1.5.1: Streak Plate

Microbial samples analyzed in microbiology labs may come from several different sources. The samples introduced to the media are known as inoculum. Samples may be taken from a variety of sources including the environment (water and soil samples) and patients in the clinical setting (i.e., sputum, fecal, urine, blood, etc.). Samples sent to microbiology laboratories for identification and analysis are typically mixed samples, meaning that they have more than one microorganism present. The microbiologist must then employ techniques that permit them to separate/isolate the individual microorganism of interest and establish a pure culture.

There are several isolation techniques employed in the laboratory setting by microbiologists to accomplish this task. These techniques include a streak plate technique, the pour plate technique, and the spread plate technique. The most common of the isolation techniques utilized is the streak plate technique. The streak plate technique allows the microbiologist to isolate a species by spreading the microorganisms in the sample across the surface of a solid media in a Petri plate, in such a manner that the sample is diluted as it is streaked, allowing organisms to develop distinct isolated colonies following incubation.

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