Final Lab Exam Flashcards
What is UV light?
- light with a wavelength from 100-400 nm
- effective in sterilizing surfaces
How does UV light affect DNA?
causes thymine dimers to form
What type of UV light kills viruses?
UV-C
How did we examine the germicidal effects of UV light on S. aureus and B subtilis?
- split a plate in half and streaked S. aureus on one side and B. subtilis on the other side
- lid of plate was removed and a paper towel was placed over the bottom half of the plate
- plate was exposed to UV radiation for assigned time
- lid was placed back on the plate and it was incubated at 35 C for 24-48 hrs
- bacterial growth was observed
What is ammonification?
organic nitrogen in decomposing tissue is converted back into ammonium (NH4+)
How did we test for ammonification in soil?
- a tube of peptone broth was inoculated with a loopful of soil
- broth was incubated at room temperature for 7 days
- ammonia was tested for using Nessler’s reagent
- faint yellow: small amount of ammonia
- deep yellow: moderate amount of ammonia
- brown precipitate: large amount of ammonia
What are biofilms?
- complex assemblages of microbes encased in an adhesive matrix and attached to a surface
- microbes use quorum sensing to send messages to one another
- quorum sensing is density dependent
- biofilm formation provides support and protection from external stressors
- can lead to infection and disease
antimicrobial agents
a natural or synthetic substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, and algae
disinfectant
a chemical liquid that destroys bacteria
antiseptic
a substance that stops or slows down the growth of microbes
antibiotic
a medicine that inhibits the growth of or destroys microorganisms
filter paper disk method
- agar pour is inoculated with a loopful of test organism and poured into a petri dish
- agar medium is allowed to solidify
- filter paper disk is dipped into disinfectant/antiseptic
- disk is placed in the center of the inoculated agar surface and pressed down with forceps
- plate is incubated for 24-48 hours at 35C
- zone of inhibition is measured from the edge of the disk to the edge of the growth
Kirby-Bauer method
- evaluates sensitivity to certain antimicrobial drugs
- agar plate is inoculated with test organism using a sterile swap
- sterilized forceps are used to pick up an antimicrobial disk and place it on the surface of the agar
- plate is incubated at 35C for 24-48 hours
- zone of inhibition is measured around the disk
- a rating of R (resistant), I (intermediate), or S (sensitive) is given for the antimicrobial
zone of inhibition
- the zone of transparency on the plate where bacteria are not growing
- measures the sensitivity of the bacteria to a compound
- small zone of inhibition: resistant
- moderate zone of inhibition: intermediate
- large zone of inhibition: sensitive
How did we evaluate the effectiveness of cleaning hands with soap, alcohol, and hand sanitizer?
- agar plate was divided into quadrants
- pads of 2 thumbs were rubbed together for 10 seconds
- unwashed left thumb pressed on bottom left quadrant
- unwashed left thumb pressed again on top left quadrant
- unwashed right thumb pressed on bottom right quadrant
- washed right thumb (alcohol, hand sanitizer, soap) pressed on top right quadrant
- plate was incubated at 35 C for 24-48 hours
- count the colonies in each quadrant and calculate percent reduction
