FIG. 5.

The high-level resistance phenomenon was found in biofilms of E. coli harboring pBR322 in the presence of subinhibitory concentrations of ampicillin and tetracycline, which confer resistance to penicillin, erythromycin, and chloramphenicol but not to kanamycin and gentamicin. Results are from a quantification assay for the total bacterial growth activity (line graph) and biofilm formation (bar graph) of MG1655(pBR322) in the presence of the antibiotic mixture, in association with separately supplemented of the following antibiotics: (A) penicillin (Pc); (B) erythromycin (Em); (C) chroramphenicol (Cp); (D) kanamycin (Km); (E) gentamicin (Gm). Results are averages of eight replicates ± standard deviations and are representative of four independent experiments. The statistically comparative MICs under each condition are shown in Table 3.