Dalbavancin Susceptibility Testing 

Dalbavancin is a long-acting lipoglycopeptide antibiotic used primarily for treating Gram-positive bacterial infections, including methicillin-resistant Staphylococcus aureus (MRSA), Streptococcus spp., and Enterococcus spp.. Due to its prolonged half-life, dalbavancin is administered as a single or two-dose regimen, making susceptibility testing essential for guiding therapy and preventing resistance development.

Testing Methods

Dalbavancin susceptibility is determined using standardized phenotypic and molecular techniques to ensure accurate resistance detection:

• Broth Microdilution (BMD): CLSI and EUCAST gold-standard method; determines MIC values for Staphylococcus spp., Streptococcus spp., and Enterococcus spp..
• Agar Dilution: Used for precise MIC determination, particularly for slow-growing Gram-positive bacteria.
• E-test (Epsilometer Test): Gradient diffusion method used in clinical microbiology labs for dalbavancin MIC determination.
• Disk Diffusion Assay: Less commonly used due to potential variability in results for lipoglycopeptides.
• Molecular Methods (PCR, Whole Genome Sequencing): Detect resistance genes such as vanA/vanB, which mediate vancomycin and dalbavancin resistance in Enterococcus spp.

Clinical Applications

Dalbavancin susceptibility testing is crucial in Gram-positive infections, particularly in the following cases:

• Complicated Skin and Soft Tissue Infections (cSSTIs): Used to confirm efficacy in MRSA and streptococcal infections.
• Osteomyelitis and Bone Infections: Ensures appropriate use in long-term infections requiring prolonged antibiotic exposure.
• Endocarditis: Investigates susceptibility in enterococcal and staphylococcal bloodstream infections.
• Prosthetic Joint Infections (PJI): Helps determine the role of dalbavancin in suppressive or curative therapy.

Dalbavancin susceptibility testing is critical for ensuring effective treatment of Gram-positive bacterial infections, particularly MRSA, Streptococcus spp., and vancomycin-resistant Enterococcus (VRE). Broth microdilution remains the gold standard, while molecular methods provide rapid resistance detection, supporting antimicrobial stewardship and infection control efforts.