Antibiotic resistance genes and antibiotic sensitivity in bacterial aerosols and their comparisons with known respiratory pathogens

Airborne transmission of antibiotic resistance genes (ARGs) has emerged as a global health threat, while their hosts’ resistance phenotype remains largely unknown. Here, culturable bacterial aerosol samples were collected from polluted air in Beijing using a portable high volume sampler (1000 L/min). Antimicrobial susceptibility testing was conducted to explore the antibiotic sensitivity of culturable bacterial aerosols to seven widely used antibiotics. As a comparison, ARG distribution and expression in two human respiratory pathogenic bacterial strains (Pseudomonas aeruginosa and Methicillin-resistant Staphylococcus aureus) and a non-pathogenic bacterial strain (Pseudomonas fluorescens) were also studied. Relative abundances of 39 ARG subtypes in three bacterial strains including Haemophilus influenzae were investigated by high throughput real-time qPCR platform. Surprisingly, 24.66% of the culturable bacterial aerosols in polluted air were resistant to vancomycin-the most powerful antibiotics to date, while 53.05% of airborne culturable bacteria were susceptible to ampicillin (β-lactams). Different bacteria demonstrated very different ARG distribution patterns of more or less skewed toward certain one ARG type. On the other hand, the vancomycin resistance gene vanB was detected both in H. influenza and P. fluorescens, however these bacteria did not exhibit anti-vancomycin phenotype. Furthermore, the resistance to ciprofloxacin (quinolones) was not observed in P. aeruginosa and P. fluorescens although these bacteria harbor abundant quinolone resistance gene qepA. Experimental data from this work show that air represents an important active reservoir of diverse ARGs, and some bacterial aerosols are harboring vancomycin resistance gene though not expressed. Results from human respiratory pathogens have further demonstrated similar findings. This work underscores the serious concern of airborne dissemination of ARBs including those resistant to vancomycin in polluted ambient environments, while revealing abundances and patterns of various ARGs in both pathogenic and non-pathogenic bacteria.