How Can a Type of Bacteria Normally Present in the Body Cause Illness?
When discussing the relationship between bacteria and the human body, it is important to keep in mind that we normally “host” billions of bacteria-collectively referred to as the normal bacterial flora. Such bacteria often provide beneficial effects for the human (or host). We also have natural “host defenses” against these bacteria, which keep the bacterial population from growing too large and limit the presence of bacteria to external organs (skin), the alimentary canal (from the mouth to the rectum), and the lower part of the genital tract (in women, the vagina and cervix). Such host defenses include intact skin and the lining of the alimentary canal, immune cells (white blood cells), and antibodies (produced by the immune system to combat infectious organisms) secreted into these areas. When bacteria live in harmony with a certain area of the human body, the bacteria are said to “colonize” that region of the body. But, if there is a breakdown in these host defenses-such as a surgi
