18 Questions
What is the formula for calculating dilution factor?
IC / FC = Dilution factor
What is the purpose of performing serial dilutions in microbiology?
To reduce the concentration of the sample for accurate colony counting.
If you wish to dilute a 15% stock solution to a final concentration of 5%, what is the dilution factor?
15/5 = 3 (dilution factor)
Explain the significance of the dilution factor in microbiological serial dilutions.
The dilution factor is the reciprocal of the dilution and is used to calculate the concentration of Colony Forming Units (CFU) per milliliter.
What is the purpose of using aseptic techniques in microbiology?
To prevent contamination from pathogens and minimize the risk of infection.
How can the dilution factor be calculated from the dilution label (e.g., 10-1, 10-2, etc.)?
The dilution factor is 10 raised to the power of the exponent in the dilution label.
List three procedures in microbiology where aseptic technique is commonly used.
Transferring cultures, Inoculating media, Isolation of pure culture
What formula is used to calculate the CFU/ml from the number of colonies on a plate and the dilution factor?
CFU/ml = Number of colonies on plate x Reciprocal of dilution factor
What are some sources of contamination that proper aseptic techniques aim to prevent?
Airborne microorganisms, Microbes from researcher’s body/lab coat, Microbes in dust
Explain the importance of maintaining a 'Pure stock culture' in microbiology.
To ensure the accuracy and reliability of experimental results.
How is the unit of CFU/ml interpreted in microbiology?
CFU/ml represents Colony Forming Units per milliliter, indicating the concentration of viable cells in the sample.
Why is it essential to count plates with colony numbers between 30 to 300 in microbiological analysis?
To ensure the accuracy of the colony count and statistical reliability of the results.
What is the formula for calculating the final volume of a solution after dilution?
C1V1=C2V2
How does the total amount of a compound (moles or mass) change when diluting a solution?
It does not change.
In a solution, how is the total mass calculated?
Concentration x volume = total mass
What is the equivalent weight of NaCl if its molecular weight is 58 g/mol?
NaCl = 2.9 g
How can a 1X saline sodium citrate (SSC) solution be prepared from a 20X stock SSC solution?
By diluting one unit (volume) of 20X solution with 19 volumes of water.
What is the formula for dilution factor when diluting a solution?
CiVi=CfVf
Study Notes
Solution Preparation
- v/v = volume of reagent per final solution volume
- Simple dilution: combining a unit volume of a liquid material with an appropriate volume of a solvent liquid to achieve the desired concentration
- Example: preparing 1X SSC solution from 20X stock SSC solution by diluting one unit of 20X solution with 19 volumes of water
Complex Solution
- To make a complex solution with two or more solid solutes, treat each solute individually
- Calculate the mass of each solute needed based on its molecular weight (MW)
- Example: preparing 5 liters of 50mM NaCl, 10mM Tris-Cl solution
Dilution Formula
- C1V1 = C2V2, where C1 and C2 are initial and final concentrations, and V1 and V2 are initial and final volumes
- Concentration x volume = total mass
- Example: 50mg of X in 100ml diluted to 1L still has 50mg of X
Serial Dilution
- Methods for diluting a solution, depending on experimental requirements
- Determine the dilution factor before diluting a solution
- Steps for serial dilution: take several sterile tubes, label with dilution factors, add diluent and stock sample, mix well, and repeat
Plate Count
- Procedure for viable counting using serial dilutions of the sample and the pour-plate method
- Calculation: No. of colonies on plate x reciprocal of dilution of sample = CFU / ml
- Example: 32 colonies on plate of 1:10,000 dilution = 320,000 CFU/mL
Colony Counting System
- Count plates with colony numbers between 30 and 300
- Use formula to calculate: Cells (CFU) per milliliter of original sample = Number of colonies in plate count x Dilution Factor / Volume of sample taken
Aseptic Techniques
- Definition: practices and procedures to prevent contamination from pathogens
- Importance: to maintain pure stock culture while transferring to a new media
- Types of contamination: airborne microorganisms, microbes from researcher's body/lab coat, lab surfaces, dust, and unsterilized glassware & equipment
- Proper aseptic techniques can minimize and eliminate the risk of contamination
Learn about diluting solutions with examples like preparing a 1X saline sodium citrate solution from a 20X stock solution. Understand the process for making complex solutions with multiple solid solutes.
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