Effect of an efflux pump inhibitor on cariogenic factors of Streptococcus mutans

Abstract

Objective To investigate the effect of an efflux pump inhibitor onthe biological characteristics of Streptococcus mutans (S.mutans) . Methods Screen efflux pump inhibitor (EPI) of S.mutans through EtBr uptaking and effluxingassays. The tested biological characteristics of S.mutans included MIC of chlorhexidine (CHX) , acid tolerance, competition ability against Streptococcus gordonii (S.gordonii) and the ability to form biofilms. The accumulation of EtBr and biological characteristics were evaluated by ANOVA and t test respectively. When α equaled to 0.05, it was considered to be significant. Results When the concentration is 128 μg/ml, reserpine inhibited the function of efflux pumps dramatically without affecting growth and metabolism of S.mutans. Therefore, reserpine can be regarded as a EPI at the concentration of 128 μg/ml. In thepresenceof 128 μg/ml reserpine, MIC of CHX decreased 75% to 0.25 μg/ml; under the environment of pH = 3 for 35 min, no viable bacteria was observed andthe results were statistically different from the results of control groups; inhibition zone against S.gordonii decreased [ (8.81 ± 0.33) mm VS (14.25 ± 0.51) mm, P<0.0001]; values of A575 represented the biomass of biofilm declined from 1.31 ± 0.01 by 63.92% to 0.47 ± 0.004 (t = 227.267, P<0.0001) and 1.94 ± 0.02 by 73% to 0.52 ± 0.003 (t = 223.730, P<0.0001) after 12 h and 24 h of incubation, respectively; the total quantity of bacteria dropped from (73.39 ± 2.56) μm3/μm2 by 24.73% to (55.24 ± 3.20) μm3/μm2 (t = 9.896, P<0.0001) . Conclusions EPI promoted Streptococcus mutans′s susceptibility to CHX notably, by weakening its acid tolerance, competition against other species, and its ability to form biofilm. These findings suggested that efflux pumps could be a new target forprevention and treatment of caries, thus EPI might be used as a new categoryof drugsfor combating caries in thefuture. Key words: Streptococcus mutans; Efflux pump; Efflux pump inhibitor; Reserpine; Cariogenic factor