) was highly sensitive (97.9%). Enrichment methods using Preston broth and Bolton broth were significantly less sensitive. Enrichment in Exeter broth promoted the recovery of C.jejuni, whilst enrichment in Bolton broth favoured C.coli. A RT-PCR detection test could identify 80% of flocks that were co-colonised with both species. This study found that 76.3% (n=127) of flocks were colonised with Campylobacter spp. The majority (95.9%) of Campylobacter-positive flocks were colonised with C.jejuni; however, approximately one-third of positive flocks were simultaneously colonised with both C.jejuni and C.coli. The findings highlight the impact of different detection methodologies on the accuracy of the estimated incidence of both C.jejuni and C.coli entering the abattoir within broiler flocks and the associated public health risks.