September 26 notes

Briana Dietrich

Hyp: E. coli can become resistant to T4 phages
• Refute: if no E. coli grew on plates with T4, but lots on 1:1 serial dilution
• Support: if there were E. coli on plates w/T4
• Hypothesis
o Random resistance?
 Bacteria are just “born” resistant, when we plate them on day 3 only R-E coli survive
 Acquired resistance
• Bacteria fight, T4 phages, some win, winners pass resistance on to offspring

1. Factors that influence bacterial growth rates

a. Osmotic pressure and availability of water-
i. Halophiles- can grow in very low water. Grow in dead sea.
1. Able to grow by greatly increasing the concentration of solutes on inside of cell. Inside is saltier then dead sea water is.
ii. Osmosis=diffusion of H20. Water rushes in or out of cells or diffuses freely. Osmotic pressure is the pressure put on cells by the movement of water.
1. ex. Having too little – concentration of water (water sucked out of cell)
2. ex. Having too much water-concentration (water flows into cell, could cause cell to explode.
3. water activity=how much available h20 in given environment. Ex pure h20= 1.0, human blood: 0.995, honey: 0.90, candy: 0.7
4. Bacteria cant survive if environmental conditions are too different from that bacteria’s ideal growth conditions.
5. staphylococci: ex. S.aureus, S. epidermiditis can survive at a water activity of 0.9
iii. Why honey doesn’t spoil, and about rubbing salt in a wound.
1. Salt in a wound used to prevent infection
a. Hurts because your cells are killed by lack of H20
b. Prevents infection for same reason (kills bacteria)

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