Lecture notes 10/7

Notes from microbiology class

October 7, 2009

What happens to E. Coli if it is put into distilled water?
• Bacteria have a cell wall – thus it would protect the E. coli from blowing up when emerged in distilled water
o Cell walls make them more resistant to osmotic pressure than eukaryotic cells
• E. Coli do not die, and they do not explode – the cell wall protects from this
o If the cell wall is compromised (by something like penicillin) then the bacteria are not resistant to osmotic pressure – then they are like eukaryotic cells

I. Factors that influence bacterial growth rates
a. Osmotic pressure and availability of water
i. Osmotic pressure:
1. Bacteria NEED to live in an aqueous environment
2. Jolly rancher by the door in class… She ate it – when it was dry
3. Jolly rancher that is wet on the carpet – didn’t eat
a. Picked up many things due to moist side
4. Cell envelope stuff protects bacteria from osmotic pressure
a. Osmosis – diffusion of water
i. Ex. – human cell put into salt water = shrivel up
5. There is some turnover in cell envelope components

ii. Water availability:
1. Distilled water – 1.0
2. Blood – 0.95 ← Everything that’s multicellular
a. E. Coli (and all bacteria that live in people) is happiest at this availability
3. Sea water - 0.90
4. Honey – 0.80
iii. Halophiles
1. Bacteria that can live in very low water availabilities
a. By having very high solute concentration inside cell, Halophiles are able to pull water into cell even when in very water-poor environment
i. The internal concentrations of solutes of the cell is still higher than external allowing water to rush into the cell
2. ‘Halo’ – salt, Latin
iv. Why honey doesn’t spoil, and about rubbing salt in a would
1. The water availability is too low in honey for the bacteria that would make us sick to live in it.
a. The bacteria that do grow in honey would explode if exposed to an availability of 0.95
2. Rubbing salt in a wound: Why does it hurt?
a. The salt will suck all of the water out of the wound, which in turn is going to shrivel all of the bacteria that could grow in a wound and the wound will be able to heal
b. Used to be a standard medical treatment – still is in third world countries

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License