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.