Publication Date: 2026
International Biodeterioration and Biodegradation (09648305)207
Cephalexin (CPX), a β-lactam antibiotic, is considered an emerging pollutant due to its incomplete removal in conventional treatment systems and its contribution to antimicrobial resistance. This study investigated a novel indigenous strain, Bacillus wiedmannii RM5, isolated from municipal activated sludge, which efficiently degraded CPX. Under optimized conditions (pH 6.5, 50 mg/L initial CPX, 60 h incubation), strain RM5 achieved 95.5 % CPX removal, as determined using OFAT and Box–Behnken design with RSM. The ddition of glucose significantly enhanced co-metabolism, leading to complete degradation within 36 h. The strain exhibited stable performance across a pH range of 6–9, temperatures of 30–45 °C, and CPX concentrations up to 400 mg/L, indicating its potential for application under real-world environmental conditions. LC–MS/MS analysis identified 13 intermediates, suggesting two concurrent enzymatic degradation pathways. These pathways involve β-lactamase-mediated ring cleavage, hydrolysis, and oxidation catalyzed by hydrolases and oxidases, leading to non-toxic mineral end products. MIC and MTT bioassays showed that, unlike untreated CPX, its degraded metabolites exhibited no antibacterial or cytotoxic activity. Bacillus wiedmannii RM5 effectively degraded CPX, amoxicillin (AMX), and ampicillin (AMP) simultaneously across diverse environmental conditions, showcasing its broad-spectrum biodegradation potential. These findings highlight Bacillus wiedmannii RM5 as a promising, safe, and effective bioremediation agent for removing β-lactam antibiotics from wastewater, offering a practical strategy to reduce pharmaceutical pollution and antibiotic resistance. © 2025 Elsevier Ltd
