Microbiology part 3

1. Bacteria and fungi can grow on nutrient agar in Petri dishes
   1. Remember to sterilize the agar plates before spreading on bacteria or fungi, in case any unwelcome micro-organisms are present
      1. 1. Collect your sample and wipe it in a zig-zag motion evenly onto the agar surface, make sure not to press too hard onto the agar
         1. for example, stroke door handle to collect microbes and then apply to the agar with a sterile cotton bud
            1. or a sterile inoculating loop (which should be sterilized and allowed to cool within each repeat)
         2. quickly place the lid back on, in case any airborne bacteria manage to pollute the agar
            1. 2. Secure the agar plate with two pieces of tape
               1. only from top to bottom - just that the lid won't fall off
                  1. Do not seal the agar plate with tape that goes " all around'
                     1. as once all the oxygen has been depleted it would strengthen the growth of the more dangerous anaerobic bacteria
                        1. 3. The Growth Stage: Incubation
                           1. The secured agar plate is placed in an incubator or a warm place, UPSIDE DOWN, for a 2-4 days
                              1. If the agar plate is not placed upside down the condensation would cause water to mix with the growing microbes
                                 1. subsequently "spreading and mixing them"
                                    1. Furthermore any water on the microbes would create an "anearobic enviroment"
                           2. In school conditions, the microbes should be grown in a temperature of 25 degrees
                              1. This is to avoid any growth of pathogens- which can be deadly to humans
                                 1. Microbes should not be cultured in a temperature between 35-40 degrees
                                    1. 4. Disposal- Cultured Microbes can either be rid of by either
                                       1. being incinerated at a high temperature
                                       2. or filled with very powerful disinfectant/bleach solution

Annotations:

• http://www.foodsafetysite.com/educators/competencies/general/bacteria/bac2.html

1. water/moisture
   1. This is for dissolving their food
      1. which is then used for energy and growth
   2. It provides a way for food to enter the cells
      1. as well as for the harmful waste leaving
2. Food/Nutrients
   1. This is essential as bacteria depend on food for energy and growth
      1. sugar
      2. starch
      3. protein
      4. fats
3. Temperature
   1. In general bacteria are able to reproduce between a large range of temperatures
      1. bacteria reproduce slowly under the temperature of 45 degrees
      2. they incinerate around 140 degrees
      3. they grow very rapidly between the temperatures 45-140 degrees
4. oxygen
   1. Some bacteria are only capable of growing in the presence of oxygen (aerobe)
   2. While some bacteria depend on no oxygen to grow (anaerobe)
   3. However a large number of bacteria can depend on either conditions
      1. called facultative anaerobes
5. pH
   1. Majority of bacteria reproduce extensively in pH 7
      1. although they are capable of
         1. growing between a pH range 4.5-10

1. Drying
   1. Without the presence of moisture
      1. Bacteria will stop growing
         1. e.g pasta
   2. among one of the most ancient techniques of presevarvation
2. Refridgeration
   1. (-2-4 degrees)
   2. slows down the growth and reproduction of microbes
      1. also the enzymes that make the food rot
         1. not as effective as freezing
3. Freezing
   1. (-18 degrees)
      1. enzymes can not function properly to continue usual cell activity
   2. slows growth of bacteria+fungi
      1. water turns to solid ice crystals
         1. dependent on water to grow
4. Salt
   1. process of osmosis
      1. water is drawn out
         1. Bacteria+fungi need water to grow
            1. e.g Bacon, Olives
5. Sugar
   1. plasmolysis
      1. remove water from microbes
         1. need water to survive
   2. e.g jam
6. Pickling
   1. Alters the pH
      1. enzymes in microbes can not function properly
         1. e.g pickles
7. Canning and Bottling
   1. can is heated than cooled
      1. thus bacteria+fungi is burnt off
8. Vacuum Packing
   1. Oxygen excluded
      1. Bacteria and Fungi are unable to respire without oxygen
9. Pasteurizaton
   1. heated to 70 degrees and then chilled
      1. microbes are incinerated
      2. for 15-30 seconds
         1. chilled at 10 degrees to stop leftover microbes from growing
   2. milk
10. Artificial Food Additives
    1. some preservation additives can be antimicrobial
       1. inhibit the growth of bacteria or fungi
       2. mold
       3. antioxidant
       4. sodium nitrate
       5. calcium pripionate
11. Curing
    1. the chemicals added dry out the surface of the food
       1. thus removing the moisture
          1. bacteria growth is impeded
             1. e.g pork with nitrates and salt
                1. = bacon and ham
12. Lye
    1. sodium hydroxide added
       1. too alkaline for bacterial growth
13. Irradiation
    1. ionizing radiation
       1. gamma rays
          1. kill microbes
             1. does not affect taste