Clinical application of Vitek-derived minimum inhibitory concentration values: Proof of concept study

Abstract

Background: Minimum inhibitory concentration (MIC) values are useful in guiding appropriate antimicrobial therapy however, routine provision and interpretation of MIC values to guide clinical decision-making is challenging.

Objectives: This proof of concept study aims to demonstrate the clinical utility and application of Vitek^®-derived MIC values through categorisation of clinical isolates as wild type.

Method: A random selection of clinically relevant Gram negative isolates routinely tested on the Vitek^® instrument were included. The Vitek^® MIC values, for selected antimicrobials at the lowest calling range of that card, were compared to the broth microdilution reference method. The specified end-point was concordance between the two results if the reference MIC was less than or equal to the EUCAST-defined epidemiological cut-off value (ECOFF) for that drug-bug combination.

Results: A total of 525 isolates were included (468 Enterobacterales and 57 Pseudomonas aeruginosa), with an overall concordance rate of 96.4% (508/525). Correct ECOFF categorisation by the Vitek^® was highest for ceftazidime and piperacillin (100%, n = 48 and n = 55, respectively) and lowest for cefepime (81.8%, n = 66).

Conclusion: Vitek^®-derived MIC values can be used to categorise organisms as wild-type if the MIC is reported at the card’s lowest calling range (≤) as there is high likelihood that the MIC is at or below the ECOFF. This has important implications for antimicrobial management, assisting in choice of agent and in improving probability of target attainment for desired pharmacodynamic targets which can translate into improved clinical outcomes.

Contribution: Minimum inhibitory concentration data from an automated antimicrobial susceptibility testing instrument can be used to guide clinical decisions.