Porphyromonas gingivalis is a bacterium that is present in high numbers in the mouths of people with gum disease (gingivitis and periodontitis), a major cause of bad breath and tooth loss. This is a close-up image of the bacteria being cultivated in the laboratory in agar dishes infused with blood from sheep, which is ideal for the bacteria growth. P. gingivalis loves growing in places with food and blood (like unclean teeth!) and will turn black by processing hemoglobin from the blood and storing it on its surface. The destruction that P. gingivalis wreaks may go far beyond gum disease, however. Studies have suggested links between P. gingivalis infection and pancreatic cancer, diabetes, rheumatoid arthritis and even Alzheimer’s disease.