New media for the numeration of cheese surface bacteria

Abstract

The characterisation of naturally occurring bacterial species present in cheese made from raw milk and/or the study of the equilibrium of the floras present during the ripening process necessitates the use of reliable culture media. Currently, there are relatively few methods available for specifically counting these microorganisms in the dairy environment. Three media were developed. These media were compared with Chapman and TSA/NaCl media for their ability to select and to allow the growth of the researched germs in 25 samples of different cheeses (Camembert, Pont l'Évêque, Livarot, Comté, Saint-Nectaire, Salers), as well as in 4 samples of raw milk. The CRBM medium (Cheese Ripening Bacteria Medium) permitted the recuperation of all ripening bacteria; this medium supplemented with bacitracine selected for the staphylococci, while supplemented with furazolidone, it permitted the numeration of corynebacteria present including the Micrococcaceae. These media were more selective against undesirable floras (enterobacteria, Bacillus spp., streptococci, yeasts and molds) and allowed a better growth of the studied bacteria. For all the types of cheese studied, the specificity of the media was satisfactory. The use of CRBM media therefore appears interesting in view of the microbiological characterisation of milk or cheeses made from raw milk.