Genotypic and phenotypic heterogeneity of Streptococcus thermophilus strains isolated from dairy products

Aims: Forty strains of Streptococcus thermophilus isolated from dairy produ cts were identified and typed by a polyphasic approach which included pheno typic and genotypic criteria. Methods and Results: Strains were identified by sugar fermentation pattern and species-specific PCR. Phenotypic diversity was evaluated by a chemometr ic model taking into account some biochemical characteristics (e.g. acidify ing and peptidase activities) of technological interest. Genotypic diversit y was evidenced by PCR fingerprinting. The overall phenotypic and genotypic information was elaborated on a multivariate statistical basis by principa l components analysis and cluster analysis, respectively. When acidifying a nd peptidase activities were considered, PCA indicated that most of the str ains isolated from Pecorino Toscano cheese were separable from the others. Similarly, most of the starter culture strains tended to separate from the cheese isolates. Conclusions: A wide strain heterogeneity among Strep. thermophilus strains isolated from dairy products was observed. Significance and Impact of the Study: A computerized analysis of genotypic and phenotypic information could be applied successfully to differentiate a nd characterize reliably and rapidly isolates occurring in different dairy products and to comprehend the technological role of specific Strep. thermo philus strains in dairy technology.