The recently issued Korean version of antimicrobial susceptibility cards for Vitek 2 system uses an adjusted antimicrobial combination that reflects Korean clinical practice and CLSI guidelines. We evaluated the two Korean antimicrobial susceptibility testing cards for gram negative rods, AST N056 and AST N055.

The results of susceptibility tests were compared between the original and Korean cards. A number of the same antimicrobials included in the both cards were 15 in AST N041-AST N056 and 17 in AST N022-AST N055. Susceptibilities to the newly added antimicrobials, aztreonam, tobramycin, and meropenem for AST N056; and cefotaxime, levofloxacin, and minocycline for AST N055 were compared with those obtained by disc diffusion test and, in case of discrepancy, by confirmative Etest or broth dilution method.

In comparison between AST N041 and AST N056 cards, the average discrepancy rate per strain was 0.34, minor error was 88.2%, and major error and very major error were both 5.9%. In comparison between AST N022 and AST055 cards, the average discrepancy rate per strain and very major error were 1.23 and 4.4%, respectively. The three antimicrobial agents added into AST N055 card showed highly discrepant results as a total of 49 items (44.1%) in 111 isolates were discrepant with very major error of 5.9% and major error of 2.0%.

AST N056 showed acceptable results in most items including the newly added antimicrobial agents. However, in the case of AST N055 card that showed a relatively high discrepancy, other indicator antibiotics should be referred to for newly added three antimicrobials. For the antibiotics that showed a high discrepancy between the original and Korean cards, a comparison study should be performed using the standard method and clinical isolates col-lected in Korea.