Practical microbiology 3

1. p ractical microbiology Culture media for microorganisms. Quantitation of Microorganisms.

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. 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.

4. . 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.

5. . 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.

6. The streak plate method: is one simple & useful technique for isolating bacteria and other microorganisms in pure culture . Pure culture technique

7. 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.

8. . 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

9. 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 * 10 8 CFU The equipments and materials used

10. 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.

11. 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

12. Colonial Morphology

13. Colonial Morphology