Dalbavancin is a semi-synthetic lipoglycopeptide antimicrobial agent that was approved by FDA for the treatment of acute bacterial skin and skin structure infections caused by Gram-positive organisms. Similar to other lipoglycopeptide agents, dalbavancin susceptibility testing can be challenging as a result of the large size of the molecule and binding properties. This study was performed to evaluate the performance of a newly developed gradient strip, the dalbavancin MIC Test Strip (MTS, Liofilchem, Roseto degli Abruzzi, Italy) compared to a broth microdilution (BMD) method against indicated Gram-positive isolates.
Methods: The study isolates tested were strains from clinical sources that included 30 S. aureus (including 11 challenge isolates with dalbavancin MICs at or above the susceptible breakpoint of 0.12 mcg/mL), 30 E.faecalis, 16 S. dysgalactiae, 14 S. anginosus, 22 S. pyogenes. QC strains (ATCC 29213, ATCC 29212 and ATCC 49619) were tested and results compared to CLSI ranges. Each isolate was tested for dalbavancin MIC by BMD (Sensititre lyophilized plates) and dalbavancin MTS on 100 mm Mueller Hinton agar (MHA) plates for S. aureus and E. faecalis and MHA+5% sheep blood for streptococci. For a subset of 11 challenge S. aureus, results were also compared to modal MIC results based on CLSI BMD method with frozen plates.
Results: As shown in table, dalbavancin MTS and BMD were within +/- one doubling dilution (essential agreement) for all S.aureus and E. faecalis. For the majority of streptococci, MTS were 1-4 dilutions lower than BMD.
|Evaluation of Dalbavancin MIC Test Strip (MTS) Compared to Broth Microdilution MIC for Relevant Gram Positive Isolates|