Bacterial streaking

Purpose

To obtain pure culture isolates from a mixed bacterial population

Materials

• Nutrient agar plate (or other selective media)
• Inoculating Loop(s)
• Flame source for sterilization

Instructions

Typical pattern used in streaking bacteria. Streaking is done in the order of Black, Orange, Blue, Purple.

1. If isolating bacteria from broth, dip loop in broth; if isolating from an agar plate, choose an individual colony and touch the tip of the loop to the top of the colony
2. Inoculate plates in initial streak in first section of plate (covering about ¼ to ⅓ of the surface) using a zig-zag motion as close to each other as possible (Black streaking in diagram)
3. Heat sterilize the loop and cool between sections
4. Streak plate on the second quarter of the plate, crossing over the initial streak area one time (Orange streaking in diagram)
5. Repeat on third quarter, crossing over the second quarter only once- being careful not to touch the first or second quarter (Blue streaking in diagram)
6. If there is enough room on the plate, repeat for a fourth quarter (Purple streaking in diagram)
7. Incubate plates at 30°C for 48 hours
8. Observe plates for growth
9. Choose individual colonies for further testing

Notes

• Be careful not to rip or gouge the agar when streaking
• It is easier to use multiple loops and alternate between them to avoid killing the bacteria with heat

Contributed by

From the University of Florida Plant Disease Clinic-GNV System Manual: originally created by Anne Vitoreli; contributed by Anne Vitoreli.