Author(s):
Silva, Miguel Ferreira da 
; Vaz-Moreira, Ivone ; Gonzalez-Pajuelo, Maria ; Nunes, Olga C. ; Manaia, Célia M.
Date: 2007
Persistent ID: http://hdl.handle.net/10400.14/6904
Origin: Veritati - Repositório Institucional da Universidade Católica Portuguesa
Subject(s): Enterobacteriaceae; Antibiotic Resistance; Disinfectants; Heavy metals; Class 1 integron
Description
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 (Po0.0001 and Po0.05, 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.
