Development of a Polymicrobial Checkerboard Assay as a Tool for Determining Combinatorial Antibiotic Effectiveness in...

Area of Science:

• Microbiology
• Pharmacology
• Infectious Diseases

Background:

• Checkerboard assays traditionally assess antimicrobial combinations using turbidity or optical density.
• These methods are limited in polymicrobial settings, failing to differentiate effects on individual species.
• Distinguishing bacteriostatic from bactericidal concentrations is crucial but often challenging.

Purpose of the Study:

• To develop a novel methodology for assessing antimicrobial drug effects in polymicrobial cultures.
• To enable species-specific viability determination without specialized equipment, maintaining high-throughput analysis.
• To differentiate bacteriostatic versus bactericidal antibiotic concentrations.

Main Methods:

• Utilized selective and differential plating for individual species identification and viability assessment within a community.
• Adapted checkerboard assay principles for a polymicrobial context.
• Compared results with traditional turbidity-based measurements.

Main Results:

• The novel method accurately determined cell viability for individual species in polymicrobial cultures.
• Demonstrated that ceftazidime and gentamicin exhibit synergistic effects against *Pseudomonas aeruginosa* in monoculture.
• Revealed antagonistic interactions between ceftazidime and gentamicin in a polymicrobial culture including *Acinetobacter baumannii*, *Staphylococcus aureus*, and *Enterococcus faecalis*.

Conclusions:

• The developed methodology allows for precise assessment of antimicrobial efficacy in complex microbial communities.
• Highlights the critical impact of community context on antibiotic synergy and antagonism.
• Proposes implementation in clinical microbiology labs to improve diagnosis and treatment strategies for polymicrobial infections.