Bacteria and infection

Bacteria are single-celled organisms. Depending on the species, they can be harmful, neutral, or beneficial to humans. When harmful bacteria invade the body, a person is said to have a bacterial infection or sepsis. In order to cause an infection, bacteria must penetrate the body. For example, they can enter through a break in the skin, by ingesting contaminated food or water, through inhaling the bacteria into the airways, or through sexual activity. The body has many defenses against invading bacteria. Sweat and oil gland secretions help kill bacteria on the skin. Mucus in the mouth and throat helps to trap inhaled bacteria before they can reach the lungs. Highly acidic stomach acid kills many bacteria found in food and water. Most bacteria that succeed in entering the body are quickly killed soon after they arrive. If, however, the body is unable to destroy the bacteria, an infection occurs. Acute infections develop suddenly, and they disappear completely when a person receives treatment or the body's immune system responds and destroys the bacteria. Chronic infections develop if the body has only limited control over the bacteria. In chronic infections, the body is never completely free of the bacteria, but symptoms disappear temporarily and then flare up later in response to physical or emotional stress or when the body is weakened by another illness. Many bacterial diseases begin as local infections in places such as the skin, throat, or bladder. If bacterial infections are left untreated, bacteria can spread by entering the bloodstream and infect other, more distant, organs. When bacteria are found in the blood stream, the condition is called septicemia or, more commonly, blood poisoning. Sepsis is a condition in which organs of the body are overwhelmed by infection. It is a leading cause of death among the elderly and those whose immune systems are compromised. Bacteria damage the body by adhering to or invading cells, altering cellular metabolism, or releasing toxic (poisonous) substances. When bacteria begin reproducing, the body's immune system has a set series of responses that attempt to control the spread of infection. The immune system consists of the spleen, thymus, lymph nodes, and white blood cells. Its reactions take time and are not always successful. Many of the symptoms associated with bacterial infections such as fever, redness, and swelling, are actually caused by the immune system's response to the invading bacteria rather than the bacteria themselves. Other reactions, such as vomiting and diarrhea caused by gastrointestinal infections, are a reaction to toxins the bacteria release as a byproduct of their metabolism.Bacterial infections are initially diagnosed on the basis of symptoms and confirmed by additional testing. If a person has an infection, a complete blood count will usually reveal an abnormally high number of white blood cells. This, however, only tells the physician that the body is fighting an infection. It does not indicate the cause (bacterial, viral, fungal) of the infection. To determine the cause of the infection, a sample of material (blood, cerebrospinal fluid, mucus, etc.) from the infection site is cultured (grown) in the laboratory and examined under the microscope, so that the species of bacteria can be determined. Cultures can also be tested to see if they are sensitive to specific antibiotics, as not all antibiotics kill all types of bacteria. Many infections, especially infections of skin wounds, can be cured by cleaning and application of an antibiotic ointment. More serious infections require oral (by mouth) or intravenous (IV, directly into a vein) antibiotic therapy. Different classes of antibiotics affect different species of bacteria. If the type of bacteria has not been determined, the physician may prescribe a broad-spectrum antibiotic that kills several of the most common types of bacteria. Symptoms often improve within a few days after antibiotic therapy is begun, but patients should always take the entire amount of antibiotic prescribed. Stopping the antibiotic early increases the chance of the infection reasserting itself within a few days.