Plasmid-Encoded Nitrogen and Carbon Pathways Enhance Metabolic Flexibility of Multidrug-Resistant Bacteria from Municipal Wastewater

Wastewater treatment plants represent a primary source of environmental dissemination of multidrug-resistant (MDR) bacteria, underscoring the urgent need for in-depth investigation of these organisms. While the resistome of MDR bacteria has been extensively studied, there remains a critical gap in understanding the role of plasmid-borne genes encoding adaptive metabolic functions. We isolated two MDR strains from municipal wastewater, Klebsiella sp. KOS9 and Pseudomonas veronii Yu15, both exhibiting resistance to antibiotics, including ampicillin, cefazolin, kanamycin, streptomycin, erythromycin, chloramphenicol, tetracycline, and ciprofloxacin. The plasmids of these strains harbored genes encoding aliphatic amidases, as well as antibiotic resistance genes (ARGs) and enzymes involved in glycogen and dTDP-L-rhamnose biosynthesis, which may contribute to virulence. In Klebsiella sp. KOS9 a single acetamidase operon, was found on the megaplasmid, along with copper and silver resistance genes. P. veronii Yu15 harbored an operon containing the acetamidase and formamidase genes on the chromosome, as well as a phylogenetically distant acetamidase operon on the conjugative megaplasmid. Both strains exhibit acetamidase activity and P. veronii Yu15 was able to utilize acetamide and formamide as sole nitrogen sources. The occurrence of ARGs and adaptive accessory genes on plasmids likely enhances the competitiveness and environmental flexibility of these MDR bacteria.