Use of PCR-based methods and PFGE for typing and monitoring homofermentative lactobacilli during Comte cheese ripening

This study investigated the genotypic characteristics of selected and wild homofermentative thermophilic lactobacilli strains during ripening of Comte cheeses, made into two cheese plants. Both amplification and restriction analysis of the 16S rRNA gene (PCR-ARDRA) and classical biochemical tests were used to identify isolates. Diversity within homofermentative lactobacilli was not found in their species composition since the same two species Lactobacillus helveticus and L. delbrueckii susbp. lactis were isolated from cheeses. In cheeses made with natural whey starter, it appeared that the most likely sources of L. helveticus and L. delbrueckii susbp. lactis were the starter and raw milk, respectively. The examination of RAPID profiles of lactobacilli strains revealed 19 RAPID groups among 50 isolates, which were different from selected starter strains. Using RAPID, REP-PCR, and PFGE to identify selected starter strains during cheese ripening, we showed that L. helveticus decreased quickly while L. delbrucekii susbp. lactis sustained high viability during ripening. The use of selected L. delbrueckii susbp. lactis strains diminished the genetic diversity among strains isolated from cheese, probably in preventing the raw milk microflora from growing. (C) 2002 Elsevier Science B.V. All rights reserved.