Abstract

Sixty (60) strains of Streptococcus thermophilus isolated from dairy traditional Egyption yoghurt samples were characterized. The yoghurt samples were collected from the local markets in Egypt. The results showed that few phages can attack S. thermophilus strains isolated from traditional Egyptian yoghurt (Zabady) samples, only three temperate phages were isolated. The isolated phages attacking samples were  induced with mitomycin C (0.05 or 0.1 μg/ml, final concentration) and characterized by SDS-polyacrylamide gel electrophoresis, PCR and electron microscope. The characterization of phages showed that the bacteriophages belonged to the family Siphoviridae and they had an isometric head and long non contractile tail. SDS polyacrylamide gels and PCR amplification showed that all isolated phages belongs to pac phage. The PCR described in this worak can detect and differentiate S. thermophilus phages in a short time, it is very sensitive and reveals a high limit of detection.

Key words: Streptococcus thermophilus, bacteriophage, SDS-polyacrylamide gel electrophoresis, PCR amplification.