Identification and characterization of Streptococcus thermophilus strains by pulsed-field gel electrophoresis

The chromosomal DNA of a number of strains of the lactic acid bacterium Streptococcus thermophilus was analysed with the aim of rapidly differentiating and assessing the characteristics of each strain. Pulsed-field gel electrophoresis was used to separate large DNA fragments formed by the restriction enzymes Sma I, Sfi I or Apa I. Hybridization with a non-radioactive DNA probe confirmed the identification of strains as Strep. thermophilus and analysis of the electrophoretic patterns differentiated some strains from others. A more extensive study of the pulsed-field electrophoresis restriction patterns of new isolates of Strep. thermophilus may facilitate assessment of their technological properties by comparison of their restriction patterns with those of reference strains.