Novel approach to enumerate clostridial endospores in milk

Clostridial contamination of raw milk causes late-blowing, a severe quality defect in cheese. Consequently, milk containing high numbers of cheese-damaging clostridial spores should not be used for the production of certain types of hard and semi-hard cheese. Currently, there is no officially standardised method available to monitor clostridial spore levels in milk, and major drawbacks like long analysis time, labour intensity, uncertainty of results and insufficient selectivity for clostridia exist for usually used conventional MPN (most probable number) techniques. Therefore, an optimised medium in combination with a semi-automated application for the enumeration of clostridia in milk was developed. The aim of this study was to evaluate this new methodology in comparison with a conventional method (using Bryant and Burkey broth) based on the analysis of 84 milk samples. Method inclusivity was further tested using pure clostridial cultures, and selectivity was assessed by molecular identification of isolates obtained from the new assay. The novel approach proved to be suitable for the detection of clostridia in both suppliers' and processed milk, also indicating that it is superior in selectivity, sensitivity and analysis time compared to conventional techniques.