OBJECTIVETo investigate the changes in the expression level of sRNA SpR19 and its potential target protein GroEL in clinical isolates of Streptococcus mutans with different cariogenicity exposed to different pH conditions and explore the possibility of using these molecules as biomarkers for assessing the cariogenicity of the bacteria.

METHODSThe total RNAs were extracted from the clinical isolates of Streptococcus mutans with high (strain 17) and low cariogenicity (strain 5) for high-throughput sequencing for profiling of the differentially expressed sRNAs. The candidate sRNA, SpR19, was selected for further study on the basis of bioinformatics analysis considering the role of its potential target in the cariogenic process. The differential expression levels of SpR19 in the strains exposed to both pH5.5 and pH7 culture conditions were verified by quantitative real-time PCR. The expression of the potential target of SpR19, GroEL, was also investigated at both the protein and mRNA level using Western blotting and quantitative real-time PCR.

RESULTSBioinformatic analysis suggested multiple potential target sites of SpR19 both in GroEL mRNA and in the upstream and downstream inter-genic regions. Under different pH conditions, the highly cariogenic strain 17 expressed consistently low levels of SpR19 as compared with the strain 5 with a low cariogenicity; GroEL showed a reverse expression pattern in the 2 strains. An inverse correlation was found between the expressions of SpR19 and GroEL.

CONCLUSIONThe highly cariogenic strain 17 expressed low levels of SpR19 and high levels of GroEL in both acidic and neutral culture conditions. SpR19 may negatively regulate the cariogenicity of Streptococcus mutants by targeting at GroEL.