Rapid and sensitive detection of Pseudomonas aeruginosa in bottled water by loop-mediated isothermal amplification

Propidium monoazide-quantitative polymerase chain reaction (PMA-qPCR) assay for rapid detection of viable and viable but non-culturable (VBNC) Pseudomonas aeruginosa in swimming pools

Lack of culturability in the viable but non-culturable (VBNC) bacteria and the ability to regain infectivity in favourable conditions is one of the new challenges of public health providers for Pseudomonas aeruginosa monitoring in environmental samples. Propidium monoazide quantitative polymerase chain reaction (PMA-qPCR) is one of the promising methods for timely detection of VBNC pathogens in environmental samples. We developed and used a method for the first time to detection of VBNC P. aeruginosa in swimming pool water samples using a membrane filter (MF). Moreover, the dominant model of the distribution of colonies on the MF and the effect of the culture medium and MF type on colony recovery by MF were evaluated. Swimming pool samples were subjected to conventional culture-based, qPCR and PMA-qPCR methods and the results were compared for the presence of VBNC P. aeruginosa in the samples. The positivity rate was 21% and 75% for P. aeruginosa in water samples as confirmed by standard culture-based and qPCR methods, respectively. Furthermore, of 24 samples, 9 (37.5%) were positive for VBNC P. aeruginosa. The developed qPCR/PMA-qPCR assay can detect the VBNC bacteria directly from aquatic samples and may result in better monitoring of recreational waters.

Development of uracil-DNA-glycosylase-supplemented loop-mediated isothermal amplification coupled with nanogold probe (UDG-LAMP-AuNP) for specific detection of Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is an important opportunistic pathogen that causes serious infections in humans, including keratitis in contact lens wearers. Therefore, establishing a rapid, specific and sensitive method for the identification of P. aeruginosa is imperative. In the present study, the uracil-DNA-glycosylase-supplemented loop-mediated isothermal amplification combined with nanogold labeled hybridization probe (UDG-LAMP-AuNP) was developed for the detection of P. aeruginosa. UDG-LAMP was performed to prevent carry over contamination and the LAMP reactions can be readily observed using the nanogold probe. A set of 4 primers and a hybridization probe were designed based on the ecfX gene. The UDG-LAMP reactions were performed at 65°C for 60 min using the ratio of 40% deoxyuridine triphosphate to 60% deoxythymidine triphosphate. The detection of UDG-LAMP products using the nanogold labeled hybridization probe, which appeared as a red-purple color, was examined at 65°C for 5 min with 40 mM MgSO₄. The UDG-LAMP-AuNP demonstrated specificity to all tested isolates of P. aeruginosa without cross reaction to other bacteria. The sensitivity for the detection of pure culture was 1.6×10³ colony-forming units (CFU) ml⁻¹ or equivalent to 3 CFU per reaction while that of polymerase chain reaction was 30 CFU per reaction. The detection limit of spiked contact lenses was 1.1×10³ CFU ml⁻¹ or equivalent to 2 CFU per reaction. In conclusion, the UDG-LAMP-AuNP assay was rapid, simple, specific and was effective for the identification of P. aeruginosa in contaminated samples.