We documented the adjunctive bacteriophage therapy to treat a chronic relapsing periprosthetic joint infection of the knee and chronic osteomyelitis of the femur caused by multidrug-resistant Pseudomonas aeruginosa . The combined antibiotic-phage treatment eradicated the infection, and no side effects to phages were observed.

Effective antimicrobials are crucial for managing Staphylococcus aureus implant-associated bone infections (IABIs), particularly for infections due to rifampin-resistant S. aureus (RRSA). Failure to remove the implant results in persistent infection; thus, prolonged suppressive antibiotic therapy may be a reasonable alternative. However, a high incidence of adverse events can necessitate the discontinuation of therapy. In this scenario, commercial Staphylococcal bacteriophage Sb-1 combined with antibiotics is an option, showing a promising synergistic activity to facilitate the treatment of biofilm infections. Therefore, we evaluated the efficacy of the inhibitory activity of five antibiotics (doxycycline, levofloxacin, clindamycin, linezolid, and rifampin) alone or combined with phage Sb-1 (10⁶ PFU/mL) in a simultaneous and staggered manner, to combat five clinical RRSA strains and the laboratory strain MRSA ATCC 43300 in 72 h by isothermal microcalorimetry. The synergistic effects were observed when phage Sb-1 (10⁶ PFU/mL) combined with antibiotics had at least 2 log-reduction lower concentrations, represented by a fractional biofilm inhibitory concentration (FBIC) of <0.25. Among the antibiotics that we tested, the synergistic effect of all six strains was achieved in phage/doxycycline and phage/linezolid combinations in a staggered manner, whereas a distinctly noticeable improvement in inhibitory activity was observed in the phage/doxycycline combination with a low concentration of doxycycline. Moreover, phage/levofloxacin and phage/clindamycin combinations also showed a synergistic inhibitory effect against five strains and four strains, respectively. Interestingly, the synergistic inhibitory activity was also observed in the doxycycline-resistant and levofloxacin-resistant profile strains. However, no inhibitory activity was observed for all of the combinations in a simultaneous manner, as well as for the phage/rifampin combination in a staggered manner. These results have implications for alternative, combined, and prolonged suppressive antimicrobial treatment approaches.

Most research on phage therapy focused on planktonic bacteria, whereas bacteriophage activity against biofilms is limited. We evaluated the capability of Staphylococcus aureus -specific bacteriophage Sb-1 to eradicate biofilm alone and in combination with different classes of antibiotics, to degrade the extracellular matrix and target persister cells. Biofilm of methicillin-resistant S. aureus (MRSA) ATCC 43300 was treated with Sb-1 alone or in (simultaneous or staggered) combination with either fosfomycin, rifampin, vancomycin, daptomycin or ciprofloxacin. The matrix was visualized by confocal fluorescent microscopy. Persister cells were treated with 10 ⁴ and 10 ⁷ PFU/mL Sb-1 for 3 hours in PBS, followed by CFU counting. Alternatively, bacteria were washed and incubated in fresh BHI medium and the bacterial growth assessed after further 24-hours. Pre-treatment with Sb-1 followed by the administration of sub-inhibitory concentrations of antibiotic exerted a considerable synergistic effect in eradicating MRSA biofilm. Sb-1 determined a dose-dependent reduction of matrix exopolysaccharide. 10 ⁷ PFU/mL Sb-1 showed direct killing activity on persisters. However, even a lower titer had lytic activity when phage-treated persister cells were inoculated in fresh medium, reverting to a normal-growing phenotype. This study provides valuable data regarding the capability of Sb-1 to enhance antibiotic efficacy, exhibiting specific antibiofilm features. Its ability to degrade the MRSA polysaccharide matrix and target persister cells makes Sb-1 suitable for the therapy of biofilm-associated infections.