title: Antimicrobial resistance patterns in Enterobacteriaceae isolated from an urban wastewater treatment plant.
abstract: Over 18 months, enterobacteria were isolated from the raw (189 isolates) and treated (156 isolates) wastewater of a municipal treatment plant. The isolates were identified as members of the genera Escherichia (76%), Shigella (7%), Klebsiella (12%) and Acinetobacter (4%). Antimicrobial susceptibility phenotypes were determined using the agar diffusion method for the antibiotics amoxicillin, gentamicin, ciprofloxacin, sulfamethoxazole/trimethoprim, tetracycline and cephalothin, the disinfectants hydrogen peroxide, sodium hypochlorite, quaternary ammonium/formaldehyde and iodine, and the heavy metals nickel, cadmium, chromium, mercury and zinc. Class 1 integrons were detected by PCR amplification using the primers CS5 and CS3. Compared with the raw influent, the treated wastewater presented higher relative proportions of Escherichia spp. isolates resistant to ciprofloxacin and cephalothin (P<0.0001 and P<0.05, respectively). Except for mercury, which showed a positive correlation with tetracycline and sulfamethoxazole/trimethoprim, no significant positive correlations were observed between antibiotic, disinfectant and heavy metal resistance. The variable regions of class 1 integrons, detected in c. 10% of the Escherichia spp. isolates, contained predominantly the gene cassettes aadA1/dhfrI.
authors.affiliation: Escola Superior de Biotecnologia, Universidade Católica Portuguesa, 4200-072 Porto, Portugal.
authors.forename: Miguel
authors.initials: M
authors.lastname: Ferreira da Silva
authors.forename: Ivone
authors.initials: I
authors.lastname: Vaz-Moreira
authors.forename: Maria
authors.initials: M
authors.lastname: Gonzalez-Pajuelo
authors.forename: Olga C
authors.initials: OC
authors.lastname: Nunes
authors.forename: Célia M
authors.initials: CM
authors.lastname: Manaia
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002947:Cities; D004202:Disinfectants / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D005618:Fresh Water / Q000382:microbiology*; D032023:Integrons / Q000235:genetics; D019216:Metals, Heavy / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D016133:Polymerase Chain Reaction; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D000900:Anti-Bacterial Agents; D004202:Disinfectants; D019216:Metals, Heavy