Evaluation of the Activity of a Combination of Three Bacteriophages Alone or in Association with Antibiotics on Staphylococcus aureus Embedded in Biofilm or Internalized in Osteoblasts

Abstract

Staphylococcus aureus is responsible for difficult-to-treat bone and joint infections (BJIs). This is related to its ability to form biofilm and to be internalized and persist inside osteoblasts. Recently, bacteriophage therapy has emerged as a promising option to improve treatment of such infections, but data on its activity against the specific bacterial lifestyles presented above remain scarce. We evaluated the activity of a combination of three bacteriophages, recently used for compassionate treatment in France, against S. aureus HG001 in a model of staphylococcal biofilm and a model of osteoblasts infection, alone or in association with vancomycin or rifampin. The activity of bacteriophages against biofilm-embedded S. aureus was dose dependent. In addition, synergistic effects were observed when bacteriophages were combined with antibiotics used at the lowest concentrations. Phage penetration into osteoblasts was observed only when the cells were infected, suggesting a S. aureus-dependent Trojan horse mechanism for internalization. The intracellular bacterial count of bacteria in infected osteoblasts treated with bacteriophages as well as with vancomycin was significantly higher than in cells treated with lysostaphin, used as a control condition, owing to the absence of intracellular activity and the rapid killing of bacteria released after the death of infected cells. These results suggest that bacteriophages are both inactive in the intracellular compartment after being internalized in infected osteoblasts and present a delayed killing effect on bacteria released after cell lysis into the extracellular compartment, which avoids preventing them from infecting other osteoblasts. The combination of bacteriophages tested was highly active against S. aureus embedded in biofilm but showed no activity against intracellular bacteria in the cell model used.

Bacteriophage Treatment: Critical Evaluation of Its Application on World Health Organization Priority Pathogens

“…In all the reviewed studies, bacteriophage was active against both planktonic cells and biofilm, showing a bactericidal effect and detachment activities against tested pathogens. Out of the nine studies, two evaluated the effect of combination therapy of phage with antibiotics against S. aureus using vancomycin/rifampicin, and teicoplanin, respectively [ 35 , 43 ]. The first S. aureus study illustrated a synergistic effect between vancomycin/rifampicin, and bacteriophage when phage was administered directly to tissue culture plates at a low concentration of phage (10 5 PFU/mL) and vancomycin (6 mg/L)/rifampicin (MIC of 0.016 mg/L) [ 35 ].…”

The Potential Innovative Use of Bacteriophages Within the DAC® Hydrogel to Treat Patients With Knee Megaprosthesis Infection Requiring “Debridement Antibiotics and Implant Retention” and Soft Tissue Coverage as Salvage Therapy

“…The activity of these two bacteriophages against the biofilm-embedded S. aureus was dose dependent. In addition, synergistic effects were observed when the bacteriophages were combined with antibiotics used at the lowest concentrations (5).…”

“…Lytic bacteriophages rapidly kill in vitro specifically the targeted bacteria and self-replicate in an exponential and self-sustained reaction ( 4 ). They are considered to have a high potential in patients with PJI as it has been demonstrated that they have a synergistic anti-biofilm activity with antibiotics ( 5 ). In a few patients with relapsing chronic PJI for whom explantation was not possible, we previously performed DAIR and used a selected cocktail of bacteriophages that was injected into the joint as compassionate therapy, with a good clinical response ( 6 ).…”

Antibiotic Tolerance of Staphylococcus aureus Biofilm in Periprosthetic Joint Infections and Antibiofilm Strategies

“…It is important to note that the time and order of treatment are important to improve antibiofilm properties of combination with antibiotics [ 107 , 108 ]. As host cells can potentially represent a reservoir of internalized bacteria and a source of reinfection, targeting internalized bacteria in cells would be a huge advantage, but there is a lack of efficiency of bacteriophages against internalized bacteria such as S. aureus [ 109 ].…”