Abstract： Objective To investigate the impact of vitamin C on bactericidal effect of allicin combined with meropenem on carbapenem- resistant Acinetobacter baumannii in vitro.Method Six carbapenemase-producing multiple drug-resistant Acinetobacter baumannii strains were identified by EDTA-Na2 paper composite method and modified three-dimensional experimental approach.The minimal inhibitory concentration (MIC) of allicin and meropenem was determined for calculation of combination inhibition fraction (FIC) index for combined therapy using MH broth.The bacterial inhibitory rates of allicin,meropenem,allicin combined with meropenem and allicin combined with vitamin C (0.25 g/L) in various concentrations were detected via microplate bio-detection assay.After adding allicin (32,64 mg/L and 128mg/L respectively) and the combination of allicin and 0.25 g/L vitamin C,the variations in glutathione,antisuperoxide anion free radicals and total thiol group levels within the bacteria were measured.Results All the six carbapenem-resistant Acinetobacter baumannii strains were found to produce carbapenemase.These six strains yielded MIC of 512 mg/L for allicin and 128 mg/L for meropenem.Allicin combined with meropenem was associated with FIG of 0.25.Various concentrations of allicin combined with meropenem resulted in a considerably higher bacterial inhibitory rates than either drug alone.By contrast,0.25 g/Lvitamin C combined with various concentrations of allicin resulted in marked reduction of bacterial inhibitory rates (all P＜0.05) as compared with equal concentration of allicin alone.In addition,lower glutathione,antisuperoxide anion and total thiol group levels (all P＜0.05) were revealed in bacteria treated with various concentrations of allicin (32,64 mg/L and 128 mg/L) as compared with control group.Increased allicin concentration was associated with gradual decline in bacterial glutathione,anti-superoxide anion and total thiol group levels (all P＜0.05).The 128 mg/L allicin-treated bacteria exhibited lower levels of glutathione [(4.52±0.71 ) mgGSH/gport vs (5.64±0.40) mgGSP/gport],anti-superoxide anion radical [ (115.21±4.24)U/L vs (145.84±2.30) U/L] and total thiol group [ (0.11±0.04) mmol/gport vs (0.18±0.03) mmol/gport],as compared with the strains treated with 128 mg/L allicin combined with 0.25 g/L vitamin C (all P＜0.05).Conclusions Allicin combined with meropenem significantly increases bactericidal and inhibitory effects on carbapenem-resistant Acinetobacter baumannii.Vitamin C may decrease bactericidal and inhibitory effect of allicin on carbapenem-resistant Acinetobacter baumannii via suppressing oxidative stress.