Identification of the oral microbiome in people with dementia in residential aged care

Background: The composition and distribution of normally inhabiting oral microflora are key determinants of oral and overall health. A symbiotic relationship between the human host and the oral microbiome promotes health while a dysbiosis results in opportunistic infections due to overgrowing normal flora or colonisation by pathogens. An altered diversity of the oral microbiome and an abundant load of harmful microorganisms in the mouth increase the risk of systemic diseases such as aspiration pneumonia for people with dementia. The four Aims and results of this thesis follow: Aim 1 involved a systematic review of published literature to identify oral pathogens associated with aspiration pneumonia and examine the evidence for the effect of professional oral care in reducing aspiration pneumonia risk for people in residential aged care. Seven databases (PUBMED/MEDLINE, CINAHL, EMBASE, COCHRANE, PROQUEST, Google Scholar, and Web of Science) were searched for relevant articles. Data were analysed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The isolation of yeast, Candida albicans (C. albicans), and bacteria of non-oral origin, for example, Escherichia coli (E. coli), was associated with mortality due to aspiration pneumonia. In addition, the beneficial effects of professional oral care in decreasing the incidence of aspiration pneumonia in aged care residents were documented. Aim 2 characterised the oral microbiome (load and type of bacteria and fungi) of people with dementia in residential aged care. Oral swabs were taken from cheek, gum, and tongue mucosa; microbial DNA were extracted, ribosomal rRNA (16S and 18S) were sequenced, and bioinformatic and statistical analyses conducted. There were no significant differences between the three sites for load of bacteria (H (2) = .89; p = .64); there were significant differences between the three sites for the type of bacteria (F (2,78) = 11.97; p <.0001) with the tongue showing the greatest diversity. The predominant bacteria belonged to the phylum Firmicutes. There were no significant differences between the three sites for load (H (2) = 2.94; p = .23) or type (F (2,77) = .46; p = .63) of fungi. The predominant fungus was yeast, Saccharomyces. Aim 3 investigated the effect of regular compared to evidence-based oral care on the oral microbiome over a six-week period. Participants with dementia self-selected into Control (n = 10) and Experimental (n = 17) Groups. Microbial sequence data from cheek, gum, and tongue mucosa, collected pre- and post-intervention, documented that evidence-based oral care resulted in significant decreases in four potentially pathogenic bacterial species and an increased abundance of Lactobacillus reuteri, a host-protective normal flora in the mouth, compared to regular oral care. There were no significant differences between groups for the abundance and type of fungi. Aim 4 explored if six weeks of evidence-based oral care could significantly reduce the absolute count of six oral pathogens specifically related to aspiration pneumonia. A quantitative polymerase chain reaction analysis of cheek, gum, and tongue specimens showed statistically significant reductions in absolute count for E. coli for cheek, gum, and tongue samples considered together (p = .0002) and for cheek (p = .01), tongue (p = .01) and gum (p = .04) samples considered separately. A significant reduction for E. coli was also noted for Control Group participants when samples from all three sites were considered together (p = .002) and for samples from the cheek (p = .02). There was no significant finding for the fungus, C. albicans. The remaining four pathogenic bacteria were unable to be analysed due to insufficient DNA concentrations in the samples. Conclusions from these studies were that next generation sequencing to document the type and load of bacteria and fungi in the mouths of people with dementia in residential care was valuable in: 1. Identifying potential pathogenic microorganisms in the mouth, including E. coli, gut-based bacteria, 2. Documenting the positive effect of evidence-based compared to regular oral care to decrease aspiration pneumonia risk, 3. Highlighting the importance of attention to the tongue, cheek, and gum in daily oral care, and 4. Supporting the call for increased involvement of dentists and oral health therapists in residential care to guide staff and promote the health and wellbeing of residents who are dependent on others for oral care.