Both are growing on the same nutrient agar petri dish.
From the sciencedaily.com
Related colonies near one another on a bed of low-nutrient agar mutually inhibit growth by secreting an antibacterial compound that in high enough concentrations becomes lethal.
From the nytimes.com
Most pathogenic bacteria are easily grown on nutrient agar, a form of solid medium that supplies carbohydrates and proteins necessary for growth of a bacterium, along with copious amounts of water.