The Effects Of Lactobacillus Salivarius ZM06 On Biofilm Formation And Genetic Transformation By Streptococcus Mutans

Oral health is ranked as one of the top ten criteria for human health by World Health Organization.Dental caries is one of the most prevalent chronic diseases of people worldwide.According to statistics,60% to 90% of school-age children and nearly 100% of adults worldwide suffer from dental caries.Streptococcus mutans is considered the principal bacterium responsible for dental caries.Nine probiotic strains of nine species were investigated for their ability to inhibit S.mutans biofilm formation using transwell-based co-culturing and a nonconnect method.The Lactobacillus salivarius ZM06 was selected for further study of its possible inhibition mechanisms and effects of genetic transformation by S.mutans.The results showed that ZM06 worked not by killing S.mutans directly but by reducing biofilm formation by S.mutans.This was confirmed by a biofilm formation assay and scanning electron microscopy.The down-regulation of biofilm formation-associated genes expression was also observed in S.mutans,including gtfB,gtfC,ftf,gbpB and gbpC.Notably,ZM06 also affected the expression of key genes in 5 signaling pathways involved in the regulation of biofilm formation in S.mutans.The gene expression analysis showed that ZM06 not only downregulated the luxS gene expression in the interspecies quorum sensing(QS)system of S.mutans but also reduced the expression of key genes(vicK,vicR,ciaH,ciaR,hk11,rr11,comD and comE)in 4 additional S.mutans signal pathways,including TCS-1(VicKR),TCS-2(CiaHR),TCS-11(HK11/RR11)and TCS-13(ComDE).These gene changes had not been previously reported in the use of probiotics against S.mutans biofilm formation.However,although ZM06 decreased the genetic transformation by S.mutans,the result was not significant.Thus,the possible mechanism may be that the signal molecules secreted by ZM06 downregulated the expression of key genes of 5 signal pathways of S.mutans,further downregulated the expression of genes directly associated with biofilm formation,and consequently,reduced the biofilm formation of S.mutans.