Practical microbiology 3

Practical microbiology 3

• 1.
  PRACTICAL MICROBIOLOGY Culture media formicroorganisms. Quantitation of Microorganisms.
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  • is specialmedium 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
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  Culture Media According tocomposition Synthetic Media Non-synthetic Media According to purpose of uses General Purpose Differential (Indicator) Selective
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  Classification according toComposition . 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.
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  . General purposemedia: 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.
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  . 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.
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  • The streakplate method: is one simple & useful technique for isolating bacteria and other microorganisms in pure culture . Pure culture technique
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  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 usedto 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
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  • Spectrophotometer orturbidimeter (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
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  PLATE COUNT METHOD Aviable 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.
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  For accurate determinationof 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
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  Colonial Morphology
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  Colonial Morphology