in today's lab
  we will assess the growth of four different bacterial species            exposed to incubation under different temperatures.
 question:
    what is the optimal growth temperature for each of these bacterial species?
 hypothesis:
    your educated guess using this information..
   
  1. M. luteus is a mesophile
  2. S. marcescens is a psychrotolerant mesophile 
  3. E. coli is a mesophile
​  4. B. stearothermophilus is a thermophile

high dry heat:
oxidizes organic material
can be used to sterilize surgical instruments
​requires longer times and temps: 2 hours and 180 degrees

Ultraviolet light inactivates microbes by
​ disrupting the structure of their DNA making them unable to replicate. 

15 lbs per inch *2

​121.5 degrees C

Water activity (aw) is a measurement of how much water in a substance is available for microorganisms to grow.

low temperatures are
primarily bacteriostatic:
 inhibiting growth/reproduction of bacteria without killing them
​by reducing enzyme activity .
can not be used for sterilization 

100 degrees C

review question:

what is the difference between bacteriostatic and bactericidal?

autoclave uses
moist heat sterilization:
steam generated under pressure kills microbes

1. regular/batch pasteurization:
    63°C for 30 min kills E. coli,
    M. tuberculosis & Salmonella 
2. HTST/flash
     72°C for 15 seconds
3. UHT
     140°C for 3 seconds can               serve to sterilize

controlling microbial growth

plus...

water activity is measured on a scale of 0.0 to 1.0 with 1.0 = pure water. 
The lower the water activity, the drier the substance and the less likely it is for that substance to serve as a growth medium for microbes.  

autoclaving

Most bacteria thrive with a higher water activity.
Certain fruits and vegetables with higher moisture content are more susceptible to bacterial spoilage.

physical growth factors and microbial growth

boiling

high moist heat:
permanently denatures DNA  and proteins
includes:

water activity is important because it affects the safety, quality, and texture of food. Water activity is used to control the growth of microorganisms like bacteria, yeasts, and mold. 
Water activity is used to control the stability of dehydrated and semi-moist foods. ​

moisture content

pasteurizing

UV radiation

 water activity in food:
fresh fruits/veggies: 0.99
fresh meat: 0.99
milk: 0.99
bacon: 0.97
bread: 0.95. 

temperature 

how do
1. temperature
2. moisture
3. UV light
​ affect microbial growth?

pickles and jams have tons
of dissolved salt and sugar which hog all the water (the solvent) leaving less available water for microbes to use.

temperature

high temperatures are
primarily bactericidal:
 capable of killing bacteria 

review question:

What was the purpose of the lab where we exposed 4 different bacterial strains to 4 different temperatures? 

Higher water activity substances tend to support more microorganisms. bacteria usually require water activity values of at least 0.91 compared to fungi which need 0.6 or so.  Every microorganism has a limit of water activity below which it will not grow.

review question:

define psychrophile, mesophile, thermophile.
why are pathogens usually mesophilic?