Chapter 24 Microbial Symbioses with Humans

Microbiome

All sites on a human that contain microorganisms are part of a ____

microbiome

a functional collection of different microbes in a particular environmental system.

microbiota

all the microbes in a microhabitat (Different microhabitats support different microbes, so the skin will have very different microbes than the mouth)

16S rRNA

allow for identification of different microbiota at different body sites.

most bacteria cannot be cultured, however, advanced DNA sequencing techniques including 16S rRNA, allow for identification of different microbiota at different body sites.

can bacteria be cultured?

monogastric

simple stomachs

omnivorous

feeds on plants and animals

Firmicutes, Bacteroidetes, Actinobacteria

common in the gastric fluid in small intestine

Firmicutes and ProteobacteriaHelicobacter pylori

common in the mucus layer of the stomach in small intestine

Helicobacter pylori

found in the gastric mucosa.

The Large Intestine

The colon is essentially an in vivo fermentation vessel, with the microbiota using nutrients derived from the digestion of food

Firmicutes gram____

gram positive

Bacteroidetes gram____

gram negative -

Proteobacteria gram ______

gram negative -

Individuals may have mostly Firmicutes, mostly Bacteroidetes, or a mix of the two

This regulates metabolism and the host’s propensity for obesity

Gut Enterotypes (3 types)

• bacteroides

• prevotella

• ruminococcus

Bacteroides

Gram negative -, obligate anaerobes

Prevotella

Gram negative -, obligate anaerobes

Ruminococcus

Gram positive +, obligate anaerobes

Interactions between gut microbiota and the brain

•Brain weight (~ 3lbs), gut microbiota weight (~ 3lbs).

•Humans: ~ 20,000 genes.

•Microbiota: ~ 100,000 genes.

Toxoplasma gondii

•infected mice/rats lose their fear of cats (mind control?).

oral cavity

a complex, heterogeneous microbial habitat

Saliva contains

antimicrobial enzymes but high concentrations of nutrients near surfaces in the mouth promote localized microbial growth.

Teeth colonized by

streptococci and anaerobes in biofilms.

•The tooth consists of a mineral matrix (enamel) surrounding living tissue, the dentin, and pulp.

Escherichia coli and Proteus mirabilis

Altered conditions can cause potential pathogens in the urethra to multiply and cause disease

Lactobacillus acidophilus

a resident organism in the vagina, ferments the glycogen, producing lactic acid.

Mouse Models

•mice have been used to good effect to study human gut microbiome interactions.

•Mice have a larger cecum than humans.

Most fermentation is completed in the mouse cecum, rather than the human large intestine

•Mice have a short life cycle and well-defined genetic lines; they can be raised in a germ-free (controlled) environment.

•antibiotic therapy

•strict dietary control

•fecal transplants

•germ-free environment

colonization begins at birth

when does colonization begin?

early colonization

•with transfer from mother  to infant Early colonizing microbes are a source of vitamins and tend to be facultative rather than obligate anaerobes.

“vaginal seeding”

C- section babies swabbed with mother’s vaginal samples

more commensal bacteria, and oligosaccharides that promote their colonization.

breast milk has _____

Inflammatory Bowel Disease (IBD)

-Chronic inflammation of the gut and disruption of homeostasis (dysbiosis).

-Antibiotic use increases the risk of developing IBD.

-Once developed, IBD may be transmissible between family members.

-Individuals with IBD have lower gut microbiome diversity.

Obese mice have more Firmicutes

Mice that are genetically obese have different microbiota than normal mice

Firmicutes

Like the mouse model, obese humans have more

dental plaque

Cells form a biofilm called___

Streptococcus and other fermenting bacteria.

dental plaque has _______

Periodontal disease

thought to contribute to several systemic conditions, including cardiovascular disease and arthritis.

Clostridium difficile

infections are associated with antibiotic use.

Clostridium difficile

is a spore-former and generally antibiotic resistant

fecal transplant.

A newer therapy for Clostridium difficile infection is a _____

Probiotics

live organisms that confer a health benefit to the host

Prebiotics

typically carbohydrates that are indigestible by human hosts but provide nutrition for fermentative gut bacteria.