Abstract
BackgroundChlorhexidine (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.ResultsThe 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.ConclusionsThe 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.
Highlights
Chlorhexidine (CHX) is used in oral care products to help control dental plaque
Genomic DNA was extracted from the isolates and the 16S rRNA gene sequenced
Maximum identities were found to Chryseobacterium culicis, Chryseobacterium indologenes, Acinetobacter johnsonii, Enterobacter ludwigii, Pseudomonas stutzeri and Streptococcus salivarius (Table 1)
Summary
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 main cause of these diseases is the complex microbiota established as dental plaque, a complex microbial biofilm [2] containing over 750 different bacterial species [3]. Bacterial biofilms show increased tolerance to antibiotics and antiseptics and resist phagocytosis as well as other components of host defense, which can lead to chronic infections [4, 5]. Some resistance has emerged in clinical isolates with reduced susceptibility to CHX such as multiresistant Staphylococcus aureus [17] and other
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