Lecture 02: Human Microbiota

What's the definition for Human Microbiota?

commensal organisms that coexist w/ humans without causing harm

Transient members of normal flora

pathogenic microbes found in the normal flora of spome indivisuals

What are sites colonized by normal flora?

skin, respiratory tract, digestive tract, urinary tract, and genital system

What are sterile sites of the human body?

-Circulatory system

-Lower respiratory tract (trachea, bronchi, lungs)

-Bladder

What are the common flora of the Respiratory tract?

1. Staphylococcus

2. Streptococcus

3. Corynebacteria

4. Neisseria

5. Haemophilus

What commonly colonize the oral cavity?

1. Streptococcus

2. Actinomyces

3. Borrelia

Why is the oral cavity a complex environment?

-Teeth surface (some microbes → biofilms, plaques, damage)

-Secretions (e.g., saliva) have antimicrobials (e.g., lysozyme)

-Diet effect → influence oral cavity microbiota

Approximately how much bacteria colonizes the gastrointestinal tract?

10^14 bacteria = LARGEST microflora biomass

What commonly colonize the gastrointestinal tract?

1. Helicobacter

2. Escherichia

What is the only area of the urinary tract that is colonized by microbiota?

Urethra

What commonly colonize the urinary tract?

1. Streptococcus

2. Escherichia

What commonly colonize the genital system?

1. Streptococcus

2. Escherichia

3. Lactobacillus

What is the current approximate average different species that make up the microbiome of a healthy individual?

~10,000 different species

Based on the Human Microbiome Project, how much more microbial cells than human cells are present in the Human Body?

10x more microbial cells than human cells

(1 human cell:10 bacterial cells)

Based on the Human Microbiome Project, how much more microbial genes than human genes are present in the Human Body?

100x more microbial genes than human cells

(1 human gene:100 bacterial genes)

How is the microbial genome data identified?

bacterial specific rRNA (16S rRNA) to identify different microbial species

Why do Gram-positive bacteria typically survive better than Gram-negative bacteria on human skin?

Some gram(+) bacteria like Staphylococcus and Corynebacteria are adapted to desiccation & dry conditions on the skin surface.

What enzyme is secreted in the tears or saliva?

Lysozyme → break down bacterial cell wall

What is a potential positive role of normal flora related to the immune system?

immune stimulation via cross-reactivity

What is the approximate surface area of the human skin that is available for colonization by microbiota?

2.0 m^2

How do certain Staphylococci derive needed nutrients if the host environment is nutrient-poor?

By lysing RBCs for Hb

What factors influence the composition of skin microflora?

-Age

-Personal hygiene

-Weather

What is the role of bacteriocins within the human microbiota?

Used by resident flora to keep invaders out