Telltale Rings

In her experiments to investigate antibiotic-resistant bacteria in the ocean, former MIT-WHOI Joint Program graduate student Megan May grew bacteria collected from beaches in petri dishes. She embedded small white discs of antibiotics. If the antibiotic effectively killed the bacteria, a ring of no bacteria forms around the discs. If no ring forms, the antibiotic is ineffective and the bacteria are antibiotic-resistant. Waste from homes, hospitals, and farms contains bacteria and antibiotics that often end up in the ocean. Antibiotics can encourage antibiotic-resistance by killing off all the susceptible bacteria and leaving only the resistant bacteria to grow and multiply. (Photo by Megan May, Woods Hole Oceanographic Institution)