Lecture 8. Control of Microbial Growth

- microbes are part of the natural environment; most are benign or benificial

gut microbes assist with digestion of carbs and proteins as well as synthesis of folic acid and vitamin K

microbes in sanitation systems decompose human wastes

microbes produce useful fermentation products (bread, beer, etc)

-some microes are pathogens so it is important to understand how to effectively disinfect surfaces or equipment in a hospital setting; control foodborne illnesses; conduct safe honme canning; understand food, drug, home product labels

1destruction of all microbes including endospores

2destruction of most but not all microbes including endospores of Clostridium botulinum

3destruction of vegetative (non-endospore forming) pathogens on living tissue

4removal of microbes from a limited area

5treatment of lower microbial counts on eating and drinking utensils

1. hospital-acquired infections

2. treatment or agent that kills microorganisms

3. teatment or agent that kills fungi

4. a treatment or agent that kills viruses

5. a treamtne or agent that kills Mycobacterium Tuberculosis (TB)

6. a treatment designed to stop growth (but doesn't sterilize). If you remove treatment, growth may resume

7. indicates bacterial contamination (from Greek for decay); also used to describe disseminated bacterial disease

8. number of dying cells per unit of time (usually per min)

1. high population load, longer period of time required to kill all the organisms

2. they inhibit death induced by antimicrobial agents

3. some disinfectants work better at warm temp

4. can protect the microorganisms from exposure to disinfectatnts

5. soem antimicobials work better at acid pH

6. ex. Pasteurization uses lower heat for a longer time to achieve the same effect that high heat for a shorter time can achieve in a destruction of microorganisms in food products

7. gram positive organisms are more susceptible to many agents than gram negative organisms.

1. damage to PM
2. damage to enzymes and other structural proteins
3. damage to nucleic acids

1. the lowest temperature at which all microorganisms are killed in 10 min time.

2. the minimal amount of time necessary to kill all organisms in a given temperature

3. the time in minutes necessary to kill 90% of the bacteria at a given temperature

1. boiling, autoclaving (canning is a subset), and pasteurization

2. kills primarily by coagulating (denaturing) proteins

3. most organisms (including viruses and fungi) 10 minute

4. most heat resistant organisms and bacterial endospores are killed by moist heat under pressure

1. the higher the pressure, the greater the temperature

2. by contact of the organism to steam or in liquids

3. seam at a pressure of 15 pounds per square inch (psi) thus 121 C kills all organisms and endospores in 15 minutes

4. small volumes. large volumes require more time

5. steam in an autoclave must contact all surfaces; instruments are wrapped in paper that can be wetted and allow the steam to contact them.

1. heat under pressure can effectively preserve food

2. ball canning guide

3. need to drive off cold air

4. solid such as meat and larger sizes (ie quarts require more time than pints)

1. Louis Pasteur to preserve wine

2. pathogenic organisms

3. treatment of milk at 63 C for 30 min

4. high temp short time (HTST) pasteurization 72 C for 15 secs

5. kills everything so it can be stored at room temp

6. coffee creamers are treated this way. Milk heated to 74 C, than passed in a film over steam, raised temperature to 140 C for 3 secs colled rapidly to 74 C

1. by oxidation

2. flaming and hot-air sterilization (place in oven at 170 C for 2 hrs

1. bacteria or other large cells

2. to sterilize heat-sensitive media, protein solutions, etc.

3. filters are .22 um and .45um in size; HEPA (high efficiency particulate air filters) in biosafety hoods remove bacteria from air.

1. ordinary refrigeration temperature (0-7 C) is bacteriostatic (reduce the metabolic rate of most microbes is so reduced that hey cannot reproduce or synthesize toxiins) not bacteriocidal

2. inhibits growth of most pathogens but not the rpsychrotropic organisms

3. freezer temperatures are bacteriostatic not bacteriocidal, but some organisms such as parasitic worms are killed by freezing.

4. Listeria Monocytogenesis

1. high salt to preserve meat

high sugar to preserve fruits

2. bacteriostatic

3. drying out

4. bacteriostatic