PMAxx™ dye is a DNA modifier used for viability PCR, invented by scientists at Biotium. PMAxx™ is a new and improved version of our popular viability dye PMA (propidium monoazide). Like PMA, PMAxx™ is a photo-reactive dye that binds to dsDNA with high affinity. Upon photolysis with visible light, PMAxx™ dye becomes covalently attached to dsDNA. The PMAxx™-modified dsDNA cannot be amplified by PCR. PMAxx™ dye is designed to be cell membrane-impermeable. Thus, in a population of live and dead cells, only dead cells are susceptible to DNA modification due to compromised cell membranes. This unique feature makes PMAxx™ highly useful in selective detection of live bacteria by qPCR.
PMAxx™ was designed by Biotium scientists to be a superior alternative to PMA. While PMA is generally effective at differentiating between live and dead bacteria by qPCR, it does not completely eliminate PCR products from dead cell DNA. This could potentially give false positive results. Biotium’s new dye PMAxx™ is much more effective at eliminating PCR amplification of dead cell DNA, and therefore provides the best discrimination between live and dead bacteria.
Since Biotium first developed PMA dye, there have been numerous publications on the use of the dye in pathogenic bacterial detection related to food and water safety, medical diagnosis and biodefense (download the PMA Reference List). PMAxx™ should be compatible with all existing PMA protocols, but with superior activity. Of course we also still sell the classic PMA dye, in water (40019) or lyophilized format (40013).
For viability PCR of Gram-negative bacteria we highly recommend using our PMA Enhancer (31038) in conjunction with PMAxx™. PMA Enhancer for Gram Negative Bacteria was designed to improve PMA-mediated discrimination between live and dead Gram-negative bacteria. When a sequence from a Gram-negative bacteria is amplified by PCR, samples pre-treated with dye and Enhancer show a decrease in the signal from dead cells, with no change in the signal from live cells. PMA Enhancer is particularly useful for samples in which bacteria were killed using mild methods such as low heat.
Biotium also provides strain-specific PMA Real-Time PCR Bacterial Viability kits with validated primers for 7 selected pathogens: M. tuberculosis, S. aureus, MRSA, Salmonella, E. coli, E. coli O157:H7 and Listeria. These kits provide everything that you need for the selective detection of your favorite species of live bacteria by real-time PCR. Don’t see your favorite strain? Let us know at firstname.lastname@example.org.
Real-Time PCR Bacterial Viability Kits
For photoactivation of PMAxx™ dye (or PMA or EMA), we recommend the use of Biotium’s PMA-Lite™ LED Photolysis Device (E90002), which is designed to conduct photolysis under controlled conditions.
- Abs = 466 nm (before photolysis)
- Abs/Em = ~510/~610 nm (following photolysis and covalent attachment to DNA/RNA)
- Dark red solution
- Store at -20°C and protect from light at all times
Garcia-Fontana, C., et al. (2016) A New Physiological Role for the DNA Molecule as a Protector against Drying Stress in Desiccation-Tolerant Microorganisms. Front. Microbiol. Dec 22; 7: 2066.
Randazzo, W., et al. (2016) Evaluation of viability PCR performance for assessing norovirus infectivity in fresh-cut vegetables and irrigation water. Int. J. Food Microbiol. Jul 16; 229: 1-6.
Randazzo, W., et al. (2017). Improving efficiency of viability-qPCR for selective detection of infectious HAV in food and water samples. J Appl Microbiol. Accepted Author Manuscript. doi:10.1111/jam.13519
Nocker, A., Cheung, C.Y., and Kamper, A.K. (2006). Comparison of propidium monoazide with ethidium monoazide for differentiation of live vs. dead bacteria by selective removal of DNA from dead cells. J. Microbio Meth. 67(2), 310-320.
Download the full PMA Reference List.