[Clonal analysis of some multiple antibiotic resistant E. coli strains isolated from river and polluted waters]

Several multiple antibiotic resistant E. coli strains isolated from river and polluted waters were compared for their genetic relatedness. Antibiotic susceptibility testing was performed for gentamycin, kanamycin, ampicillin, tetracycline, chloramphenicol, ceftazidime and cefotaxime, as described by Kirby-Bauer disk diffusion method following NCCLS recommendations. Minimum inhibitory concentrations (MICs) were performed using dilution method in Mueller-Hinton broth with a 0.06-64 micrograms/ml concentration range for all antimicrobials and bacterial inoculum of about 1-2 x 10(8) CFU/ml. For the data analysis NCCLS breakpoints for resistance and sensitivity were used. Genomic DNA was isolated from E. coli strains by CTAB method and digested to completion with HindIII enzyme. Genetic characterization was performed by agarose gel electrophoresis and spectrophotometric analysis. Genetic similarity and clustering were calculated using NISIS program. All E. coli strains isolated from river and polluted waters show a high incidence of multiple antibiotic resistance phenotype, 16% of them being resistant to 7, 6 and 4 antibiotics, 40% to 5 and 8% to 2 antibiotics, respectively. A moderate resistance was observed to kanamycin (higher than 30%) and cefotaxime (68%). The percentage of resistant E. coli strains ranged from 76% (to ampicillin, gentamicin and chloramphenicol) to 85% (to ceftazidime). The best results (resistance about 99%) were obtained with tetracycline. Screening for plasmids relieved the presence into 4 E. coli strains of several plasmids ranging from 3.8 kpb to more than 50 kpb. The number of fragments produced by HindIII digestion of genomic DNA ranged from 11 to 25, with sizes of approximately 22 to more than 750 kb. The phenotypic data shows the dynamic flow of multiple antibioresistant E. coli strains in aquatic media (river and polluted waters). Electrophoretic patterns analysis reflects the incidence and diversity of analyzed plasmids. DNA fingerprinting with genomic DNA RE suggested that, depending of the isolation source, E. coli strains could be grouped in two distinct populations with a different plasmid diversity.