CULTURE MEDIA FOR NON-SPORULATING GRAM-POSITIVE FOOD SPOILAGE BACTERIA

The spoilage association especially of protein-rich foods can be dominated by Gram-positive bacteria, notably lactic acid bacteria (LAB) which affect vacuum packaged refrigerated processed meats and some dairy products. New food ecosystems are being created by novel packaging and processing technologies, resulting in spoilage associations differing from those previously reported. In addition, improvement in identification methods, allow the detection and isolation of 'novel' bacterial groups, e.g., Carnobacterium spp. This review considers the genera Aerococcus, Brevibacterium, Brochothrix, Carnobacterium, Kurthia, Lactobacillus, Leuconostoc, Microbacterium, Micrococcus, Pediococcus and Propionibacterium. Strictly selective procedures, including incubation temperature and atmosphere, are not yet available for the genera Aerococcus, Brevibacterium, Microbacterium and Micrococcus, and only with some limitations for Kurthia and Propionibacterium. On the other hand, a causative role in food spoilage has not been established clearly for all those groups, some of which may be 'opportunistic' in their behaviour. The LAB groups Lactobacillus, Leuconostoc and Pediococcus ('LLP-Group') often share similar habitats and show similar physiological behaviour on a number of elective and selective media. Modifications to increase selectivity have been based mainly on de Man, Rogosa and Sharpe (MRS) or Rogosa agar, and include pH reduction, supplementation with chemical preservatives (e.g., sorbic acid and nitrate) and the use of reduced atmospheres or suboptimal incubation temperatures. Carnobacteria differ from other LAB in their non-aciduric nature, and selective plating procedures use high-pH media (pH 8-9) by which competitors (mainly lactobacilli) are eliminated.