Background: Prevention of rapidly spreading of antibiotic-defeating germs is major challenge today. Using of phages as the adjuvants to antimicrobials to address the threat of antibiotic resistance (AR) is very promising. But developing of simple and sensitive methods for phage activity evaluation in a fast manner is limited, because of phages are “living organisms” with high specificity to bacteria.

The optimal management of phage activity evaluation is highly impotent to prevent infections in the way to improve effectiveness of antibiotic-phage synergistic treatment and slow down the resistance development to both bacteria and phage.

Methods. Newly isolated phages of Pseudomonas aeruginosa and Klebsiella pneumoniae from different natural and industrial sewage environments and with sequenced genome were applied to study comparison of results produced from the methods of MD/SP (Multiple Dilutions on Single Plates), PLC (Phage Liquid Culturing) and BTR (Bacterial Tetrazolium Reduction). OmniLog™ system of redox chemistry to automatically measure cell respiration, a marker for bacterial growth.

The phage lytic activity was tested against a large bacterial matrix (103 P. aeruginosa and 172 K. pneumoniae strains). Efficiency of plating (EOP) was determined using both the agar plaquing and kinetic clearing methods and the results were correlated in parallel with TR and colony-forming reduction (CFR) in a multi-well-spot format.

Results: Based on EOP results, the host coverage of the selected phages of both P. aeruginosa and K. pneumoniae was about 80% individually. The given approach of phage lytic activity evaluation included pfu/ml and cfu/ml enumerations with correlation-adjustment to TR for a given timepoint. This approach will facilitate further development of phage lytic activity and emerging phage-resistance mutants’ determination, and selection of candidate therapeutic phages.