TABLE 1.
MIC50, MIC90, range of MICs, and susceptibility of 1,730 clinical isolates of H. influenzaea
| Antimicrobial agent | Overall (n = 1,730)
|
β-Lactamase positive (n = 399)
|
β-Lactamase negative (n = 1,331)
|
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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| MIC (μg/ml)
|
No. (%) of strains
|
MICs (μg/ml)
|
No. (%) of strains
|
MICs (μg/ml)
|
No. (%) of strains
|
|||||||||||
| MIC50 | MIC90 | Range of MICs | Susceptible | Intermediate | Resistant | MIC50 | MIC90 | Susceptible | Intermediate | Resistant | MIC50 | MIC90 | Susceptible | Intermediate | Resistant | |
| Penicillin | 1 | ≥16 | ≤0.015–≥16 | NA | NA | NA | ≥16 | ≥16 | NA | NA | NA | 0.5 | 4 | NA | NA | NA |
| Amoxicillin | 1 | ≥16 | ≤0.015–≥16 | NA | NA | NA | ≥16 | ≥16 | NA | NA | NA | 1 | 4 | NA | NA | NA |
| Ampicillin | ≤0.5 | ≥8 | ≤0.5–≥8 | 1,209 (69.9) | 96 (5.5) | 425 (24.6) | ≥8 | ≥8 | 39 (9.7) | 9 (2.3) | 351 (88) | ≤0.5 | 2 | 1,170 (87.9) | 87 (6.5)b | 74 (5.6)b |
| Amox-clavc | 1 | 2 | ≤0.015–8 | 1,722 (99.5) | NA | 8 (0.5) | 1 | 4 | 397 (99.5) | NA | 2 (0.5) | 0.5 | 2 | 1,325 (99.5) | NA | 6 (0.5) |
| Cefaclor | 4 | 8 | ≤1–≥64 | 1,581 (91.4) | 99 (5.7) | 50 (2.9) | 8 | ≥64 | 281 (70.4) | 75 (18.8) | 43 (10.8) | 4 | 8 | 1,699 (97.7) | 24 (1.8) | 7 (0.5) |
| Cefuroxime | 1 | 4 | ≤0.25–8 | 1,718 (99.3) | 12 (0.7) | 0 | 1 | 4 | 392 (98.2) | 7 (1.8) | 0 | 1 | 4 | 1,725 (99.6) | 5 (0.4) | 0 |
| Cefixime | ≤0.25 | ≤0.25 | ≤0.25–≥8 | 1,727 (99.8) | NA | NA | ≤0.25 | ≤0.25 | 397 (99.5) | NA | NA | ≤0.25 | ≤0.25 | 1,330 (99.9) | NA | NA |
| Cefotaxime | ≤0.25 | ≤0.25 | ≤0.25–8 | 1,729 (99.9) | NA | NA | ≤0.25 | ≤0.25 | 399 (100) | NA | NA | ≤0.25 | ≤0.25 | 1,330 (99.9) | NA | NA |
| Erythromycin | 4 | 8 | ≤0.12–≥64 | NA | NA | NA | 4 | 8 | NA | NA | NA | 4 | 8 | NA | NA | NA |
| Clarithromycin | 4 | 16 | ≤0.25–≥64 | 1,546 (89.4) | 159 (9.2) | 25 (1.4) | 8 | 16 | 353 (88.5) | 40 (10) | 6 (1.5) | 4 | 16 | 1,193 (89.7) | 119 (8.9) | 19 (1.4) |
| Azithromycin | 0.5 | 2 | ≤0.12–≥64 | 1,712 (98.9) | NA | NA | 0.5 | 2 | 393 (98.5) | NA | NA | 0.5 | 2 | 1,319 (99.1) | NA | NA |
| Ciprofloxacin | ≤0.5 | ≤0.5 | ≤0.5–4 | 1,728 (99.9) | NA | NA | ≤0.5 | ≤0.5 | 399 (100) | NA | NA | ≤0.5 | ≤0.5 | 1,329 (99.8) | NA | NA |
NCCLS 2000 breakpoint criteria concentrations are expressed in micrograms per milliliter for susceptible, intermediate, and resistant categories are: penicillin, NA/NA/NA (NA, no NCCLS breakpoint criteria); amoxicillin, NA/NA/NA (but the results of ampicillin susceptibility tests should be used to predict the activity of amoxicillin); ampicillin, ≤1/2/≥4; amoxicillin-clavulanate, ≤4/NA/≥8; cefaclor, ≤8/16/≥32; cefuroxime, ≤4/8/≥16; cefixime, ≤1/NA/NA; cefotaxime, ≤2/NA/NA; erythromycin, NA/NA/NA; clarithromycin, ≤8/16/≥32; azithromycin, ≤4/NA/NA; ciprofloxacin, ≤1/NA/NA.
According to NCCLS, BLNAR strains should be considered resistant to amoxicillin-clavulanate, cefaclor, and cefuroxime despite apparent in vitro susceptibility of some BLNAR strains to these agents.
Amox-clav; amoxicillin-clavulanate (2:1); concentrations refer to amoxicillin.