Effect of Veillonella parvula on the antimicrobial resistance and gene expression of Streptococcus mutans grown in a dual-species biofilm

Introduction: Our previous studies showed that Streptococcus mutans and Veillonella parvula dual-species biofilms have a different acid production profile and a higher resistance to chlorhexidine than their single-species counterparts. The aim of the current study was to test whether the susceptibility of S. mutans grown in the presence of V. parvula is also decreased when it is exposed to various other antimicrobials. Furthermore, the aim was to identify other changes in the physiology of S. mutans when V. parvula was present using transcriptomics. Methods: Susceptibility to antimicrobials was assessed in killing experiments. Transcript levels in S. mutans were measured with the help of S. mutans microarrays. Results: When V. parvula was present, S. mutans showed an increase in survival after exposure to various antimicrobials. Furthermore, this co-existence altered the physiology of S. mutans. The expression of genes coding for proteins involved in amino acid synthesis, the signal recognition particle-translocation pathway, purine metabolism, intracellular polysaccharide synthesis, and protein synthesis all changed. Conclusion: Growing in a biofilm together with a non-pathogenic bacterium like V. parvula changes the physiology of S. mutans, and gives this bacterium an advantage in surviving antimicrobial treatment. Thus, the study of pathogens implicated in polymicrobial diseases, such as caries and periodontitis, should be focused more on multispecies biofilms. In addition, the testing of susceptibility to currently used and new antimicrobials should be performed on a multispecies microbial community rather than with single pathogens.