Co-occurrence of antibiotics and heavy metal resistance in microbes isolated from lakes, India

The rising levels of heavy metals and antibiotics in municipal sewage and sludge pose a significant environmental and public health concern. These pollutants exert selection pressure on microbial communities, promoting co-selection of heavy metal and antibiotic resistance in bacteria. In this study, water samples were collected from Lake Agara, HSR Layout, Bangalore, Karnataka, India, to investigate this phenomenon. Mercury concentration was determined using atomic absorption spectrometry (AAS), while the presence of antibiotics was analysed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Mercury-resistant bacteria were isolated using the Mathena criteria after mass seeding and subsequently characterized biochemically and identified molecularly. The mercury concentration was 0.9078 mg/L. LC-MS/MS confirmed the presence of penicillin, streptomycin, and methicillin. Six mercury-resistant bacterial isolates were identified as Staphylococcus warneri SAHSPC1, Staphylococcus pasteuri SAHSPC2, Staphylococcus aureus SAHSPC3, Pseudomonas citronellolis SAHSPC4, Pseudomonas koreensis SAHSPC5, and Rheinheimera chironomi SAHSPC6. Antibiotic sensitivity testing showed that all Staphylococcus and Pseudomonas strains were resistant to at least one antibiotic. These findings highlight the role of polluted water bodies in promoting co-selection and spread of multidrug-resistant bacteria, raising serious implications for environmental and human health.