Why streak plate technique

However, this is not necessarily true. With species in which the cells form a characteristic grouping during cell divisions, the colony-forming unit may develop from a group of cells rather than form a single cell. For example, clusters of staphylococci, chains of streptococci, etc.

Note: Bi-plate inoculation of samples from the sterile sites is often done in diagnostic laboratories to save handling time and space. Examine the colonies grown in the plate carefully.

All colonies should have the same general appearance. If there is more than one type of colony, each type should be streaked again on a separate plate to obtain a pure culture.

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Last updated on June 17th, CLED cysteine-, lactose-, and electrolyte-deficient agar is a differential culture medium primarily used for isolation and enumeration of bacteria especially from urine samples. CLED is preferred over a combination of […]. News Ticker. Appropriate method to streak plate for isolation of bacteria. Contents 1 Principle of Streaking 1. Quadrant Streaking for isolation into pure culture.

Bi-plate streaking. The modern streak plate method has evolved from the efforts by Robert Koch and other microbiologists to obtain pure culture of bacteria in order to study them. The dilution or isolation by streaking procedure was originally developed by Loeffler and Gaffky in Koch's laboratory, which involves the dilution of bacteria by systematically streaking them over the surface of the agar in a petri dish to obtain isolated colonies which will subsequently grow into mass of cells, or isolated colonies.

If the agar surface grows microorganisms which are all the genetically same, the culture is then considered as a pure culture. The commonly used petri dishes are of hundred millimetre diameter. The agar surface of the plate should be dry without any moisture such as condensation drops.

The source of inoculums can be clinical specimen, environmental swab, sedimented urine, broth or solid culture. In the streaking procedure, a sterile loop or swab is used to obtain an uncontaminated microbial culture.

The process is called "picking colonies" when it is done from an agar plate with isolated colonies and is transferred to a new agar or gelatin plate using a sterile loop or needle. The inoculating loop or needle is then streaked over an agar surface. On the initial region of the streak, many microorganisms are deposited resulting in confluent growth or the growth of culture over the entire surface of the streaked area.

The loop is sterilized by heating the loop in the blue flame of the Bunsen burner, between streaking different sections, or zones and thus lesser microorganisms are deposited as the streaking progresses. The streaking process will dilutes out the sample that was placed in the initial region of the agar surface. There are two most commonly used streak patterns, a three sector "T streak " and a four quadrant streak methods.

Growths of micro organisms require nutrients and environment conditions. Nutrient preparations made in laboratory, used for the growth of the organism are called media singular: medium. Three physical forms are used: liquid or broth media; semisolid media; and solid media. Liquid media, such as nutrient broth, tryptic soy broth, or brain heart infusion broth, can be used to propagate large numbers of microorganisms in fermentation studies and for biochemical tests.

Semisolid media can also be used in fermentation studies, in determining bacterial motility, and in promoting anaerobic growth. Solid media, such as nutrient agar or blood agar, are used for the surface growth of microorganisms in order to observe colony appearance, 2 for pure culture isolations, 3 lot storage of cultures, and 4 to observe specific biochemical reactions. While in the liquefied state, solid media can be poured into either a test tube or petri plate dish and if the agar is poured into a petri plate, the plate is designated an agar plate.

Bacteria display a wide variety of nutritional and physical requirements for their growth. Nutrient agar is a complex medium as it contains ingredients with unknown amounts or types of nutrients. Nutrient agar typically contains 0. Nutrient broth is made identically, omitting the agar. Beef extract is the commercially prepared dehydrated form of autolysed beef and is provided in the form of a paste.

Peptone source is casein milk protein that has been digested with the action of the enzyme pepsin. Peptone is dehydrated and supplied in the medium as powdered form. Peptone and beef Extract is a mixture of amino acids and peptides. Beef Extract also contains digest products which are water soluble, other macromolecules such as nucleic acids, fats, polysaccharides as well as vitamins and trace minerals cannot be chemically defined.

There are many ingredients in the media which are complex, which includes yeast extract, tryptone, and others. The importance of complex media is that they will support the growth of a wide range of micro organisms.

Agar is obtained from red algae in which it is a supplement of polysaccharide polygalacturonic acid in their cell walls. Tryptic soy agar is the medium that supports the growth of most of the fastidious organisms.

Example: Streptococc i, and some members of the genera Neisseria , Corynebacterium , Brucella , Listeria , Vibrio , Pasteurella , Erysipelothrix , etc.