Phage activity againstStaphylococcus aureusis impaired in plasma and synovial fluid

Abstract

S. aureus is a pathogen that frequently causes severe morbidity and phage therapy is being discussed as an alternative to antibiotics for the treatment of S. aureus infections. In this in vitro and animal study, we demonstrated that the activity of anti-staphylococcal phages is severely impaired in plasma and synovial fluid. Despite phage replication in these matrices, lysis of the bacteria was slower than phage propagation, and no reduction of the bacterial population was observed. This phage inhibition is due to a 99% reduction of phage adsorption, already at 10% plasma concentration. Coagulation factors bind S. aureus resulting in the formation of aggregates and blood clots that protect the bacterium from the phages. This was confirmed by the finding that purified fibrinogen is sufficient to impair phage activity. In contrast, dissolution of the clots by tissue plasminogen activator (tPA) partially restored phage activity. Consistent with these in vitro findings, phage treatment did not reduce bacterial burdens in a neutropenic mouse S. aureus thigh infection model. In summary, phage treatment of S. aureus infections may be fundamentally challenging, and more investigation is needed prior to proceeding to in-human trials.

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.…”

“…Furthermore, the host-specificity of the pathogen is also an important criterion. In the case of S. aureus, diluted plasma from human and guinea pig were found to prevent phage infection (40). We found that mice and rabbit sera did not prevent φA25 infection, highlighting the difficulty to use in vivo models other than the NHPs or the human challenge model (25,49) to characterize phage efficacy against S. pyogenes.…”

“…This is likely a consequence of the decrease in serum decoration of bacteria following their division. With the data obtained with plasma and fibrinogen for S. aureus (40), these are the first examples of a phenotypic resistance mechanism employing exogenous proteins rather than an adaptation of the transcriptome.…”

“…Growth rates, spatial and population structures, bystander microbiota or available resources are parameters that widely differ between the Petri dish and the infection site (8,36). Not surprisingly, the in vitro efficacy of several Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus phages has failed to be transposed in vivo (37)(38)(39)(40). Consequently, the success of phage therapy requires a better understanding of the phage-host interactions in in vivo and/or ex vivo conditions (8,41,42).…”

“…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).…”