Molecular Typing of Dental Plaque Bacteria with Reduced Susceptibility to Chlorhexidine and Multidrug Resistance رسالة ماجستير

Abstract

Background.Chlorhexidine (CHX), is a cationic bisbiguanide biocide. It is used in oral care products to decrease plaque accumulation. Long-term use of antimicrobials such as CHX in oral care as mouthwash and toothpaste may be a contributing factor in the developing of multiple drug resistance Methods.In this study, dental plaque isolates were grown on nutrient agar containing 2 μg/ml Chlorhexidine gluconate to screen for bacteria with reduced CHX susceptibility. The isolates identified by 16S rRNA gene sequencing and disc diffusion method were used to determinein antibiotic resistance profiles. In order to determine the isolates ability to form biofilms in the presence of CHX, they were grown in microtiter plates for 2 days, then the optical density was mesured. Real time PCR was used to measure the expression of HlyD-like periplasmic adaptor gene of the tripartite efflux pump encoded by the CIN01S_RS05745 locus following exposure to 2μg/ml CHX in the resistant bacteria. Results. The isolates were found to be sensitive to variable antibiotics including vancomycin, erythromycin, and amikacin. Two bacterial species isolates, Bacillus stratosphericus and Bacillus aerphilus, were able to grow planktonically and form biofilms in the presence of 3.3 μg/ml CHX. One bacterial isolate, Aggregatibacter, showed significant resistance to CHX and demonstrated significant expression of the HlyD-like periplasmic adaptor gene of the tripartite efflux pump encoded by the CIN01S_RS05745 locus following exposure to 2μg/ml CHX. This indicates the may pump play a direct role and mediate the bacterial resistance to CHX since in its absence, the expression of this gene was not detected. Conclusions. The use of mouth wash containing CHX should be accompanied with vigilance about the development of resistant bacteria to the drug and other antibiotics following long term exposure to these compounds.