MIP 300 Final Exam Prep test with Questions
and Verified Answers
Why is it necessary to match the bacterial inoculum against a 0.5 McFarland standard? -
✔✔This is to match the density of the inoculum so that each bacteria tested has
approximately the same number of cells
A zone of inhibition of at least 14 mm indicates that an E. coli isolate is susceptible to
ampicillin, but a staphylococcal isolate is determined to be susceptible only if the zone
of inhibition is at least 29 mm. Why is there a difference in how the results are
interpreted for this antibiotic for these two types of isolates? - ✔✔Ampicillin acts as
an irreversible inhibitor of transpeptidase which the cell uses to make the cell wall.
Gram neg bacteria have a smaller ppg layer so it will not be as effective against them as
they are to gram pos. This is why the zone of inhibition is smaller than gram pos.
Based on your results which of the antibiotics that were tested would you recommend
to the physician for use in treating an e. coli infection? - ✔✔Our results showed that
all antibiotics except penicillin G, E.coli is susceptible to. Based on out results,
Trimethoprim sulfamethoxazole had the greatest zone of inhibition based on its S zone.
Thus, it had the greatest impact on the cells and would be most effective.
Based on your results which of the antibiotics that were tested would you NOT
recommend to the physician for use in treating an E.coli infection - ✔✔I would not
recommend penicillin G as it had a zone of inhibition of 0 mm so it seems E.coli is
resistant to it based on our results.
Why is penicillin toxic to bacteria but not to humans? - ✔✔Due to selective toxicity.
Penicillin inhibits ppg cell wall synthesis exclusive to bacteria. So it will kill bacteria but
not eukaryotic cells.
, Tetracycline has many side effects in humans including severe sun sensitivity. Why
would tetracycline be more likely to make you ill than penicillin? - ✔✔Tetracycline
targets the 30s subunit of ribosomes, which we have in our mitochondria.
disinfectant - ✔✔any chemical agent used to destroy or inhibit the growth of harmful
organisms on inanimate objects
antiseptic - ✔✔antimicrobial that can be used on living tissue
physical means of microbial control - ✔✔heat, radiation, and filtration
Chemical means of microbial control - ✔✔This includes halogens, phenolics, alcohols,
heavy metals, quaternary ammonium compounds, aldehydes, and gases
pour plate technique - ✔✔diluted bacteria is mixed with heated agar and poured into
petri, showing the different biochemical needs among the bacteria
lenticule colonies - ✔✔bacterial colonies growing in the agar with an oval shape
colony forming unit (CFU) - ✔✔term used to define the cell or group of cells that
produces a colony when transferred to plated media. each colony arises from one cell.
Colonies are counted and the number of CFU's in 1 ml of the inoculum is determined.
Why was it necessary to pipet a small amount of sample into a petri dish before
exposure to UV light, instead of simply exposing the entire sample? - ✔✔As you
increase population size you have to increase exposure time so we decreased the
population size in order to expose it to UV for only 5 minutes
and Verified Answers
Why is it necessary to match the bacterial inoculum against a 0.5 McFarland standard? -
✔✔This is to match the density of the inoculum so that each bacteria tested has
approximately the same number of cells
A zone of inhibition of at least 14 mm indicates that an E. coli isolate is susceptible to
ampicillin, but a staphylococcal isolate is determined to be susceptible only if the zone
of inhibition is at least 29 mm. Why is there a difference in how the results are
interpreted for this antibiotic for these two types of isolates? - ✔✔Ampicillin acts as
an irreversible inhibitor of transpeptidase which the cell uses to make the cell wall.
Gram neg bacteria have a smaller ppg layer so it will not be as effective against them as
they are to gram pos. This is why the zone of inhibition is smaller than gram pos.
Based on your results which of the antibiotics that were tested would you recommend
to the physician for use in treating an e. coli infection? - ✔✔Our results showed that
all antibiotics except penicillin G, E.coli is susceptible to. Based on out results,
Trimethoprim sulfamethoxazole had the greatest zone of inhibition based on its S zone.
Thus, it had the greatest impact on the cells and would be most effective.
Based on your results which of the antibiotics that were tested would you NOT
recommend to the physician for use in treating an E.coli infection - ✔✔I would not
recommend penicillin G as it had a zone of inhibition of 0 mm so it seems E.coli is
resistant to it based on our results.
Why is penicillin toxic to bacteria but not to humans? - ✔✔Due to selective toxicity.
Penicillin inhibits ppg cell wall synthesis exclusive to bacteria. So it will kill bacteria but
not eukaryotic cells.
, Tetracycline has many side effects in humans including severe sun sensitivity. Why
would tetracycline be more likely to make you ill than penicillin? - ✔✔Tetracycline
targets the 30s subunit of ribosomes, which we have in our mitochondria.
disinfectant - ✔✔any chemical agent used to destroy or inhibit the growth of harmful
organisms on inanimate objects
antiseptic - ✔✔antimicrobial that can be used on living tissue
physical means of microbial control - ✔✔heat, radiation, and filtration
Chemical means of microbial control - ✔✔This includes halogens, phenolics, alcohols,
heavy metals, quaternary ammonium compounds, aldehydes, and gases
pour plate technique - ✔✔diluted bacteria is mixed with heated agar and poured into
petri, showing the different biochemical needs among the bacteria
lenticule colonies - ✔✔bacterial colonies growing in the agar with an oval shape
colony forming unit (CFU) - ✔✔term used to define the cell or group of cells that
produces a colony when transferred to plated media. each colony arises from one cell.
Colonies are counted and the number of CFU's in 1 ml of the inoculum is determined.
Why was it necessary to pipet a small amount of sample into a petri dish before
exposure to UV light, instead of simply exposing the entire sample? - ✔✔As you
increase population size you have to increase exposure time so we decreased the
population size in order to expose it to UV for only 5 minutes
