Fig. 2

Effect of yegN and z4861 deletion on antibiotic susceptibility. a, b Susceptibility of WT, Δz4861 and ΔyegN to different antibiotics belonging to different classes. A column chart of inhibition zone diameters (measured in mm) generated by different antibiotic discs applied to WT, Δz4861 and ΔyegN (a) or the same three isolates in comparison to the double mutant and NC (b). Significant differences in the mean zone diameters of the three strains were observed with the fluoroquinolones class represented by ciprofloxacin and lomefloxacin, while no significant differences were observed with other antibiotics (P >0.05). CIP ciprofloxacin, C chloramphenicol, LOM lomefloxacin, SXT sulphamethoxazole/trimethoprim, AK amikacin, CT colistin, AZM azithromycin, CN gentamicin, TE tetracycline, TOB tobramycin. The significance was determined by paired Student’s t-test. The data represent the means of three independent experiments and the error bars represent the standard deviation (SD). c Growth curves of the different mutants, WT, and NC strains in presence of sub-MIC concentration (0.0075 mg/l) of ciprofloxacin. No significant differences in the growth pattern of the five strains were observed till 4 h of incubation, but significant differences were observed between WT, NC and the three mutants starting from 6 h of incubation. No significant differences among the three mutants till 8 h of incubation were observed (P < 0.05). d Growth of the five strains, expressed at OD600 after 24 h incubation with sub-MIC concentration of ciprofloxacin. Significant differences were observed between the growth extent of WT, NC and the three mutants. No significant differences among the three mutants (P < 0.05). For c, d, analysis of variance (ANOVA) was used to estimate statistical significance. The data presented are the mean of three independent experiments, and the error bars represent the standard deviation (SD)