Inhibition of Clostridium tyrobutyricum in cheese by Lactobacillus gasseri

A semi-hard cheese produced from milk artificially contaminated with Clostridium tyrobutyricum spores (2.5×10 3 mL −1) was used as a model for studying the ability of bacteriocin-producing Lactobacillus gasseri K7 (Rif r) to inhibit clostridia. The added lactobacilli did not inhibit the primary starter culture ( Streptococcus thermophilus), but inhibited non-starter mesophilic lactobacilli. Late blowing as a result of Cl. tyrobutyricum outgrowth and butyric acid fermentation occurred in all cheeses however it was reduced in cheeses with added Lb. gasseri. After 6 weeks, the average amount of butyric acid was significantly higher in cheeses without added lactobacilli (1.43 vs. 0.70 g kg −1). At the end of 8-weeks ripening, 2.8×10 7 cfu g −1 of K7 (Rif r) viable cells were detected. Using the total DNA from cheeses with added K7 (Rif r) strain, PCR products were amplified with primers specific for Lactobacillus, Lb. gasseri and K7 bacteriocin gene.