GENOTYPING CHARACTERIZATIONS ADN ANTIBIOTIC RESISTANCE OF STREPTOCOCCUS THERMOPHILUS STRAINS ISOLATED FROM DIFFERENT YOGURT BRANDS

This paper reported antibiotic resistance and PFGE genetic typing of Streptococcus thermophilus stains isolated from different yogurt brands in Chinese market. In total, 42 strains isolated from 43 yogurt samples were identified as S. thermophilus stains by 16S rDNA sequence analysis. The investigation of antibiotic-resistance profiles revealed that those isolates were resistant to erythromycin (69.05 %), clindamycin (73.81 %), chloramphenicol (61.90 %) and fosfomycin (19.05 %), and were susceptible to other 13 kinds of antibiotics. The genetic typing of S. thermophilus stains was examined by pulsed-field gel electrophoresis (PFGE) of chromosomal DNA digested with SmaI. The enzyme restriction profiles showed the 42 S. thermophilus isolates were divided into 14 PFGE types, and further analysis showed the PFGE profile did not completely match with antibiotic resistance profile. The antibiotic resistance and PFGE pattern database generated in this study suggest that the safety evaluation of S. thermophilus should be paid more attention and will provide basic for information of food safe assessment of yogurt.