Human Plasma Significantly Reduces Bacteriophage Infectivity Against Staphylococcus aureus Clinical Isolates

Abstract

Bacteriophage therapy has been regaining interest as a potential therapeutic in treating a wide range of infections. However, there is a paucity of knowledge regarding numerous aspects of bacteriophage therapy, thereby hindering the development of proper treatment protocols and effective clinical trials. In this report, the activities of three bacteriophages are evaluated against clinical bacterial isolates in the presence and absence of human plasma (HP). The bacteriophages used in this experiment were residual therapeutic doses from the United States Food and Drug Administration (FDA) approved compassionate use cases to treat recalcitrant prosthetic joint infections (PJIs). Herein we demonstrate that in the presence of HP, the infectivity of these Staphylococcal bacteriophages was significantly reduced compared to the infectivity in the absence of HP. Inhibition of infectivity ranged from 48% to 81% for two methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates independently infected with the same bacteriophage and 98% for a third MRSA clinical isolate infected with a different bacteriophage. In contrast, bacteriophage infectivity of an Enterococcus faecalis clinical isolate was not affected by the presence of HP. We hypothesize that the inhibition is correlated with plasma proteins binding to Staphylococcal surface proteins masking the receptors associated with bacteriophage attachment, thereby reducing infectivity. This has clinical ramifications for bacteriophage therapy use in treating Staphylococcal bacteremia and periprosthetic joint infections.

Do bacteriophages have activity in synovial fluid and against synovial fluid induced bacterial aggregates?

“…When bacteria interact with polymers, the wall teichoic acid receptor is masked or obscured thereby hindering bacteriophages from attaching to this binding receptor. In human plasma this has also been previously reported 23,24 . These findings are important for clinicians to be cognizant about because if a bacteriophage cannot bind to a surface receptor no lysis will occur.…”

Microcalorimetry: A Novel Application to Measure In Vitro Phage Susceptibility of Staphylococcus aureus in Human Serum

“…More accurate results regarding phage susceptibility could potentially be achieved by resembling physiological conditions during bacterial infection, including phage susceptibility testing in the presence of human serum. However, the OD assay is not suitable to test phage susceptibility in this way, as serum components (such as fibrinogen and immune globulins) cause S. aureus to clump together in aggregates [ 65 ]. Microcalorimetry (MC) measures the metabolic activity of bacteria instead of optical density and is therefore not affected by S. aureus aggregation.…”

“…Nevertheless, these results confirm previous observations by Shinde et al (2022), who showed reduced phage infectivity under similar conditions. However, in the study of Shinde et al, bacterial aggregation was observed to be a limitation of the test [ 65 ]. The lack of phage susceptibility in serum could, in part, be due to a reduced growth rate of S. aureus in human serum, resulting in reduced phage propagation [ 73 , 74 ].…”

Phage therapy in prosthetic joint infections caused by Staphylococcus aureus – A literature review

“…Shinde et al. examined the effect of 10% human plasma on the lytic efficacy of two phages (Staphylococcal phage 1 and 3) against multiple S. aureus isolates in vitro [ 42 ]. It was found out that human plasma diminished the phages' infectivity substantially.…”