Antibiotic-resistant Acinetobacter baumannii is associated with nosocomial infections worldwide. Here, we used clinically isolated A. baumannii strains as models to demonstrate whether antibiotic resistance is correlated with an increased susceptibility to bacteriophages. In this study, 24 active phages capable of infecting A. baumannii were isolated from various environments, and the susceptibilities of both antibiotic-sensitive and antibiotic-resistant strains of A. baumannii to different phages were compared. In our study, a total of 403 clinically isolated A. baumannii strains were identified. On average, the phage infection percentage of the antibiotic-resistant A. baumannii strains was 84% (from 81–86%), whereas the infection percentage in the antibiotic-sensitive A. baumannii strains was only 56.5% (from 49–64%). In addition, the risk of phage infection for A. baumannii was significantly increased in the strains that were resistant to at least four antibiotics and exhibited a dose-dependent response (p-trend < 0.0001). Among all of the A. baumannii isolates, 75.6% were phage typeable. The results of phage typing might also reveal the antibiotic-resistant profiles of clinical A. baumannii strains. In conclusion, phage susceptibility represents an evolutionary trade-off in A. baumannii strains that show adaptations for antibiotic resistance, particularly in medical environments that have high antibiotic use.

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.

Vancomycin-sensitive and vancomycin-resistant Enterococcus (VSE and VRE) species have become a significant health problem. CHROMagar medium, which permits direct, color-based identification of target pathogens, could potentially be used to rapidly monitor airborne VSE and VRE. In this study, the efficiency of CHROMagar VRE medium without vancomycin supplementation (CVSE) for collecting airborne vancomycin-sensitive Enterococcus faecalis was evaluated in a chamber study. Subsequently, the performance of bioaerosol samplers combined with CVSE and CHROMagar VRE (CVRE) was evaluated in a hospital environment, a wastewater treatment plant, and a pig-rearing facility. Our results demonstrated that an Andersen impactor was much more effective than a Nuclepore filter for collecting airborne E. faecalis at relative humidity levels of 30% and 55%. In addition, approximately 10% of the isolated environmental Enterococcus strains were vancomycin-resistant. The average sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the colony identification were 58.5%, 81.3%, 5.5%, and 99.1%, respectively, for CVSE and 100%, 88.3%, 8.4%, and 100%, respectively, for CVRE. These findings indicate that the use of CHROMagar might provide a rapid method for detecting airborne VSE or VRE, shortening the detection time to 24-48 h. However, any mauve-colored colonies recovered on CVSE or CVRE by air sampling should be subjected to further identification tests.