Lab 6 Flashcards
(23 cards)
Purpose of catalase test
a differential test for Gram positive cocci,
essential for identifying some pathogenic strains
Result of catalase test
+ Staphylococcus (pathogenic and catalase positive)
+ Streptococcus
(catalase negative).
what are some beta lactam antibiotics
Penicillin and Ampicillin
What are some antibiotics that target protein synthesis
Chloramphenicol, Tetracycline and Streptomycin.
chemical germicides is also known as
The Use-Dilution tets
Whats the use-dilution test
expose bacterial cells to varying concnetrations of a germicial agent for a specific length of time, then incoulated into fresh media.
If any bacteria survive after germidicde -> you would see growth in broth (evident as turbidity)
Aseptic technqie is necesar
Effect of bleach, hydrogen perodixde, and ethanol on E. coli and S. epidermidis
For the chemical chermicide test you need to
Resuspend the cells pellet, add nutrient broth
Penicillin is a
narrow spectrum antibiotic (targets gram positive)
What are broad spectrum antibiotics
can target both gram positive and gram negative suhc as chloramphenicol
What method does the antimicrobial susceptibility test use
Disk difficusion method
By comparing the zone of inhibition to an interpretive zone chart, you can determine
the antibiotics’ minimum inhibitory concentration (MIC)
What standard conditions must there be
- A McFarland standard tube -> ensure that broth cultures used have the same cell density
- Mueller Hinton agar plates -> same depth and thickness
- Concentraion of antibiotic disk must match that in the zone diameter interpretive chart
beta lactam antibiotics only effect cells that are
actively dividing
Beta lactam antibiotics only affect
cells that are gorwing and actively making cell walls
How do beta lactam antibiotics work
they work by inhibiting the transpeptidases that are neded to bridge the peptidoglycan subunits
What are some beta lactam antibitoics
cephalosporin
penicillin
How do beta lactam antibiotics work
strucutre of antibiotic similar to the peptidgolygyln cross link subunit
as a result transpeptidase binds equally well to both the peptidoglycan and the antibiotic
in the prescne e of beta lactam antibiotics -> cell wall not stable -> cells lyse
what does beta lactmase do
hydroglyzes the beta lactam ring
How to test for beta lactamse
using a disc that contains cephalosporin -> put the culture over
If there is beta lactamase, the disk will turn
Pink
What is catalse
Its an enzyme produced by microorganisms that can break down hydrogen peroxide into water and oxygen gas.
Prtects the cell against oxidative damange and reactive oxygen species
Catalase is synthesized by
areobic and facultiative anaerobic bacteria that use oxygen as a terminal electron acceptor
