Harmful Bacteria. Some of the harmful types of bacteria are those which can cause disease or adversely affect one's health, and these include: Mycobacteria, which are rod-shaped, and neither Gram-positive nor Gram-negative microorganisms that can cause infections of the lungs, skin and other parts of the body.The most common diseases associated with these bacteria are leprosyand tuberculosis.ycobacteria, which are rod-shaped, and neither Gram-positive nor Gram-negative microorganisms that can cause infections of the lungs, skin and other parts of the body. The most common diseases associated with these bacteria are leprosyand tuberculosis.