Table of Contents
In the lethal effect of ultraviolet radiation on microbial growth experiment, why was the lid removed from the plate before exposure to the UV light? Because UV radiation cannot penetrate through plastic.
Why was the cover used the UV light exercise?
The purpose of this exercise is to demonstrate the comparative effect of UV on two bacterial populations. This could have been accomplished without the cardboard cover. UV radiation does not penetrate well. The cover is used as a control to illustrate the amount of growth in the absence of UV exposure.
Why wouldn’t it be advisable to compare growth of the organism on each plate to each other?
why wouldn’t it be advisable to compare growth of the organisms on each plate to each other? there are at least two answers to this question. You do not know how the inhibitors may have affected the growth of the different organisms. So you can’t compare growth on selective media.
How would you expect both positive and negative results to be affected if you were to add glucose to the medium quizlet?
What is the starch hydrolysis amylase test? How would you expect both positive and negative results to be affected if you were to add glucose to the medium in the starch hydrolysis test? The glucose would cause the starch breakdown to be slower resulting in a false negativ. What is the DNA Hydrolysis DNase test?.
Which organism survived the longest exposure Why do you suppose it?
megaterium survived the longest because it contains spores, which are resistant to heat. Why were you told to remove the plate covers prior to exposing them to UV?.
Do you think you should remove the cover of the petri dish when exposing to UV light Why or why not?
1. The directions are not clear and do not mention removing the cover from the Petri dish. However, since plastics can block or scatter some UV rays, it would be better to remove it for the experiment.
Why did you put your bacterial plates in a dark drawer after exposing them to UV before placing them in the incubator?
3. Put your plates (with the half lids) under UV light for the appropriate exposure time. UV light can burn your skin and eyes.
Why is it important to notice and record of each bacteria grow on a selective media?
Selective media favor the growth of some microorganisms while inhibiting others. Differential media help distinguish bacteria by the color of the colonies or the change in the medium.
Would Removing colistin and nalidixic acid from CNA?
Would removing colistin and nalidixic acid from CNA alter the medium’s sensitivity or specificity? It would alter specificity because organisms that shouldn’t grow on it would. It wouldn’t likely alter sensitivity because you would probably still be able to detect growth of organisms that should grow on it.
Why is it necessary to use two controls rather than just one?
It is important to use 2 controls because the tubes show “no color change” under 2 different conditions (anaerobic and aerobic). All enterics are facultative anaerobes; they have both respiratory and fermentative enzymes. contamination with an aerobic organism occurred AFTER the mineral oil was added.
Why is a positive and negative control used for each biochemical test?
Why is a positive and a negative control used for each biochemical test? The first two answers only: It allows you to visualize what a positive and what a negative result looks like, respectively. It allows you to see if your reagents are working correctly.
What was the purpose of incubating the unopened plates?
The purpose of incubating unopened plates is to check in there is contamination in the media preparation phase.
What is the purpose of using positive and negative controls used in a biochemical test?
A positve control ensure that all the reagents are working properly and the test is performed correct. The negative control ensures that that are no false negative results.
What do you expect to see on the MSA and Na plates?
Growth on the MSA and NA plates was recorded as “good growth”, “poor growth” or “no growth”. These are qualitative and, at least for the first two, subjective terms. This means that bacteria that are sensative to salt would grow on the NA, but not on the MSA.
Were the uninoculated controls positive or negative controls and what purpose did they serve?
Were the uninoculated controls in this lab positive or negative, and what purpose did they serve? The controls were negative, and served as color comparison for experimental tubes as well as verification for media sterility.
Why is it important to perform the reagent tests last?
Why is it important to perform the reagent tests last? If it does not ferment glucose, or have a positive result on at least 3 other tests then it is probably not enteric or not identified by the test. Organism could have performed poorly. MacConkey reveal gram status and ferment lactose.
What did you conclude from observing the plate that was exposed to UV radiation with the lid on?
It was a control, because visible light does no have UV. **What did you conclude from observing the plate that was exposed to UV radiation with the lid on? It had poor penetrating ability.
How does UV radiation affect microbial growth?
In the process of controlling microorganisms, UV light damages their DNA, where organisms grow by cell division and genetic information is transmitted from a generation of cells to the next by the splitting of the DNA. This will reduce the ability of the DNA to multiply and cause disease.
Can UV penetrate a Petri dish lid?
The UV failed totally to penetrate thin (66 µm) paper or Petri dish plastic, although it did penetrate plastic sandwich wrap.
Why should you never set the lid of the Petri dish or the test tube cap on the bench top?
Never set them on the table, as they could pick up contaminants. Also, keep the lid over a plate when removing inoculum, as this will help prevent environmental contamination. Always flame the lip of a culture tube when you open it and before you replace the cap.
Why is it necessary to flame the mouth of the tube before and after performing an inoculation?
Flaming the Mouth of the Test Tube: Passing the mouth of a tube through the flame of a Bunsen burner creates a convection current which forces air out of the tube. This prevents airborne contaminants from entering the tube.
How do you identify bacteria on a Petri dish?
Bacteria. Each distinct circular colony should represent an individual bacterial cell or group that has divided repeatedly. Being kept in one place, the resulting cells have accumulated to form a visible patch. Most bacterial colonies appear white, cream, or yellow in color, and fairly circular in shape.
