Optimal Effective Concentration Combinations and synergy evaluations for binary antimicrobial combinations in vitro.

Area of Science:

• Microbiology
• Pharmacology
• Computational Biology

Background:

• Binary antimicrobial combinations are crucial for combating resistance.
• Evaluating combination efficacy requires robust methodologies.
• Existing synergy models (Loewe, Bliss) have limitations.

Purpose of the Study:

• To comparatively analyze Optimal Effective Concentration Combinations (OPECCs) against traditional synergy models.
• To assess the utility of different strategies for analyzing binary antimicrobial combinations.
• To inform the development of effective therapeutic strategies against antimicrobial resistance.

Main Methods:

• Tested binary combinations of Benzalkonium chloride, Chlorhexidine, Cetylpyridinium chloride, and Ciprofloxacin against E. coli and S. aureus.
• Derived OPECCs and synergy evaluations using Loewe and Bliss models.
• Utilized OD measurements after aerobic incubation at 37°C in Mueller-Hinton medium.

Main Results:

• OPECCs were determinable and consistently below minimum effective concentrations for single agents.
• Synergy scores varied widely (-13.4 to 11.2), with higher scores for the Bliss model.
• Concentration pairs at maximum synergy showed inconsistent antibacterial assessments and did not correlate with OPECCs or effectiveness.

Conclusions:

• Synergy models based on additivity/independence assumptions may identify non-effective concentration pairs.
• OPECC method directly identifies effective combinations from experimental data, independent of model assumptions.
• OPECC offers a complementary approach for accurate identification of effective antimicrobial combinations, aiding resistance management.