On the picture we can see Campylobacter jejuni growing on a special blood-free, charcoal-based selective medium agar (CSM), used for the isolation of the bacterium from food, water or sick patients with diarrhoe.
Selective medium means a nutrient medium which makes only one bacterial species or group possible to grow on and inhibits all the others. This kind of nutrient media can be used for the selection of microbes from samples which contain many different microbes. The selectivity of the nutrient medium can be based on the special substrate-utilising ability of the bacterium to be selected or its resistance against some antibiotics, which inhibit their companions.
A blood-free, charcoal-based selective medium (CSM) consisting of a Columbia agar base, activated charcoal (4 g/liter), hematin (0.032 g/liter), sodium pyruvate (0.1 g/liter), cefoperazone (32 mg/liter), vancomycin (20 mg/liter), and cycloheximide (100 mg/liter) supported the growth of Campylobacter jejuni and C. coli with colony counts equivalent to those obtained on antibiotic-free horse blood agar.