Quantitative assessment of Campylobacter spp. levels with real-time PCR methods at different stages of the broiler food chain

The importance of thermotolerant Campylobacter spp. as a food-borne pathogen continues to increase and there is a great need for rapid quantitative results in routine diagnostics. However, currently, only the culture-based ISO method is authorized for use in the context of official food control. The present study therefore aimed to assess the suitability of a qPCR method for a rapid quantitative determination of Campylobacter spp. at different stages in the poultry production chain and its equivalence with the culture-based method. Samples from two processors were collected and evaluated both separately and together. Censored regression (Tobit) models have been used to establish a relationship between Campylobacter qPCR counts on the carcasses and explanatory variables of processor and meat counts. Further, correlations of qPCR Campylobacter spp. counts at the different stages of production were calculated. In addition, the comparative data between microbiological enumeration and qPCR results were statistically analyzed. In the correlation calculation of the qPCR results, a highly significant relationship between the Campylobacter spp. counts of the neck skin samples to breast fillet and leg samples could be calculated, indicating a good prediction of Campylobacter spp. loads in these samples. The intercalating dye ethidium monoazide (EMA) was used to see whether the correlations between microbiological counts and qPCR results were improved by pretreating fecal and cecal samples before qPCR analysis. It was shown that the observed values of scatter plots between the qPCR-based and the culture-based methods were strongly correlated. However, on average, the qPCR results were two log(10) CFU/mL levels higher than the microbiological counts. However, the classical culture-based method for food hygiene risk assessment cannot be replaced one-to-one by the qPCR or EMA-qPCR. The qPCR method can rather be used for the rapid identification of particularly highly contaminated flocks.