Time-kill curves of the 2 strains subjected to constant concentrations of antibiotic.

Evolution of the bacterial population (log10 CFU/mL) for the MSSA (A and B) and MRSA (C and D) strains after exposure to 70μg/mL amikacin (blue) or 18μg/mL vancomycin (green) or the combination of both (red) over 24hours in MHB (A and C) and in RPMI (B and D). The marks represent the mean ±SD of the bacterial counts for the different tested treatments (n = 2 for each treatment). Curves with open squares represent the bacterial counts on a large initial inoculum and curves with crosses represent the bacterial counts on a standard initial inoculum. (LOD = 2.5 log10 CFU/mL). For the low inoculum of MSSA in MHB and RPMI (A and B), there was no difference between drugs alone or in combination. For the high inoculum of MSSA, there was no difference between drugs in MHB (A) but vancomycin led to significantly higher bacterial counts than amikacin and the combination in RPMI (B). For the low inoculum of MRSA, there was no difference between drugs alone or in combination in MHB (C) but amikacin led to significantly higher bacterial counts than vancomycin and combination in RPMI (D). For the high inoculum of MRSA, there was no difference between drugs in MHB (C) but amikacin led to significantly higher bacterial counts than the combination in RPMI (D).