Response of culturable bacteria and their resistance to air purification across compartments

The increasing threat of antimicrobial resistance (AMR) in environmental settings, particularly in indoor air, requires robust surveillance and mitigation strategies. This study assessed the taxonomic composition and AMR profiles of human-, airborne- and surface-associated bacteria collected from two indoor environments: office spaces in Valencia (Spain) and school classrooms in Dublin (Ireland).

Sampling was conducted before and after deployment of portable air purification systems. Samples were analyzed using culture-based methods, MALDI-TOF MS identification, antibiotic susceptibility testing, and PCR detection of resistance genes.

A total of 341 bacteria were recovered. In office air, isolates decreased substantially after air purification (from 41 to 5), with post-intervention samples dominated by Staphylococcus spp. and no detectable resistance genes. In contrast, human-associated samples showed reduced diversity, but increased relative abundance of Staphylococcus spp. (from 15% to 65%), alongside a higher proportion of non-susceptible isolates (from 20 to 31). In the school environment, airborne isolates and resistance prevalence decreased following intervention (from 102 to 47 and 43% to 21%, respectively), while surface-associated communities showed smaller reductions in total isolates (from 53 to 43), but a notable decline in resistant phenotypes (from 22 to 9), accompanied by shifts in community composition.

Overall, air purification was associated with a strong reduction in airborne bacterial recovery and AMR burden, while surface and human-associated microbiota remained more stable. These findings highlight the compartment-specific effects of air purification and support the need for integrated indoor air quality management strategies combining air-targeted interventions with broader environmental control measures to limit AMR dissemination in built environments.