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Background: The treatment of polymicrobial biofilms with antimicrobial compounds results in not only an overall loss of viability, but also compositional shifts. While DNA-based technologies may be more appropriate for the assessment of bacterial composition than culturing, these techniques amplify DNA from both live and dead cells. Propidium monoazide (PMA) has been used to discriminate between live and dead cells by blocking the DNA from membrane-damaged cells from being amplified. Aim: This study evaluated the use of PMA in a saliva-derived polymicrobial biofilm model subjected to a single chlorhexidine (CHX) treatment. Materials and Methods: The effects of PMA on viable cells were tested using both untreated and PMA-treated saliva as an inoculum. Viability was determined by plate counts, metabolic activity was determined by lactic acid production, and biofilm composition was assessed by 16S rRNA gene amplicon sequencing. Results: Exposure to a 0.2% CHX rinse (meridol® perio) reduced the viability and metabolic activity of 48-hour biofilms. The shift in biofilm composition observed after the CHX exposure was enhanced after a post-rinse PMA treatment. PMA treatment had a small effect on the measured composition of water-rinsed biofilms. Treating saliva with PMA reduced bacterial viability and shifted the bacterial composition of saliva and saliva-derived biofilms. Conclusion: The removal of DNA from non-viable cells with PMA treatment was shown to elicit an improvement in the detection of shifts in in vitro polymicrobial biofilms after antimicrobial treatment. However, PMA also influenced the ability of cells to grow, indicating that PMA should be used with caution. © 2014 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Streptococcal cell wall (SCW)-induced arthritis is a chronic, erosive polyarthritis that can be induced in susceptible Lewis rats by one i.p. injection of an aqueous, slerile suspension of SCW. F344 rats are resistant to chronic joint inflammation. Our previous studies showed a correlation between susceptibility to SCW-induced arthritis and the ability to mount SCW-specific T cell responses, suggesting tolerance to SCW as a putative mechanism. Here we prevented the induction of tolerance lo bacterial epitopes in F344 rats by using them germ-free and analysed susceptibility to arthritis subsequently. In addition, we conventionalized germ-free F344 rats at different times before induction of arthritis. Our results show that germ-free F344 rats are susceptible to SCW-induced arthritis with a similar severity, chronicity. incidence and onset as Lewis rats. Moreover. T cells isolated from germ-free F344 rats were able to respond to SCW. Conventionalization dramatically moderates arthritis and makes T cells unresponsive to SCW again. Thus, in normal rats (F344) a stale of tolerance to arthritogenic epilopes is induced (neonatally) and maintained through life by the bacterial flora, resulting in resistance to bacterium-induced artritides. In arthritis-prone (Lewis) rats, this tolerance is deficient and/or easily broken. [ABSTRACT FROM AUTHOR]