I have been trying to collect bacteria from human fecal sample to run on MT-PCR, however, for some reason, the concentration of human DNA is quite low and could not confirmed on PCR. My technique is making a solution of fecal sample with PBS in 1g per 10 ml, centrifuge at 500g for 3 minutes and collect supernatant, repeat three times and final centrifuge is 20000g at 4 Celsius degrees for 20 minutes. Beside it give very good concentration of bacteria, but I also need a good concentration of human DNA also. Should I lower centrifuge force or reduce time? Thank you for you help.