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Background/purposes Treatment of Staphylococcus aureus infections is challenging owing to widespread multidrug resistance. There is now considerable interest in the potential of combination therapies. Although linezolid/fosfomycin combination appears to be a promising treatment option based on in vitro data, further preclinical work is needed. In this study, the Galleria mellonella system was employed to study the in vivo efficacy of this combination in order to determine whether it should be explored further for the treatment of S. aureus infections. Methods The antimicrobial activity of linezolid and fosfomycin alone and in combination was assessed versus four S. aureus. Synergy studies were performed using the microtitre plate chequerboard assay and time-kill methodology. The in vivo activity of linezolid/fosfomycin combination was assessed using a G. mellonella larvae model. Results The combination of linezolid and fosfomycin was synergistic and bacteriostatic against four tested strains. Treatment of G. mellonella larvae infected with lethal doses of S. aureus resulted in significantly enhanced survival rates when low-dose of combination has no significant differences with high-dose combination (P > 0.05), G. mellonella hemolymph burden of S. aureus suggest that combination therapy with rapid and sustained bacteriostatic activity compared monotherapy. Conclusion This work indicated that linezolid combination with fosfomycin has synergistic effect against S. aureus in vitro and in an experimental G. mellonella model, and it suggests that high-dose of linezolid and fosfomycin may not necessary.

Objectives To explore the in vitro and in vivo antibacterial activity of linezolid/fosfomycin combination against vancomycin-susceptible and -resistant enterococci (VSE and VRE), and provide a theoretical basis for the treatment of VRE. Methods The checkerboard method and time-kill curve study were used to evaluate the efficacy of linezolid combined with fosfomycin against VSE and VRE. The transmission electron microscopy (TEM) was employed to observe the cell morphology of bacteria treated with each drug alone or in combination, which further elucidate the mechanism of action of antibiotic combination therapy. The Galleria mellonella infection model was constructed to demonstrate the in vivo efficacy of linezolid plus fosfomycin for VSE and VRE infection. Results The fractional inhibitory concentration index (FICI) values of all strains suggested that linezolid showed synergy or additivity in combination with fosfomycin against five of the six strains. Time-kill experiments demonstrated that the combination of linezolid-fosfomycin at 1×MIC or 2×MIC led to higher degree of bacterial killing without regrowth for all isolates tested than each monotherapy. TEM images showed that the combination treatment damaged the bacterial cell morphology more obviously than each drug alone. In the Galleria mellonella infection model, the enhanced survival rate of the combination treatment compared with linezolid monotherapy (P

Objectives Linezolid combination therapy is recommended for the treatment of Staphylococcus aureus (S. aureus) infections. However, the optimal regimen of the combination therapy for S. aureus is unknown. The objective of this study was to investigate the antibacterial activity, post-antibiotic effect (PAE), and post-antibiotic subminimum inhibitory concentration (MIC) effect (PA-SME) of linezolid alone and in combination with fosfomycin against eleven clinical isolates of S. aureus. Methods The synergistic effects and antibacterial activity of linezolid and fosfomycin were assessed by checkerboard and time-kill assays. To determine the PAE and PA-SME, S. aureus strains in the logarithmic phase of growth were exposed for 1, 2, and 3 hours to the antibiotics, alone and in combination. Recovery periods of test strains were evaluated using viable counting after dilution. Results Synergistic effects were observed for eight strains and no antagonism was found with any combination. Moreover, linezolid combined with fosfomycin at 4x MIC showed the best synergistic antibacterial effect, and this effect was retained after 24 hours. In addition, both the antibiotics alone and in combination showed increased PAE and PA-SME values in a concentration- and time-dependent manner. Conclusion Linezolid combined with fosfomycin exerted a good antibacterial effect against S. aureus, and the combinations have significant PAE and PA-SME.

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of serious infections. Linezolid and teicoplanin are widely used in the treatment of infections caused by MRSA. However, the efficacy and safety of linezolid compared with teicoplanin remains controversial. The purpose of this study was to systematically review the efficacy and safety of linezolid versus teicoplanin for the treatment of MRSA infections. Methodology: A meta-analysis was performed on the published studies. Pooled relative risk (RR) and 95% confidence interval (95% CI) were calculated to determine whether there were significant differences between the linezolid group and the teicoplanin group on the efficacy and safety. Results: Seventeen studies were included, involving 2,040 patients. The results showed that linezolid was associated with better clinical cure rate (RR = 1.14, 95% CI = 1.08-1.21, p < 0.00001) and microbiological eradication rate (RR = 1.28, 95% CI = 1.18-1.39, p < 0.00001) compared with teicoplanin. There were no statistically significant differences between the two groups in the treatment of MRSA infections regarding the adverse events (RR = 1.15, 95% CI = 0.97-1.35, p = 0.10) and the mortality (RR = 0.85, 95% CI = 0.61-1.18, p = 0.33). Conclusions: The results suggest that linezolid may be a better choice for the treatment of patients with MRSA infections. However, our recommendation is that the decision about treating MRSA infections with linezolid or with teicoplanin should depend on local availability, patient population, dosage regimens, costs and safety, rather than presumed differences in efficacy.