Bacteria are single-celled microorganisms that come in three basic shapes - rod-shaped bacilli, round cocci, or spiral. They reproduce through cell division and need to consume nutrients to survive. While most bacteria are harmless or even helpful, some pathogenic bacteria can cause illness in humans. Pathogens are acquired through direct or indirect contact with infected people or animals or by consuming contaminated food or water. Proper hygiene like handwashing and safe food handling can help reduce the risk of pathogen transmission.