Human Microbiota Overview
Human Microbiota
Human Microbiota Overview
Locations in the human body that host diverse microbial communities.
Microbiota typically refers to the organisms that live in symbiotic relationships.
Symbiosis defined as "to live together" and includes several types of relationships:
Mutualism: both organisms benefit.
Commensalism: one organism benefits while the other is neither helped nor harmed.
Parasitism: one organism benefits at the expense of the other.
Composition of Human Microbiota by Body Site
Eye (Transient)
Major bacteria:
Staphylococcus (coagulase-negative)
Nose
Major bacteria:
Staphylococcus (coagulase-negative)
S. aureus
Haemophilus spp.
Viridans streptococci
Streptococcus pneumoniae
Skin
Major bacteria:
Staphylococcus (coagulase-negative)
S. aureus
Propionibacterium acnes
Haemophilus spp.
Viridans streptococci
Mycobacterium spp.
Bacillus spp.
Urethra
Major bacteria:
Staphylococcus (coagulase-negative)
S. aureus
Diphtheroids
Bacteroides spp.
Viridans streptococci
Mycobacterium spp.
Fusobacterium spp.
Peptostreptococcus spp.
Candida spp.
Vagina
Major bacteria:
Lactobacillus spp.
Peptostreptococcus spp.
Diphtheroids
Viridans streptococci
Bacteroides spp.
Gardnerella vaginalis
Candida spp.
Clostridium spp.
Ear
Major bacteria:
Staphylococcus (coagulase-negative)
Diphtheroids
Pseudomonas spp.
Enterobacteriaceae
Stomach
Major bacteria:
Staphylococcus (coagulase-negative)
Lactobacillus spp.
Viridans streptococci
Helicobacter spp.
Small Intestine
Major bacteria:
Lactobacillus spp.
Bacteroides spp.
Viridans streptococci
Clostridium spp.
Enterococcus spp.
Enterobacteriaceae
Oropharynx
Major bacteria:
Staphylococcus (coagulase-negative)
S. aureus
Haemophilus spp.
Viridans streptococci
Streptococcus pneumoniae
Veillonella spp.
Prevotella spp.
Fusobacterium spp.
Candida spp.
Moraxella spp.
Neisseria spp.
Actinomyces spp.
Eikenella corrodens
Large Intestine
Major bacteria:
Bacteroides spp.
Fusobacterium spp.
Staphylococcus (coagulase-negative)
S. aureus
Escherichia coli
Proteus spp.
Klebsiella spp.
Pseudomonas spp.
Peptostreptococcus spp.
Actinomyces spp.
Mycobacterium spp.
Enterococcus spp.
Acinetobacter spp.
Learning Outcomes
Compare the composition of microbiomes from different areas of the body.
List the benefits provided by our microbiota.
Explain the intercommunication mechanisms between human cells and microbiota.
Discuss how the human body utilizes microbiota to prevent infections.
Describe the hygiene hypothesis and its potential role of microbiota in preventing allergies and other modern diseases.
Benefits of Human Microbiota
General Characteristics:
Microbiota colonization begins in utero and continues through birth and external environmental exposure.
Most microbial species are largely unidentified and exhibit individuality across human hosts as suggested by metagenomic DNA sequencing.
Microbiota is dynamic and reacts to changes in diet, social connections, and pet exposures.
Resident Microbiota
Characteristics:
Persist for a lifetime on the host.
Primarily commensal.
Established significantly during the early months post-birth.
Transient Microbiota
Characteristics:
Temporary presence in the host’s environment.
Exhibit similar locations to resident microbiota but unable to establish long-term presence due to:
Competitive interaction with resident microbiota.
Elimination by host immune responses.
Changes in host environment affecting viability.
Microbial Ecosystems
Skin: 10^4 - 10^6 cfu/sweat gland; 1:10 aerobic to anaerobic ratio. Primary sources include birth canal, oral and external environments.
Mouth: 10^6 - 10^8 cfu; 1:10 aerobic to anaerobic ratio. Initial acquisition from birth canal, caregivers, and then food, water, and fingers.
Genitourinary Tract: 10^8 - 10^9 cfu/vagina/urethra; 1:100 aerobic to anaerobic ratio. Microbiota originates from the surrounding environment.
Intestine: 10^11 cfu/cm³; 1:1,000 aerobic to anaerobic ratio; predominantly established as a fetus, followed by nutrition from mother and subsequent food and water ingestion.
Skin Microbiota
Functions:
Prevention of excessive water loss and temperature regulation.
Act as a barrier against pathogens with thick skin layers made primarily of dead cells, limiting pathogen infiltration.
Populated predominantly by Gram-positive bacteria due to their resilience to dryness and salt.
Common Skin Bacteria:
Staphylococcus epidermidis.
Propionibacterium acnes: associated with acne.
Eye Microbiota
Colonization:
Eye is protected by the lacrimal apparatus which produces tears containing lysozyme that can destroy bacteria.
Common conditions such as pink-eye may result from bacterial infections like Streptococcus pneumoniae
Oral and Nasal Cavities Microbiota
Engagement through adherence on teeth and gums predominantly via glycocalyx; biofilm formation leads to dental issues.
Common bacterium includes Streptococcus thermophilus associated with oral cavity health.
Gastrointestinal Tract Microbiota
Stomach: Very acidic; majority of microbes are killed but organisms like Helicobacter pylori employ mechanisms to survive (urease activity increases local pH).
Small Intestine: Bile salts influence the microbial population and prevent imbalances.
Conclusion
The interplay between microbiota, nutrition, and health is complex. Advances such as Fecal Microbiota Transplants (FMTs) and understanding of microbial roles indicate promising future directions to enhance health and mitigate disease.