Determination of phage susceptibility as a clinical diagnostic tool: A routine perspective

Abstract

As the global burden of disease caused by multidrug resistant bacteria is a major source of concern, credible clinical alternatives to antibiotic therapy, such as personalized phage therapy, are actively explored. Although phage therapy has been used for more than a century, the issue of an easy to implement diagnostic tool for determining phage susceptibility that meets current routine clinical needs is still open. In this Review, we summarize the existing methods used for determining phage activity on bacteria, including the three reference methods: the spot test, the double agar overlay plaque assay, and the Appelmans method. The first two methods rely on the principle of challenging the overnight growth of a lawn of bacteria in an agar matrix to a known relative phage to bacteria concentration and represent good screening tools to determine if the tested phage can be used for a “passive” and or “active” treatment. Beside these methods, several techniques, based on “real-time” growth kinetics assays (GKA) have been developed or are under development. They all monitor the growth of clinical isolates in the presence of phages, but use various detection methods, from classical optical density to more sophisticated techniques such as computer-assisted imagery, flow-cytometry, quantitative real-time polymerase chain reaction (qPCR) or metabolic indicators. Practical considerations as well as information provided about phage activity are reviewed for each technique. Finally, we also discuss the analytical and interpretative requirements for the implementation of a phage susceptibility testing tool in routine clinical microbiology.

Genetic determinants of host tropism in Klebsiella phages

“…In total, there were six S8 phage-bacteria combinations that showed a positive spot but that did not yield a productive infection in liquid ( Figure 6 A). These spots were very turbid, which may suggest phage replication in a subset of bacterial cells 50 ( Figure 6 E). We thus hypothesized that S8/S9 turbid spots might be the result of phage replication in a subset of acapsular or low-capsular-producer bacteria.…”

Advanced detection of cervical cancer biomarkers using engineered filamentous phage nanofibers

“…Fd phages , specific to bacterial hosts, do not infect or harm mammalian cells and are remarkably stable under a range of environmental conditions, rendering them ideal for diagnostic applications (Wang et al 2022 ). Furthermore, fd phages can be easily propagated and produced in large quantities, facilitating the development of cost-effective and scalable diagnostic assays (Daubie et al 2022 ; González-Mora et al 2020 ). Furthermore, fd phage can be engineered or selected to specifically target specific biomarkers (Parmley and Smith 1988 ).…”

Administration of Bacteriophages via Nebulization during Mechanical Ventilation: In Vitro Study and Lung Deposition in Macaques

“…It was applied to the final selection of the anti-PA phages with the aim of achieving at least 80% coverage on a representative panel. Both the plaque assay and broth assay are two widely recognized methods to characterize phage activity [ 51 , 52 ]. EOP is the gold standard to define phage efficacy, and we propose to calculate the MIC of phages, which is an essential requirement to set the clinical active dose.…”