Biodegradation of ciprofloxacin by Exiguobacterium sp. from tropical river sediments: an integrated approach

• Tropical bacteria Exiguobacterium sp. (T-316) degrades CIP in water efficiently. • Exiguobacterium sp. removed 74% of ciprofloxacin via co-metabolic processes. • Residual antibiotic activity in post-treated water showed a complete reduction. • Strategy integrates resistance profiling, biodegradation, and ecotoxicological tests. Ciprofloxacin (CIP) is a widely used broad-spectrum antibiotic. Its persistence and hydrophobic nature pose environmental risks to aquatic ecosystems. There is a lack of studies on the isolation and characterization of antibiotic-degrading microorganisms, especially in tropical ecosystems; although bacterial resistance to antibiotics in aquatic systems have been extensively studied. This study introduces a comprehensive methodological approach to evaluate the biodegradation potential of autochthonous bacteria, specifically Exiguobacterium sp. (T-316), isolated from the sediments of the Almendares River in Havana. The methodology integrates three key stages: (1) assessment of antibiotic resistance profiles, including the determination of minimum inhibitory concentration (MIC) for CIP, (2) evaluation of biodegradation capacity, and (3) measurement of residual antibiotic activity in post-treated water. Exiguobacterium sp. strain displayed a ciprofloxacin MIC of 7 µg mL −1 , indicating resistance. Biodegradation assays demonstrated this strain degraded 74.36 % of CIP in model water systems through co-metabolism (biodegradation of CIP using a co-substrate for metabolic support), with significant differences in the presence of a co-substrate. The final CIP concentration in effluents was significantly lower than the initial concentration. Notably, transformation products were detected after 72 h, regardless of glucose supplementation. The residual antibiotic activity in water treated under co-metabolic conditions showed a complete (100 %) reduction. This framework provides a robust and reproducible strategy for identifying and characterizing environmental bacterial strains with antibiotic degradation potential, especially relevant to underrepresented tropical ecosystems, despite their high microbial diversity. This study supports the development of sustainable processes for treating antibiotic-contaminated water, and is the first comprehensive report on CIP biodegradation in Cuba.