Comparison of Dalbavancin MIC Values Determined by Etest (AB BIODISK) and Reference Dilution Methods Using Gram-Positive Organisms

Abstract

While standardized microdilution testing methodologies and quality control ranges exist for the novel glycolipopeptide dalbavancin, no testing methods have been described that are immediately available for routine use in clinical laboratories. In this study, we found that the dalbavancin Etest (AB BIODISK, Solna, Sweden) procedure demonstrated a high degree of agreement (100% within ؎2 log 2 dilution steps) with the standardized broth microdilution method, validating the use of the Etest as an alternative test for investigational or clinical purposes following regulatory approval.The continued emergence of resistance phenotypes among gram-positive pathogens has compromised the empirical usage of many targeted, traditional antimicrobials and necessitated the development of new agents displaying stability to the most commonly occurring resistance mechanisms. Among agents currently undergoing regulatory review is dalbavancin (formerly BI-397), a once-weekly, parenterally administered semisynthetic glycopeptide derivative of the natural glycopeptide A-40,926 produced by a 3,3-dimethylaminopropyl amide substitution on the peptide carboxyl group (9). The mechanism of bactericidal activity is similar to that of other glycopeptides, via interference with bacterial cell wall biosynthesis through binding to the terminal D-alanyl-D-alanine of nascent peptidoglycan chains. Dalbavancin has demonstrated potent activity against clinically relevant aerobic and anaerobic gram-positive organisms, including oxacillin (methicillin)-resistant staphylococci, penicillin-resistant Streptococcus pneumoniae, and certain vancomycin-resistant enterococci (vanB phenotypes), and has proven efficacy in clinical trials with skin and soft-tissue infections (3,4,8,13,14).The Clinical and Laboratory Standards Institute (CLSI; formerly the National Committee for Clinical Laboratory Standards [NCCLS]) reference broth microdilution MIC testing methodology and quality control (QC) guidelines for dalbavancin have been reported on previously, and the use of dryform broth microdilution panels for routine laboratory testing has also been validated (1, 2, 5, 6, 10). Importantly, the incorporation of the surfactant polysorbate-80 into dalbavancincontaining wells in reference frozen-form panels has been found to be critical for accuracy and reproducibility of MIC results (2, 5, 7).The purpose of this investigation was primarily to validate the use of the Etest (AB BIODISK, Solna, Sweden) as a commercial antimicrobial susceptibility test method for determining the susceptibility of indicated bacterial species to dalbavancin, comparing results with those MICs generated by the broth microdilution method, and secondarily to investigate comparability with the agar dilution method (10, 12). Given the familiarity with the Etest among laboratories and the ease of use (and the current absence of dalbavancin disk diffusion or automated system methods), this validation would permit clinical laboratories to test dalbavancin in support of clinical trials, surveillance i...

Factors Influencing Broth Microdilution Antimicrobial Susceptibility Test Results for Dalbavancin, a New Glycopeptide Agent

“…As recommended by the CLSI (4) and Jones and coworkers (1,6), addition of P-80 can most easily be incorporated during the preparation of the broth dilution series for dalbavancin without introducing P-80 to the testing wells of other agents via the inoculum water. Performance characteristics were shown to be more stable when dilutions were prepared by adding P-80 at the outset.…”

Effect of Polysorbate 80 on Oritavancin Binding to Plastic Surfaces: Implications for Susceptibility Testing

“…The broth microdilution methodology with polysorbate 80 has been used in a number of recent studies with dalbavancin (7,9,10,16). Polysorbate 80 has also been shown to have an effect on the broth microdilution MICs of polymyxins against gram-negative bacteria, reducing the MICs by 2 to 3 doubling dilutions (17).…”

A Reference Broth Microdilution Method for Dalbavancin <em>In Vitro</em> Susceptibility Testing of Bacteria that Grow Aerobically

“…As has been previously presented and shown in Figure 1, dalbavancin agar dilution (AD) MICs are typically 2-8 fold higher compared to the current BMD reference 12,13,14 . Unlike BMD, the addition of 0.002% P-80 does not affect dalbavancin AD MIC results Pos Ctrl.…”