Hospital-Associated Synanthropic Insects as Carriers of Methicillin-Resistant Staphylococcus aureus: Evidence from Lahore, Pakistan

The issue of antimicrobial resistance (AMR) is significant in the world, and one of the most important types of pathogens that transmit both nosocomial and community infections is methicillin-resistant Staphylococcus aureus (MRSA). Objectives: To determine the existence of antibiotic-resistant Gram-positive bacteria in hospital-related insects, to describe the resistance mechanisms and biofilm-forming capabilities of the bacteria. Methods: Two hundred houseflies were taken from one hospital, which was a tertiary care hospital in Lahore. The isolates of S. aureus were determined by mannitol fermentation, Gram stain, and standard biochemical assays. The Kirby-Bauer disk diffusion method of performing antimicrobial susceptibility testing was conducted as per CLSI (2023) guidelines. A microtiter plate assay was used to determine biofilm formation. PCR detection of the mecA and mecC genes was done by extracting their genomic DNA. The agar well diffusion assay was employed to determine the activity of FGE as a single entity and in conjunction with the 3-lactam antibiotics. Results: Sixteen S. aureus isolates (8% of the flies) were recovered. All isolates were methicillin-resistant and carried the mecA gene, while the mecC gene was absent. Resistance was universal to oxacillin (100%) and nitrofurantoin (100%), and was high against erythromycin (87.5%) and rifampicin (75%). Most isolates (62.5%) were strong biofilm producers. Conclusions: Hospital-associated houseflies can serve as reservoirs and potential vectors for multidrug-resistant, biofilm-forming MRSA. The synergy observed between FGE and β-lactam antibiotics highlights the potential of plant-derived adjuncts in addressing resistant infections.