Detection of viable antibiotic-resistant/sensitive Acinetobacter baumannii in indoor air by propidium monoazide quantitative polymerase chain reaction.

Acinetobacter baumannii represents a significant cause of nosocomial infections. Therefore, we combined real-time quantitative polymerase chain reaction (PCR) with the propidium monoazide (PMA-qPCR) to assess the feasibility of detecting viable, airborne A. baumannii. The biological collection efficiencies of three samplers for collecting airborne A. baumannii were evaluated by PMA-qPCR in a chamber study. After sampling, the effects of storage in collection fluid on A. baumannii were evaluated. The results showed that the culturable ratio of A. baumannii measured using the culture method was significantly correlated with the viable ratio measured using PMA-qPCR, but was not significantly correlated with the qPCR results. It was indicated that the AGI-30 impinger and the BioSampler were much more effective than the Nuclepore filter sampler for collecting airborne A. baumannii. The storage temperature was critical for aerosol samples, as the loss of viable A. baumannii was minimized when the PMA-bound DNA was stored at -20°C or if the collected cells were stored at 4°C and subsequently processed by PMA-qPCR within 1 month. The PMA-qPCR method was also to distinguish between colistin-sensitive and colistin-resistant A. baumannii, and no colistin-sensitive A. baumannii was detected by PMA-qPCR upon treatment of the BioSampler collection medium with 2 μg/ml colistin for 5 min.