title: Bacteriocin immunity proteins play a role in quorum-sensing system regulated antimicrobial sensitivity of Streptococcus mutans UA159.
abstract: OBJECTIVE
  Antimicrobial sensitivity of Streptococcus mutans can be modulated by putative bacteriocin immunity proteins. Bacteria use a quorum sensing (QS) system to regulate physiological activities including bacteriocin production, antimicrobial response, and biofilm formation. QS system of S. mutans is dependent on competence stimulating peptide (CSP), whose precursor is encoded by comC. However, whether bacteriocin immunity proteins play a role in QS system regulated S. mutans antimicrobial sensitivity is still unknown. We hypothesize that bacteriocin immunity proteins encoded by immA and immB play roles in QS regulated antimicrobial sensitivity in S. mutans UA159.
  
  
  METHODS
  In this study, sensitivity of S. mutans UA 159 comC mutant in planktonic and biofilm states to clinically used antimicrobials was investigated by the plate count method and confocal laser scanning microscopy. The effect of immA and immB inactivation on S. mutans antimicrobial sensitivity was studied. The expression of immA and immB in S. mutans comC mutant before and after chlorhexidine (CHX) treatment was also examined.
  
  
  RESULTS
  It was found that comC, immA and immB mutation resulted in enhanced antimicrobial sensitivity to sodium fluoride (NaF), CHX and ampicillin (AMP) in planktonic states. After 2% CHX treatment, the live/dead cell ratio in comC mutant and wild strain biofilms decreased 67% and 39% (P<0.05). The expression of immA and immB was up-regulated in wild strain after CHX treatment, while the up-regulation of immB was largely inhibited in comC mutant (P<0.05).
  
  
  CONCLUSIONS
  These findings suggest that the effect of S. mutans UA159 comC mutation on antimicrobial sensitivity can be due, in part, to attenuation of the expression of the bacteriocin immunity proteins related genes.
authors.affiliation: Institute of Stomatological Research, Guanghua School of Stomatology, Sun Yat-sen University, 74 Zhong Shan Er Road, Guangzhou, China.
authors.forename: Wei-Lu
authors.initials: WL
authors.lastname: Wang
authors.forename: Jia
authors.initials: J
authors.lastname: Liu
authors.forename: Yong-Biao
authors.initials: YB
authors.lastname: Huo
authors.forename: Jun-Qi
authors.initials: JQ
authors.lastname: Ling
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000494:pharmacology*; D001430:Bacteriocins / Q000235:genetics / Q000276:immunology*; D018441:Biofilms / Q000187:drug effects; D002710:Chlorhexidine / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial; D007109:Immunity / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D053038:Quorum Sensing / Q000187:drug effects* / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012969:Sodium Fluoride / Q000494:pharmacology; D013295:Streptococcus mutans / Q000187:drug effects* / Q000235:genetics; D015854:Up-Regulation
chemical_list: D000890:Anti-Infective Agents; D001430:Bacteriocins; D012333:RNA, Messenger; D000667:Ampicillin; D012969:Sodium Fluoride; D002710:Chlorhexidine