TABLE 3.
Distribution of MIC values for the 178 LA-MRSA-CC398 isolates identified in this study
| Antimicrobial agent(s) | No. of isolates with MIC (mg/L) of: |
Isolates that are: |
|||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Susceptible |
Intermediate |
Resistanta |
|||||||||||||||||||||
| 0.008 | 0.015 | 0.03 | 0.06 | 0.12 | 0.25 | 0.5 | 1 | 2 | 4 | 8 | 16 | 32 | 64 | 128 | 256 | 512 | n | % | n | % | n | % | |
| Oxacillin | X | - | - | - | - | - | - | - | - | 13 | 71 | 94 | X | X | X | X | X | - | - | 178 | 100 | ||
| Penicillinb | X | - | - | - | - | - | - | 1 | - | 4 | 21 | 83 | 43 | 26 | X | X | X | - | - | 178 | 100 | ||
| Ampicillinb | X | X | - | - | - | - | - | 1 | - | 13 | 48 | 75 | 24 | 14 | 3 | X | X | - | - | 178 | 100 | ||
| Amoxicillin/clavulanic acidb,c | X | X | - | - | - | - | - | 1 | 21 | 100 | 46 | 9 | 1 | - | X | X | X | - | - | 178 | 100 | ||
| Ceftiofurb | X | X | - | - | - | - | - | - | 2 | 86 | 62 | 21 | 4 | 2 | 1 | X | X | - | - | 178 | 100 | ||
| Cefquinomeb | X | - | - | - | - | - | - | 7 | 90 | 59 | 21 | 1 | - | X | X | X | X | - | - | 178 | 100 | ||
| Cefotaximeb | X | - | - | - | - | - | - | - | - | 2 | 92 | 62 | 19 | 3 | X | X | X | - | - | 178 | 100 | ||
| Cefoperazoneb | X | X | X | - | - | - | - | - | - | - | 91 | 66 | 17 | 4 | X | X | X | - | - | 178 | 100 | ||
| Erythromycin | X | - | - | - | - | 23 | 47 | 1 | 1 | 1 | - | 1 | - | 104 | X | X | X | 70 | 39 | 3 | 2 | 105 | 59 |
| Tylosin tartrate | X | X | X | - | - | - | - | 58 | 26 | 1 | 1 | 1 | - | - | - | 91 | X | ||||||
| Tilmicosin | X | X | X | - | - | - | 1 | 70 | 5 | 4 | 3 | 1 | - | - | - | 94 | X | ||||||
| Clindamycin | X | X | - | 3 | 47 | 16 | 4 | - | - | - | 11 | 4 | 1 | - | 92 | X | X | 70 | 39 | - | - | 108 | 61 |
| Pirlimycin | X | X | - | - | - | 12 | 44 | 12 | 1 | - | 1 | 8 | 8 | - | 92 | X | X | ||||||
| Enrofloxacin | - | - | 3 | 84 | 48 | 6 | 14 | 6 | 14 | 3 | - | X | X | X | X | X | 161 | 90 | - | - | 17 | 10 | |
| Gentamicin | X | X | X | X | - | 51 | 75 | 14 | 1 | 11 | 10 | - | 5 | 8 | 3 | - | X | 152 | 85 | 10 | 6 | 16 | 9 |
| Tetracycline | X | X | X | X | - | - | - | - | - | - | - | - | 1 | 10 | 167 | - | X | - | - | - | - | 178 | 100 |
| Sulfamethoxazole/trimethoprimc | X | - | 2 | 65 | 17 | 16 | 39 | 22 | 9 | 8 | - | - | - | X | X | X | X | 170 | 96 | 8 | 4 | ||
| Vancomycin | X | - | - | - | - | - | 94 | 82 | 2 | - | - | - | - | X | X | X | X | 178 | 100 | - | - | - | - |
Isolates were classified as susceptible, intermediate, or resistant if breakpoints were available in the CLSI document VET01S or M100 (97, 98). Despite the lack of breakpoints, isolates that showed high MIC values of enrofloxacin (≥4 mg/L) were considered resistant (3).
Since oxacillin-resistant staphylococci are resistant to all currently available β-lactams, except for ceftaroline, resistance to these agents can be deduced from the oxacillin MIC values (97, 98).
MIC values of amoxicillin/clavulanic acid (2:1) and sulfamethoxazole/trimethoprim (19:1) are given as amoxicillin and trimethoprim MIC values, respectively. Concentrations not included in the test panel are marked with an X or italic text. Isolates displayed in the lowest not-tested concentration showed growth in the highest test concentration, and the MIC is equal to or greater than the concentration following the highest test concentration. Black vertical lines indicate, if available, the CLSI breakpoints used to classify the isolates as susceptible, intermediate (if available), or resistant.