Microbiology part 3

Microbiology part 3

1. Explain How to culture bacteria safely

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

2. Discuss the conditions under which microbes thrive

   • http://www.foodsafetysite.com/educators/competencies/general/bacteria/bac2.html
   • water/moisture
     • This is for dissolving their food
       • which is then used for energy and growth
     • It provides a way for food to enter the cells
       • as well as for the harmful waste leaving
   • Food/Nutrients
     • This is essential as bacteria depend on food for energy and growth
       • sugar
       • starch
       • protein
       • fats
   • Temperature
     • In general bacteria are able to reproduce between a large range of temperatures
       • bacteria reproduce slowly under the temperature of 45 degrees
       • they incinerate around 140 degrees
       • they grow very rapidly between the temperatures 45-140 degrees
   • oxygen
     • Some bacteria are only capable of growing in the presence of oxygen (aerobe)
     • While some bacteria depend on no oxygen to grow (anaerobe)
     • However a large number of bacteria can depend on either conditions
       • called facultative anaerobes
   • pH
     • Majority of bacteria reproduce extensively in pH 7
       • although they are capable of
         • growing between a pH range 4.5-10

3. Discuss the different methods of preserving food

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