18 Questions
Define aseptic technique and its importance in microbiology.
Aseptic technique involves practices and procedures to prevent contamination from pathogens in microbiology. It is important for minimizing the risk of infection and maintaining pure stock cultures.
Explain the concept of dilution factor and provide an example calculation.
The dilution factor is calculated by dividing the initial concentration of a solution by the final concentration desired. For example, diluting a 10% stock solution to 2% gives a dilution factor of 5.
What are the key sources of contamination that aseptic techniques aim to prevent?
The key sources of contamination include airborne microorganisms (including fungi), microbes from researcher's body/lab coat, lab bench top/other surfaces, microbes in dust, and microbes in unsterilized glassware & equipment.
How can dilution be used to achieve a desired final concentration of a solution?
Dilution involves adding a calculated volume of solvent to a known volume of the initial solution to achieve the desired final concentration.
What are some common microbiological procedures where aseptic techniques are crucial?
Aseptic techniques are crucial in transferring cultures, inoculating media, isolating pure cultures, and conducting microbiological tests.
Explain how aseptic techniques can minimize or eliminate the risk of contamination in microbiological work.
Proper aseptic techniques prevent contamination by minimizing exposure to pathogens from various sources like air, surfaces, and unsterilized equipment.
What is the definition of a normal solution?
A normal solution is a solution that contains 1 gram equivalent weight of the solute per liter of solution.
Explain the concept of unit definitions in the context of solutions.
Unit definitions in solutions refer to the precise measurement of concentration or amount of solute in a given volume of solution.
How is Molarity calculated in a solution?
Molarity (M) is calculated by dividing the number of moles of solute by the volume of solution in liters.
What is the Equivalent Weight of a substance and how is it used in solution preparation?
The Equivalent Weight of a substance is the weight that is equivalent to 1 mole of hydrogen ions. It is used to calculate the amount of substance needed to prepare solutions with specific concentrations.
Explain the concept of Simple Dilution in preparing solutions.
Simple Dilution involves diluting a concentrated solution by adding a solvent to achieve the desired concentration.
How can the formula C1V1=C2V2 be applied in diluting a solution?
The formula C1V1=C2V2 is used to calculate the volume of stock solution needed to prepare a desired concentration of final solution by dilution.
What is the purpose of using serial dilutions in microbiology?
To reduce the concentration of the sample to a countable range.
How is the dilution factor related to the dilution used in microbiology?
The dilution factor is the reciprocal of the dilution used.
Explain the calculation involved in determining the Colony Forming Units (CFU) per milliliter of original sample.
Number of colonies in plate count X Dilution Factor
Why is it important to count plates with colony numbers ranging from 30 to 300?
To ensure accuracy and statistical relevance in the colony count.
What is the significance of using a growth medium instead of water as a diluent in microbiological dilutions?
A growth medium may yield a higher recovery of viable cells compared to water.
How does the volume of sample taken affect the calculation of CFU/ml?
The volume of sample taken directly impacts the final CFU/ml calculation.
Study Notes
Solution Preparation
- v/v represents volume of reagent per final solution volume.
- A simple dilution involves combining a unit volume of a liquid material with a solvent liquid to achieve the desired concentration.
- Example: Preparing 1X SSC solution from 20X stock SSC solution by diluting 1 unit of 20X solution with 19 volumes of water.
Complex Solution Preparation
- To make a complex solution with multiple solid solutes, treat each solute individually.
- Example: Preparing 5 liters of 50mM NaCl, 10mM Tris-Cl solution by calculating the required mass of NaCl (2.9g) and Tris-Cl (1.57g) and adding both to a container with water to desired volume.
Dilution Principles
- The total amount of a compound (moles or mass) remains constant during dilution.
- C1V1=C2V2, where C1 and C2 are initial and final concentrations, and V1 and V2 are initial and final volumes.
- Dilution factor is calculated by dividing the initial concentration by the final concentration desired.
Aseptic Techniques
- Aseptic technique involves practices and procedures to prevent contamination from pathogens.
- Microbiologists use aseptic technique for various procedures, including transferring cultures, inoculating media, isolating pure cultures, and microbiological tests.
- Proper aseptic techniques minimize the risk of contamination from airborne microorganisms, researcher's body/lab coat, lab surfaces, dust, and unsterilized glassware.
Serial Dilution and Plate Count
- Serial dilution involves transferring a sample to sterile tubes with diluent, mixing well, and repeating the process to achieve desired dilutions.
- Plate count involves calculating the number of colony-forming units (CFU) per milliliter of original sample using the formula: No. of colonies on plate x reciprocal of dilution of sample.
- The dilution factor is the reciprocal of the dilution.
Learn how to calculate the dilution factor in chemistry by dividing the initial concentration by the final concentration desired. Practice with examples such as diluting a 10% stock solution to a final concentration of 2%.
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