Human Complement Inhibits Myophages against Pseudomonas aeruginosa

Abstract

Therapeutic bacteriophages (phages) are primarily chosen based on their in vitro bacteriolytic activity. Although anti-phage antibodies are known to inhibit phage infection, the influence of other immune system components is less well known. An important anti-bacterial and anti-viral innate immune system that may interact with phages is the complement system, a cascade of proteases that recognizes and targets invading microorganisms. In this research, we aimed to study the effects of serum components such as complement on the infectivity of different phages targeting Pseudomonas aeruginosa. We used a fluorescence-based assay to monitor the killing of P. aeruginosa by phages of different morphotypes in the presence of human serum. Our results reveal that several myophages are inhibited by serum in a concentration-dependent way, while the activity of four podophages and one siphophage tested in this study is not affected by serum. By using specific nanobodies blocking different components of the complement cascade, we showed that activation of the classical complement pathway is a driver of phage inhibition. To determine the mechanism of inhibition, we produced bioorthogonally labeled fluorescent phages to study their binding by means of microscopy and flow cytometry. We show that phage adsorption is hampered in the presence of active complement. Our results indicate that interactions with complement may affect the in vivo activity of therapeutically administered phages. A better understanding of this phenomenon is essential to optimize the design and application of therapeutic phage cocktails.

TheStreptococcus pyogenesM protein is involved in phenotypic resistance to phage A25 infection in presence of human serum

“…Vibrio cholerae decreases the production of the phage ICP1 receptor (LPS O1-antigen) in response to intestinal bile acids and anaerobiosis, preventing phage predation (47). As well, recent works reported a negative effect of human plasma, particularly fibrinogen and synovial fluid, as well as the complement system, on S. aureus and P. aeruginosa phages infection (40,44,48). With our observations, all these data urge to isolate and select phages in conditions mimicking the "end-user" settings.…”

“…Phages-bacteria interactions in a relevant physiological context have recently begun to be characterized (39,40,(43)(44)(45)(46)(47)(48). For instance, both E. coli and P. aeruginosa increase the production of biofilms in mouse gut and human cystic fibrosis-like environment, respectively, reducing phages infection (39,46).…”

A Novel Bacteriophage Infecting Multi-Drug- and Extended-Drug-Resistant Pseudomonas aeruginosa Strains

“…The complement system is a crucial component of the human innate immune system, which fights bacteria and viruses and may interact with bacteriophages, as has been previously described [ 64 , 65 ]. As can be seen in the results, human serum does not compromise the viability or pathogenicity of F1Pa, similarly to other Podoviridae bacteriophages, whose human serum stability has been investigated [ 66 , 67 ].…”