Micro - Lab Disinfectant

What is an antibiotic? A synthetic chemical that kills bacteria A chemical that inhibits microbial growth An organism that inhibits the growth of other organisms All available answers are characteristics of an antibiotic.

A chemical that inhibits microbial growth

After performing this lab, your lab partner decides that she will disinfect her forceps with bleach rather than with alcohol. Why is this a bad idea? Some residual bleach may remain on the forceps. Therefore, you could accidentally mess up your experiments by adding bleach to them without even knowing. Bleach can adversely (and dangerously) react with certain laboratory chemicals. Bleach takes much longer to kill than does alcohol. All available answer choices are true.

All available answer choices are true.

Since longer exposures to disinfectants result in better disinfection, why don't we just disinfect everything we need to for a minimum of 5 days? This is impractical financially. Long exposures could begin to adversely affect delicate objects. This may increase the probability of someone being exposed to the harsh disinfectants. All available answers are correct.

All available answers are correct.

Why is it critical to use aseptic technique when transferring the antibiotic disks to the agar? Contaminating organisms could produce their own antibiotics. Contaminating microorganisms could break down the antibiotics. Contaminating microorganisms could alter the diffusion of the antibiotics through the agar. All available answers are correct.

All available answers are correct.

Compare the zone of inhibition chart for ampicillin (when testing Gram-positive organisms) and chloramphenicol. What might you predict based on these data? Chloramphenicol: 12 mm zone of inhibition Ampicillin: 26 mm zone of inhibition Ampicillin diffuses much faster/farther into the agar than does chloramphenicol. Most organisms are resistant to chloramphenicol but not to ampicillin. Ampicillin is a much more potent antibiotic than chloramphenicol. Most organisms are resistant to ampicillin, but not to chloramphenicol.

Ampicillin diffuses much faster/farther into the agar than does chloramphenicol.

You have a spill in the lab, contaminating the benchtop with an organism that is very naturally resistant to disinfectants. How might you increase the potency of the disinfectant you use? Increase the concentration of the disinfectant Alter the pH of the disinfectant Decrease the concentration of the disinfectant, but leave it on for a longer time All available answers are correct.

Increase the concentration of the disinfectant

Think about those household cleaners that claim to kill 99.99% of germs. Which of the following experiments would best test this claim? Swab an entire desk. Determine the number of bacteria on the swab. Disinfect the desk, and reswab. Determine the number of bacteria remaining. Inoculate a broth with bacteria swabbed off of a desk. Determine the number of bacteria in the tube. Subject the contents to the disinfectant. Determine the number of bacteria still in the tube. Impregnate a disk with the disinfectant. Place this disk on an agar plate which has been fully inoculated with a particular bacterium. Determine the zone of inhibition. Swab a desk before and after you disinfect it. Place the swabs in broth, and see if they grow.

Inoculate a broth with bacteria swabbed off of a desk. Determine the number of bacteria in the tube. Subject the contents to the disinfectant. Determine the number of bacteria still in the tube.

You measure the zone of inhibition around a rifampin disk as 17 mm. How would you report the susceptibility of this organism to rifampin? Indeterminant Ausceptible Intermediate Resistant

Intermediate

Which of the following best describes what a single Kirby-Bauer plate is testing? Do different antibiotics diffuse the same distance through agar? Is a particular bacterium susceptible to any of a variety of antibiotics? Are a variety of bacteria susceptible to a single antibiotic? All available answer choices are possibilities.

Is a particular bacterium susceptible to any of a variety of antibiotics?

Why is lab disinfectant often used as a control when testing a new substance's ability to kill microorganisms in broth? It ensures that your testing system is working since you know lab disinfectant will kill certain microorganisms. You are always trying to find something that works better than lab disinfectant. All available answers are correct. Lab disinfectant is very concentrated, so this will allow you to determine how concentrated the test chemical is.

It ensures that your testing system is working since you know lab disinfectant will kill certain

Some household disinfectants claim that they kill 99.99% of germs. Do you think this is likely? It is impossible to evaluate this claim without knowing how they did the experiment. No, nothing is potent enough to kill that many germs. Yes, many household germs are very susceptible to disinfectants.

It is impossible to evaluate this claim without knowing how they did the experiment.

You perform a Kirby-Bauer assay with two antibiotics. Antibiotic X has a zone of inhibition of 9 mm. Antibiotic Y has a zone of inhibition of 11 mm. Which antibiotic is better at killing this particular microorganism? Antibiotic Y Antibiotic X and Y, which have identical antimicrobial activities Antibiotic X It is impossible to tell from the information given.

It is impossible to tell from the information given.

Which of the following is NOT an environmental condition that needs to be considered when selecting a disinfectant? Length of exposure pH Temperature Type of material to be disinfected

Length of exposure

You perform a Kirby-Bauer assay, but you neglect to use aseptic technique. Your plate becomes contaminated with a bright red organism. You can easily tell this organism apart from the one you intended to inoculate (which has grown into a nice lawn all over the plate). In order to conserve time, you measure the zone of inhibition for your intended organism, ignoring the contaminants. Are you assured to get the correct answer using this method? Yes, but you would have to subtract 1-2 mm from the intended organism's zone of inhibition to account for the presence of the contaminant. Yes, you can easily tell the two organisms apart, ensuring that you measure only the zone of inhibition for the correct organism. No, the contaminant adds too many variables to make this assay usable. Yes, but you have to factor in the zone of inhibition for the contaminant as well.

No, the contaminant adds too many variables to make this assay usable.

What are the three possible outcomes for each antibiotic: microorganism pair in a Kirby-Bauer assay? Stunted, robust, or intermediate Similar, reversion, or indeterminate Susceptible, resistant, or intermediate Susceptible, resistant, or indeterminate

Susceptible, resistant, or intermediate

What is a zone of inhibition? The area around the Bunsen burner that is considered sterile The area around the antibiotic disk in which bacteria cannot grow The area between two antagonistic antibiotics The area in which antibiotics are inhibited from killing bacteria

The area around the antibiotic disk in which bacteria cannot grow

Why are the tests performed in the lab not always a good indicator of how effective a disinfectant will be in the real world? The lab tests use more toxic versions of the disinfectants. The lab tests use unreasonably high concentrations of the disinfectants. The lab tests often involve lots of bacteria growing on nutrient agar; nutrient agar is rarely disinfected in reality. All available answers are correct.

The lab tests often involve lots of bacteria growing on nutrient agar; nutrient agar is rarely disinfected in reality.

Which of the following characteristics does NOT need to be standardized in a Kirby-Bauer assay? The size of the antibiotic disk The number of bacteria plated The thickness of the agar The method used to develop a bacterial lawn on the agar plate

The method used to develop a bacterial lawn on the agar plate

As a control for an experiment, you add a disk impregnated with a relatively low amount of alcohol to a plate on which you had streaked a large quantity of bacteria. After incubating this at 37°C for 2 days, you are surprised by the small zone of inhibition. Which of the following could explain these data? This was a poor control. Alcohol is not a disinfectant. The small amount of alcohol evaporated and, therefore, could not kill the bacteria. You added too much alcohol to the disk. None of the above is correct.

The small amount of alcohol evaporated and, therefore, could not kill the bacteria.

What does the Kirby-Bauer test assess? The susceptibility of an organism to a set of antibiotics The ability of a microorganism to swim away from an antibiotic The ability of an organism to mutate in the presence of an antibiotic The ability of a microorganism to secrete an antibiotic

The susceptibility of an organism to a set of antibiotics

You and your lab partner decide to test the effectiveness of two particular phenolic compounds in killing bacteria. You each add 10 µl of one of the compounds to your test and incubate it. Because of a miscommunication, you incubate at 37°C and your partner incubates at 25°C. Based on the results, it appears that your compound killed many more bacteria than did your partner's. What could explain this data? The temperature of your plate increased its permeability. So, the results may simply be a function of greater diffusion rather than better effectiveness. You have to rerun the experiment because the higher temperature may have made your compound more effective. Your compound must have a much greater intrinsic killing ability. Your compounds are so vastly structurally different, you cannot directly compare them.

You have to rerun the experiment because the higher temperature may have made your compound more effective.

Why must you consider the pH of the location you plan to treat with a disinfectant? The pH may alter the potency of the disinfectant. The pH may alter the interaction between the disinfectant and the microbe. The pH may alter the susceptibility of the microbe. All available answers are correct.

All available answers are correct.

Why is it critical that disks impregnated with disinfectants be placed as far from one another as possible on the agar plate? If they are too close together, they may enhance one another's effect. If they are too close to one another, it will be hard to interpret the results. If they are too close together, they may antagonize each other's effects. All of the above are correct.

All of the above are correct.

Which of the following is most resistant to disinfectants? Bacterial endospores Viruses Gram-positive bacteria Fungi

Bacterial endospores

You perform a Kirby-Bauer test for a patient with a bladder infection caused by a Gram-positive organism. Considering the following data, which antibiotic would you prescribe? Chloramphenicol: 12 mm zone of inhibition Cefoxitin: 18 mm zone of inhibition Streptomycin: 14 mm zone of inhibition Ampicillin: 26 mm zone of inhibition Chloramphenicol Cefoxitin Streptomycin Ampicillin

Cefoxitin

What is the difference between a disinfectant and an antiseptic? Disinfectants are used on inanimate objects, antiseptics are used on living tissue. Disinfectants are used on living tissue, antiseptics are used on inanimate objects. Disinfectants kill pathogens, while antiseptics kill all microorganisms. Disinfectants kill all microorganisms, antiseptics kill only pathogens.

Disinfectants are used on inanimate objects, antiseptics are used on living tissue.

Which of the following is indicative of an effective disinfectant? Reversion mutations occur in the bacterial population. The media shows growth with or near the chemical you're testing. The pH of the media will be altered, thus changing the color of the media. None of the above is correct.

None of the above is correct.

Which chemical is best to use for disinfection regardless of the environmental or microbiological conditions? Bleach Hydrogen peroxide Phenol None of the available answers are correct.

None of the available answers are correct.

You measure the zone of inhibition around an erythromycin disk as 12 mm. How would you report the susceptibility of this organism to erythromycin? Susceptible Indeterminant Resistant Intermediate

Resistant

You measure the zone of inhibition around a tetracycline disk as 19 mm. How would you report the susceptibility of this organism to tetracycline? Intermediate Resistant Susceptible Indeterminant

Susceptible

What characteristic of the Kirby-Bauer test helps scientists to determine if a microorganism is susceptible to an antibiotic? The ability of the microorganism to degrade the agar around the antibiotic disks A pH change that alters the color of the agar surrounding the antibiotic disk The diameter of the zone of inhibition surrounding the antibiotic disks The size of the colonies the organism forms

The diameter of the zone of inhibition surrounding the antibiotic disks