Lecture 5 Flashcards
What does a pH scale indicate?
It expresses the hydrogen ion concentration of aqueous solutions.
A pH of a solution is given what logarithm and what unit of measure?
It’s given a negative logarithm of hydrogen ion concentration expressed in moles/litre.
Give an example of a basic pH level, an acidic pH level and a neutral.
Basic= 10-11
Acidi=10-2
Neutral=10-7
What is the difference of one pH unit in hydrogen ions.
10 times
How do you adjust the pH level of a culture medium in order to make the pH favourable for microbial growth. Explain the procedure for both mediums that are too acidic or too basic.
A culture medium that is too acidic= adding an alkaline substance such as NaOH (sodium hydroxyde).
A culture medium that is too basic= adding an acidic substance such as HCl (hydrogen chloride).
What type of substance can be added to a medium in order to keep the pH level constant during growth.
A buffer.
What is the most common method of sterilization and in what device is this achieved?
Steam at 121 degrees celsius. Autoclave.
Define inoculate.
To add microorganisms to a medium.
Define contamination.
Introduction undesired microorganism into a culture or other material.
Define aseptic technique.
Reducing the chances of contamination.
Enumerate the techniques to use while isolating microorganisms.
Streak plates Pour plates Inhibition or killing undesired microorganisms Dilution method Single cell isolation
Explain the procedure of streak plate
A steril loop or needle is used to lightly streak the surface of an agar plate. The pattern of streaking is important (first streak lines up, second streak lines across the top, third streaks downwards and then a zigzag in the middle). The plate will then be incubated in order to multiply colonies.
True or false. A colony can be seen to the naked eye.
True
True of false. A pure culture can’t be obtain by a streak plate method.
False. You can obtain a pure culture by this method.
Explain the preparation of a pour plate method.
A pour plate is a dilution of a sample of the mixed culture and adding a small volume to the dilution to melted agar. The mix is then added to a Petri plate to solidify then incubated.
Define the results of a pour plate method.
If dilution was appropriate, well separated colonies will be appreciated.
What two types of colonies does the pour plate method provide?
A subsurface colony (within the Agar).
A surface colony
True or false, the same species colonies will have similar appearances from the pour plate method. Elaborate.
False, same species colonies may have different appearances.
Elaborate on the method of inhibition or killing of the undesired microorganism.
The addition of a chemical to the medium, which will stump the growth or kill unwanted microbes while permitting the wanted species to multiply.
Give an example of a product used to facilitate the killing of unwanted microorganisms this method.
Basic dyes such as Crystal Violet or brilliant green will inhibit the growth or kill Gram-positive bacterial and permit the isolation Gram-negative bacteria.
Explain the dilution method.
The dilution method is used to isolate only the most predominate bacteria in the medium.
What liquid is considered a suitable diluent?
Water.
Name 3 acceptable ways of representing a 1 in 10 dilution.
1:10, 1/10, 10-1
Calculate the dilution made when 0.2 mL of 10-2 dilution is added to 4.8mL of diluent with the formula D2=(V1xD1)/V2
D2=(0.2x 10-2)/5 (.2+4.8) 5 D2=(2/100 x 1/100) /5 D2=(0.2 x 0.01) /5 D2=0.002 / 5 D2=0.0004 D2= 4/10000 D2=1/1250
