Delafloxacin  Susceptibility Testing 

Delafloxacin is a fluoroquinolone antibiotic with broad-spectrum activity, particularly effective against Gram-positive pathogens (MRSA, Streptococcus spp.) and Gram-negative bacteria (Pseudomonas aeruginosa, Enterobacterales). It is primarily used for acute bacterial skin and skin structure infections (ABSSSI) and community-acquired bacterial pneumonia (CABP). Susceptibility testing is essential due to increasing fluoroquinolone resistance and the need for precise antimicrobial stewardship.

Testing Methods

Delafloxacin 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., Enterobacterales, and Pseudomonas aeruginosa.
• Agar Dilution: Used for MIC determination but less frequently applied in clinical settings.
• E-test (Epsilometer Test): Gradient diffusion method for delafloxacin MIC determination, useful in routine microbiology labs.
• Disk Diffusion Assay: Provides zone diameter measurements for qualitative susceptibility interpretation based on CLSI/EUCAST breakpoints.
• Molecular Methods (PCR, Whole Genome Sequencing): Detects mutations in gyrA, gyrB, parC, and parE genes that contribute to fluoroquinolone resistance.

Clinical Applications

Delafloxacin susceptibility testing is crucial in Gram-positive and Gram-negative infections, particularly in the following cases:

• Acute Bacterial Skin and Skin Structure Infections (ABSSSI): Ensures effective treatment of MRSA and Streptococcus spp. infections.
• Community-Acquired Bacterial Pneumonia (CABP): Evaluates efficacy against Streptococcus pneumoniae and Haemophilus influenzae.
• Multidrug-Resistant (MDR) Gram-Negative Infections: Determines activity against Pseudomonas aeruginosa and Enterobacterales.
• Complicated Urinary Tract Infections (cUTIs): Investigates potential use in resistant uropathogens.

Delafloxacin susceptibility testing is critical for Gram-positive and Gram-negative bacterial infections, particularly for MRSA, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Enterobacterales. Broth microdilution remains the gold standard, while molecular methods provide rapid resistance detection, supporting antimicrobial stewardship and infection control efforts.