Table 1.
Antimicrobial Susceptibility Testing profile of M. chelonae, performed twice at two different national reference laboratories. The second sets of AST were performed several months after the original isolate was obtained; the isolate used for this 2nd set of AST was re-isolated and grown from an original agar slant that was saved at our hospital’s clinical microbiology laboratory. Clarithromycin was initially reported as susceptible by reference laboratory #2, but all other AST tests demonstrated resistance to clarithromycin. Interpretations for several antibiotics were provided by laboratory #2 based on a laboratory developed broth microdilution test that has not been cleared by the U.S. Food and Drug Administration (FDA).
| Antimicrobial agent | Antimicrobial Susceptibility Testing results by laboratory:MIC (Interpretation) |
|||
|---|---|---|---|---|
| Laboratory #1; initial AST | Laboratory #2; initial AST | Laboratory #1; repeat AST | Laboratory #2; repeat AST | |
| Routinely tested antimicrobial agents with breakpoints | ||||
| Amikacin | 32 (I) | <=8 (S) | 16 (S) | <=8 (S) |
| Cefoxitin | >128 (R) | >128 (R) | >128 (R) | >128 (R) |
| Ciprofloxacin | >4 (R) | 2 (I) | >4 (R) | 8 (R) |
| Clarithromycin | 16 (R) | 2 (S) | 8 (R) | 16 (R) |
| Doxycycline | >16 (R) | >16 (R) | >16 (R) | >16 (R) |
| Imipenem | 16 (I) | 8 (I) | 32 (R) | >16 (TR) |
| Linezolid | 16 (I) | 8 (S) | 16 (I) | 16 (I) |
| Minocycline | >8 (R) | >8 (R) | ||
| Moxifloxacin | >8 (R) | 2 (I) | >8 (R) | >4 (R) |
| Tobramycin | 2 (S) | >16 (R) | 2 (S) | <=2 (S) |
| Trimethoprim/sulfamethoxazole | 4/76 (R) | 4/76 (R) | ||
| Additional antimicrobial agents, without established breakpoints[1], [2] | ||||
| Clofazimine | <=0.5 (S) | <=0.5 (S) | ||
| Tigecycline | 0.25 (NP) | <=0.25 (TS) | 0.12 (NP) | <=0.25 (TS) |
| Kanamycin | <=8 (TS) | <=8 (TS) | ||
Abbreviations: AST, antimicrobial susceptibility testing; S, susceptible; I, intermediate susceptible; R, resistant; TS, tentative interpretation susceptible; TR, tentative interpretation resistant; NP, not provided; TMP/SMX, Trimethoprim-Sulfamethoxazole.