Evaluation of culture-based and molecular detection methods for Campylobacter in New Zealand raw cows' milk.

Abstract

This study evaluated the performance of a commercial molecular detection method (mericon Campylobacter triple kit real-time/quantitative (q)PCR) and a selective plating medium (R&F Campylobacter jejuni/Campylobacter coli Chromogenic Plating Medium (CCPM)) against a culture-based reference method (ISO 10272-1:2017 detection procedure B) for the detection of Campylobacter from raw milk enrichment broths. New Zealand raw cows' milk and Ultra-High Temperature-processed milk samples were inoculated with 50, 125 and 500 colony forming units of C. jejuni and C. coli cocktail per analytical unit. Samples were tested for Campylobacter after 0, 24- and 48h refrigeration. ISO 10272-1:2017 proved to be a sensitive detection method (77/80 positive samples); detection only failed for some milk samples tested 48h postinoculation. CCPM was as effective as Cefoperazone Charcoal Deoxycholate Agar for selective plating of Campylobacter raw milk enrichments (78/80 positive samples). However, the qPCR detected Campylobacter in only 42/80 samples and qPCR reaction inhibition was observed. The ISO 10272-1:2017 method was a more sensitive method for Campylobacter detection from raw milk than the mericon Campylobacter triple kit qPCR, and CCPM was a useful complementary medium to mCCDA where one of these media is required by the standard. In regions where testing is required or recommended, optimized methods for Campylobacter detection from raw milk will reduce risk to the raw milk consumer. Although molecular methods are generally touted as a rapid alternative to culture, issues with inhibition due to matrix components mean that culture-based methods might provide the most sensitive option for Campylobacter detection in raw milk. Findings also emphasize the importance of minimizing the time between milk collection and testing for Campylobacter.