Bacterial infections are caused by pathogenic bacteria that invades an area of the body that is normally sterile, such as the bladder, according to Healthgrades. They also occur when they enter parts of the body such as the mouth, vagina and intestines, then crowd out the helpful bacteria residing there.
There are many different kinds of pathogenic bacteria that cause infections ranging from mild to life threatening, explains Healthgrades. The danger increases if the infection is not recognized and treated. Physical symptoms most often occur in pathogenic bacterial infections that target a certain body part. For example, according to WebMD, a bacterial infection in the bladder can cause a burning sensation with urination, frequent urge to urinate, difficulty urinating or blood in the urine, while a bacterial infection or abscess in a tooth can cause pain, localized swelling or an open draining sore on the side of the gum.
Healthgrades states that pathogenic bacteria can invade the body in many ways, such as ingesting food that is infected; contamination that enters through a bite, cut or abrasion; sexual contact with an infected person; sharing needles used for tattoos or drugs; or by inhaling contaminated airborne droplets through the nose or mouth and into the lungs.