Sublethal interaction factor (SIF), a growth-based method to analyze antibiotic combinations at sub-inhibitory...

Area of Science:

• Microbiology
• Pharmacology
• Environmental Science

Background:

• Antibiotic resistance is a critical global issue impacting healthcare and ecosystems.
• Combination antibiotic therapies are used to combat resistance, but interactions are unpredictable.
• Current methods often study antibiotic interactions at lethal concentrations, not sublethal ones.

Purpose of the Study:

• To develop and validate a novel assay for quantifying antibiotic interactions at sublethal concentrations.
• To provide a reliable method for assessing the efficacy of antibiotic combinations in realistic scenarios.

Main Methods:

• Development of the sublethal interaction factor (SIF) assay, based on the Bliss independence model.
• Utilizing the entire bacterial growth curve for analysis, not just growth rates.
• Validation of the SIF assay against the established CombiANT assay.

Main Results:

• The SIF assay reliably quantifies antibiotic combination effects at sublethal concentrations.
• SIF assay demonstrated high sensitivity and specificity, comparable to existing methods.
• SIF showed a strong correlation with the fractional inhibitory concentration index (FICi).

Conclusions:

• The SIF assay offers a simplified and effective approach to analyze antibiotic interactions at sub-inhibitory levels.
• This method has broad applicability for studying drug interactions, antibiotic combinations, and phage therapy.
• The SIF assay is easily implementable in laboratory settings for advancing antimicrobial research.