Selective mediums
Growth on MacConkey agar.
This is a differential and selective medium, which inhibits the growth of large positive bacteria and favours the growth of gram-negative and enteric bacilli (normally found in the intestinal tract) while differentiating between those that are able to ferment lactose and those that are not. The medium is seeded with one of the isolation techniques and incubated at 37oºC for 24 hours. After this time, observe the development of colonies. Lactose-utilising bacteria produce acidity, which lowers the pH to 7,1 ± 0,2 resulting in the appearance of pink or red colonies. Non-fermenting bacteria will appear white or transparent.
