Lecture 7. Microbial Growth

Provides insight for prevention of growth of pathogenic organisms and organisms responsible for food posioning or food spoilage

*cold-loving, can grow at 0 C (grow at -10-12 C)

* grow at moderate temperatures (10-38 C)

*prefers hot tempeatures (40-62ish)

*prefer to grow about 80 C. this group contains the archaea
microrganisms have an optimum groth temp (best growth), -a minimum growth growth temperature (lowest temp at which they can grow, and a maximum growth temp (highest temperature at which they can grow. range about 30 C
-37 C

2 groups:
Strict psychrophiles; grow at 0 to 15 C (native to deep oceans, polar regions

psychrotrophs: grow at 0 C but prefer warmer temp of 20-30 C and wont grow about 40 C

-grow at refrigerator temperature. refridgeration greatly slows growth of most pathogenic organisms but psychrotropys can grow slowly

-low temperature food spoilage

- 0-5 and 50-60 C
- 5-15 C
- 15-50 C
- -30 to 0 and above 62 C

The 2 inch deep pan because it takes 45 min to an hour to cool/is at optimal growth temp for bacteria while 6 inch deep pan take 6 hours/at optimal growth temperature for bacteria

Physical: temp, ph (grow best in narrow pH ranges), osmotic pressure (get nutrients from the surrounding water thus they require water fo growth and are made up fo 80-90% water)

-chemical: C, N, S, P, trace elements, and O for aerobic species

- 6.5-7.5

- that is why lactic acid produced by fermentation inhibits other bacterial growht in food like sauerkraut and pickels

- few bacteria that prefer acidic pH

- concentration of solute outside cell is greater than inside

- same inside and out

- concentration of solute is lower outside than inside cell

- 0.85% NaCl

- a salty environment (10& NaCl) inwhich cells lose water through a process called plasmolysis (cells shrinks and dies). That is why high salt concentration of sauerkraut and pickles prevents spoilage

- very high concentration of suger

- few bacteria that require high salt concentration

- hypotonic soln bc water moves into the cell and it burst

- sugar and AA
- AA, ammonia, or nitrogen gas in air
- AA (cysteines) or sulfate ions
- phosphate ions
- K, Mg, Ca, and trace elements

-require oxygen so grows on top of tube broth

-prefer oxygen, but can live without oxygen. they switch to using fermentation or anaerobic respiration (nitrate ions or other electron acceptors) and keep growing more slowly so you will find them floating on top of broth or in the middle of the broth...ex. E coli.

-obligate anaerobes- can't tolerate oxygen..ex (1) clostridium botulinum the agent of botulism (organisms grow in sealed food jars not processed by pressure cooking. (2) Clostridium tetani, the agent of tetanus (lockjaw)- Each of these species is an obligate anaerobe, gram positive , and endospore-forming.

Aerobic bacteria produce superoxide free radicals in small amounts during normal respiration. These free radicals ar toxic. They are converted to less toxic hyrogen peroxide and oxygen by superoxide dismutase (SOD). Hydrogen peroxide is also toxic. The enzymes catalase and peroxidase neutralize hydrogen peroxide

-vitamins, AA, purines, and pyrimidines
-*culture medium: nutrients for growth
*inoculum: microbes that are introduced
*culture: microbes that grow

Nutrients appropriate for the organisms to grow
-water
-adjusted ph
-oxygen at opprop level for organism that is growing
-proper incubation temp
-sterile to start with
-1.5% agar may be added to give the medium firmness. agar is a complex carbohydrate made from a marine alga used in cooking.