Pus is an 
exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of 
inflammation during 
infection.
[1] An accumulation of pus in an enclosed tissue space is known as an 
abscess, whereas a visible collection of pus within or beneath the 
epidermis is known as a 
pustule or 
pimple.
Pus consists of a thin, 
protein-rich fluid, known as 
liquor puris, and dead 
leukocytes from the body's 
immune response (mostly 
neutrophils). During infection, 
macrophages release 
cytokines which trigger neutrophils to seek the site of infection by 
chemotaxis. There, the neutrophils engulf and destroy the bacteria and the bacteria resist the immune response by releasing toxins called 
leukocidins.
[2] As the neutrophils die off from toxins and old age, they are 
destroyed by macrophages, forming the viscous pus.
Bacteria that cause pus are called 
suppurative, 
pyogenic,
[2][3] or 
purulent. If the agent also creates 
mucus, it is called 
mucopurulent. Purulent infections can be treated with an 
antiseptic.
Despite normally being of a whitish-yellow hue, changes in the color 
of pus can be observed under certain circumstances. Pus is sometimes 
green because of the presence of 
myeloperoxidase,
 an intensely green antibacterial protein produced by some types of 
white blood cells. Green, foul-smelling pus is found in certain 
infections of 
Pseudomonas aeruginosa. The greenish color is a result of the pyocyanin bacterial pigment it produces. 
Amoebic abscesses of the 
liver produce brownish pus, which is described as looking like "anchovy paste". Pus can also have a foul odor.
In almost all cases when there is a collection of pus in the body, 
the clinician will try to create an opening for it to evacuate - this 
principle has been distilled into the famous Latin aphorism "
Ubi pus, ibi evacua!"
Some common disease processes caused by pyogenic infections are 
impetigo, 
osteomyelitis, 
septic arthritis, and 
necrotizing fasciitis.
[4][not in citation given]
Pyogenic bacteria
A great many species of bacteria may be pyogenic. The most commonly found include:
[5][unreliable medical source?]
Exudate
From Wikipedia, the free encyclopedia
An 
exudate is any 
fluid that filters from the 
circulatory system into 
lesions or areas of 
inflammation. It can apply to plants as well as animals. Its composition varies but generally includes water and the dissolved 
solutes of the main circulatory fluid such as sap or blood. In the case of blood it will contain some or all 
plasma proteins, 
white blood cells, 
platelets, and in the case of local 
vascular damage: 
red blood cells.
 In plants, it can be a healing and defensive response to repel insect 
attack, or it can be an offensive habit to repel other incompatible or 
competitive plants. Organisms that feed on exudate are known as 
exudativores; for example, the 
Vampire Bat exhibits 
hematophagy, and the 
Pygmy marmoset is an 
obligate gummivore[1] (primarily eats tree gum).
In humans, exudate can be a pus-like or clear fluid. When an injury 
occurs, leaving skin exposed, it leaks out of the blood vessels and into
 nearby tissues. The fluid is composed of serum, fibrin, and white blood
 cells. Exudate may ooze from cuts or from areas of infection or 
inflammation.
[2]
Inflammation
From Wikipedia, the free encyclopedia
Inflammation (
Latin, 
īnflammō, "I ignite, set alight") is part of the complex biological response of 
vascular tissues to harmful stimuli, such as 
pathogens, damaged cells, or irritants.
[1]
 The classical signs of acute inflammation are pain, heat, redness, 
swelling, and loss of function. Inflammation is a protective attempt by 
the organism to remove the injurious stimuli and to initiate the healing
 process. Inflammation is not a synonym for 
infection,
 even in cases where inflammation is caused by infection. Although 
infection is caused by a microorganism, inflammation is one of the 
responses of the organism to the pathogen. However, inflammation is a 
stereotyped response, and therefore it is considered as a mechanism of 
innate immunity, as compared to 
adaptive immunity, which is specific for each pathogen.
[2]
Progressive destruction of the tissue would compromise the survival 
of the organism. However, chronic inflammation can also lead to a host 
of diseases, such as 
hay fever, 
periodontitis, 
atherosclerosis, 
rheumatoid arthritis, and even cancer (e.g., 
gallbladder carcinoma). It is for that reason that inflammation is normally closely regulated by the body.
Inflammation can be classified as either 
acute or 
chronic. 
Acute inflammation is the initial response of the body to harmful stimuli and is achieved by the increased movement of 
plasma and 
leukocytes (especially 
granulocytes)
 from the blood into the injured tissues. A cascade of biochemical 
events propagates and matures the inflammatory response, involving the 
local 
vascular system, the 
immune system, and various cells within the injured tissue. Prolonged inflammation, known as 
chronic inflammation,
 leads to a progressive shift in the type of cells present at the site 
of inflammation and is characterized by simultaneous destruction and 
healing of the tissue from the inflammatory process.
Staphylococcus aureus
From Wikipedia, the free encyclopedia
Staphylococcus aureus is a 
bacterium that is a member of the 
Firmicutes, and is frequently found in the human respiratory tract and on the skin. Although 
S. aureus is not always 
pathogenic, it is a common cause of skin infections (e.g. 
boils), respiratory disease (e.g. 
sinusitis), and 
food poisoning. Disease-associated strains often promote infections by producing potent protein 
toxins, and expressing cell-surface proteins that 
bind and inactivate antibodies. The emergence of 
antibiotic-resistant forms of pathogenic 
S. aureus (e.g. 
MRSA) is a worldwide problem in clinical medicine.
Staphylococcus was first identified in 
Aberdeen, 
Scotland (1880) by the 
surgeon Sir 
Alexander Ogston in 
pus from a surgical abscess in a knee joint.
[1] This name was later appended to 
Staphylococcus aureus
 by Rosenbach who was credited by the official system of nomenclature at
 the time. It is estimated that 20% of the human population are 
long-term carriers of 
S. aureus[2] which can be found as part of the normal 
skin flora and in anterior nares of the nasal passages.
[2][3] S. aureus is the most common species of staphylococcus to cause 
Staph infections and is a successful pathogen due to a combination of nasal carriage and bacterial immuno-evasive strategies.
[2][3] S. aureus can cause a range of illnesses, from minor skin 
infections, such as 
pimples, 
impetigo, 
boils (furuncles), 
cellulitis folliculitis, 
carbuncles, 
scalded skin syndrome, and 
abscesses, to life-threatening diseases such as 
pneumonia, 
meningitis, 
osteomyelitis, 
endocarditis, 
toxic shock syndrome (TSS), 
bacteremia, and 
sepsis. Its incidence ranges from skin, soft tissue, respiratory, bone, joint, endovascular to 
wound infections. It is still one of the five most common causes of 
nosocomial infections
 and is often the cause of postsurgical wound infections. Each year, 
some 500,000 patients in American hospitals contract a staphylococcal 
infection.
[4]