Fig 4. MTT assays of K. pneumonia biofilm growth confirms synergistic action of AZM and CMS.

The effect of azithromycin (AZM) and colistin methanesulfonate (CMS) on K. pneumonia ATCC 10031 biofilm growth was investigated using the metabolic indicator dye MTT with absorbance (A₅₇₀) measurements after 24 h incubation. Mean relative A₅₇₀ ± SE (n = 3) is shown, with no-AZM (control) treatments indicated by dark circles, 3 mg/L AZM by grey circles and 9 mg/L AZM by white circles (trends are suggested by dashed curves). Means not connected by the same letters are significantly different (LSMeans Differences Tukey HSD, alpha = 0.05 for mixed-effects model of relative A₅₇₀). Small triangles indicate planktonic and biofilm minimum inhibitory concentrations (MIC) where relative A₅₇₀ was first significantly reduced by CMS for each AZM treatment.