How does streak plate work

When working with cultures of living organisms, it is extremely important to maintain the environments in which cells are cultured and manipulated as free of other organisms as possible. This means passing rims and lids through the flame produced by a Bunsen burner in order to kill microorganisms coming in contact with those surfaces. Sterile technique, in general, is a learned state-of-being, or mantra, where every utilization of any sterile material comes with the caveat of taking every precaution to ensure it remains as free of contaminants as possible for as long as possible.

A serial dilution is the step-wise dilution of a substance in solution. Usually the dilution factor at each step is constant, resulting in a geometric progression of the concentration in a logarithmic fashion.

A ten-fold serial dilution could be 1 M, 0. A culture of microbes can be diluted in the same fashion. For a ten-fold dilution on a 1 mL scale, vials are filled with microliters of water or media, and microliters of the stock microbial solution are serially transferred, with thorough mixing after every dilution step. The dilution of microbes is very important to get to microbes diluted enough to count on a spread plate described later. In microbiology, streaking is a technique used to isolate a pure strain from a single species of microorganism, often bacteria.

Samples can then be taken from the resulting colonies and a microbiological culture can be grown on a new plate so that the organism can be identified, studied, or tested. 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 11th, Pour plate method is usually the method of choice for counting the number of colony-forming bacteria present in a liquid specimen. Because the sample is mixed with the molten […]. 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.

It is also used by expert practitioners to start new maintained cultures by picking off an appropriate isolated colony of an identifiable species with a sterile loop and growing the cells in sterile nutrient broth. This is the method used by professional microbiologists and is best reserved for older students working in a relatively dust and draught-free laboratory.

At all times hold the loop as still as possible. Make sure that a small amount of the culture is carried over. Microbiology teacher resources Society for General Microbiology — source of Basic Practical Microbiology, an excellent manual of laboratory techniques and Practical Microbiology for Secondary Schools, a selection of tried and tested practicals using microorganisms.