lab quiz 3 Flashcards
anitseptic vs disinfectant and examples
antiseptic - inhibit microbial growth on living tissue -alcohol
disinfectant- chemical agents used on inanimate objects example - bleach
What factors influence the size of the zone of inhibition produced by a chemical?
how well it diffuses into the agar, how long lasting it is, solubility
how might the physical differences between gram + and gram - bacteria contribute to differences in chemical resistances?
how they affect the cell wall
Antibiotics and antimicrobial drugs
antibiotics- compounds produced by molds or bacteria- inhibits growth and kills
antimicrobial - chemical that inhibits growth and kills microorganisms
broad and narrow spectrum antibiotics
broad- wide variety of bacteria
narrow - only a small group of bacteria
what factors influence the size of the zone of inhibition for an antibiotic?
diffusibility of the agent, size of the inoculum, and type of medium
why are certain gram - bacteria more resistant than gram + bacteria to antbiotics that attack cytoplasmic targets
gram - has a cell wall and selectively permeable cell membrane
why are gram positive bacteria typically more resistant than gram - bacteria to antibiotics that disrupt plasma membranes such as polymyxin B
because it has a thick layer of peptidoglycan
if a bacterial isolate shows intermediate to moderate resistance to an antibiotic, how might this antibiotic still be successfully used in the treatment of his microbe
a drug can still be effective by simply increasing the dosage or having 2 drugs that will have a better effect to treat a disease
what specific medium must be used in testing the effectiveness of antibiotics
mueller hinton II
for what purposes is alcohol a useful antiseptic
treat skin before inoculations of drawing blood
what advantages does alcohol have over hand soap for antiseptics of the skin
it kills bacteria on the skin
why does treatment of human skin with alcohol not create a completely sterile enviornment?
not all organisms are susceptible and some may be hiding in crevices under our skin
define the term colony
visible microbial growth on solid medium that originated from single parent cell and produced daughter cells
what colony characteristics can be used for differentiation of bacterial species? compare s.marcessens to m.luteus
size, color, shape and texture
s marcessens - red
m.lutus = yellow
why is dilution a necessary part of pure culture preparation?
essential for seperating cell so it grows into isolated colonies
what advantages does a streak plate method have over a pour plate method
economical in materials and time
what advantages does the pour plate method have over the streak plate method
less skill required
why is the loop flamed before it is placed in a culture tube? why is it flamed after completing the inoculation
sterilize the loop of any microbes on it
before inoculating and pouring molten nutrient agar into a plate, why must the agar first be cooled to 50C
to avoid condensation
explain why plates should be inverted during incubatin
to prevent condensation and prevent contamination
