The primary method to differentiate between aerobic and anaerobic bacteria involves using a test tube containing thioglycollate nutrient broth. Thioglycollate broth is a reduced media that binds to any available oxygen in the medium, effectively removing it and creating an environment suitable for the growth of anaerobic bacteria. Anaerobic bacteria will settle at the bottom of the tube, whereas aerobic bacteria will thrive near the top of the test tube. On a side note, a small amount of oxygen can sometimes diffuse into the upper portion of the broth. To visually identify areas with higher oxygen levels, the resazurin indicator is used. This indicator changes color (to light pink) in the presence of oxygen.