Physiologic and genetic characterization of clinical isolates of Streptococcus mutans

Author(s)

Marlise Inêz Klein

• Document type: Doctoral Thesis
• Press: Piracicaba, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Odontologia de Piracicaba
• Defense date: 2006-09-25

Examining board members

Reginaldo Bruno Gonçalves; Edvaldo Antonio Ribeiro Rosa; José Francisco Höfling; Wanderley Dias da Silveira; Jaime Aparecido Cury

• Advisor: Reginaldo Bruno Gonçalves; Renata de Oliveira Mattos Graner

Abstract

Streptococcus mutans is considered the primary etiological agent of human dental caries, an important public health problem in Brazil. The purpose of this thesis was to evaluate genetic and physiologic properties related with virulence in clinical isolates of Streptococcus mutans. The quorum-sensing system, that induces and regulates genetic competence, depends on cellular density and also may play a role in biofilm growth and structure in S. mutans species. A screening of genes of the quorum-sensing system and genes involved with genetic transformation was performed. The analysis revealed that ali genes are widespread within the S. mutans species, and some genes presented polymorphisms. These data are new in the scientific literature. Furthermore, clinical genotypes of S. mutans were subjected to genetic and physiological analysis, including tolerance and acid adaptation to low pH, ability to form stable biofilm and growth kinetic under different conditions (pH and carbon source). The profile of gene expression confirms the data found in the physiologic assays. The studied strains shown heterogenic behavior at the same environmental challenge, that could favor these strains survive in the oral cavity, an environmental with several stress conditions. The data obtained here, and supported by scientific literature, suggest that besides ATPase activity' the sugar:phosphotransferase systems (PTS) could help to mount an adaptive acid tolerance response in S. mutans. Taken together all data obtained in this thesis may help to understand S. mutans biological processes. (AU)