Quantitative comparison of thermotolerant Campylobacter spp. growth in Preston broth with and without growth supplement.

Cultural detection of thermotolerant Campylobacter is challenging. ISO 10272-1:2017/Amd1:2023 recommends direct streaking or enrichment with either Bolton broth or Preston broth with growth supplement (FBP). From a collection of 123 isolates from food and animal origin, growth in Preston broth without FBP was detected on mCCDA for 56 % C. jejuni, 16 % C. coli, and 10 % C. lari enrichments. Supplementation with FBP improved growth so that all C. jejuni, 67 % C. coli and 85 % C. lari enrichments were positive on mCCDA. In comparison, Bolton broth enrichments were positive for all isolates, except for 7 % C. jejuni enrichments. Different efficiencies of enrichment were confirmed by quantitative Real-time PCR. Enrichment performances of Preston selective supplements from four different companies were compared and FBP concordantly improved Campylobacter detection in Preston broth. Moreover, food matrices were inoculated with freshly cultured Campylobacter. The presence of chicken meat, spinach and egg shells but not chicken skin considerably enhanced growth of fresh Campylobacter in Preston. Here, FBP led to no or marginal growth enhancement. Stressed Campylobacter were obtained by adding fresh Campylobacter to food matrices and incubating them aerobically at cold temperature prior to enrichment, mimicking storage conditions. After stress in raw milk, addition of FBP improved the median level of enrichment in Preston by 6.5 logCampylobacter/ml. In other matrices, enrichment levels of stressed cells were slightly higher in Preston with FBP than without. Campylobacter growth in Bolton was highest with 8.8-9.4 logCampylobacter/ml after 48 h. In conclusion, FBP improved detection in Preston broth. However, enrichment in Bolton broth was most efficient under our test conditions. Reliable performance evaluation of enrichment media might be monitored by qPCR, using naturally stressed Campylobacter in the presence of food matrix with intrinsic microbiota.