Objective:

The aim of the study was to investigate the antimicrobial effect of Moxifloxacin (MXF), radio (Na131I) and cold (K127I) iodinated MXF on methicillin susceptible Staphylococcus aureus ATCC 35556 (MSSA) biofilms.

Methods:

MXF was labeled with Na131I using the iodogen method. The optimum radiodination conditions for 131I-MXF was determined by thin-layer radio chromatography studies. Thin-layer radio chromatography (TLRC) chromatograms were obtained by using Cyclone Plus Storage Phosphor System. The MICs of MXF, 127I-MXF and 131I-MXF were determined using the microdilution broth method according to CLSI criteria. Time kill curves were performed over 24 h using an inoculum of 2×105 (CFU/mL). Biofilms were grown in microtitre plates, dyed with crystal violet and the mean optical density (OD630) was used for quantification. Biofilms were incubated MXF, 127I-MXF and 131I-MXF at various concentration (0.03 to 64 µg/mL).

Results:

MXF was labeled with 131I iodogen method. 131I-MXF was obtained with high a yield 95±3%. The MIC values for MXF, 127I-MXF and 131I-MXF was 0.06 µg/mL. Bactericidal activity was demonstrated at 0.25 µg/mL 4 hour for MXF, 127I-MXF and 131I-MXF. At MIC levels, MXF, 127I-MXF and 131I-MXF was not showed a marked reduction of metabolic activity in the S. aureus biofilm. The ODs of biofilm after incubation with an increasing antibiotic concentration were significantly lower than the ODs of biofilms without antibiotic p≤005. The radiolabeled MXF was most effective than MXF, 127I-MXF in reducing the number of bacteria in biofilm. After 24 h incubation Log10 CFU/mL values for 32 µg/mL antibiotic concentration: Control, MXF, 127I-MXF and 131I-MXF were 9.5, 4.3, 4.8 and 3.1, respectively.

Conclusion:

131I and 127I were used alone there was no penetration of the S. aureus biofilm and no damage. In contrast our results demonstrate that the radiolabeled Moxifloxacin (131I-MXF) have potent anti-biofilm activity against S. aureus compare to MXF, 127I-MXF and media control. This is suggested that, 131I labeled antibiotic may have harmful effect on biofilm structure.

Keywords: Biofilm,moxifloxacin,radioiodination,staphylococcus aureus ATCC 35556