The Journal of antimicrobial chemotherapy · 2026
In vitro susceptibility of Cutibacterium acnes to dalbavancin: comparison between gradient test and the agar dilution reference method.
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Svensson Sara, Jacobsson Susanne, Matuschek Erika, Söderquist Bo
Аннотация
BACKGROUND: Cutibacterium acnes, a human commensal, occasionally causes infections requiring long-term antibiotic treatment, including periprosthetic joint infections. Dalbavancin is a new lipoglycopeptide that allows intermittent dosing because of its exceptionally long half-life. However, data on susceptibility of C. acnes to dalbavancin are lacking, and no EUCAST breakpoints have been defined.
OBJECTIVES: To determine the MIC distribution of C. acnes for dalbavancin, and to compare the gradient test to the agar dilution reference method.
METHODS: C. acnes isolates were obtained from tissue samples from arthroplasties (n = 117), skin samples (n = 15), and positive blood cultures (n = 85). Antibiotic susceptibility was tested by agar dilution according to EUCAST methodology for anaerobic bacteria (±polysorbate 80) and by gradient test.
RESULTS: MIC50 and MIC90 for dalbavancin against C. acnes were 0.03 and 0.06 mg/L using agar dilution, and 0.004 and 0.008 mg/L with the gradient test. The gradient test yielded 3-fold lower MIC values than agar dilution. No significant difference was observed when polysorbate 80 was added to the agar dilution test. When vancomycin was tested as a comparator, the MICs did not differ between the agar dilution and gradient tests; MIC50 and MIC90 were 0.5 mg/L in both tests.
CONCLUSIONS: C. acnes showed significantly lower MIC values for dalbavancin than for vancomycin, highlighting the potential of dalbavancin as a therapeutic option. The gradient test yielded significantly lower MICs for dalbavancin than the reference method for anaerobes, agar dilution, suggesting that the gradient test for dalbavancin may not be a reliable method for antibiotic susceptibility testing (AST) of C. acnes.
OBJECTIVES: To determine the MIC distribution of C. acnes for dalbavancin, and to compare the gradient test to the agar dilution reference method.
METHODS: C. acnes isolates were obtained from tissue samples from arthroplasties (n = 117), skin samples (n = 15), and positive blood cultures (n = 85). Antibiotic susceptibility was tested by agar dilution according to EUCAST methodology for anaerobic bacteria (±polysorbate 80) and by gradient test.
RESULTS: MIC50 and MIC90 for dalbavancin against C. acnes were 0.03 and 0.06 mg/L using agar dilution, and 0.004 and 0.008 mg/L with the gradient test. The gradient test yielded 3-fold lower MIC values than agar dilution. No significant difference was observed when polysorbate 80 was added to the agar dilution test. When vancomycin was tested as a comparator, the MICs did not differ between the agar dilution and gradient tests; MIC50 and MIC90 were 0.5 mg/L in both tests.
CONCLUSIONS: C. acnes showed significantly lower MIC values for dalbavancin than for vancomycin, highlighting the potential of dalbavancin as a therapeutic option. The gradient test yielded significantly lower MICs for dalbavancin than the reference method for anaerobes, agar dilution, suggesting that the gradient test for dalbavancin may not be a reliable method for antibiotic susceptibility testing (AST) of C. acnes.