Preparation of samples and analysis of chromosomal DNA fragmentation by pulsed field gel electrophoresis (PFGE) was performed exactly as described (30) . PFGE was conducted in a CHEF-DRIII Chiller System (Bio-Rad). One percent agarose gels were run in 0.5% Tris borate-EDTA buffer at 148C with an angle of 1208 with a voltage of 6 V/cm and switch times of 60-90 s for 24 h. Gels stained in ethidium bromide were analysed after destaining using Syngene Gene Genius Bioimaging System.