Genotyping of Lactobacillus delbrueckii subsp. bulgaricus and determination of the number and forms of rrn operons in L. delbrueckii and its subspecies.

Three different approaches (whole-cell protein profiles, DNA fingerprinting combined with pulsed-field gel electrophoresis and analysis of rDNA genes) were used to characterize thirty-one strains of Lactobacillus delbrueckii subsp. bulgaricus from different dairy products, and three type strains belonging to L. delbrueckii subsp. delbrueckii, L. delbrueckii subsp. lactis and L. delbrueckii subsp. bulgaricus. Moreover, the number and different forms of rrn operons in L. delbrueckii and its subspecies were defined. At the strain typing level, Notl macrorestriction analysis permitted grouping of the 32 strains of L. delbrueckii subsp. bulgaricus into 23 restriction patterns, providing a high degree of discriminatory power. Among whole-cell protein profiles, PCR analysis of rDNA genes and ribotyping, the latter method seemed to be the most reliable approach to characterizing the subspecies belonging to L. delbrueckii. Ribotyping combined with enzymes such as HindIII and EcoRI showed that at least six rrn operons were present in L. delbrueckii and its subspecies; two forms of rrn operons were present in the subspecies lactis and bulgaricus and four forms were present in the subspecies delbrueckii.