Some Common Methods for Isolating Bacteria
Another common method for isolating bacteria from infected leaves as well as other plant parts is to cut several small sections, five to 10 millimeter squares, from the margin of an infected lesion so as to contain both diseased and healthy-looking tissue.
These are placed in a surface sterilant solution, making sure that the surface is wet, and after about 15 to 30 seconds the sections are taken out aseptically one by one at regular 10 to 15_second intervals, so that each of them has been sterilized for different times. The sections are then blotted dry on clean, sterile paper towels or are washed in three changes of sterile water, and finally placed on the nutrient medium, usually three to five per dish.
Those sections surface-sterilized the shortest time usually contain contaminants along with the pathogen, while those surface-sterilized the longest produce no growth at all because all organisms have been killed by the surface sterilant. Some of the sections left in the surface sterilant for intermediate periods of time, however, will allow only the pathogen to grow in culture in pure colonies. These colonies of bacteria are then subcultured aseptically for further study.