In the latest Lab on a Chip, researchers from the Samsung Advanced Institute of Technology (SAIT), South Korea, published a new method of extracting DNA from gram-positive bacteria for molecular diagnostics. DNA is often extracted using a bead-beater, an aggressive device used in many laboratories to disrupt cellular material with small ceramic beads and a lot of force. The samples are agitated at about 2000 oscillations per minute and, as a side effect, heat 10 degrees due to collisions of these beads.
The new system uses two glass plates around a PDMS (polydimethylsiloxane) membrane to form a microfluidic chip. The device contains channels, valves and a pneumatic inlet to facilitate pneumatic vibrations of the membrane. Beads are added in a chamber where they are accelerated by the deflection of the membrane. The DNA is then extracted from the bead-beaten lysed cells and available for molecular identification in a PCR-based diagnostic system.
Gram-positive bacteria like methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) contain a peptidoglycan layer which makes it hard to enzymatically lyse these cells. This new method clears the way to detect gram positive bacteria in an automated flow path of a nucleic acid-based micro-total analysis system.