A comparison of phage susceptibility testing with two liquid high-throughput methods.

Area of Science:

• Microbiology
• Molecular Biology
• Biotechnology

Background:

• Phage therapy offers a promising alternative to antibiotics for combating escalating drug-resistant bacterial infections.
• Patient-specific testing of phage activity is essential due to strain-specific phage efficacy.
• Standardized, clinically validated methods for phage susceptibility testing (PST) are critically needed.

Purpose of the Study:

• To compare the performance and reproducibility of two high-throughput, liquid-based PST assays.
• To evaluate the clinical utility of these assays for assessing phage activity against various bacterial pathogens.

Main Methods:

• Two high-throughput assays were compared: Biolog Omnilog (respiration/colorimetric) and Agilent BioTek Cytation 7 (optical density).
• Fifty-five phages were tested against their susceptible bacterial hosts (E. coli, S. aureus, P. aeruginosa, A. baumannii, E. faecalis) and non-susceptible controls.
• Assay validity was assessed using coefficient of variance (CV) and interclass correlation coefficients (ICC) for reproducibility.

Main Results:

• Both assays demonstrated high validity rates for susceptible bacteria (87% Biolog, 84% Agilent) and non-susceptible controls (100%).
• A hold time cutpoint of 8 hours showed 100% result agreement between the two assays.
• Inter-assay agreement varied from moderate to excellent for susceptible isolates, and was excellent for non-susceptible isolates.

Conclusions:

• Both high-throughput PST assays provide statistically good to fair reproducibility for assessing phage susceptibility.
• These validated methods can support the clinical application of phage therapy by enabling precise, patient-specific treatment selection.
• Further standardization of PST methods is essential for the widespread adoption of phage therapy.