title: Dental plaque bacteria with reduced susceptibility to chlorhexidine are multidrug resistant.
abstract: Chlorhexidine (CHX) is used in oral care products to help control dental plaque. In this study dental plaque bacteria were grown on media containing 2 μg/ml chlorhexidine gluconate to screen for bacteria with reduced CHX susceptibility. The isolates were characterized by 16S rRNA gene sequencing and antibiotic resistance profiles were determined using the disc diffusion method.
  
  
  
  The isolates were variably resistant to multiple drugs including ampicillin, kanamycin, gentamicin and tetracycline. Two species, Chryseobacterium culicis and Chryseobacterium indologenes were able to grow planktonically and form biofilms in the presence of 32 μg/ml CHX. In the CHX and multidrug resistant C. indologenes we demonstrated a 19-fold up-regulation of expression of the HlyD-like periplasmic adaptor protein of a tripartite efflux pump upon exposure to 16 μg/ml CHX suggesting that multidrug resistance may be mediated by this system. Exposure of biofilms of these resistant species to undiluted commercial CHX mouthwash for intervals from 5 to 60 s indicated that the mouthwash was unlikely to eliminate them from dental plaque in vivo.
  
  
  
  The study highlights the requirement for increased vigilance of the presence of multidrug resistant bacteria in dental plaque and raises a potential risk of long-term use of oral care products containing antimicrobial agents for the control of dental plaque.
authors.affiliation: Department of Microbiology and Molecular Genetics, University of the Punjab Quaid-e-Azam Campus, Lahore, Pakistan.|Oral Health Cooperative Research Centre, Melbourne Dental School, and The Bio21 Institute, The University of Melbourne, Melbourne, VIC, 3010, Australia.
authors.forename: Hafiz Ghulam Murtaza
authors.initials: HG
authors.lastname: Saleem
authors.affiliation: Oral Health Cooperative Research Centre, Melbourne Dental School, and The Bio21 Institute, The University of Melbourne, Melbourne, VIC, 3010, Australia.
authors.forename: Christine Ann
authors.initials: CA
authors.lastname: Seers
authors.affiliation: Department of Microbiology and Molecular Genetics, University of the Punjab Quaid-e-Azam Campus, Lahore, Pakistan.
authors.forename: Anjum Nasim
authors.initials: AN
authors.lastname: Sabri
authors.affiliation: Oral Health Cooperative Research Centre, Melbourne Dental School, and The Bio21 Institute, The University of Melbourne, Melbourne, VIC, 3010, Australia. e.reynolds@unimelb.edu.au.
authors.forename: Eric Charles
authors.initials: EC
authors.lastname: Reynolds
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D001483:Base Sequence; D018441:Biofilms / Q000187:drug effects; D002710:Chlorhexidine / Q000008:administration & dosage / Q000494:pharmacology*; D045247:Chryseobacterium / Q000187:drug effects; D003773:Dental Plaque / Q000382:microbiology*; D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods; D004352:Drug Resistance, Microbial; D024901:Drug Resistance, Multiple, Bacterial; D005839:Gentamicins / Q000494:pharmacology; D007612:Kanamycin / Q000494:pharmacology; D008826:Microbial Sensitivity Tests / Q000379:methods; D050296:Microbial Viability / Q000187:drug effects; D009067:Mouthwashes / Q000494:pharmacology; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013752:Tetracycline / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D005839:Gentamicins; D009067:Mouthwashes; D012336:RNA, Ribosomal, 16S; D007612:Kanamycin; D000667:Ampicillin; D013752:Tetracycline; D002710:Chlorhexidine
keywords: Antimicrobial resistance; Chlorhexidine; Chryseobacterium culicis; Chyseobacterium indologenes