In this study, we examined whether application of DNase I can serve as differential eliminator of DNAs from dead cells, leaving viable probiotic lactic acid bacteria such as Lactobacillus acidophilus to be assessed by polymerase chain reaction (PCR). When dead cells were treated with DNase I, DNA amplification was not completely suppressed. Increasing the concentration of DNase I, up to 66 u/100 μL, and the preparation of dead cells using high temperatures did not seem to make difference in the level of PCR product from the dead bacteria. Assessment of free DNA degradation, when mixed with dead cells, showed that stability of free DNAs or their degradation by DNase I was not affected by presence of the dead cells. In conclusion, we tend to suggest that for using this technique, one should take great deal of caution and that its reliability should be tested for different species independently.

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