Pharmaceutical disposal facilitates the mobilization of resistance determinants among microbiota of polluted environment.

The emergence of resistance on exposure to pharmaceuticals among microorganisms has raised serious concern in the therapeutic approach against infectious diseases. Effluents discharge from hospitals, industries, and urban settlements containing pharmaceuticals and other toxic compounds into the aquatic ecosystem selects bacterial population against them; thereby promotes acquisition and dissemination of resistant traits among the inhabitant microbiota. The present study was aimed to determine the prevalence and multidrug resistance pattern of Extended Spectrum β-lactamase (ESBL) producing and non-producing bacterial isolates from the heavily polluted Delhi stretch of river Yamuna, India. Additionally, the role of abiotic factors in the dissemination of conjugative plasmids harbouring resistance genes was also studied using J53 as recipient and resistant isolates as donor strains. Of the 227 non-duplicate bacterial isolates, 60% (136) were identified as ESBL and 40% (91) as ESBL. ESBL isolates were found highly resistant to β-lactam and non-β-lactam classes of antibiotics compared with the ESBL isolates. 68% of ESBL and 24% of ESBL isolates showed an MAR index of ≥0.5. Surprisingly, multidrug resistance (MDR), extensively drug resistance (XDR), and pandrug resistance (PDR) phenotype were observed for 78.6%, 16.9%, and 0.7% of ESBL and 90%, 3%, and none for PDR among ESBL isolates. Conjugation under different conditions showed a higher mobilization rate at neutral pH (7-7.5) for ESBL isolates. Conjugation frequency was maximum at 40 °C for the isolate MRB6 (4.1 × 10) and MRE32 (4.89 × 10) and at 35 °C for MRA11 (4.89 × 10). The transconjugants obtained were found tolerating different concentrations of mercuric chloride (0.0002-0.2 mg/L). Increased biofilm formation for ESBL isolates was observed on supplementing media with HgCl (2 μg/mL) either singly or in combination with CTX (10 μg/mL). The present study demonstrates that anthropogenically influenced aquatic environments act as a reservoir of MDR, XDR, and even PDR strains; thereby posing a potent public health risk.