Bacterial infections can come from anywhere. If you do not practice proper hygiene or you have visited a place that is not exactly hygienic, then you can get a bacterial infection. There are many types of bacteria and each bacterium can cause a different condition or disease depending on the body part that it infects. If bacteria infect the eye it can lead to conjunctivitis. If it infects the throat it can lead to laryngitis or pharyngitis. If it infects your tonsils it will lead to tonsillitis. If it infects your urethra the infection becomes urinary tract infection. If the bacterium infects your skin the infection becomes skin infection.
The truth is that there are literally quite a number of bacteria and that many of them have still yet to be discovered. Nevertheless, among the types of bacteria that have already been indexed and archived, some are not harmful, some can do harm but are not very serious, some are harmful but can be treated easily with antibiotics, and some are very harmful and most antibiotics do not work on them. But for most cases of bacteria and the type of bacterial infection they can do, most can be treated using antibiotics.