Combined effect of arginine and fluoride on the growth of Lactobacillus rhamnosus GG

Abstract

The\xa0objectives of the in vitro study\xa0were: (1)\xa0to investigate the effect of combining L-arginine (Arg)\xa0and NaF on the growth of\xa0 Lactobacillus rhamnosus\xa0 GG (LRG); and (2) to identify an optimum synergistic concentration for the synbiotic (Arg\u2009+\u2009LRG)-fluoride (SF) therapy.\xa01% Arg\u2009+\u20092000-ppm NaF (A-SF)\xa0and 2%\xa0Arg\u2009+\u20092000-ppm NaF (B-SF) demonstrated antagonism against LRG (FIC\u2009>\u20094.0). Both XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) and WST-8 (2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt) assays showed that A-SF and B-SF enhanced\xa0the\xa0growth of LRG when compared to 2000-ppm NaF and LRG control. Colony forming units, bacterial weight, and biofilm thickness of\xa0A-SF and B-SF were significantly higher than 2000-ppm NaF\xa0and LRG control. Biofilm imaging depicted that 2000-ppm NaF inhibited biofilm formation; while 1%/2% Arg, A-SF, and B-SF increased biofilm growth of LRG.\xa0Lactic acid formation was the lowest for 2000-ppm NaF, followed by A-SF and then B-SF. The SF buffer potential after 24\xa0h was the highest for B-SF, and then A-SF. Biofilm pH for B-SF was closest to neutral. Fluoride,\xa0Arg\xa0and LRG\xa0bioavailability remained unaffected in B-SF.\xa0The relative gene expression for\xa0 arcA , argG ,\xa0and\xa0 argH \xa0was significantly higher for B-SF than the respective controls.\xa0In conclusion, combining 2% Arg,\xa02000-ppm NaF, and\xa0LRG provides an optimum synbiotic-fluoride synergism.