GREEN-SYNTHESIZED ZINC OXIDE NANOPARTICLES FROM CYMBOPOGON CITRATUS EXHIBIT ENHANCED ANTIBACTERIAL AND ANTIBIOFILM ACTIVITY AGAINST MULTIDRUG-RESISTANT ESCHERICHIA COLI ISOLATED FROM RETAIL FISH

Shuvajit Mondal, Pooja Das, Aniruddha Mukherjee, Anirban Mukherjee*, Banhisikha Singh*

ABSTRACT

The increasing prevalence of multidrug-resistant (MDR) foodborne bacteria has created an urgent need for sustainable antimicrobial alternatives capable of overcoming conventional antibiotic resistance. The present study investigated the antibacterial and antibiofilm potential of green-synthesized zinc oxide nanoparticles (ZnO NPs) prepared using Cymbopogon citratus leaf extract against MDR bacterial isolates recovered from retail fish. Bacterial isolates were obtained using standard microbiological methods and screened for antibiotic susceptibility to identify the most resistant isolate. Among the recovered bacteria, Escherichia coli exhibited the highest level of multidrug resistance and was selected for subsequent investigations. Comparative evaluation of six medicinal plant extracts identified C. citratus as the most active antibacterial candidate and was therefore employed for nanoparticle synthesis. The synthesized ZnO nanoparticles were characterized by UV–Visible spectroscopy and evaluated for antibacterial efficacy using agar well diffusion, minimum inhibitory concentration (MIC), growth kinetics, biofilm eradication, biofilm inhibition, MTT cell viability assay, and SDS–PAGE protein profiling. ZnO nanoparticles exhibited markedly greater antibacterial activity than the crude methanolic extract, with the DMSO formulation producing the highest inhibitory activity. Nanoparticle treatment significantly suppressed bacterial growth, reduced biofilm formation, disrupted established biofilms, and decreased bacterial cell viability. MIC analysis further demonstrated enhanced antibacterial potency of ZnO nanoparticles compared with the plant extract alone. Alterations in SDS–PAGE protein profiles suggested treatment-associated changes in bacterial protein expression under nanoparticle exposure. Collectively, these findings demonstrate that C. citratus-mediated ZnO nanoparticles possess superior antibacterial and antibiofilm efficacy against MDR E. coli isolated from retail fish and highlight their potential as an environmentally sustainable strategy for controlling foodborne bacterial contamination.

Keywords: Escherichia coli, Cymbopogon citratus, zinc oxide nanoparticles, green synthesis, multidrug resistance, foodborne pathogens.