PMA-qPCR-Based Viable Cell Enumeration for Live Biotherapeutics

No, PMA-qPCR is generally viewed as a complementary method rather than a direct, universal replacement for traditional plate counting. It provides the greatest value when dealing with sample types known to have high proportions of VBNC cells, highly complex matrices where plate reading is obscured, or when turnaround time is critical. The choice of method should always depend on the specific strain characteristics, product type, testing goals, and any relevant project guidelines.

Processes like lyophilization or prolonged storage can cause bacteria to enter a Viable But Non-Culturable (VBNC) state. These cells do not grow on agar plates but remain metabolically active. PMA-qPCR can quantify intact DNA in both culturable and VBNC cells, providing an alternative estimate of the viable population without requiring in vitro replication.

Propidium Monoazide (PMA) is a photo-reactive dye that is generally impermeable to intact cell membranes. It enters cells with compromised membranes (considered dead cells). Upon exposure to bright light, PMA covalently cross-links with the DNA inside these cells. This cross-linked DNA cannot be effectively amplified during the subsequent qPCR step, thereby reducing the signal from the dead cell population.

Yes, provided that appropriate strain-specific primers can be designed and validated. A key part of our service is testing primer specificity against other species present in a mixture, ensuring that the target sequence can be distinctly quantified within a blended formulation.

The timeline depends on the complexity of the sample matrix and the target strain. Typically, initial primer design and feasibility testing take 2-3 weeks, followed by 3-4 weeks for comprehensive PMA optimization, standard curve establishment, and SOP generation. We work closely with your team to align deliverables with your project milestones.