Lecture 16 – Symbiosis

“together living” (sym-together; bio and biosis-living) -> it means when two organisms (of different species) are living together in a close relationship.

If two parents are living together and raising children, that’s not symbiosis.

Symbiosis - we’re talking about organisms of different species that have come together for some reason, usually at least one of them benefiting from that.

Resident microbiota and transient microbiota

Microbiota refers to microbes that live on the human body.

Algae are doing photosynthesis to produce food for themselves from the sun and make enough for the fungus as well.The fungal hyphae are surrounding the algae so that they can absorb food.

In return, fungus (lichens) is providing them with a habitat and protection

the competition between normal microbes and pathogens for nutrients and space.

importance: reinforces the body’s defense by limiting the ability of pathogens to colonize the skin and mucous membranes

Staphylococcus, micrococcus (uv resistant)

Most are considered commensal

Propionibacterium

Not commensal

Produces propionic acid but they are also the major cause of acne.

This organism can be somewhat of a parasite.

Because while it can be pretty easy to prove that one partner is getting a benefit, it can be very challenging to prove that the other partner is not getting a benefit or a harm.

“Commensal” bacteria may compete with pathogens for food and space - this is a benefit but not a clear and specific benefit.

Streptococcus, other LAB

- S. mutans most responsible for dental plaque

*S. salivarius - some strains of this that are used as oral probiotics fight S. mutans

- Other LAB can decay teeth with acid

Intestines have very high microbial growth -> colon/large instestine

Anaerobic environment

Lactobacilli

Enterococci

Enterobacteria

Enterococcus faecalis

Bacteroides

Bifidobacterium

Eubacterium

Peptococcus

Peptostreptococcus

Ruminococcus

Clostridia

are delivered by aseptic Caesarian-section and raised in sterile environment

- Very susceptible to infection

- Poor nutrient absorption

- Require high vitamin diets

Benefit one another

E.coli benefit: residence in colon and absorb nutrients from the intestine

Human benefit: e.coli kills other bacteria that can be dangerous and protect from infection; e.coli also produces vitamins K and B

is an opportunistic pathogen if they colonize a new area of the body.

Most strains of this in the gut are commensal to mutualistic (beneficial/neutral). However, if they get from the gut into the urinary tract, they can cause UTIs.

where bacteria are found: urethra

which bacteria are found in the urethra: e.coli

Healthy populations of Lactobacillus prevent bacterial vaginosis (C. albicans)

Antibiotics can disrupt healthy vaginal microbiota

Decreased lactobacillus = higher chance of bacterial vaginosis

lungs are axenic

1. Ciliary escalator: epithelial lining of the respiratory tract and it removes microbes

- Pseudostratified ciliated columnar epithelium

*Ciliated cells

*Goblet cells - produce sticky mucus

2. Things (bacteria, etc) you breathe are gonna get stuck in mucus

3. Ciliated cells are gonna push whatever is trapped in the mucus as well as the mucus up up and up out of the respiratory tract into the throat

4. Once the mucus gets up to the throat, usually it gets swallowed down into the stomach where the stomach acid will destroy it

5. In the alveoli, we have macrophages so that if something does happen to bypass the ciliary escalator and get all the way into the alveoli, these macrophages are waiting for them and they will attack and kill most things that get there