Dental plaque samples were collected by board-certified periodontists using sterile paper points at baseline prior to any dental treatment and labeled in numbers according to sampling sequences. The paper points were placed in the mesiobuccal sulci of the first molar in each quadrant for 1 minute and then immersed immediately in an Eppendorf tube containing 0.5 ml of Tris-EDTA (TE) buffer (pH 7.5) (Wang et al., 2009 (link)). Oral bacteria were harvested by centrifugation, and the bacterial pellet was resuspended in 100 µl TE buffer. Bacterial chromosomal DNA was released by two cycles of freezing at -80°C overnight and boiling for 10 minutes.
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