Antibiotic resistance in healthcare settings. Prevalence and levels of tet(M) resistance gene in saliva of dental students

Rationale: Antibiotic resistance compromises achievements of modern medicine and is a major threat to the society. The oral cavity has the distinct microbial community that serves as a reservoir for determinants of antibiotic resistance. Tet(M) gene is abundant in bacteria residing in the oral cavity and is often identified in oral specimens. Absolute quantification of resistance genes copies allows quantitative studying the factors possibly associated with these numbers. Bacterial aerosol at the workplace may pose occupational risk. Exposure to aerosolized bacteria may contribute to increased resistance genes copy numbers in oral bacteria of dental personnel. Objective: To investigate the prevalence and levels of tet(M) resistance gene in saliva samples collected from two observational groups and any associated factors that might influence the levels of tet(M). Methods: Saliva samples were collected from 83 healthy dental students of Institute of clinical dentistry, UiT, Norway, in the period from 1 June to 27 November 2015. The study participants were grouped by their study year: 41 newly recruited students and 42 senior students. The latter were exposed to dental office environment as a part of the practice skill exercises. The quantification of tet(M) gene copies in DNA extracted from the saliva samples was done using droplet digital PCR (ddPCR) methodology. Self-administered questionnaires were distributed in order to obtain demographic and health-related variables. To find out whether the two observational groups had different number of tet(M) gene copies, Mann-Whitney-Wilcoxon test was used. Pearson's correlation coefficient and the linear regression analysis were used to reveal any association between antibiotic consumption and tet(M) gene copy numbers found in the samples. Results: Each saliva sample was positive for tet(M) gene (100% prevalence). The number of tet(M) gene copies was not significantly different between the two groups with and without exposure to dental office environment. The history of antibiotic courses taken in the past was not correlated with tet(M) gene copy number. Conclusion: exposure to dental office environment does not influence significantly the tet(M) gene copy number in saliva samples in the study population. The number of antibiotic courses did not seem to be associated with the tet(M) copy numbers.