Why streak plate

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.

The agar itself is a white, amber color. Suspend 40 grams in 1 liter distilled or deionised water. Heat to boiling to dissolve completely. Cool to room temperature. Sterilizing media to above 0 C for 15 minutes in an autoclave destroys nearly all living cells and spores. If screw caped bottles are used, the cap must be loosened prior to sterilization process. It is convenient to use 1L capped bottles for preparing large quantities. To promote cooling, handling, and pouring, we usually prepare them with mL medium.

Agar does not deliver uniformly when melted. To assure a uniform distribution for pouring into plates or tubes is to drop a magnetic stir bar in the flask or bottle, then stir the medium after sterilization gently, while the media cools. Stirring spreads the agar evenly. The agar is immediately poured into a sterile, dry petri plate while holding the top carefully above the petri plate bottom in order to avoid contamination. Replace the top, allow the agar to cool and harden, and store the petri plates in an inverted position.

When storing petri plates, do not stack them more than three high, or use a special petri plate storage holder. The agar is then poured into the plates using aseptic technique, preferably in a sterile cabinet laminar air flow cabinet. Cite this Simulator:. Objective: To obtain isolated microbial colonies from an inoculum by creating areas of increasing dilution on an agar petriplate. Principle: The streak plate method is a rapid qualitative isolation method.

Importance of Streaking: The human body has billions of bacteria which constitutes the normal flora fighting against the invading pathogens. Types of Media: Growths of micro organisms require nutrients and environment conditions. Media and Media Components: Bacteria display a wide variety of nutritional and physical requirements for their growth.

Media Sterilization: Sterilizing media to above 0 C for 15 minutes in an autoclave destroys nearly all living cells and spores. When these lone bacterial cells divide and give rise to thousands and thousands of new bacterial cells, an isolated colony is formed. Pure cultures can be obtained by picking well-isolated colonies and re-streaking these on fresh agar plates. A common assumption is an isolated colony of bacteria is the progeny of a single bacterial cell i.

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. 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 […]. Last updated on June 21st, Microorganisms can produce different types of volatile compounds that may give characteristics smell, pleasant scent, or pungent odor. Production of these volatile chemicals depends on the metabolic characteristics of […].

Last updated on June 11th, Spread plate technique is a viable counting method employed to plate a liquid sample for the purpose of isolating or counting the bacteria present in that sample.

A perfect spread plate technique […]. News Ticker. Appropriate method to streak plate for isolation of bacteria.