Occurrence of antimicrobial-resistant Enterobacterales in compost derived from urban organic waste and sewage sludge

Abstract

Abstract Composting mixtures of urban organic waste and treated domestic sewage sludge has increasingly been adopted to recycle nutrients and reduce fertilizer dependency in agriculture. However, the microbiological safety of these materials remains insufficiently explored, particularly regarding the occurrence and persistence of antimicrobial-resistant bacteria. This study investigated the occurrence and phenotypic profiles of antimicrobial resistance (AMR) in Enterobacterales isolated from compost produced from organic fractions of municipal solid waste and treated domestic sewage sludge. A total of 74 isolates were identified, including Klebsiella spp. (n = 36) and Escherichia coli (n = 17). Among these isolates, 64.9% were classified as multidrug-resistant (MDR), whereas none met the criteria for extensively drug-resistant or pandrug-resistant phenotypes. The highest resistance rates were observed for cephalosporins (68.9%), aminoglycosides (55.4%), and β-lactam/β-lactamase inhibitor combinations (48.7%). These findings demonstrate that composted biosolids can harbor diverse populations of MDR Enterobacterales even after treatment processes. The results highlight composted biosolids as potential environmental reservoirs of antimicrobial resistance and provide baseline microbiological data for future investigations on resistance persistence in waste-derived organic amendments.