Human Microbiome Flashcards
Human Microbiome
Describes the microorganisms (bacteria, fungi, protozoa, and viruses), mostly bacteria, that continuously inhabit the human body
“Normal Micriobiota” or “Normal Flora”
They normally have a commensalistic or mutatlistic relationship
Fetus - sterile or not sterile?
The fetus is sterile = NO normal flora
Then newborns start having the normal flora from the mother, air, food and the environment
Introduction of flora
A process: Exposure -> Contamination -> Colonization
Complete colonization occurs within:
Hours (skin & nasopharynx)
Days (intestinal tract)
Week/Weeks (lower GI)
Organs - sterile or not sterile?
Our internal organs are sterile
Ex. spleen, liver, pancreas, bladder, CSF, blood (unless during infection)
Skin & Mucous Membranes- sterile or not sterile?
The surface tissues (i.e. skin & mucous membranes) are constantly in contact with environmental organisms and become readily colonized by various microbial species
Normal flora differ from one human to another depending on?
- Age
- Diet
- Medications (antibiotics)
- Maternal stress
- Infant feeding practices (breast-feeding vs diet formula)
- Mode of delivery (C-section vs vaginal)
Two Types of Flora - Resident vs Transient
- Resident Flora: relatively fixed types of microorganisms regularly found in a given area at a given age
- If disturbed, they promptly reestablish themselves
- The microbes of the normal resident flora are harmless
- They may produce disease IF introduced into foreign locations in large numbers & if predisposing factors are present - Transient Flora: non-pathogenic or potentially pathogenic microorganisms that inhibit the skin or mucous membranes for hours, days, or weeks
- Generally of little significance as long as the normal resident flora remains intact
- However, IF the resident flora is disturbed, transient microorganisms may colonize, proliferate, and produce disease
Why are they transient?
- May be washed by bathing
- May be flushed by tears, sweat, urine, feces
- May not survive acidic or alkaline pH of the site
- May not be able to compete w/ resident normal flora
- May be killed by substances produced by the resident normal flora
Where do we find normal flora?
Resident normal flora are found in sites exposed to the outside world!
- Skin
- Eyes & Ears
- Respiratory Tract
- Oral Cavity
- Gastrointestinal Tract
- Urogenital Tract
Skin
- Generally dry, acid environment that does not support the growth of most microorganisms
- Sweat glands, sebaceous glands, and hair follicles are readily colonized by gram-positive bacteria & other normal flora of the skin
Can acquire transient bacteria from enviro - but gets washed off or die
Resident Bacteria of the Skin
Aerobic: staphylococcus epidermis (majority) & staphylococcus aureus
Anaerobic Bacteria + Propionibacterum acnes
Eyes
The conjunctiva of the eye has primarily S. epidermis, followed by S. aureus, and others
Some skin normal flora are also present, but at fewer amounts
Tears (lysozyme enzymes), mucus, and oil will protect the conjunctiva of the eye from colonization by more bacteria
Ears
Middle & Inner Ear = usually sterile
Outer Ear & Auditory Canal = same normal flora of skin
Respiratory System
Upper
Nose & Throat = many microorganisms
Nasopharynx = streptococcus pneumoniae
Lower Respiratory Tract = usually sterile
Mouth
Complex microbial habitat
Most common = S. aureus & S. epidermis
Teeth & GIngiva = Streptococcus mutans (tooth decay & heart problems)
Stomach
Only a few d/t gastric enzymes and acidic pH
Small Intestine
Upper - Only a few b/c bile kills them
Lower - lactobacilli & enterococci
Large Intestine
More bacteria than any other part of the gut!!
99% = anaerobic Bacteroides spp.
Many are opportunists
Also many fungi, protozoa, and viruses
Urinary Tract
Kidneys, Ureters, and Urinary Bladder = sterile
Lower Urethra & External Opening = bacteria, yeast & viruses (same bacteria present on skin)
Male & Female Genitals
Sterile except vagina
Vagina = Lactobacillus acidophilus
4 Beneficial Functions of Normal Flora
- Protection
- Growth & Immune Development
- Production of Vitamins
- Modulation of CNS activity
Beneficial Functions - Protection
Protect our organs & systems that are in direct contact w/ the external environment from invading pathogens
May involve:
-Space occupation
-Competition for receptors/binding sites on host cells
-Competition for nutrients
-Production of bacteriocins (toxins)
Examples: E.coli prevents growth of Shigella spp; large intestine community prevents growth of C. diff; vaginal community prevents growth of Candida albicans
Beneficial Functions - Development of immune system
Newborns, normal flora stimulates the development of the immune system
Beneficial Functions - Production of Vitamins
Gut bacteria aid digestion by breaking down plant fibers into short-chain fatty acids that intestinal cells can access
Provide Vitamins K & B12
Beneficial Functions - Modulation of CNS activity
Suggested modulation of CNS activity: brain-gut-microbe communication in health & disease
Harmful Effect of Normal Flora
- When displaced from normal site of body
- When individuals are immunocompromised or their number increase under abnormal conditions, the normal flora can overgrow & become pathogenic
PREbiotics vs PRObiotics
PREbiotics: fiber-rich foods – substrate for normal flora to re-establish (food for flora)
PRObiotics: microorganism preparations to re-establish normal flora (actual microorganisms)
