Abstract: Objective: To construct Streptococcus mutans (S.mutans) fluoride-resistant strain UA159-FR with gtfB gene inactive to investigate the function of gtfB gene in fluoride-resistant strain. Methods: The S.mutans fluoride-resistant strain UA159-FR was cultured and used as a template to amplify the upstream and downstream homologous arm fragments of the gtfB gene. The kan gene was amplified by using the plasmid pEGFP-N1 as a template. Homologous recombination fragments of three fragments were obtained by overlap extension polymerase chain reaction (OE-PCR) and ligated with pEASY-Blunt Cloning Vector to form recombinant plasmids. The recombinant plasmids were identified by PCR and sequencing. The recombinant fragment was electrotransformed into UA159-FR competent cells to obtain the inactivated strain and identified by PCR. Results: The recombinant plasmids were successfully constructed via being identified by PCR and sequencing. It was identified by PCR that UA159-FR with gtfB gene inactive was obtained. Conclusion: The recombinant fragments of gtfB gene of S.mutans with its recombinant plasmids and the S.mutans fluoride-resistant strain UA159-FR with gtfB gene inactive were successfully constructed and could be used to study the function of gtfB gene.

Key words: Fluoride-resistant streptococcus mutans, GtfB gene, Overlap extension polymerase chain reaction, Homologous recombination, Gene inactivation