TABLE 2

Inhibitory characteristics of antimicrobials

AntimicrobialGrowth inhibition profile (μg/ml)aBreakpoint (μg/ml)Fractional potencym
IntracellularAxenic
IC50 (95% CI)MICIC50 (95% CI)MIC
Ciprofloxacin0.011 (0.010–0.012)0.0300.0033 (0.0027–0.0040)0.0161b,i33
Levofloxacin0.005 (0.005–0.006)0.0160.0039 (0.0037–0.0042)0.0162b125
Gatifloxacin0.0040 (0.0037–0.0043)0.0160.0040 (0.0038–0.0043)0.0162b125
Moxifloxacin0.0052 (0.0048–0.0055)0.0160.0073 (0.0068–0.0078)0.0160.5c,i31
Pefloxacin∼0.017j0.0300.013 (0.012- 0.015)0.060NA
Flumequine0.12 (0.11–0.14)0.250.034 (0.031–0.037)0.120NA
Rifampin0.002(0.002–0.003)0.0080.00015 (0.00015–0.00016)0.000481c,h125
Minocycline∼0.03j0.1280.047 (0.041–0.054)44b16
Doxycycline0.090 (0.076–0.11)0.2500.013 (0.011- 0.015)0.2504b8
Tigecycline∼0.12j0.480f0.71 (0.580.86)162g4.2
Tetracycline0.11 (0.86–1.4)4.03.5 (0.72–17.0)>164b1
Erythromycin0.37 (0.31- 0.43)2.00.041 (0.036–0.047)0.4801c0.5
Azithromycin∼ 0.063j0.250.010 (0.0091–0.012)0.1281c4
Josamycin0.069 (0.067–0.71)0.250.073 (0.069–0.077)0.4802e8
Roxithromycin0.064 (0.061–0.066)0.250.0045 (0.0041–0.0050)0.128≤1d4
Clarithromycin0.021 (0.019–0.024)0.1280.0030 (0.0029–0.0031)0.0321d8
Chloramphenicol∼ 0.25j10.042 (0.038- 0.045)18b8
Florfenicol0.210.5NDND2f4
Clindamycin∼ 1j80.83 (0.72- 0.095)80.5c0.06
Fusidic acid∼ 1j40.0055 (0.0048–0.0063)0.1281d0.25
Meropenem1.7 (1.2–2.3)>16,0.047 (0.042–0.052)0.2501b<0.06
Ceftriaxone0.39 (0.31–0.50)>160.015 (0.013- 0.017)0.4801b<0.06
Amikacin4.5 (1.2–17.2)>81.1(0.89–1.4)416b≤1
Gentamicin∼4k>8∼4k84b≤0.25
KanamycinNAl>8NAl>816b<1
  • a The MIC is defined as the lowest concentration that confers greater than 99% reduction (IC99) in luminescent signal in all replicates. CI, confidence interval; ND, not done; NA, not applicable.

  • b Susceptibility breakpoints are based on the Enterobacteriaceae CLSI standard (58).

  • c Susceptibility breakpoints are based on the S. aureus CLSI standard (58).

  • d Susceptibility breakpoints are based on the S. aureus EUCAST standard (59).

  • e Susceptibility breakpoints are based on reference 60.

  • f Susceptibility breakpoints are based on reference 36.

  • g Susceptibility breakpoints are based on U.S. FDA criteria (61).

  • h The EUCAST S. aureus rifampin breakpoint is 0.06 (59).

  • i The EUCAST breakpoints for ciprofloxacin and moxifloxacin are the same at 0.5μg/ml.

  • j Best-fit parameters do not allow unambiguous determination of the IC50. Confidence intervals are therefore not given.

  • k Approximate IC50 determined visually from dose-response graph as four parameter nonlinear regression interpolation was noninformative.

  • l Without activity at all concentrations tested.

  • m Fractional potency is the susceptibility breakpoint divided by the MIC for intracellular growth.