[Isolation and identification of probiotics from yoghourt in Beijing]

To carry out isolation and the viable plate count of probiotics from yoghourt. To investigate the antimicrobial susceptibility of strains to penicillin, gentamicin, ampicillin, vancomycin, clindamycin and erythromycin.

Probiotics were recovered and counted from yoghourt by plate count method. The recovered isolates were characterized by Gram's stain, biochemical test, antimicrobial susceptibility test.

MRS medium and (36 +/- 1) degrees C were the optimum condition of culture. In total, 52 probiotic isolates were recovered from 31 yoghourt products, 12 (38.7%) products showed a lower probiotic quantity than 1 x 10(6) cfu/ml of the national stantard, and 19 (61.3%) products were higher than 1 x 10(6) cfu/ml. Gram's stain showed that 37 isolates were gram positive bacilli and 15 isolates were positive coccus. These 52 isolates were grouped into six species by biochemical method, including L. bulgaricus, S. thermophilus, L. acidophilus, L. casei, L. delbrueckii and L. fermentum. All 52 isolates were susceptible to penicillin and ampicillin, one isolate was resistant to both clindamycin and erythromycin, four isolates were resistant to vancomycin.

Most of yoghourt products contained sufficient viable probiotics as required by the national standard. A small quantity of isolates were resistant to some antimicrobials and multi -drug resistant isolates were also found.