Validation by interlaboratory trials of EN ISO 10272 - Microbiology of the food chain - Horizontal method for detection and enumeration of Campylobacter spp. - Part 1: Detection method

Abstract

During the last decade Campylobacter has been the most commonly reported gastrointestinal bacterial infection in humans in the European Union. The use of a sensitive detection method based on enrichment of Campylobacter spp. is often needed when examining foods. However, as background flora developed resistance to third generation β-lactams used in selective culture media, the ISO method was adapted. It now consists of three different procedures (A, B, and C) depending on the expected concentration and condition of Campylobacter and the background microflora. As the diagnostic sensitivity of the detection test varies between laboratories, this justifies the validation of the method in an interlaboratory study.The matrices selected for testing in the collaborative trials were frozen spinach (procedure A, Bolton enrichment broth), minced meat (procedure A, Bolton enrichment broth), raw milk (procedure B, Preston enrichment broth), chicken skin (procedure B, Preston enrichment broth), and broiler caecal material (procedure C, direct plating on mCCD agar). Each matrix was artificially inoculated with a different Campylobacter strain at a low and high contamination level, and with sterile diluent for ‘blanks’. Seventeen laboratories participated in the interlaboratory study. The sensitivity and specificity of the methods for the five selected matrices were determined, as well as the level of detection (LOD50). Calculated LOD50 values ranged from 0.84 cfu/test portion in frozen spinach and 2.2 cfu/test portion in minced meat to 14 cfu/test portion in chicken skin and 57 cfu/test portion in raw milk, all based on test portions of 10 g. The test portion size for broiler caecal material was a 10 μl-loop, yielding a LOD50 of 6.1 cfu/test portion. The validation data were incorporated in the newly published ISO standard EN ISO 10272-1:2017 - Microbiology of the food chain - Horizontal method for detection and enumeration of Campylobacter - Part 1: Detection method.