Application of municipal wastewater-derived Escherichia coli and Enterococcus faecium in mitigating ciprofloxacin phytotoxicity in crops

Abstract Ciprofloxacin (CIP) is frequently detected in environmental matrices due to incomplete removal during wastewater treatment, posing risks to sustainable agriculture through phytotoxicity and the promotion of antimicrobial resistance. This study isolated and characterised CIP-resistant bacteria from municipal wastewater in Lahore, Pakistan, and evaluated their potential for CIP bioremediation and phytotoxicity reduction in edible crops. Two potent isolates were identified through 16S rRNA sequencing as Escherichia coli and Enterococcus faecium . In biodegradation assays, the bacterial consortium demonstrated high removal efficiency, achieving up to 100% CIP degradation under optimal conditions (40 °C, pH 6.5), confirmed using HPLC. The process followed Michaelis–Menten kinetics, with E. faecium exhibiting a higher degradation rate (Vmax = 8.26 mg L⁻ 1 day⁻ 1 ) than E. coli (Vmax = 6.37 mg L⁻ 1 day⁻ 1 ). Phytotoxicity assays conducted using CIP-contaminated irrigation water (0.1–500 mg L⁻ 1 ) showed that application of the consortium substantially improved seedling performance in carrot ( Daucus carota ), pea ( Pisum sativum ), radish ( Raphanus sativus ), lettuce ( Lactuca sativa ), and spinach ( Spinacia oleracea ). The consortium enhanced the germination index by 56–199% and increased the seedling vigour index by up to 337% compared with CIP-only treatments. All measured stress-tolerance indices (root and shoot length, fresh and dry weight) increased significantly, while the phytotoxicity index decreased in bacterially treated groups. Overall, the consortium effectively degraded CIP and mitigated its phytotoxic impacts, demonstrating strong potential as a sustainable biological strategy for treating antibiotic-contaminated water and protecting crop productivity.