Isolation and Antibiotic Resistance Profiling of Coliform Bacteria from the Gandak River During the Monsoon Season at Hajipur, Bihar, India

The occurrence of antibiotic-resistant bacteria in freshwater ecosystems is an emerging environmental and public health issue. This study investigated antibiotic-resistant coliform bacteria in the Gandak River at Hajipur. Water samples were collected from upstream, midstream, and downstream sites and coliform density was determined using the Most Probable Number (MPN) method. Bacterial isolates were obtained on selective media and identified through morphological and biochemical characterization. Antibiotic susceptibility testing was performed using the Kirby–Bauer disc diffusion method. The isolates were tentatively identified as Escherichia coli, Klebsiella pneumoniae, Enterobacter spp., Citrobacter spp., Proteus spp., and Pseudomonas aeruginosa. The isolates exhibited high resistance toward Penicillin, Amoxicillin and Erythromycin, whereas greater sensitivity was observed against Ciprofloxacin, Levofloxacin, Ofloxacin and Gentamicin. Several isolates showed multidrug resistance, particularly in downstream samples influenced by anthropogenic activities. The findings of the present investigation indicate significant microbial pollution in the Gandak River and highlight the role of freshwater ecosystems as potential reservoirs of antimicrobial resistance. Continuous microbiological monitoring, effective wastewater treatment infrastructure, and proper management of municipal and hospital waste are therefore essential to minimize the environmental spread of antibiotic-resistant bacteria and associated public health risks.