Isolation of anticlostridially active lactobacilli from semi-hard cheese

The group of 7 strains of facultatively heterofermentative lactobacilli (FHL) of the non starter lactic acid bacteria (NSLAB) isolated from semi-hard cheeses using a well agar diffusion assay possessed a different level of inhibition activity against 16 different strains of Clostridium sp. belonging to the species Cl. butyricum, Cl. tyrobutyricum, Cl. beijerinckii, and Cl. sporogenes. Two selected strains with the production of partially indentified anticlostridially active inhibitory substances, Lb. paracasei ST68 (producing hydrogen peroxide) and Lb. paracasei 171R2 (producing bacteriocin and hydrogen peroxide), were tested for the inhibition activity against gas producing Cl. butyricum 10702 and Cl. tyrobutyricum 184 in cheese slurry. The effects of both strains were different in reducing the numbers of gas producing Cl. butyricum 10702 by > 3 log cycles and Cl. tyrobutyricum 184 by > 1 log cycles in cheese slurry during the tested storage periods of 24 days at 13°C. The Cl. tyrobutyricum strains isolated from spoiled cheese were identified by species-specific PCR for Cl. tyrobutyricum.