Isolation of cultivable thermophilic lactic acid bacteria from cheeses made with mesophilic starter and molecular comparison with dairy-related Lactobacillus helveticus strains.

AIMS: To isolate cultivable thermophilic lactic acid bacteria from cheeses made with mesophilic starter and compare them with dairy-related Lactobacillus helveticus strains using molecular typing methods. METHODS AND
RESULTS: The number of thermophilic bacteria in seven commercial cheeses manufactured with mesophilic starters was estimated to be <10 CFU g(-1). Implementation of an enumeration step in the isolation method made it possible to isolate one thermophilic strain from each of five of seven cheeses. Comparing repetitive sequence PCR (rep-PCR) profiles of the isolates with dairy-related Lact. helveticus strains indicated that one isolate was a Lact. helveticus. Partial sequencing of 16S rRNA confirmed this, and the remaining four strains were identified as Lactobacillus delbrueckii, Lactobacillus fermentum and Enterococcus faecium. The rep-PCR profile of the isolated Lact. helveticus was identical to the rep-PCR profile of the Lact. helveticus adjunct culture used in the specific cheese, but their pulsed field gel electrophoresis profiles differed slightly.
CONCLUSION: It was possible to isolate cultivable thermophilic bacteria from ripened cheeses manufactured with mesophilic starter and thermophilic adjunct cultures by using an enumeration step. SIGNIFICANCE AND IMPACT OF THE STUDY: Isolation of cultivable thermophilic bacteria from ripened cheeses made with mesophilic starters offers an original source for new dairy-relevant cultures.