Synergistic efficacy of phages along with vancomycin for eradication of vancomycin-resistant Enterococcus faecalis...

The upsurge of antibiotic resistance is a significant challenge to public health, and the dry pipeline of new antibiotics has prompted the discovery of alternative treatment approaches. Enterococcus faecalis (E. faecalis) isolates are often multidrug-resistant, posing challenges to antibiotic therapy. Bacteriophage therapy is being explored as an alternative method to treat the growing population of antibiotic-resistant infections. Nevertheless, many inherent limitations of phages diminish their therapeutic utility, notably the restricted host range and quick development of mutants. The specific types and quantities of bacteriophages and antibiotics may be crucial in generating the optimal phage-antibiotic synergy.

To optimize the doses, order, and timing to optimize the synergy of phages and vancomycin on different bacteria states.

A volume of 180 μL of E. faecalis bacteria in the logarithmic growth phase, with a concentration of approximately 1 × 10⁸ colony forming units (CFUs)/mL, was introduced onto a microtitre plate. Subsequently, 20 μL of phage suspension (1 × 10⁶ PFUs/mL), vancomycin (16 µg/mL), or a combination of both was introduced into the designated wells in the specified sequence and incubated at 37 °C for 48 hours. The number of live bacteria was counted at different time points using standardized CFU counting protocols.

The biofilm model demonstrated that combining phages with vancomycin can eradicate the biofilm. Sequential therapy, involving phage application 8 hours before the antibiotic at a concentration of 10⁸ PFUs/mL, proved the most efficient in eliminating the biofilms and killing the planktonic form of E. faecalis.

The combination of phage ɸEFP01 at a higher concentration with a subinhibitory concentration of vancomycin yields a synergistic antibacterial outcome on E. faecalis strain resistant to vancomycin.