Anticlostridial activity of Lactobacillus isolated from semi-hard cheeses

Non-starter lactic acid bacteria grow to high numbers in semi-hard cheeses during ripening, and may suppress harmful bacteria. In this study, about 400 Lactobacillus isolates from Danish semi-hard cheeses were identified to species level using internal transcribed spacer-polymerase chain reaction (ITS-PCR) analysis. The majority of isolates belonged to the Lb. paracasei complex and were classified into approximately 135 types using pulsed field gel electrophoresis (PFGE). Lactobacillus isolates representing all the different PFGE types were screened, using an agar well diffusion assay, for antimicrobial activity against 15 single-strain Clostridium cultures. Almost half of the isolates possessed anticlostridial activity, and 10% possessed a broad and consistent activity. Nine strains were further investigated for properties of importance for use as mixed cultures in cheese and silage. The results showed that anticlostridial non-starter Lactobacillus growing in high quality semi-hard cheeses could be useful as protective adjunct cultures against the growth of Clostridium.