Antibiotic resistance and plasmid DNA contents of Streptococcus thermophilus strains isolated from Turkish yoghurts

摘要

Sixty six strains were isolated from yoghurt samples obtained from various villages in different regions of Turkey and thirty four were identified as Streptococcus thermophilus. They were examined for antibiotic resistance and plasmid carriage. The susceptibility of the isolates to 8 antibiotics (vancomycin, tetracycline, chloramphenicol, erythromycin, cephalothin, ampicillin-sulbactam, gentamicin and penicillin G) was determined with disk diffusion method. Most of the Strep. thermophilus were resistant to gentamicin (79%) and penicillin G (64%) and most strains were also sensitive to chloramphenicol (94%) and tetracycline (88%). In plasmid DNA analyses, 7 strains did not contain any plasmid DNA, while in other it ranged from 1 to 5. The molecular weights of these plasmids varied from 1.88 to 19.89 kb. An interaction was observed between the resistance to antibiotics and the occurrence of plasmids in some Strep. thermophilus strains. The resistance of most antibiotics was determined in B55.S, B56.S and B58.S strains containing five plasmid DNAs. However, no correlation was observed between the resistance to antibiotics and the occurrence of plasmids in some strains.