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Kitchen Streak Plate and Lab Report

Samantha Smith BS 203

Introduction: The scientific objective of this experiment is to isolate microbes on a streak plate. A streak plate is a common type of isolation technique. Identifying the microbe is achieved by the quadrant streak plate method. Streaking for isolation of microbes involved dilution of organism until there are individual colonies that can then be stained and seen under the microscope.

Materials and Methods: Materials included in this experiment include 

Honey Nut Cheerios as small particles

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Ragu marinara sauce as the medium

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Disposable paper plate as the agar plate

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Scoop as the loop or transfer device

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Solo cup containing water as the particle remover

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Solo cup as the culture tube

The small particles and medium are mixed together in a culture tube to begin the experiment. The loop is then sterilized and gathered a sample from the culture tube. After the sample is

collected from the culture tube, the microbe is then streaked onto the agar plate using the quadrant streak method. Once the first streak has been made on the agar, the loop was resterilized. Using that same sterilized loop, it was streaked through the inoculated quadrant and streaked into the next quadrant. This process was repeated until all four quadrants were streaked. Please note under normal circumstances in a lab, the agar would then be placed into an incubator and would be evaluated for isolation of bacterial colonies. For this home experiment, the incubator was not performed.

Results: Observation of the materials in the beginning were mixed. There was a thick liquid mixed with particles that were large, round, and textured. After the first quadrant streak was made, the streak looked to be mixed. The large, rounded particles surface still look textured. The particles had raised elevations with smooth surfaces. Evaluation of the second quadrant streak, the second quadrant contained less particles, only about 2-3. After the third streak, the medium became more spread out and translucent. The fourth streak in contained two isolated particles. The characteristics were as follows: Size – 3mm , Shape - circular, Margin – entire, smooth, Surface – Smooth, Texture – dry, Elevations – raised, Color – tan/beige, opaque.

Discussion: Normally a gram stain would be completed after the isolation of colonies on an agar plate. Gram stain is a differential stain that differentiates organisms. Gram negative and gram positive cells are identified by differences in the cell wall. Although gram staining would be the next step applied to this lab, it was not accomplished due to being a home lab. Gram staining would be the

determining factor to identifying the microbe that was originally isolated from the beginning. It would allow for the characteristics to be seen to determine the microbe. By performing a quadrant streak, this allowed the microbe to be isolated and colonized to view the single microbe.

References:

Leboffe, Michael J. Microbiology: Laboratory Theory and Application. Morton Pub. Co., 2013.

“Bacterial Isolation.” Microbiology Resource Center - Truckee Meadows Community College, www.tmcc.edu/microbiology-resource-center/lab-protocols/bacterial-isolation.

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