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.