Antibiotic Susceptibility and Methicillin Resistance in Staphylococcal Isolates from Water Samples in Dharwad and Surrounding Districts of North Karnataka

ABSTRACT: Incidences of methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant (MDR) staphylococci are rising globally, prompting the need to understand human exposure routes, including water sources. This study aimed to analyse water samples from different sources and locations in North Karnataka over a six-month period (November 2021 to April 2022) to determine the prevalence and antibiotic susceptibility of staphylococcal isolates. Water samples were collected using standard microbiological techniques and analysed. Staphylococci were detected in 35.5% (55/155) of the samples and identified using phenotypic tests such as Gram stain, catalase test, and growth and fermentation on mannitol salt media. Methicillin resistance was assessed via cefoxitin disk diffusion, and the presence of the mecA gene was tested by PCR. Among the 55 isolates, 23.6% were resistant to cefoxitin and considered methicillin-resistant, while 36.4% carried the mecA gene. Antibiogram results showed the highest susceptibility to gentamicin (100%) and the lowest to penicillin (12.7%) and oxacillin (1.8%). The nuc gene, encoding thermonuclease, was present in 20% (11/55) of the isolates. Multiple antibiotic resistance (MAR) indices ranged from 0.08 to 0.67, with most staphylococci resistant to at least two antibiotics, and 54.55% (30/55) were MDR. These findings highlight the importance of water, sanitation, and hygiene (WASH) initiatives in reducing the spread of antimicrobial resistance in environmental bacteria.