PMA based real-time fluorescent LAMP for detection of Vibrio parahaemolyticus in viable but nonculturable state

Vibrio parahaemolyticus is a crucial foodborne pathogen. The viable but non-culturable (VBNC) state of V. parahaemolyticus cannot be detected by traditional culture methods. The objective of this study was to develop and evaluate a method that combines propidium monoazide (PMA) treatment with real-time fluorescent loop-mediated isothermal amplification (RF-LAMP) to detect and quantify VBNC cells of V. parahaemolyticus. Different states of cells were treated with PMA in dark for 5 min and subsequently exposed to a 650 W halogen lamp for 5 min. The cells were collected and DNA was amplified by RF-LAMP. The primers which targeted six distinct regions in the tlh gene of V. parahaemolyticus were used for the PMA-RF-LAMP assay. The results indicated that the treatment with 4 μg/mL of PMA and a further exposure to light for 5 min was suitable for PMA-RF-LAMP to distinguish viable cells from dead cells of V. parahaemolyticus. The developed assay exhibited remarkably high specificity, sensitivity and rapidity, without any cross reaction with the tested non-V. parahaemolyticus strains. There was good linear correlation between Ct values and log copy/mL in the range of 6.8–6.8 × 107 copy/mL, with the reaction endpoints less than 30 cycles (30 min). It could detect as low as 14 copy/g of V. parahaemolyticus in spiked seafood samples (pomfret, shrimp, scallop, oyster and salted fish) without any interference from food matrices, dead cells and other bacteria.