Streak Plate Method and isolation techniques

In order to be able to properly identify a bacterial species, it is necessary to obtain well isolated colonies. The principle is to exhaust an initial deposit by making successive smears in different directions (hence the name of the technique: exhaustion by the quadrant method).

Several techniques are commonly applied: 3, 4 or 5 successive spreads

Ⅰ. Principle of isolation by streak plate method

Quadrant seeding (general purpose) is useful for most samples. The relative number of organisms can be estimated based on the extent of growth beyond the area of origin of the inoculum.

Steps of streak plate method

Ⅱ. Semi-quantitative seeding

« Example »

  • 10 Colonies with a 1µl loop correspond to 104 cfu/mL
  • 10 Colonies with a 1µl loop correspond to 103 cfu/mL

☰ bacteriological inoculation loop

öse (or loop ), the inoculation loop is a portable tool that ends in a small metal loop. The loop can be used to smear microorganisms on agar in a petri dish or to transfer them from one test tube to another. Before each use, the inoculation loop must be sterilized so that the cultures are not contaminated.

bacteriological inoculation loop