Mapping of antibiotic resistant enterococci in wastewater treatment plants in Greece

Abstract

The widespread as well as the injudicious use of antimicrobial agents has generated an intense ecological imbalance through the emergence and spread of antibiotic resistant microorganisms, pathogenic or non-pathogenic. Agricultural use of sewage sludge bears numerous beneficial aspects, but it may also pose a potential threat for the environment and public health. In this study, potential environmental risks from sewage sludge application on soil are investigated, with emphasis on the spread of antibiotic resistant enterococci. Sixty-four samples of dewatered sludge from 56 wastewater treatment plants in Greece were analysed. The enterococcal density ranged from 1.8 × 103 to 1.14 × 107 cfu/g of dewatered sludge. The size of the enterococci population was not influenced by the size of the treatment plant. From the samples examined, 617 different Enterococcus spp. strains were isolated. Their antibiotic susceptibility was evaluated against 12 different antibiotics, representing a broad range of antimicrobial agents, using the disc diffusion method. The geographical distribution of antibiotic resistance demonstrated a widespread resistance to several antibiotics, including a substantial (14%) presence of multiresistance. Results demonstrate a high prevalence of antimicrobial agents’ resistance in sewage sludge microorganisms. This may pose a threat to public health, if sludge is applied to the soil without some type of prior sanitisation.