MIP 302 Test with Questions and Verified
Answers
Why was the 0.5ml of E. coli cells that was added to each of the soft agar deeps not
taken into consideration when determining the final dilution of the phage. -
✔✔Because when calculating dilutions you take the volume of phage added. It
doesn't have anything to do with the number of bacteria.
If you had 43 plaques on a plate inoculated with 1 ml of a 10^-6 dilution of phage, how
many plaques would you expect to see on a plate inoculated with 1 ml of a 10^-5
dilution of phage? - ✔✔PFUs/ml = 43 PFUs/(10^-6)(1.0ml) = 4.3x10^7 PFUs/ml
#PFUs = (4.3 x 10^7 PFUs/ml)(1.0ml)(10^-5) = 430 PFUs
You wish to make a 1/5 dilution of a sample. Only 10 ml pipettes measured in
increments of 1 ml are available for you to use. How could you make this dilution in 1
step? Please indicate the volume of sample that would be added to a given amount of
diluent. - ✔✔Yes you could do this in one step. 1 ml sample + 4 mls diluent = 1 ml
sample /5 ml total = 1/5
chemotherapeutic agents - ✔✔used to control microbial growth and may be either
bactericidal or bacteriostatic. They must also be more toxic to the pathogen than to the
host.
five principle mechanisms by which chemotherapeutic antibiotics are anti-bacterial -
✔✔1. inhibition of cell wall synthesis
2. inhibition of protein synthesis
3. inhibition of nucleic acid synthesis
4. cell membrane disruption
5. metabolic antagonism
, 1. Inhibition of cell wall synthesis - ✔✔penicillin, cephalosporins, bacitracin,
vancomycin. They have similar chemical structure to NAM peptidoglycan precursor. The
beta-lactam rings appear to bind to the enzymes used to form the peptide interbridges.
Inhibition of protein synthesis - ✔✔streptomycin, gentamicin, chloramphenicol, and
tetracycline all target some aspect of protein synthesis. They bind to either the 30s or
50s subunits preventing translation
inhibition of nucleic acid synthesis - ✔✔ciprofloxacin, norfloxacin, and ofloxacin all
inhibit bacterial gyrase, thus interrupting DNA replication and transcription. Rifampin
binds to the DNA dependent RNAP thus blocking synthesis
cell membrane disruption - ✔✔polymyxin B binds to the plasma membrane of
bacterial cells and disrupts its structure and permeability properties
metabolic antagonism - ✔✔resemble the structure of a precursor for folic acid
synthesis. Results in inhibition of folic acid synthesis and cell death
McFarland Standards - ✔✔1. the density of the inoculum being tested is matched to
that observed in the McFarland Standard to ensure that approximately the same
number of bacterial cells are inoculated on the plate for each test
2. the medium used is Mueller-Hinton agar, which ensures that the medium has the
same composition, consistency, and depth for each test.
3. the same amount of the specific antibody incorporated in each disk to ensure that the
antibiotic concentration is the same for each test
4. the plates are incubated at the same temperature for the same amount of time and in
the same atmospheric environment
5. the isolate is determined to be susceptible or resistant based on a list of standardized
measurements for the diameter of the zone of inhibition surrounding the antibiotic disk
Answers
Why was the 0.5ml of E. coli cells that was added to each of the soft agar deeps not
taken into consideration when determining the final dilution of the phage. -
✔✔Because when calculating dilutions you take the volume of phage added. It
doesn't have anything to do with the number of bacteria.
If you had 43 plaques on a plate inoculated with 1 ml of a 10^-6 dilution of phage, how
many plaques would you expect to see on a plate inoculated with 1 ml of a 10^-5
dilution of phage? - ✔✔PFUs/ml = 43 PFUs/(10^-6)(1.0ml) = 4.3x10^7 PFUs/ml
#PFUs = (4.3 x 10^7 PFUs/ml)(1.0ml)(10^-5) = 430 PFUs
You wish to make a 1/5 dilution of a sample. Only 10 ml pipettes measured in
increments of 1 ml are available for you to use. How could you make this dilution in 1
step? Please indicate the volume of sample that would be added to a given amount of
diluent. - ✔✔Yes you could do this in one step. 1 ml sample + 4 mls diluent = 1 ml
sample /5 ml total = 1/5
chemotherapeutic agents - ✔✔used to control microbial growth and may be either
bactericidal or bacteriostatic. They must also be more toxic to the pathogen than to the
host.
five principle mechanisms by which chemotherapeutic antibiotics are anti-bacterial -
✔✔1. inhibition of cell wall synthesis
2. inhibition of protein synthesis
3. inhibition of nucleic acid synthesis
4. cell membrane disruption
5. metabolic antagonism
, 1. Inhibition of cell wall synthesis - ✔✔penicillin, cephalosporins, bacitracin,
vancomycin. They have similar chemical structure to NAM peptidoglycan precursor. The
beta-lactam rings appear to bind to the enzymes used to form the peptide interbridges.
Inhibition of protein synthesis - ✔✔streptomycin, gentamicin, chloramphenicol, and
tetracycline all target some aspect of protein synthesis. They bind to either the 30s or
50s subunits preventing translation
inhibition of nucleic acid synthesis - ✔✔ciprofloxacin, norfloxacin, and ofloxacin all
inhibit bacterial gyrase, thus interrupting DNA replication and transcription. Rifampin
binds to the DNA dependent RNAP thus blocking synthesis
cell membrane disruption - ✔✔polymyxin B binds to the plasma membrane of
bacterial cells and disrupts its structure and permeability properties
metabolic antagonism - ✔✔resemble the structure of a precursor for folic acid
synthesis. Results in inhibition of folic acid synthesis and cell death
McFarland Standards - ✔✔1. the density of the inoculum being tested is matched to
that observed in the McFarland Standard to ensure that approximately the same
number of bacterial cells are inoculated on the plate for each test
2. the medium used is Mueller-Hinton agar, which ensures that the medium has the
same composition, consistency, and depth for each test.
3. the same amount of the specific antibody incorporated in each disk to ensure that the
antibiotic concentration is the same for each test
4. the plates are incubated at the same temperature for the same amount of time and in
the same atmospheric environment
5. the isolate is determined to be susceptible or resistant based on a list of standardized
measurements for the diameter of the zone of inhibition surrounding the antibiotic disk
