Staphylococcus aureus is a spherical bacteria that usually resides on the skin or in the mucous membranes of humans and some animals. Out of the 30 types of Staph bacteria, Staphylococcus aureus is the most common and is normally the cause of the majority of infections. Everyone has staph bacteria living on their skin, but only only about 50% of them have MRSA (Methicillin-resistant Staphylococcus aureus which are difficult to treat with antibiotics).  It can only cause an infection by entering your bloodstream, usually accomplished by entering a scrape or wound, which could then cause a variety of minor and chronic infections.Between the years 1999 and 2003, the rate of deaths from S. aureus have doubled. The cells are immobile, do not require oxygen, and do not form spores.  They reproduce asexually and form clumps that resemble grapes.
Staphylococcus in Greek is "staphyle" which means a cluster of grapes and "kokkos" which means berry. It is named this because underneath a microscope, the clusters of bacteria look like clusters of grapes.  They are about 1 micrometer spherical, yellow cells that are gram-positive. When they are gram stained they become purple.
They contain catalase,  an enzyme that can convert millions of hydrogen peroxide molecules to oxygen and water per second. It is a possible pathogen, which means it can potentially be infectious and produce diseases. Almost every one of the strains produce coagulase, which converts fibrinogen into fibrin which causes the blood to clot. 
S. aureus reproduces asexually. It starts this process by making exact copies of the DNA located in the plasma membrane. The membrane stretches out and separates the DNA molecules. The cells form a hollow space which eventually divides out into two new cells. The new cell's wall attaches itself to the old cell wall which is why they form in bunches. This cell will eventually reproduce and cells will attach onto it. 
They get carried from person to person by an infected person making skin contact with another, who will then also carry it. Then they will make skin contact with other people and so on. It can also be produced by toxins being made which results in food poisoning or toxic shock syndrome. 
Staphylococcus aureus inhabits the bacteria of the nose, axillae and skin.  About 25% to 30% of people carry it, but if they are healthy and have a strong immune system, they probably aren't affected by it.  Staph often breaks down blood cells on bacterial substances. It grows by aerobic respiration, but does not need oxygen to survive. Through fermentation of glucose it can produce lactic acid. The bacteria grows in places with 15% sodium chloride and temperatures ranging from 15 degrees to 45 degrees. 
Besides S. aureus and S. intermedius, all other Stapholocci are gram-negative. They are usually hemolytic and can tolerate salt. They can benefit from living in humans, however humans usually aren't harmed except when it enters a break in the skin or they have a weak immune system. It can also live on some animals. Proteins they have on their membrane cause them to colonize their host.
If the bacteria ends up getting into the body, antibodies can be released from the body to hopefully neutralize the bacteria and prevent infection. S. aureus has several toxins it can release: a-toxin, the most potent and destructive, b-toxins, which are rare but damage cell membranes, o-toxin, which is in most strains but is unknown to what it actually does, and y-toxin and leukocidin, which also damage the membranes of weaker cells. 
S. auereus causes a handful of diseases in humans. Toxic shock syndrome, food poisoning, pneumonia, urinary tract infections, furuncules, boils, pus-forming infections and toxins, scalded skin syndrome, and hospital acquired infections are only a few of the infections it causes.  MRSA (Methicillin resistant Staphylococcus aureus) is a strain of S. aureus that is resistant to most antibiotics. As it keeps adapting, researchers are constantly having to invent new antibiotics to kill the bacteria. In the past, it has only been discovered in hospitals, but is spreading throughout the community. This is called CA-MRSA.
One of the most serious of the diseases is the Staphylococcal scalded skin syndrome (SSSS). It makes the skin layers separate and causes lots of blistering, especially in large sections. It is similar to when someone gets a large burn. It can eventually lead to death if not treated right away by antibiotics inserted with an IV to get it directly to the blood veins. The skin must also be covered and protected to prevent drying. 
The bacteria can be passed on from person to person by skin contact and can infect you through cuts, scrapes, or other minor abrasions. In hospitals it grows around surgical wounds or medical devices left in the body.  They can become serious if the staph enters a cut or scrape and gets swept into the bloodstream and carried throughout the body.  People who are at a higher risk are newborns, people with a weakened immune system, and people who already have a serious illness or condition. The way you can tell if you have a staph infection is if you have a series of red, swollen bumps that are painful and may be filled with pus.
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