Chapter 14 (Normal Human Microbiota)

Symbiosis

the relationship between normal microbiota and the host

Commensalism

one organism benefits and the other is unaffected

mutualism

both organisms benefit

Parasitism

One organism benefits and the other is harmed

microbiome

all of the microorganisms that live in a particular environment, such as a human body

virome

the entire population of viruses associated with the human body

transient microbiota

the microorganisms that are present in an animal for a short time without causing a disease

colonization

the ability of the microbe to stay attached to the body surface and replicate

adhesions

allow microbiota to attach to host cells

Gut-Brain Axis

brain activity alters gut function; gut microbiome can alter nervous system

food digestion, synthesizing vitamins, interfering with pathogen colonization (microbial antagonism), training and enhancing function of the immune system (produce immunomodulins), "Virtual organ system"

benefits of a microbiome:

immunomodulins

modify the secretion of cytokines; regulator

immunocompromised hosts

Individuals with weakened immune systems; susceptible to infection

opportunistic pathogens

cause disease when the host's defenses are compromised or when they grow in part of the body that is not natural to them

dysbiosis

microbial imbalance that causes adverse effects in humans

hygiene hypothesis

suggests that limiting exposure to pathogens may lower immune tolerance and the ability to cope with harmless antigens

Mouth, nose, lung, stomach, intestines, vagina, skin

Major the sites of colonization:

bioburden

number of microorganisms that typically inhabit an environment

The Skin

Acidic, high salt, low moisture, can contain lysozyme, mostly Gram + organisms

ex: Staph. epidermidis; Bacillus spp; yeasts

The Eye

Low bioburden, contains lysozyme, continual "washing" with tears, mostly transient bacteria

conjunctivitis

inflammation of the conjunctiva (outer eye)

The Nose (nasal cavity)

moist, mucous-lined, airflow constantly brings in microbes; transient microbes from environment

Pharynx

throat; from nasal cavity to trachea and esophagus

nasopharynx

part of the pharynx directly behind the nasal passages

oropharynx

central portion of the pharynx between the roof of the mouth and the upper edge of the epiglottis

The Oral Cavity

defense with saliva (mechanically washes), contains lysozyme; microbes must adhere to survive here; dybiosis: bacteria fermenting = acid production, periodontal disease, bacteremia

oral cavity dysbiosis

bacteria fermenting causes acid production which breaks down tooth enamel, periodontal disease, bacteremia

Early oral cavity colonizers

Acquired within hours after birth from environment

- Steptococcus, Actinomyces, Lactobacillus, Some yeasts

After teeth emerge colonizers

Anaerobes colonize; Provotella, Fusobacterium

Biofilm formation in oral cavity

Steptococcus mutans and Streptococcus salivarius; produce a glycocalyx (helps stick to teeth and each other); forms dental plaque

Tooth surfaces: More aerobic

Below gums and tonsil crypts: Anaerobic

Oxygen dependance differences within the oral cavity:

teeth anaerobes

Fermentation causes acid production (dissolved tooth enamel), prevotella and fusobacterium; emergence of these begins colonization

upper respiratory system

nose, nasal cavity, paranasal sinuses, pharynx; highest bioburden of resp. tract; cilia keep microbes in nasopharynx or are funneled to stomach

lower respiratory system

trachea, bronchi, lungs

mucociliary escalator

cilia that transport mucus and foreign material out of the lower respiratory tract; sweeps foreign particles up and out of the lungs

The respiratory tract

similar to the nasal and oral cavities; streptococcus, prevotella, veillonella

respiratory tract dysbiosis

respiratory infections, chronic obstructive pulmonary disease (COPD), cystic fibrosis

The stomach

Acidic pH, lethal to most bacteria; low bioburden

ex: Streptococcus and Veillonella; H. pylori can grow in mucous lining of stomach

stomach dysbiosis

Malnourishment causes stomach pH to be higher (more microbes can survive); H pylori overgrowth can cause gastritis & gastric ulcers

The intestine

the digestive tube from stomach to anus; bacteroidetes and firmicutes phyla mainly; bile from pancreas is alkaline

dysbiosis = bloating, flatulence, deadly infection, inflammatory bowel disease

Intestine dysbiosis

bloating, flatulence; more deadly infections, inflammatory bowel disease

duodenum and jejunum

pH ~ 8; Limits growth; Mostly gram + (lactococci and enterococci and Actinobacteria)

ileum and colon

pH ~ 5-7; lower levels of bile salts; very diverse ecosystem; normal human intestine has 10^11 bacteria per gram of feces; anaerobes and facultative anaerobes

ferment unused energy substrates, train the immune system, prevent growth of pathogenic bacteria, regulate the development of the gut, produce vitamins for the host, produce hormones

Functions of Gastrointestinal tract microbiota:

genitourinary tract

urinary tract and reproductive organs

kidneys and ureters

which parts of the urinary tract should be microbe free?

urinary bladder

small number of microbes; mainly anaerobes

urethra

flow of urine out forces microbes out; mostly organisms on the outside; staphylococcus epidermidis

vagina

pH 4.5, acidic; lactobaccillus spp.

genitourinary tract dysbiosis

UTIs of the bladder or kidneys; yeast infections of vagina; correlation of microbiome and susceptibility to STDs

microbiome therapy

treats diseases by restoring a healthy balance to the body's microbial communities, commonly addressing gut dysbiosis to combat infections, inflammation, and metabolic disorders

prebiotics

nutrients that encourage the growth of beneficial microbes

probiotics

live microbes applied to or ingested into the body, intended to exert a beneficial effect

Fecal microbiota transplant

the process of transplantation of fecal bacteria from a healthy individual into a recipient

phage therapy

treatment of bacterial diseases using bacteriophages specific to a particular bacterium