Bayesian analysis of culture and PCR methods for detection of Campylobacter spp. in broiler caecal samples

Abstract

The objective of this study was to estimate the sensitivity and specificity of a culture method and a polymerase chain reaction (PCR) method for detection of two Campylobacter species: C. jejuni and C. coli. Data were collected during a 3-year survey of UK broiler flocks, and consisted of parallel sampling of caeca from 436 batches of birds by both PCR and culture. Batches were stratified by season (summer/non-summer) and whether they were the first depopulation of the flock, resulting in four sub-populations. A Bayesian approach in the absence of a gold standard was adopted, and the sensitivity and specificity of the PCR and culture for each Campylobacter subtype was estimated, along with the true C. jejuni and C. coli prevalence in each sub-population. Results indicated that the sensitivity of the culture method was higher than that of PCR in detecting both species when the samples were derived from populations infected with at most one species of Campylobacter. However, from a mixed population, the sensitivity of culture for detecting both C. jejuni or C. coli is reduced while PCR is potentially able to detect both species, although the total probability of correctly identifying at least one species by PCR is similar to that of the culture method.

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

“…DNA extracts were collected from 250 μ l of each pooled sample using an ExtractMaster ™ Fecal DNA Extraction Kit (Epicentre Biotechnologies, Madison, USA) as previously described (Arnold et al., ).…”

“…Amplification was after an initial hold at 95°C for 15 min, followed by 40 cycles of 94°C for 30 s, 60°C for 30 s and 72°C for 30 s; fluorescence was read at the 60°C position. A cycle threshold (CT) of between 10 and 32 was viewed as a positive result for either the mapA probe or ceuE probe as previously described (Arnold et al., ).…”

“…A survey of Campylobacter in broilers at slaughter across the EU reported that 60.4% of colonised flocks carried C. jejuni and the remainder carried C. coli (Anonymous, ). This survey only identified a single Campylobacter colony per flock and could not account for the scenario where flocks are co‐colonised with both species (Arnold et al., ; de Boer et al., ).…”

“…More accurate estimates of the prevalence of both C. coli and C. jejuni would enhance epidemiological understanding, risk assessment and control options, as research suggests that epidemiological characteristics in broiler flocks differ between species. C. coli has a more pronounced seasonal peak (Lawes et al., ; Arnold et al., ) and may be more prevalent in older flocks or free‐range flocks (El‐Shibiny et al., ; Anonymous, ; Lawes et al., ). Accurate prevalence estimates require knowledge of the sensitivity of the detection methodologies employed.…”

“…Comparative studies have shown mCCDA to have similar or better performance than alternative media used for faecal‐ and caecal‐type cultures by direct culture (Potturi‐Venkata et al., ; Rodgers et al., , ; Ugarte‐Ruiz et al., ), and it is specified in an international standard method (Anonymous, ). To estimate the sensitivity of direct culture on mCCDA for detection of C. jejuni or C. coli, our group has applied Bayesian modelling in the absence of a gold standard reference test, which has indicated greater sensitivity for C. jejuni relative to C. coli (Vidal et al., ; Arnold et al., ). Comparative studies of different enrichment broths against direct culture have provided variable results and increases and decreases in sensitivity for Campylobacter spp.…”