Interlaboratory comparison of Pseudomonas aeruginosa phage susceptibility testing.

Standardized approaches to phage susceptibility testing (PST) are essential to inform selection of phages for study in patients with bacterial infections. There is no reference standard for assessing bacterial susceptibility to phage. We compared agreement between PST performed at three centers: two centers using a liquid assay standardized between the sites with the third, a plaque assay. Four Pseudomonas aeruginosa phages: PaWRA01ø11 (EPa11), PaWRA01ø39 (EPa39), PaWRA02ø83 (EPa83), PaWRA02ø87 (EPa87), and a cocktail of all four phages were tested against 145 P . aeruginosa isolates. Comparisons were made within measurements at the two sites performing the liquid assay and between these two sites. Agreement was assessed based on coverage probability (CP ₈ ), total deviation index, concordance correlation coefficient (CCC), measurement accuracy, and precision. For the liquid assay, there was satisfactory agreement among triplicate measurements made on different days at site 1, and high agreement based on accuracy and precision between duplicate measurements made on the same run at site 2. There was fair accuracy between measurements of the two sites performing the liquid assay, with CCCs below 0.6 for all phages tested. When compared to the plaque assay (performed once at site 3), there was less agreement between results of the liquid and plaque assays than between the two sites performing the liquid assay. Similar findings to the larger group were noted in the subset of 46 P . aeruginosa isolates from cystic fibrosis. Results of this study suggest that reproducibility of PST methods needs further development.
Competing Interests: The material has been reviewed by the Walter Reed Army Institute of Research. There is no objection to its presentation and/or publication. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting true views of the Department of the Army, the Department of Defense, or the National Institutes of Health. R.P. reports grants from ContraFect, TenNor Therapeutics Limited, and BioFire and is a onsultant to Curetis, PathoQuest, Selux Diagnostics, 1928 Diagnostics, PhAST, Torus Biosystems, Day Zero Diagnostics, Mammoth Biosciences, and Qvella; monies are paid to Mayo Clinic. Mayo Clinic and R.P. have a relationship with Pathogenomix. R.P. has research supported by Adaptive Phage Therapeutics (APT). Mayo Clinic has a royalty-bearing know-how agreement and equity in APT. R.P. is also a consultant to Netflix, Abbott Laboratories, Oxford Nanopore Technologies, and CARB-X. In addition, R.P. has a patent on Bordetella pertussis/Bordetella parapertussis PCR issued, a patent on a device/method for sonication with royalties paid by Samsung to Mayo Clinic, and a patent on an anti-biofilm substance issued. R.P. receives honoraria from the NBME, Up-to-Date, and the Infectious Diseases Board Review Course. M.N., A.F., and Walter Reed Army Institute of Research have a royalty-bearing licensing agreement with APT. J.R.F, M.L, A.N. and P.A. are employees at APT.