Antibiotic resistance in bacteria associated with coarse atmospheric particulate matter in an urban area

To assess antibiotic resistance in airborne bacteria associated with coarse particulate matter (PM10) in an urban area, with specific considerations about the Staphylococcus genus.

Disc diffusion test was performed on 243 microbial strains, isolated from PM10 in winter and summer and belonging to families Pseudomonadaceae and Enterobacteriaceae and genera Acinetobacter, Enterococcus and Staphylococcus. Staphylococci resistances were the most heterogeneous, being distributed among almost all tested antibiotics. Staphylococcus isolates resistant to some selected antibiotics were further investigated for the presence of the corresponding genetic determinants. Only tetK, which mediates the tetracycline resistance through the action of an efflux protein, was found in almost all resistant isolates.

The lack of specific genetic determinants makes their transmission among staphylococci less likely. This may reduce the theoretical risk associated with the inhalation of airborne micro-organisms.

Although the spreading of antibiotic resistant micro-organisms is of particular concern in clinical settings, the origin of antibiotic resistance genes can be traced in natural environments. As behaviour, viability and transport of bacteria in the atmospheric compartment suffer from a lack of information, the evaluation of the actual risk posed by airborne micro-organisms to human health is still challenging.