Studies On Arthrobacter Oxydans Dextranase For Degradating Dental Biofilm

Dextranase is an enzyme which catalyzes endohydrolysis of ɑ-1,6glycoside linkages inrandom sites of dextran. It is widely used in sugar production process, medical low moleculardextran production and treatment of dental plaque. This study is aimed to isolate andidentify a dextranse-producing strain, optimize fermentation conditions and study itsapplication in treatment of dental biofilm. The main contents and results were as follows:(1)20dextranase-producing stains were isolated from samples collected in Yellow Seaof Lianyungang. Among these stains, KQ11which was isolated from sea mud showed thehighest dextranase activity. According to the morphological characteristics, physiologicalcharacteristics, biochemical characteristics, the fatty acids and16s rDNA sequence of KQ11,it was identified as Arthrobacter oxydans KQ11. The optimal growth conditions of the strainwere30℃, pH7.5, and a NaCl concentration of4g/L.(2) The fermentation medium and culture conditions of KQ11were studied. It was foundthat the optimal fermentation medium components were bran5g/L, sodium nitrate1.5g/L,sodium chloride3g/L, dextran6g/L, pH6.0. The optimal fermentation conditions were assuch: liquid volume50mL/250mL, inoculum size4%, rotation speed160r/min, temperature30℃, fermentationperiod30h. The dextranse activity was4.697U/mL under the optimizedconditions,1.68times higer than the orginal dextranase activity.(3) The dextranase exhibited maximal activity at45℃, pH5.5. The enzyme had athermal stability and exhibited good stability at the pH among5.5-8.0.(4) The inhibition and degradation effects of dextranase obtained from KQ11on dentalbiofilm were studied. The dextranase from KQ11had significant inhibitory effect on themixed-species dental biofilm and S. mutans biofilm. In addition it also could degrade thepreformed biofilm. The minimum biofilm inhibitory concentration (MBIC) of S. mutans was2U/mL (MBIC50) and6U/mL (MBIC90). The minimum biofilm reduction concentration of S.mutans was5U/mL (MBRC50). So the action concentration of KQ11dextranase wasdeterminded as6U/mL. After treating the preformed biofilm, the dry weight of S. mutansbiofilm and dental biofilm of mixed-species were reduced by21%and17%respectively, thenumber of viable cells among the biofilms and the thickness of the biofilms also showedobvious downward trend.(5) Research about mouthwash containing dextranase of KQ11for degradating dentalbiofilm in vitro was conducted. Considering the inhibitory effect on dental biofilm and thedextranase stability, the mouthwash components of the mouthwash were as follows: SLS0.1mM, sorbitol180g/L, sodium acetate180g/L, glycerol15mL/100mL, p-hydroxy benzoicacid compound sodium ester0.4g/L, dextranase6U/mL. Then the effect of the mouthwashcomprising dextranase on dental biofilm in vitro was estimated. It was found that themouthwash containing KQ11dextranase had a better effect than the group without thedextranase, the effect on S.mutans biofilm was superior to the effect on mixed-species dentalbiofilm. In addition, the mouthwash comprising KQ11dextranase also had certaindegradation effect on the preformed dental biofilm.