Page 11 - MDJ Volume 47 Number 2 ( Jul-Dec 2024)

Babu Osman, et al.: Oral microbiome in the elderly
have been observed in patients with chronic systemic Several studies have shown that Actinomyces spp. play a
diseases such as DM and Crohn’s disease, often related to significant role in the onset of root surface caries. [54,56,57]
diet and nutrition. The association between the gut and It is interesting to explore whether dysbiosis in diabetic older
[44]
oral microbiota remains unclear, but the oral microbiota adults causes alterations in the oral microbiome, leading
is thought to change in response to local and general to a higher incidence of dental caries. A study examining
conditions. The oral microbiome plays a crucial role in the oral microbial composition in T2DM patients found
[45]
maintaining a normal oral ecological balance and in the an abundance of Aggregatibacter, Neisseria, Gemella,
development of oral diseases. Significant evidence supports Eikenella, Selenomonas, Actinomyces, Capnocytophaga,
the association between endogenous and exogenous Fusobacterium, Veillonella and Streptococcus genera in
factors, oral microbiota and systemic disorders. The the subgingival area. Another study found significantly
[46]
[58]
oral microbiota is colonised by a variety of bacteria, higher levels of Actinomyces and Selenomonas and lower
with more than 700 bacterial species identified to date. levels of Alloprevotella in diabetic patients compared to
[10]
The dominant bacterial phyla in the oral microbiota are non-diabetics. This suggests that environmental changes
[59]
Firmicutes, Actinobacteria, Fusobacteria, Proteobacteria in the oral cavity and the destruction of the host immune
and Bacteroidetes, which normally co-exist harmoniously system due to DM tend to affect the oral microbiome
with the host. [47]
[44]
composition. The presence of Porphyromonas gingivalis
Dysbiosis, a microbial imbalance, can occur due to in a periodontal disease activates periodontal tissue
behavioural factors such as poor diet and oral hygiene degradation and increases insulin resistance. A study by
or deteriorating general health due to reduced immune Long et al. compared the oral microbiome profiles of
system, medications, medical conditions and genetics. diabetic African Americans with non-diabetics and found
Dental caries is not caused by a single pathogen but by that a higher abundance of bacteria phylum Actinobacteria
a dysbiotic microbial community, characterised by an was associated with lower diabetes risk. These studies
[45]
imbalance leading to an overabundance of acidogenic show that the oral microbiome is an important factor for
[10]
and aciduric bacteria. These bacteria lower the pH the maintenance of human health and thus unravelling the
in the oral environment, promoting demineralisation relationship between diabetes and the oral microbiome is
and inhibiting the growth of beneficial, non-cariogenic of utmost interest.
[48]
microorganisms. Figure 1 illustrates the process
by which caries can develop as a result of dysbiosis. MetagenoMIc sequencIng In oral MIcrobIoMe
S. mutans and Streptococcus sobrinus are the most
prevalent cariogenic species in humans, found in higher analysIs
proportions in caries-active individuals compared to Metagenomics has significantly advanced our
caries-free ones. [49,50] Although lactobacilli are significant understanding of dental caries by identifying microbial
contributors to dental caries, [51-53] there is little evidence to communities and their functional capabilities. NGS employs
support their role in caries initiation. Despite being highly metagenomic technology to identify and characterise
aciduric and acidogenic, lactobacilli do not colonise the genomes of microorganisms such as bacteria, viruses
tooth enamel and are often cultured from established and fungi. NGS allows for the detailed analysis of raw
[54]
carious lesions instead. Non-mutans streptococci, or amplified DNA from microbial communities like the
including Streptococcus sanguinis, Streptococcus oralis, oral microbiome. Unlike earlier genetic research that
Streptococcus gordonii and Streptococcus mitis, also only assessed the presence or absence of oral microbiota,
play a role in dental caries. [54,55] However, compared to metagenomic sequencing provides valuable information on
mutans streptococci and lactobacilli, there is still a lack of the function of the oral microbiome by directly sequencing
evidence of their pathogenicity in experimental animals. the majority of DNA present in a sample, capturing a wide

Figure 1: Microbial imbalance (dysbiosis) leading to dental caries

Malaysian Dental Journal ¦ Volume 47 ¦ Issue 2 ¦ July-December 2024 5