Eravacycline Susceptibility Testing 

Eravacycline is a fluorocycline-class tetracycline derivative with broad-spectrum activity against multidrug-resistant (MDR) Gram-positive and Gram-negative pathogens, including carbapenem-resistant Enterobacterales (CRE) and Acinetobacter baumannii. It is primarily used for treating complicated intra-abdominal infections (cIAIs) and other MDR-related infections. Due to rising resistance in tetracycline-class antibiotics, susceptibility testing is crucial for guiding therapy and monitoring resistance patterns.

Testing Methods

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

• Broth Microdilution (BMD): CLSI and EUCAST gold-standard method for determining MIC values in Enterobacterales, Acinetobacter spp., and Staphylococcus spp.
• Agar Dilution: Less commonly used but provides precise MIC values for resistant pathogens.
• E-test (Epsilometer Test): Gradient diffusion method for quantitative MIC determination, commonly employed in clinical microbiology labs.
• Disk Diffusion Assay: Not recommended due to variable diffusion properties of eravacycline.
• Molecular Methods (PCR, Whole Genome Sequencing): Detects resistance genes such as tet(X), tet(A-E), and efflux pump-associated mutations, which contribute to reduced eravacycline susceptibility.

Clinical Applications

Eravacycline susceptibility testing is crucial for treating MDR Gram-negative and Gram-positive infections, particularly in the following cases:

• Complicated Intra-Abdominal Infections (cIAIs): Evaluates efficacy against MDR Enterobacterales and Acinetobacter baumannii.
• Carbapenem-Resistant Enterobacterales (CRE) Infections: Ensures susceptibility of Klebsiella pneumoniae, Escherichia coli, and Enterobacter spp. to eravacycline.
• Multidrug-Resistant Acinetobacter Infections: Determines activity against Acinetobacter baumannii, a common nosocomial pathogen.
• Methicillin-Resistant Staphylococcus aureus (MRSA) Infections: Evaluates susceptibility in cases where alternative therapies are required.

Eravacycline susceptibility testing is essential for MDR Gram-negative and Gram-positive infections, particularly for CRE, Acinetobacter baumannii, and MRSA. Broth microdilution remains the gold standard, while molecular detection of resistance genes enhances rapid resistance monitoring, supporting antimicrobial stewardship and precision therapy.