Ethan Flint

How to do a Bacterial Streak Plate

Bacterial plating is one of the most widely used laboratory techniques in Microbiology. Some of the purposes for plating include determination of bacterial species, determination of bacterial count, and continuation of a bacterial culture. Although various methods of bacterial plating exist, the following instruction set technique will be describe the technique of streak plating.

Streak plating is used to isolate single colonies of bacteria. This isolation is beneficial when trying to distinguish one bacterium from another if using a culture with multiple specimens. The orientation of the streaking done on the agar plate is what causes the isolation of single colonies. The purpose of this streaking exercise however, will be the continuation of the bacterial culture because the original bacterial culture used is a single species.

Important Items:

Agar Plate Bacteria Culture Inoculation Loop Bunsen Burner Incubator Gloves Fire Sparker

Troubleshooting tips:

When streaking the agar plate, take your time. Rushing can cause mistakes in aseptic techniques and overlooking important steps.

With maintaining sterility in plating, it is beneficial to think yourself; “What in my technique can cause foreign bacteria from colonizing?”

Plating involves a “feel” for the motion of loop on the plate. Tilting the inoculation loop too vertical will stab the agar; too many zig-zags on the plate will not dilute the specimen enough. Don’t feel frustrated when plating for the first time, you experience problems.

NOTE: It is critical that caution and attention for your surroundings must be taken when doing

streak plating. This means cleaning your desk before and after use with the proper solvents and reducing cross contamination of foreign material (phones, bodily fluids, etc.). Most importantly the use of gloves for protection is a necessity.

2. Turning on the Bunsen burner:

Turn gas lever until hissing comes from burner

Use sparker over Bunsen burner and ignite the flame

Adjust the level of flame by turning the gas lever to reduce risk of burn.

1. Labeling the Plate

Near the edge, label the bottom of the clean agar plate to be streaked with the following:

Your name, Date, Name of Culture

-By labeling the bottom of the plate, the identification of the plate will still be

possible if an accidental loss of the top of the petri dish occurs.

3. Flaming the inoculation loop

Place the loop in the bluest part of the flame. This is the hottest part of the flame.

Hold loop until it turns a fiery orange color, to ensure that the loop has been sterilized and no foreign bacteria will mix with original colony

Cool down the loop for 5-10 seconds so the heat does not kill the bacteria to be scraped.

NOTE: It is critical that caution and attention for your surroundings must be taken when doing

streak plating. This means cleaning your desk before and after use with the proper solvents and reducing cross contamination of foreign material (phones, bodily fluids, etc.). Most importantly the use of gloves for protection is a necessity.