microbiology 2 Flashcards
2 ways to measure AB sensitivity
measure zone of inhibition surrounding the AB discs on bacterial plate
using the E-test to measure minimum inhibitory concentration for specific AB
which AB has the biggest zone of inhibition
ampicillin
what does the minimum inhibitory concentration show
gives exact concentration of AB needed to kill/inhibit bacterial growth
method for measuring AB sensitivity
measure diameter of zones of inhibition for diff AB
compare to table to see if sensitive/resistant
examine E test plate and determine conc of ampicillin needed to kill bacteria
nutrient agar
a simple medium used to grown bacteria
usually contains peptone, meat extract and NaCl plus agar
blood agar
nutrient agar base with sterile blood (horse/sheep)
suitable for testing haemolysis
MacConkey Agar
selective medium used to separate coliforms and intestinal pathogens
contains bile salts - inhibit growth of non-intestinal pathogens
contains lactose, peptone, dye neutral red
neutral red - pH indicator, acidic = pink, basic = yellow
used to determine lactose fermentation
if lactose is fermented, acid is produced = acidic
if lactose not fermented - use peptone instead - NH3 made as biproduct - increases pH
diagnostic sensitivity test agar
medium for AB sensitivity testing
none of ingredients interfere with action of AB
base allows diffusion of large molecule AB
how do you determine which AB to use
the one that gives the bigger difference between the actual zone of inhibition on your plate and the reference sensitivity number
gram stain and shape of staphylococcus
+ve
grape like clusters
gram stain and shape of streptococcus
+ve
chains
gram stain and shape of E coli
-ve
rods
gram stain and shape of Neisseria
-ve
Diplococci
gram stain and shape of enterococcus
+ve
long chains
