Validation of a Relative Centrifugal Force method for the enumeration and detection of Campylobacter from chicken carcass rinsates

Campylobacteriosis is the most frequently notified foodborne disease in New Zealand and poultry is the predominant infection source. New Zealand monitors Campylobacter present in poultry carcass rinsates under the National Microbiological Database (NMD) programme. To better monitor Campylobacter control improvements, a more sensitive method is required that can enumerate rinsates with lower Campylobacter numbers. This study developed a modification of the current NMD method involving adding a relative centrifugal force (RCF) step for concentrating Campylobacter from poultry carcass rinsates. Centrifugation for 30 min significantly improved Campylobacter recovery compared with 15 min (p < 0.001), but there were no differences between RCFs of 3500, 4000 and 4430 x g (p = 0.992). RCF and NMD method performances were compared in a single laboratory validation study that used different inoculation levels of twelve Campylobacter strains, including poultry isolates. Campylobacter was detected from more samples (p < 0.001) using the RCF method (93 of 126; 73.8 %) than the NMD method (65 of 126; 51.6 %). The RCF method had a seven-fold lower detection limit (28 colony forming units (CFU)/400 ml) than the NMD method (200 CFU/400 ml). The detection limit accounted for an observed 70.3 % of the inoculated CFU captured within the centrifuged pellet. Campylobacter was also detected from significantly more (p < 0.001) commercial chicken rinsate samples tested by poultry industry laboratories using the RCF method (257 of 863; 29.8 %) than the NMD method (114 of 863; 13.2 %). Taken together, results support the RCF method as a modification of the NMD method to enumerate lower numbers of Campylobacter in rinsates.