Bacteria
Bacteria are an order of life. Modern pathology and medicine are based on the findings of Louis Pasteur that bacteria cause many ailments, which antibiotic medicine can cure. Bacteria evolve resistances to certain types of antibiotics, making their continued treatment in a recurrent infection difficult at times.[1]
Bacteria are tiny one-celled organisms present throughout the environment that require a microscope to be seen. The vast majority of bacteria are not harmful to human beings. Many of them are normally found on or in the human body, and not only do not cause disease, but provide some benefit. For example, the human gut normally contain a complement of intestinal flora which assist digestion.
Some food products involve bacteria in their production. Sour cream, buttermilk, yogurt, and some kinds of cheese contain living cultures of live bacteria when eaten. Vinegar is traditionally produced by the growth of the Acetobacter bacterium in wine. (Wine itself is produced, not by bacteria, but by yeast, which is also a microorganism.)
While not all bacteria are harmful, some cause disease. The technical term for these is pathogenic bacteria (pathogenic being nothing more than a combination of the Greek roots for "disease" and "causing").
Examples of bacterial disease include diphtheria, pertussis, tetanus, Haemophilus influenza and pneumococcus (pneumonia).