MIC 206 - Lab 7

UV light ranges in wavelength from…

100 to 400 nm

UV light

• commonly used to sterilize hospitals and laboratories

• germicidal effects of US can mutate/alter DNA with cells

UV effect on DNA

DNA absorbs UV, pyrimidine (thymine) dimers form between adjacent thymine or cytosine molecules in the DNA strand

these mutations in essential genes can lead to death

photoreactivation

process that repairs damaged DNA by using visible light (300-500nm) to activate DNA repair enzymes like DNA photolyase and pyrimidine dimerase

• these can monomerize the dimer and reverse the original reaction

DNA photolyase

DNA repair enzyme that monomerizes the dimer and reverses original reaction

endonuclease

a DNA repair enzyme that removes damaged DNA and allows DNA polymerase to add back missing nucleotide

What kind of bacteria is most resistant to effects of UV?

endospores; layers of endospores are impenetrable due to their ability to withstand extremely harsh conditions while maintaining their structure

two examples of ways UV light can be blocked…

1. plastic lenses

2. sunblock

UV light has low level of penetration!

bacteria — below optimal temp

decreased metabolism and inhibition of growth

bacteria — too much heat

damage of cell membrane, proteins, and nucleic acids

moist heat

most effective method of microbial control

• can penetrate the cells and damage the proteins

3 methods of moist heat control

boiling, autoclaving, pasteurization

pasteurization

kills pathogens & organisms that cause food spoilage without altering taste of food

63C for 30mins OR 72C for 15sec

boiling

100C for 10mins will kill most bacterial and fungal cells

NOT effective against endospores

autoclaving

most effective method for killing endospores & sterilizing equipment

15psi @ 121C for 15mins

e. coli

gram negative

b. sub

endospore former

s. epi

gram positive

p. fragi

biofilm producer

e. aero

gram negative

s. marc

biofilm producer

psychrophile

optimum temp between -5C and 20C

deep oceans—- arctic and antarctic

grow in refrigerator, produce toxins and cause food spoilage

mesophile

optimum temperature between 20C and 40C

most bacteria that cause disease in humans (pathogens)

• body temp is 37C and they can grow

thermophile

optimum temperature between 40C and 80C

not affected by pasteurization

hot springs and water vents on sea floor

hyperthermophile

optimum temperature above 80C

geysers and volcanoes

can survive boiling