Host_microbe_ES_06052024.pdf

Microbe-host interaction Presented by Dr Eby Sim Faculty of Medicine and Health [email protected] Originally developed by: Dr Christina Adler Faculty of Medicine and Health The University of Sydney Page 1  Learning objectives Define the terms commensals, s...

Microbe-host interaction Presented by Dr Eby Sim Faculty of Medicine and Health [email protected] Originally developed by: Dr Christina Adler Faculty of Medicine and Health The University of Sydney Page 1  Learning objectives Define the terms commensals, symbiosis and colonization Understand that humans are holobionts Understand why different bacteria colonise different body sites Understand why commensal microorganisms are beneficial to us The University of Sydney Page 2  Host – microbe interactions The University of Sydney Page 3  Definitions Infection/Colonisation: acquisition of micro-organisms by the host Commensalism: a state of infection that results in no damage to the host Symbiosis/mutualism: a state of infection where both the host and microbe benefit The University of Sydney Page 4  Humans as holobionts – Holobiont = host + microbiome – Microbiome = all microbes that share our body space – Humans carry 1014 microbial cells and 1013 human cells – Humans need our microbiome: – Beneficial tasks – Protection from foreign substances and pathogens The University of Sydney Page 5  Microbiome - commensals – ‘Normal’ microbes present on the skin and in the oral, respiratory and gastrointestinal tracts. Not internal tissues. – Protect host against pathogens – Provide nutrients for host – Acquired in first year of life The University of Sydney Page 6  Microbiome composition – Huge diversity in composition – Bacteria – Fungi – Viruses – Some members are culturable, most cannot be cultured. – Culture-independent methods The University of Sydney Page 7  16S ribosomal RNA sequencing – 16S rRNA, a subunit of the ribosome – Slow rate of evolution. – Highly-conserved between bacteria and archaea. – But has hypervariable regions to study diversity López-Aladid, R., (2023) Sci Rep. doi: 10.1038/s41598-023-30764-z The University of Sydney Page 8  Shotgun metagenomics – Sequencing of every nucleic acid within a given sample. – DNA and/or RNA – Bacteria – Viruses – Fungi – Even host… – Allows for extended characterisation of the “community” – Subtyping – AMR genes – Virulence genes The University of Sydney Page 9  Metagenomics can be used for insights into population dynamics The University of Sydney Page 10  Host microbiome varies with body site The University of Sydney Page 11  Skin microbiota – Environment: slightly acidic, high salt, low water content and inhibitory substances – Bacteria on superficial skin (dead cells) and sweat glands – Bacteria partially degrade Carmona-Cruz S, et al., (2022) Front Cell Infect skin oil to volatile fatty acids Microbiol. doi: 10.3389/fcimb.2022.834135. = body odour The University of Sydney Page 12  Respiratory microbiota Natalini, J.G. (2023) Nat Rev Microbiol. doi:10.1038/s41579- 022-00821-x The University of Sydney Page 13  Gut microbiota – Stomach = highly acidic, few viable bacteria – Small intestine = acid + bile juices, few viable bacteria – Large intestine = huge diversity 1012 cells/gram stool – Symbiotic relationships: – Produce biotin and vitamin K – Prevent pathogens from colonizing. – Absorption of nutrients The University of Sydney Page 14  Oral microbiota – Mouth colonized soon after birth – After tooth eruption, increase in anaerobes (Porphymonas, Prevotella and Fusobacterium sp.) – Symbiotic relationship: – Oral microbiota alter taste perception – Super-tasters vs non- tasters – Varied tongue microbiota Cattaneo C, Gargari G, Koirala R, et al. New insights into the relationship between taste perception and oral microbiota composition. Sci Rep. 2019;9(1):3549. The University of Sydney Page 15  Changes to the oral microbiota Vanhatalo, A., et al., Nitrate-responsive oral microbiome modulates nitric oxide homeostasis and blood pressure in humans. Free Radic Biol Med, 2018. 124: p. 21-30. The University of Sydney Page 16  Homeostasis and dysbiosis Example of dysbiosis: Obesity – Germ free (GF) versus conventional mice – Same diet – GF mice could eat more and gain less weight than conventional mice – Microbiota affected caloric absorption Dental conditions caused by microbiome dysbiosis – Dental caries – Periodontal disease Bäckhed, F. et al. The gut microbiota as an environmental factor that – Oral cancer regulates fat storage. Proc. Natl Acad. Sci. USA 101, 15718–15723 (2004). The University of Sydney Page 17  Summary – Humans are holobionts. – Microbes can either be beneficial or cause harm. – The microbiome across the human body is diverse. – Microbiome can be in flux. The University of Sydney Page 18