FIG. 7.
Influence of gentamicin on the activities of antibiotics against intracellular L. monocytogenes. The cells were incubated for 5 h with the Ce of gentamicin and concentrations of the other antibiotics corresponding to their Cmax, as follows: gentamicin (GEN), Cmax = 18 mg/liter; ampicillin (AMP), Cmax = 50 mg/liter); meropenem (MEM), Cmax = 50 mg/liter; azithromycin (AZM), Cmax = 0.4 mg/liter; ciprofloxacin (CIP), Cmax = 4.3 mg/liter; moxifloxacin (MXF), Cmax = 4 mg/liter. Intracellular activity (ordinate) is defined as the difference in the log bacterial counts (numbers of CFU) between cells incubated without antibiotic and (i) cells incubated with gentamicin alone, (ii) cells incubated with each of the other antibiotics alone, or (iii) cells incubated with the combination of gentamicin and the corresponding antibiotic. Each value used for the calculation was the arithmetic mean of three independent determinations. P values between cells exposed to an antibiotic plus gentamicin and cells exposed to an antibiotic alone, as determined by Student's t test, were not significant (NS) or <0.05 or less (asterisks).