Streak or spot all eight bacteria on the same petri plate. Incubate about 12 to 36 hours. Flood plate with dilute iodine. The starch will be stained black, but you will see clearing around the streaks of Bacillus and other species that use starch. Part of our home microbiology at home series.
Microbiologists usually work with pure cultures containing a single strain of the microbe they want.
However, before 1850, pure culture methods were unknown. To obtain the desired microflora in a food process, cooks and food processors used conditions which were known to produce the desired result. Ladies who had cool earthen cellars often were more successful at keeping the starter alive and they gave regular portions to their neighbors. Maintaining a semipure culture by suitable conditions and food supply is called selective enrichment. In the next page of this series, we will again work with food processing microbes, but we will learn pure culture methods.