July 9th – Bacteroides melaninogenicus is a species of bacterium in the normal flora of the upper respiratory tract. It is an important human pathogen in various anaerobic infections, often mixed with other aerobic and anaerobic bacteria. B. melaninogenicus is an anaerobic, Gram-negative rod, named for its black colonies, and black pigment. The name Bacteroides melaninogenicus was later changed to Prevotella melaninogenica. Steroids may facilitate growth. Prevotella spp. are part of the normal human oral and vaginal flora and are the predominant anaerobic, Gram-negative bacilli recovered from anaerobic infections of the respiratory tract. These include aspiration pneumonia, lung abscesses, and chronic otitis media and sinusitis. They have been recovered also from abscesses and burns around the oral cavity, human bites, paronychia, urinary tract infection, brain abscesses, osteomyelitis, and bacteremia associated with upper respiratory tract infections. Prevotella spp. play a major role in the pathogenesis of periodontal disease and periodontal abscesses. The prevalence of P. melaninogenics is high in the dental plaque of persons with Down syndrome. This bacterium synthesizes collagenase in periodontal disease.