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ABSTRACTBackground Bacteria respond to changes in their environment, such as nutrient depletion and antimicrobials exposure. Antimicrobials result not only in bacterial death, but also have a hand in determining species abundances and ecology of the oral biofilms. Proximity of dead bacterial cells to living ones is an important environmental change or stress factor. Dead bacteria represent high concentrations of nutrients, such as proteins, lipids, sugars, and nucleic acids. Living bacteria can use these biomasses as a nutrients source, which is termed necrotrophy.Aim This study investigates the effect of exposing living oral bacteria (planktonic and biofilms) to their dead siblings after being killed by heat or hydrogen peroxide.Results Tested bacterial species showed different responses towards the dead cells, depending on the mode of killing, the nutritional value of the culture media, and the the dead cells density. The multispecies oral biofilms showed different responses towards the supplementation of dead cells during biofilm development, while matured biofilms were more resilient.Conclusion This study indicates that dead bacteria resulting from antiseptics use may imbalance the nutrient availability in the oral cavity, resulting in overgrowth of opportunistic species, and hence ecological changes in oral communities, or introducing new bacterial phenotypes.

Background: Modulation of the commensal oral microbiota constitutes a promising preventive/therapeutic approach in oral healthcare. The use of prebiotics for maintaining/restoring the health-associated homeostasis of the oral microbiota has become an important research topic. Aims: This study hypothesised that in vitro 14-species oral biofilms can be modulated by (in)direct stimulation of beneficial/commensal bacteria with new potential prebiotic substrates tested at 1 M and 1%(w/v), resulting in more host-compatible biofilms with fewer pathogens, decreased virulence and less inflammatory potential. Methods: Established biofilms were repeatedly rinsed with N-acetyl-D-glucosamine, α-D-lactose, D-(+)-trehalose or D-(+)-raffinose at 1 M or 1%(w/v). Biofilm composition, metabolic profile, virulence and inflammatory potential were eventually determined. Results: Repeated rinsing caused a shift towards a more health-associated microbiological composition, an altered metabolic profile, often downregulated virulence gene expression and decreased the inflammatory potential on oral keratinocytes. At 1 M, the substrates had pronounced effects on all biofilm aspects, whereas at 1%(w/v) they had a pronounced effect on virulence gene expression and a limited effect on inflammatory potential. Conclusion: Overall, this study identified four new potential prebiotic substrates that exhibit different modulatory effects at two different concentrations that cause in vitro multi-species oral biofilms to become more host-compatible.