Prospecting the biodegradation of ciprofloxacin by Stutzerimonas stutzeri R2 and Exiguobacterium indicum strain R4 isolated from pharmaceutical wastewater

Ciprofloxacin (CIP), an emerging micro-pollutant antibiotic, poses an environmental threat due to its resistance to high-temperature decomposition, aiding antibiotic resistance spread. Conventional degradation generates toxic byproducts, while biodegradation offers an efficient and eco-friendly means to eliminate CIP. In this study, ciprofloxacin-degrading strains were isolated from pharmaceutical wastewater using an enrichment technique. Isolated strains R2 and R4 were identified as Stutzerimonas stutzeri and Exiguobacterium indicum, respectively, based on their 16S rRNA gene sequence. Ciprofloxacin degrading potential of these strains was tested in shake flask fermentation and quantified using spectrophotometric assays and ultra-high-performance liquid chromatography (UHPLC). UHPLC analysis revealed that in co-metabolism, R2 achieved 51 and 77% degradation, and R4 achieved 60 and 68% after 5 and 10 days of incubation. When CIP served as the only carbon source, R2 degraded it by 23 and 35%, while R4 degrade it by 19% and 28 in 5 and 10 days, respectively. Spectrophotometric analyses produced congruent results with UHPLC. Notably, in co-metabolism, R2 and R4 achieved 66 and 88% degradation within the 5 days. Moreover, the degraded residues displayed reduced antimicrobial activity against Escherichia coli and Staphylococcus aureus. In conclusion, both strains show potential for degrading CIP, aiding in mitigating pharmaceuticals and environmental pollutants.