Host Microbe Relationship

What is symbiosis?

A relationship between two different species that live closely together

What is mutualism?

Obligatory relationship where both species benefit from each other

What is commensalism?

A relationship where one organism benefits and the other is neither harmed or helped

What is epibiotic predation?

Predator attaches to the surface of its prey, releases enzymes that break down the surface and sucks out the nutrients from inside

What is endobiotic predation?

Predator goes inside prey’s cell and eats in from within

Example of endobiotic predator

Bdellovibrio, searches for gram negative bacteria, attaches to the surface, bores a hole and enters space between membrane, reproduces until it bursts

What is parasitism?

A relationship where the parasite benefits and the host is harmed

Define pathogenicity

How effective a parasite is at causing disease in its host

Define resistance

How well the host can fight off a disease

Define susceptibility

How easily a host can be infected

Example of a parasitic microbe

Enterobius Vermicularis a parasitic worm that infects human intestines by living in the gut, laying eggs around anus and feeding off host nutrients

What is the microbiome?

The collection of all microbes that live in and on your body

When does microbiome development begin and how can baby pick up microbes?

At birth, early colonization and through vaginal birth from mom’s vaginal and gut microbes and through C-section from caregiver’s skin

What are oligosaccharides?

Special sugars in breast milk that Bifidobacteria breaks down

How does Bifidobacteria benefit the baby?

Uses oligosaccharides for energy, Lowers gut pH, slow growth of harmful bacteria

What are the skin’s antimicrobial features?

Keratinocytes, Lysozyme, Tight junctions, Dry environment, Low pH

What is Staphylococcus epidermidis and its role?

A harmless skin microbe that takes up space and nutrients from harmful bacteria to prevent their growth

What kind of microbes dominate before teeth appear and after teeth?

Aerobic microbes before and anaerobic microbes after

What are the mouth’s antimicrobial defenses?

Lysozyme and Lactoperoxidase system which produces oxygen radicals that kill microbes

What does Streptococcus salivarius do?

A microbe that lives in the mouth and throat that helps prevent infections

What is Streptococcus mutans and why is it harmful?

A cavity causing microbe that makes sticky dextran from sugar to form dental plaque, leading to acid production and enamel damage.

How does S. mutans cause cavities?

Glycotransferase + sugar = dextra (helps for plaque), food gets trapped in plaque = tartar (calculus), anaerobes grow in plaque and ferments sugar = lactic acid which lower pH and damages enamel = cavities

What is the pH of the stomach and its role in microbial defense?

Low pH which is very acidic that kills microbes

Which microbe can survive stomach acid and cause ulcers?

Helicobacter pylori

What do bile and pancreatic enzymes do in the duodenum and jejunum?

They lower the number of microbes

Which part of the small intestine has more microbes and what types?

Ileum has more microbes, especially anaerobes like Lactobacillus and Bacteroides.

Which part of the GI tract has the highest number of microbes?

The large intestine (colon)

What are the functions of microbes in the large intestine?

Ferments undigested food and produce SCFAs, vitamin K, B12, and gas.

What gases do fermenters and methanogens produce in the colon?

Fermenters: H₂ and CO₂; Methanogens: methane

What natural defenses protect the upper respiratory tract?

Cilia, mucus, lysosomes, and macrophages

Which parts of the urogenital tract are normally sterile?

Kidneys, ureters, and bladder.

What part of the urogenital tract has some microbes, especially in females?

urethra

How do urinary tract infections (UTIs) commonly occur? And what pathogens cause it?

E coli enter the urethra and travel up the urinary tract

What type of bacteria dominates the vagina and why are they important?

Lactobacillus produce lactic acid to keep the pH low and prevent yeast overgrowth

What is the “functional core microbiome”?

Essential gut microbes that perform key functions regardless of their exact species.

What are some important functions of the functional core microbiome?

Digesting food, fermenting fiber, and helping maintain homeostasis.

Why are gut microbes important for digesting food?

Humans can’t digest complex carbs like fiber, but microbes break them down into energy

What short-chain fatty acids are produced by fermenting fiber?

Acetate, propionate, and butyrate

What do SCFAs do in the body?

Provide energy to gut cells and regulate fat storage and hunger signals

How are SCFA imbalances linked to obesity?

Too much acetate and too little propionate/butyrate may increase fat storage and insulin production.