The cooperation of pharmacologic-dose ascorbate with ceftriaxone against staphylococcus aureus through bactericidal synergy and enhanced macrophage killing activity

Abstract

Background: Ascorbate is a low-cost compound with a known bactericidal-synergy to antibitics. However, the synergy depends on concentrations and organisms. Thus, the synergy test by time-kill assay might be appropriate for the screening of the synergy. Objective: We aimed to test the adjuvant property of ascorbate with ceftriaxone, a frequently prescribed β-lactam antibiotic. Method: Ascorbate was tested with several bacteria from the American Type Culture Collection (ATCC) including Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii and Escherichia coli for i) bactericidal property of ascorbate, alone or with ceftriaxone-combination, by time-kill assay, ii) an influence on the killing-activity of bone-marrow-derived macrophage and iii) the attenuation of myositis mouse model. Result: The bactericidal synergy (determined with time-kill assay at 24 h) against S. aureus, but not other selected bacteria, was demonstrated in ascorbate (10 and 40 mM) plus ceftriaxone at the minimal inhibitory concentration (1x MIC). Ascorbate alone, without antibiotic, enhanced macrophage killing-activity and directly eliminated bacteria at the concentration 10–40 mM and 250 mM, respectively (both properties presented against S. aureus and P. aeruginosa, but not other bacteria). Ascorbate with ceftriaxone also reduced bacterial burdens in muscle and serum cytokines of S. aureus-myositis mouse model. Moreover, the synergy against the clinical isolated methicillin resistant S. aureus (MRSA) by time-kill assay and myositis model also presented. Conclusion: Ascorbate-ceftriaxone synergy against S. aureus was demonstrated by time-kill assay and myositis model. Time-kill assy might be valuable as a screening test to select the patients that potentially benefit from ascorbate-ceftriaxone adjuvant therapy.