2. • is special medium used in microbiological laboratories to
grow different kinds of microorganisms.
• A culture may be solid or liquid. The solid culture media is
composed of a brown jelly like substance known as agar.
Culture Media
3. Culture Media
According to composition
Synthetic
Media
Non-synthetic
Media
According to purpose of
uses
General
Purpose
Differential
(Indicator)
Selective
4. Classification according to Composition
. Synthetic Media: A medium in which only pure
chemicals in definite concentrations are used, these
media are usually used for specific purpose such as
enrichments of autotrophs or in vitamin assay work.
. Non-synthetic Media: A medium in which the exact
chemical composition of each of the constituents is
not certainly known, these complex media are prepared
from raw materials such as ( Meat extract – yeast
extract and various sugars ) . They support the growth
of variety of microorganisms.
5. . General purpose media: support the growth of a large variety
of microbes. For example: nutrient agar.
. Differential (Indicator) media: contain reagents or chemicals
that produce differences in growth that allow the observer to
differentiate between types of microbes. For example : Blood
agar media or media containing PH indicator.
Classification according to the purpose of
uses.
6. . Selective Media : Allow for the growth of only certain
types of organisms due to the addition of inhibitors or
specific carbon source.
For example : addition of sodium azide to a medium
would inhibit the growth of organisms using
respiration but would permit growth or organisms
using only fermentation.
For example : if a particular medium contains lactose
as a sole carbon source then the lactose fermenting
organisms in a mixed culture would tend to outgrow
the other types.
7. • The streak plate method: is one simple & useful technique
for isolating bacteria and other microorganisms in pure
culture .
Pure culture technique
8.
9. Quantitation of Microorganisms
• Provides general information on the various methods
used to estimate the number of microorganisms in a given
sample.
• It is limited to methods used for the enumeration of
microbial cells and not the measurements of microbial
cellular mass.
QUANTIFICATION
STANDARD PLATE
COUNT
TURBIDIMETRIC
10. . Is used to measure the turbidity in a suitable liquid
medium inoculated with a given microorganism.
. It is based on the correlation between the turbidity and
changes in the microbial cell number.
. Standard optical density (OD) or turbidimetric curves then
used to estimate the number of microbial cells.
Turbidimetric Method
11. • Spectrophotometer or turbidimeter (Wave length range of
420 to 615 nm)
• Cuvettes, pipettes, specific growth media .
• The typical turbidimetric standard used is the McFarland
ex. If E.coli is used , the 0.5 McFarland standard is
equivalent to an approximate conc. Of 1.5 * 108 CFU
The equipments and materials used
12.
13. PLATE COUNT METHOD
A viable cell: Is defined as a cell which is able to divide and
form a population (or colony).
1- A viable cell count is usually done by diluting the original
sample.
2- Plating aliquots of the dilutions onto an appropriate culture
medium.
3- Then incubating the plates under proper conditions so that
colonies are formed.
4- After incubation, the colonies are counted and from a
knowledge of the dilution used, the original number of viable
cells can be calculated.
14.
15.
16.
17. For accurate determination of the total number of viable
cells: The total number of viable cells is usually reported as
Colony-Forming Units (CFUs) rather than cell numbers.
A plate having 30-300 colonies is chosen because this
range is considered statistically significant.
If there are less than 30 colonies on the plate: small
errors in dilution technique or the presence of a few
contaminants will have a drastic effect on the final count.
if there are more than 300 colonies on the plate: there
will be poor isolation and colonies will have grown together.
PLATE COUNT METHOD
