Table 1. Minimal Inhibitory Concentration (MIC50, MIC90 and range) values of Brucella abortus strains isolated from cattle in Brazil, 1977–2009, to eight antimicrobials used in the treatment of human brucellosis.
| Antimicrobial agent | MIC range a | MIC50 b | MIC90 c | Resistance | ||||
|---|---|---|---|---|---|---|---|---|
| Value | no. d | Value | no. | CP e | no. f | % g | ||
| Amikacin | 2.0–≥256 (8) | 4.0 | 97 | 8.0 | 144 | – | – | – |
| Ciprofloxacin | 0.5–2.0 (3) | 0.5 | 146 | 0.5 | 146 | >1.0 | 1 | 0.68 |
| Doxycycline | ≤0.06–2,0 (6) | 0.5 | 133 | 0.5 | 133 | >1.0 | 0 | 0 |
| Streptomycin | 0.125–≥256 (12) | 2.0 | 141 | 2.0 | 141 | >16 | 2 | 1.36 |
| Gentamicin | 0.25–≥256 (11) | 1.0 | 141 | 1.0 | 141 | >4.0 | 5 | 3.40 |
| Ofloxacin | 0.5–1.0 (2) | 0.5 | 142 | 0.5 | 142 | >2.0 | 0 | 0 |
| Rifampin | 0.125–8.0 (7) | 1.0 | 90 | 2.0 | 144 | ≥4.0 h | 3 | 2.04 |
| Trimethoprim-sulfamethoxazole | 0.1/1.9–12.8/243.2 (8) | 0.8/15.2 | 134 | 0.8/15.2 | 134 | >2/38 | 2 | 1.36 |
aVariation of MIC values (number of dilution variations) for every antimicrobial
bMinimum Inhibitory Concentration required to inhibit the growth of 50% of the strains
cMinimum Inhibitory Concentration required to inhibit the growth of 90% of the strains
dNumber of sensitive strains in the MIC established
eBreakpoint of resistance for Brucella spp. strains (μg/mL)
fNumber of resistant strains
gPercentage of resistant strains
hThe breakpoints for rifampin are: resistance ≥ 4.0 μg/mL, intermediate 2.0 μg/mL and sensitivity ≤ 1.0 μg/mL.