Distribution and antibiotic resistance patterns of airborne staphylococci in urban environments of Delhi, India

Airborne microbial contamination, especially involving antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs), poses a growing public health concern in urban environments. This study explores the prevalence and diversity of staphylococci, including methicillin-resistant staphylococci (MRS), in bioaerosols from various urban settings in Delhi, India. Indoor and outdoor air samples showed significantly high staphylococcal loads far above the WHO's recommended limit of 1000 CFU/m³ for microbial exposure. Seasonal variations revealed a peak in airborne MRS during winter, while monsoon rains reduced outdoor bioaerosol contamination. Eight staphylococcal species were identified, with Staphylococcus epidermidis and Staphylococcus arlettae being the most prevalent human- and animal-associated species, respectively. Notably, 73% of MRS isolates exhibited multidrug resistance (MDR), showing resistance to macrolides, β-lactams, and other commonly used antibiotics. Genotypic analysis confirmed the presence of ARGs among airborne MRS encoding resistance for beta-lactam, trimethoprim, gentamicin, macrolides, chloramphenicol and lincosamides. Notably, with 14 out of 36 MDR isolates carrying the mecA gene encoding for methicillin resistance. This study emphasizes the potential health risks posed by airborne reservoirs of antibiotic resistance in urban environments and underscores the urgent need for comprehensive environmental AMR surveillance to develop effective mitigation strategies.