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Human Microbiome
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Human Microbiome

Overview
  • The normal human flora comprises bacteria and yeasts; moreover, bacterial cells outnumber the host's cells by 10:1.
  • Microorganisms of the normal flora are "commensals" because they benefit the host, but do not harm it.
  • Individual's specific microbiome is influenced by hygiene, diet, water sources, drugs and medications, and exposure to environmental toxins.
  • The normal flora impacts human health and disease:
– The microbiome guides immune system development. – Protects against colonization by pathogenic microbes; and, in the gut, contributes to digestion and metabolism. – The human microbiome is also associated with pathology.
  • Opportunistic pathogens are members of the normal flora that cause disease in immunosuppressed individuals or if the microbes move to a new anatomical niche.
  • Strict pathogens are micro-organisms that always cause disease.
  • Dysbiosis, aka, dysbacteriosis, occurs when disruption of the normal flora allows pathogenic microbes to flourish.
– For example, some antibiotics kill off protective microbes in the gut, therefore facilitating overgrowth of toxin-producing microbes.
Holobiont
Comprises the human host plus its microbiome; this is sometimes referred to as a "superorganism."
  • The core microbiome comprises those microorganisms present in more than 95% of individuals at specific anatomical sites.
  • The secondary microbiome comprises the microorganisms that are more variable among individuals.

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