Bacterial infections are primarily trasmitted by ingestion of contaminated food or water, by inhalation, through physical contact with animals or infected persons, or from one part of the body where they are harmless to another part where they cause illness. and, contrary to popular belief, can be beneficial or detrimental, depending on how they interact with their host. A relatively small number of bacteria causes diseases in humans. Some of the most deadly diseases and devastating epidemics in human history have been caused by bacteria, including dysentery, plague, diphtheria, and tubercolosis. Some bacterial infections are common in childhood, such as strep throat and ear infections. Bacterial infections typically present with localized redness and heat, inflammation (swelling) and pain. Bacterial infections tend to present localized pain more frequently than viral infections (not always). Even with a throat infection, a bacterial one will usually have more severe pain on one side of the throat. If there is pain in just one ear, it is more likely to be a bacterial infection. These drugs either kill the bacteria or prevent them from reproducing.