Microbial Growth & Culture and Sensitivity Flashcards
bacterial growth is an increase in
number
during Stationary phase there is a net increase in cell numbers
false
growth of bacteria on solid agar media
typically results in:
colony
one factor that will slow down rapid growth of bacteria in broth is
A. Increase in waste products
B. Decrease in nutrients
C. Decrease in oxygen availability
D. All of these
D
which stage of growth would we expect to see the highest concentration of bacterial cells in broth?
A. Lag phase
B. Log phase
C. Stationary phase
D. Death phase
stationary
why is the study of bacterial growth important?
to utilize or inoculate known numbers of the bacterial isolate and to assess whether a particular strain of bacteria are adapted to a particular medium
how is microbial growth measured?
either directly or indirectly
CFU or bacterial cell counts are…
direct measures
turbidity, metabolic products, and oxygen consumption are…
indirect measures
consists of diluting the sample several times and transferring of specific volume of the sufficiently diluted sample onto agar plate using either pour plate or spread plate method
Standard Plate Count
Colonies which have grown on the subsurface of the agar are counted and reported as…
colony forming units (CFU)
used in the preparation of the serial dilution of the sample
sterile saline solution or phosphate buffer diluent
number of colonies that can be counted in a plate
25 to 250
assumptions that are based around the method
(1) the culture is homogenous; (2) the colonies to be counted are between 25 to 250 colonies; and (3) each colony has risen from a viable bacterial cell that has divided several times to produce distinct growth on the agar.
labels for the test tubes and plates of SPC
1:10, 1:100, 1:1000. 1:10000, 1:100000
incubation temperature and duration
35C and 24 hours
> 250 colonies
Too Many To Count (TMTC)
< 25 colonies
Too Few To Count (TFTC)
formula for SPC
CFU/ml = no. of colonies x reciprocal of dilution / volume of culture plate
an indirect method of determining bacterial population.
Turbidimetric Method
formula for SPC
CFU/ml = no. of colonies x reciprocal of dilution / volume of culture plate
measures (turbidity) cloudiness
turbidimetric method
used for turbidimetric method
Colorimeter and UV-Vis Spectrophotometer
turbidimetric method is expressed as
% transmittance (amount of light passing through)
absorbance in plotting the bacterial growth
Optical Density (OD)
formula for optical density
OD = 2-log(%T)
a statistical method used to estimate the viable numbers of bacteria in a sample by inoculating broth in 10-fold dilutions and is based on the principle of extinction dilution
most probably number (MPN)
- carbon dioxide
- ATP
- DNA
metabolic activity
- standard plate count
- filtration
- MPN
- direct microscopic count
direct methods
- Turbidimetric
- Metabolic Activity
- Dry Weight
indirect methods
specifically target bacteria and are used to treat bacterial infections
antibiotics
encompass a broader range of products that act on microbes in general
antimicrobials
The determination of antibiotic susceptibility
of a particular pathogen to antimicrobial
agents.
culture and sensitivity
a laboratory procedure performed by medical technologists (clinical laboratory scientists) to identify which antimicrobial regimen is specifically effective for individual patients
antimicrobial susceptibility testing (AST)
culture media for AST?
mueller-hinton agar (MHA)
- Agar diffusion method or the disc diffusion method
*In this test, a number of small, sterile filter paper disks of uniform size
kirby-bauer disc method
sizes of paper disks in the kirby-bauer disc method
6 mm
used to standardize the approximate number of bacteria in a liquid suspension by comparing the turbidity of the test suspension with that of the McFarland Standard.
mcfarland standard
preparation of mcfarland standard
ass 0.05 ml of 1% Barium chloride to 9.5 of 1% Sulfuric acid
how long and at what temperature should you store the mcfarland standard?
up to 6 months in the dark at room temp (20 to 25C)
how would you check the accuracy of the density prepared mcfarland standard using a…
spectrophotometer with a 1-cm light path
absorbance at 625 nm should be
0.08 to 0.1 for 0.5 mcfarland standard
If the saline with the inoculum is more turbid than the standard,
dilute with more sterile saline solution until equally turbid
If the saline with the inoculum is less turbid than the standard,
add more inoculum, mix and then compare until equally turbid
If the saline with the inoculum is less turbid than the standard,
add more inoculum, mix and then compare until equally turbid
a circular area around the spot of the antibiotic in which the bacteria colonies do not grow
zone of inhibition (ZOI)
<10 mm and 10-13
resistant zoi
14-19 mm
intermediate zoi
<10 mm and 10-13
resistant zoi
> 19 mm
susceptible zoi
Determines the lowest concentration of an antimicrobial agent that prevents visible growth of a microorganism.
minimum inhibitory concentration (MIC)
methods for MIX
oAgar Dilution
oBroth Dilution
Macrodilution
Microdilution
antimicrobial resistance happens when microorganisms change when they are exposed to antimicrobial drugs
– World Health Organization
Antibiotic resistance happens when the germs no longer respond to the antibiotics designed to inhibit the growth (-static) or directly kill them (-cidal)
– Centers for Disease Control and
Prevention
origins of resistance
- natural resistance
- acquired resistance
mechanisms of resistance
- limiting drug uptake
- drug efflux
- β - lactamases
- Modification of Drug Targets
β – lactamase Inhibitors
*Amoxicillin + Clavulanic acid (Co-amoxiclav)
*Ticarcillin + Clavulanic acid
*Ampicillin + Sulbactam
*Piperacillin + Tazobactam
