Staphylococcus is a group of bacteria that can cause a number of diseases as a result of infection of various tissues of the body. Staphylococcus is more familiarly known as Staph (pronounced "staff").
Staph-related illness can range from mild and requiring no treatment to severe and potentially fatal.
The name Staphylococcus comes from the Greek staphyle, meaning a bunch of grapes, andkokkos, meaning berry, and that is what Staph bacteria look like under the microscope, like a bunch of grapes or little round berries. (In technical terms, these are gram-positive, facultative anaerobic, usually unencapsulated cocci).
Over 30 different types of Staphylococci can infect humans, but most infections are caused by Staphylococcus aureus. Staphylococci can be found normally in the nose and on the skin (and less commonly in other locations) of 25%-30% of healthy adults.
In the majority of cases, the bacteria do not cause disease. However, damage to the skin or other injury may allow the bacteria to overcome the natural protective mechanisms of the body, leading to infection.
Most staph infections that are visible usually have a reddish, swollen, and tender area at the site of infection. Often the site oozes pus or has some crusty covering with drainage. Sites of infection can be small like a pimple or large like a carbuncle. Cellulitis often shows redness and swelling without pus, but impetigo shows a crusty weeping rash with an occasional blister.
Scalded skin syndrome shows extensive skin redness with bullae (fluid- or pus-filled blisters). Infected catheters and other implanted devices usually show redness, pus, and tenderness at the skin entry site.
Deep abscesses, pneumonia, osteomyelitis, and most other internal infections are only seen by X-ray and other imaging techniques or are not visible at all (for example, toxic shock, food poisoning).
The appearances described above are only suggestive of staph infection; proof of infection depends on bacterial culture and subsequent identification of the infecting agent.
A staph infection is caused by a Staphylococcus (or "staph") bacteria. Actually, about 25% of people normally carry staph in the nose, mouth, genitals, and anal area. The foot is also very prone to pick up bacteria from the floor. The infection often begins with a little cut, which gets infected with bacteria.
These staph infections range from a simple boil to antibiotic-resistant infections to flesh-eating infections. The difference between all these is the strength of the infection, how deep it goes, how fast it spreads, and how treatable it is with antibiotics. The antibiotic-resistant infections are more common in North America, because of our overuse of antibiotics.
One type of staph infection that involves skin is called cellulitis and affects the skin's deeper layers. It is treatable with antibiotics.
This type of infection is very common in the general population - and more common and more severe in people with weak immune systems. People who have diabetes or weakened immunity are particularly prone to developing cellulitis.
What types of diseases are caused by Staph?
Skin infections (see above) are the most common type of disease produced by Staphylococcus. Staph infections of the skin can progress to impetigo (a crusting of the skin) or cellulitis (inflammation of the connective tissue under the skin, leading to swelling and redness of the area).
In rare situations, a serious complication known as scalded skin syndrome (see below) can develop. In breastfeeding women, Staph can result in mastitis (inflammation of the breast) or in abscess of the breast. Staphylococcal breast abscesses can release bacteria into the mother's milk.
When the bacteria enter the bloodstream and spread to other organs, a number of serious infections can occur. Spread of the organisms to the bloodstream is known as bacteremia or sepsis. Staphylococcal pneumonia predominantly affects people with underlying lung disease and can lead to abscess formation within the lungs. Infection of the heart valves (endocarditis) can lead to heart failure. Spread of Staphylococci to the bones can result in severe inflammation of the bones known as osteomyelitis.
When Staph bacteria are present in the blood, a condition known as staphylococcal sepsis (widespread infection of the bloodstream) or staphylococcal bacteremia exists. Staphylococcal sepsis is a leading cause of shock and circulatory collapse, leading to death, in people with severe burns over large areas of the body.
When untreated, Staph aureus sepsis carries a mortality (death) rate of over 80%. Although not common, Staph aureus has been reported as a cause of chorioamnionitis and neonatal sepsis in pregnancy, but group B streptococci are the most common bacterial cause of this life-threatening condition for the fetus.
Staphylococcal infections are contagious and can be transmitted from person to person. Since pus from infected wounds may contain the bacteria, proper hygiene and handwashing is required when caring for Staph-infected wounds.
Staphylococcal food poisoning is an illness of the bowels that causes nausea, vomiting, diarrhea, and dehydration. It is caused by eating foods contaminated with toxins produced by Staphylococcus aureus. Symptoms usually develop within one to six hours after eating contaminated food. The illness usually lasts for one to three days and resolves on its own. Patients with this illness are not contagious, since toxins are not transmitted from one person to another.
Toxic shock syndrome is an illness caused by toxins secreted by Staph aureus bacteria growing under conditions in which there is little or no oxygen. Toxic shock syndrome is characterized by the sudden onset of high fever, vomiting, diarrhea, and muscle aches, followed by low blood pressure (hypotension), which can lead to shock and death. There may be a rash resembling sunburn, with peeling of skin. Toxic shock syndrome was originally described and still occurs especially in menstruating women using tampons.
Minor skin infections are usually treated with an antibiotic ointment such as a nonprescription triple-antibiotic mixture. In some cases, oral antibiotics may be given for skin infections. Additionally, if abscesses are present, they are surgically drained.
More serious and life-threatening infections are treated with intravenous antibiotics. The choice of antibiotic depends on the susceptibility of the particular staphylococcal strain as determined by culture results in the laboratory. Some Staph strains, such as MRSA (see next section), are resistant to many antibiotics.
What is antibiotic-resistant Staph aureus?
Methicillin-resistant Staphylococcus aureus, known as MRSA, is a type of Staphylococcus aureus that is resistant to the antibiotic methicillin and other drugs in the same class, including penicillin, amoxicillin, and oxacillin.
MRSA is one example of a so-called "superbug", an informal term used to describe a strain of bacteria that has become resistant to the antibiotics usually used to treat it. MRSA first appeared in patients in hospitals and other health facilities, especially among the elderly, the very sick, and those with an open wound (such as a bedsore) or catheter in the body. In these settings, MRSA is referred to as health-care-associated MRSA (HA-MRSA).
MRSA has since been found to cause illness in the community outside of hospitals and other health facilities and is known as community-associated MRSA (CA-MRSA) in this setting. MRSA in the community is associated with recent antibiotic use, sharing contaminated items, having active skin diseases or injuries, poor hygiene, and living in crowded settings.
The U.S. Centers for Disease Control and Prevention (CDC) estimates that about 12% of MRSA infections are now community-associated, but this percentage can vary by community and patient population.
MRSA infections are usually mild superficial infections of the skin that can be treated successfully with proper skin care and antibiotics. MRSA, however, can be difficult to treat and can progress to life-threatening blood or bone infections because there are fewer effective antibiotics available for treatment.
The transmission of MRSA is largely from people with active MRSA skin infections. MRSA is almost always spread by direct physical contact and not through the air. Spread may also occur through indirect contact by touching objects (such as towels, sheets, wound dressings, clothes, workout areas, sports equipment) contaminated by the infected skin of a person with MRSA.
Just as S. aureus can be carried on the skin or in the nose without causing any disease, MRSA can be carried in this way also. In contrast to the relatively high (25%-30%) percentage of adults who are colonized by Staph aureus in the nose (these people have Staph bacteria present that do not cause illness), only about 2% of healthy people carry MRSA in the nose. There are no symptoms associated with carrying Staph in general or MRSA in the nose.
A drug known as mupirocin has been shown to be effective in some cases for treating and eliminating MRSA from the nose of healthy carriers, but decolonization (treating of carriers to remove the bacteria) is usually not recommended unless there has been an outbreak of MRSA or evidence that an individual or group of people may be the source of the outbreak.
More recently, strains of Staph aureus have been identified that are resistant to the antibiotic vancomycin, which is normally effective in treating Staph infections. These bacteria are referred to as vancomycin-intermediate resistance S. aureus (VISA) and vancomycin-resistant Staph aureus (VRSA).
What are complications of Staph infections?
Scalded skin syndrome is a potentially serious side effect of infection with Staph bacteria that produce a specific protein which loosens the "cement" holding the various layers of the skin together. This allows blister formation and sloughing of the top layer of skin. If it occurs over large body regions, it can be deadly, similar to a large surface area of the body having been burned.
It is necessary to treat scalded skin syndrome with intravenous antibiotics and to protect the skin from allowing dehydration to occur if large areas peel off. The disease occurs predominantly in children but can occur in anyone. It is known formally as staphylococcal scalded skin syndrome.