Abstract
We aimed to assess the comparability of daptomycin (DAP) antimicrobial susceptibility testing (AST) for Enterococcus faecalis (E. faecalis) using the VITEK-2 P639 card and the broth microdilution (BMD) method. The AST results of DAP of 356 E. faecalis were compared with those of two methods. Whole-genome sequencing was conducted, and clinical data were analyzed. The overall categorical agreement (CA) between the two methods was 28.4%, and the essential agreement (EA) was 20.2%. Through subgroup analysis, in the DAP-susceptible group by VITEK-2, the CA was 100%, and the EA was 45%. In the DAP-nonsusceptible group by VITEK-2, VITEK-2 misclassified 7.4% of the susceptible isolates as resistant and 92.2% as intermediate, with a CA of 0.4% and an EA of 12.1%. In clinical E. faecalis, as the MIC by VITEK-2 increased, the comparability between the two methods exhibited a significant decrease. There was no significant correlation between the results of VITEK-2 and those of Ca(2+)-deficient BMD. None of the 40-sequenced E. faecalis isolates carried known DAP resistance genes. Five patients (2.0%) with DNSE detected by VITEK-2 but susceptible by BMD were treated with DAP, and the anti-infective effect was associated with the application of DAP. The VITEK 2 system may overcall DAP Non-Susceptible Enterococcus in E. faecalis. We recommend a policy of not reporting DAP MICs of ≥4 µg/mL from the VITEK 2 without confirmation by a reference method, thereby preventing the unnecessary avoidance of a potentially effective therapeutic agent. IMPORTANCE: The overall CA of AST results for DAP between VITEK-2 and BMD was 28.4%, with an EA of 20.2%. In the DAP-sensitive group, CA was 100%, but in the DAP-nonsensitive group, VITEK-2 misclassified 7.4% of sensitive isolates as resistant and 92.2% as intermediate. The consistency between VITEK-2 and BMD decreased significantly as the VITEK-2 MIC value increased. No significant correlation was found between VITEK-2 results and Ca(2+)-deficient BMD. None of the sequenced E. faecalis isolates carried known DAP resistance genes. If the DAP MIC value ≥ 4 detected by VITEK-2 is not reported, it may lead to the loss of daptomycin susceptibility data in clinical practice and also cause bias in the national bacterial resistance detection results.