Unit 6--Microbiology

Chapter 19

continued

Microorganisms & You

• A. Competition:• Food for heterotrophs

typically are carbon-based macromolecules:

• Carbohydrates, lipids, & proteins

• Bacteria & fungus are responsible for food spoilage because many are saprobes

B. Food & Microorganisms:1) Making cheese

• Bacteria placed in an anaerobic environment, and the milk breaks down to form cheese

• Milk (sugar source) + little oxygen -> lactic acid + protein solids + curds

2) Making cured meats• Some bacteria are able to ferment meat

products• The final products are sausages, bologna,

salami, country cured hams, etc

3) Making spirits• Some fungus (yeast) are able to ferment fruit

juices to produce alcoholic beverages• The final products are wine (from grapes),• Sake (from rice), vodka (from potato), beer (from

grains), etc

4) Making breads

• Some fungus (yeast) ferment plant starches producing alcohol & CO2

• The CO2 is trapped within the flour mixture, causing the dough to rise

• While the alcohol is burned off when baking

5) Making pickled vegetables

• For example, sauerkraut is a product of lactic acid fermentation of cabbage by the lactobacillus bacterium

• Salt is added to prevent bacteria from spoiling the product

How else are bacteria helpful?• C. Nitrogen-fixation

• decomposing bacteria convert atmospheric N2 for use by autotrophs

• D. Symbiotic bacteria allow a host to live a different lifestyle than would normally be possible

• E. Cyanobacteria (& unicellular algae) produce most of the world’s oxygen by photosynthesis

F. Microorganisms & your health

Antibiotics that kill pathogenic microorganisms are made from microorganisms

Using sterile plates with aseptic techniques

• Aseptic • sterile or free of microorganisms• pathogenic • disease-causing• purpose = to avoid contaminating cultures

with unwanted species & prevent self-infection. Even “safe” or nonpathogenic bacteria can be harmful in large amounts or in the wrong place (such as the eyes)

Aseptic techniques

• Streaking = do not tear the agar; application can be done with inoculating loops or cotton-tips

• Sterilization is a must! Use bleach or…• flaming:

– heat loops in flame until it glows orange

– pass open lips of test tubes through flame several times (after removing & before replacing stoppers)

Filter paper disks(for sensitivity tests)

• Soak filter paper disks in different bactericides– one should be in sterile water as a control

• place on agar plate which already contains bacteria

• incubate (as needed—24 to 72 hours)• bacteria grows uniformly wherever their growth

is not inhibited by bactericide– zone of inhibition (halo) =

where no growth occurs: the larger the halo, the more effective the bactericide

Assignment• Mark off the bottom of petri plate into 4 sections. Put a

small number (1-4) on outside edge of each section.• Use a Q-tip to gather specimens from around the D hall.

Bring your samples back to class for streaking on one section of disk (remember your number & group letter.)

• Use sterile forceps to apply paper disk, coated with antibacterial soap to your section of the plate. (Seal with Parafilm & incubate.)

• 48 (?) hours later: examine appearance of colonies. Note color, texture,etc. Also look for other non-bacterial growth, such as molds.