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An abscess is an enclosed collection of pus.
Specialty Infectious disease

Pus is an exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of inflammation during bacterial or fungal infection. [1] [2] 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, pimple, or spot.


An exudate is a fluid emitted by an organism through pores or a wound, a process known as exuding or exudation. Exudate is derived from exude, "to ooze," from the Latin exsūdāre, "to sweat".

Inflammation Signs of activation of the immune system

Inflammation is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecular mediators. The function of inflammation is to eliminate the initial cause of cell injury, clear out necrotic cells and tissues damaged from the original insult and the inflammatory process, and initiate tissue repair.

Infection invasion of a host by disease-causing organisms

Infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce. Infectious disease, also known as transmissible disease or communicable disease, is illness resulting from an infection.


Pus consists of a thin, protein-rich fluid, historically known as liquor puris, [3] [4] and dead leukocytes from the body's immune response (mostly neutrophils). [5] During infection, macrophages release cytokines which trigger neutrophils to seek the site of infection by chemotaxis. There, the neutrophils release granules which destroy the bacteria. The bacteria resist the immune response by releasing toxins called leukocidins. [6] As the neutrophils die off from toxins and old age, they are destroyed by macrophages, forming the viscous pus.

Protein Biological molecule consisting of chains of amino acid residues

Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells, and organisms, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific three-dimensional structure that determines its activity.

Immune response immune system process that functions in the calibrated response of an organism to a potential internal or invasive threat

The Immune response is the body's response caused by its immune system being activated by antigens. The immune response can include immunity to pathogenic microorganisms and its products, allergies, graft rejections, as well as autoimmunity to self-antigens. In this process the main cells involved are T cells and B cells, and macrophages. These cells produce lymphokines that influence the other host cells' activities. B cells, when activated by helper T cells undergo clonal expansion. B cells differentiate into plasma cells, which are short lived and secrete antibodies, and memory B cells, which are long lived and produce a fast, remembered response when exposed to the same infection in the future. B cells mature to produce immunoglobulins, that react with antigens. At the same time, macrophages process the antigens into immunogenic units which stimulate B lymphocytes to differentiate into antibody-secreting plasma cells, stimulating the T cells to release lymphokines.

Macrophage type of white blood cell

Macrophages are a type of white blood cell, of the immune system, that engulfs and digests cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the type of proteins specific to healthy body cells on its surface in a process called phagocytosis.

Bacteria that cause pus are called pyogenic. [6] [7]

Although pus is normally of a whitish-yellow hue, changes in the color 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 bacterial pigment pyocyanin that it produces. Amoebic abscesses of the liver produce brownish pus, which is described as looking like "anchovy paste". Pus from anaerobic infections can more often have a foul odor. [8]

Myeloperoxidase protein-coding gene in the species Homo sapiens

Myeloperoxidase (MPO) is a peroxidase enzyme that in humans is encoded by the MPO gene on chromosome 17. MPO is most abundantly expressed in neutrophil granulocytes, and produces hypohalous acids to carry out their antimicrobial activity. It is a lysosomal protein stored in azurophilic granules of the neutrophil and released into the extracellular space during degranulation. Neutrophil myeloperoxidase has a heme pigment, which causes its green color in secretions rich in neutrophils, such as pus and some forms of mucus. The green color contributed to its outdated name verdoperoxidase.

<i>Pseudomonas aeruginosa</i> common bacterium

Pseudomonas aeruginosa is a common encapsulated, Gram-negative, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, P. aeruginosa is a multidrug resistant pathogen recognized for its ubiquity, its intrinsically advanced antibiotic resistance mechanisms, and its association with serious illnesses – hospital-acquired infections such as ventilator-associated pneumonia and various sepsis syndromes.

Pyocyanin chemical compound

Pyocyanin (PCN) is one of the many toxins produced and secreted by the Gram negative bacterium Pseudomonas aeruginosa. Pyocyanin is a blue, secondary metabolite with the ability to oxidise and reduce other molecules and therefore kill microbes competing against P. aeruginosa as well as mammalian cells of the lungs which P. aeruginosa has infected during cystic fibrosis. Since pyocyanin is a zwitterion at blood pH, it is easily able to cross the cell membrane. There are three different states in which pyocyanin can exist: oxidized, monovalently reduced or divalently reduced. Mitochondria play an important role in the cycling of pyocyanin between its redox states. Due to its redox-active properties, pyocyanin generates reactive oxygen species.

In almost all cases when there is a collection of pus in the body, a clinician will try to create an opening to drain it. This principle has been distilled into the famous Latin aphorism " Ubi pus, ibi evacua " ("Where there is pus, evacuate it").

An aphorism is a concise, terse, laconic, and/or memorable expression of a general truth or principle. They are often handed down by tradition from generation to generation. The concept is distinct from those of an adage, brocard, chiasmus, epigram, maxim, principle, proverb, and saying; some of these concepts are species of aphorism.

Ubi pus, ibi evacua is a Latin aphorism or adage, often cited in medicine, meaning "where [there is] pus, there evacuate [it]". It refers to what clinicians should do when there is a collection of pus in the body; that is, to create an opening for it to evacuate. A contemporary expression of the same sentiment is also used: "if there's pus about, let it out".

Some disease processes caused by pyogenic infections are impetigo, osteomyelitis, septic arthritis, and necrotizing fasciitis. [9] [ failed verification ]

Impetigo human disease

Impetigo is a bacterial infection that involves the superficial skin. The most common presentation is yellowish crusts on the face, arms, or legs. Less commonly there may be large blisters which affect the groin or armpits. The lesions may be painful or itchy. Fever is uncommon.

Osteomyelitis bone inflammation disease that has material basis in infection located in bone or located in bone marrow

Osteomyelitis (OM) is an infection of bone. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The long bones of the arms and legs are most commonly involved in children, while the feet, spine, and hips are most commonly involved in adults.

Septic arthritis arthritis that involves infection by a pathogen located in joint

Septic arthritis, also known as joint infection or infectious arthritis, is the invasion of a joint by an infectious agent resulting in joint inflammation. Symptoms typically include redness, heat and pain in a single joint associated with a decreased ability to move the joint. Onset is usually rapid. Other symptoms may include fever, weakness and headache. Occasionally, more than one joint may be involved.

Eye with conjunctivitis exuding pus Swollen eye with conjunctivitis.jpg
Eye with conjunctivitis exuding pus
Duodenoscopy image of hepatopancreatic ampulla with pus exuding from it, indicative of cholangitis Cholangitis.jpg
Duodenoscopy image of hepatopancreatic ampulla with pus exuding from it, indicative of cholangitis

Pyogenic bacteria

A great many species of bacteria may be involved in the production of pus. The most commonly found include: [10] [ unreliable medical source? ]

Staphylococcus aureus bacteria is the most common cause of boils.

Historical terminology

In the pre-asepsis era, surgeon Frederick Treves (1853–1923) wrote, "Practically all major wounds suppurated. Pus was the most common subject of converse [among surgeons], because it was the most prominent feature in the surgeon's work. It was classified according to degrees of vileness." [11] :347 But pus of the right kind was considered desirable. [12] :80 "If a patient was lucky ... a thick cream-colored odorless fluid would appear within five or six days"; such "laudable" pus was considered "a sure sign that the wound would heal" [11] :344 because it meant "Nature has put up a bold fight against the invader". [13] "On the other hand, if the pus gradually became watery, blood tinged and foul smelling, it was designated 'sanious' [14] [or 'ill-conditioned'] [15] and the wound condition was considered unfavorable". [14] It later came to be understood that "laudable" pus generally implied an invasion of relatively benign staphylococcus, while "ill-conditioned" pus usually meant the more dangerous streptococcus was present. [11] :345 [14] :247

See also

Related Research Articles


A coccus is any bacterium or archaeon that has a spherical, ovoid, or generally round shape. Bacteria are categorized based on their shapes into three classes: cocci (spherical-shaped), bacillus (rod-shaped) and spirochetes (spiral-shaped) cells. Coccus refers to the shape of the bacteria, and can contain multiple genera, such as staphylococci or streptococci. Cocci can grow in pairs, chains, or clusters, depending on their orientation and attachment during cell division. Contrast to many bacilli-shaped bacteria, most cocci bacteria do not have flagella and are non-motile.

Aztreonam chemical compound

Aztreonam, sold under the brand name Azactam among others, is an antibiotic used primarily to treat infections caused by gram-negative bacteria such as Pseudomonas aeruginosa. This may include bone infections, endometritis, intra abdominal infections, pneumonia, urinary tract infections, and sepsis. It is given by injection into a vein or muscle or breathed in as a mist.

Bacterial pneumonia is a type of pneumonia caused by bacterial infection.

Bacterial capsule

The bacterial capsule is a very large structure of many bacteria. It is a polysaccharide layer that lies outside the cell envelope, and is thus deemed part of the outer envelope of a bacterial cell. It is a well-organized layer, not easily washed off, and it can be the cause of various diseases.

Mastoiditis middle ear disease characterized by an inflammation of the mucosal lining of the mastoid antrum and the mastoid air cell system inside the mastoid process

Mastoiditis is the result of an infection that extends to the air cells of the skull behind the ear. Specifically, it is an inflammation of the mucosal lining of the mastoid antrum and mastoid air cell system inside the mastoid process. The mastoid process is the portion of the temporal bone of the skull that is behind the ear. The mastoid process contains open, air-containing spaces. Mastoiditis is usually caused by untreated acute otitis media and used to be a leading cause of child mortality. With the development of antibiotics, however, mastoiditis has become quite rare in developed countries where surgical treatment is now much less frequent and more conservative, unlike former times. Additionally, there is no evidence that the drop in antibiotic prescribing for otitis media has increased the incidence of mastoiditis, raising the possibility that the drop in reported cases is due to a confounding factor such as childhood immunizations against Haemophilus and Streptococcus. Untreated, the infection can spread to surrounding structures, including the brain, causing serious complications.

Lung abscess lung disease characterized by microbial infection which causes a type of liquefactive necrosis of the pulmonary tissue and formation of cavities containing necrotic debris or fluid

Lung abscess is a type of liquefactive necrosis of the lung tissue and formation of cavities containing necrotic debris or fluid caused by microbial infection.

Cefepime chemical compound

Cefepime is a fourth-generation cephalosporin antibiotic. Cefepime has an extended spectrum of activity against Gram-positive and Gram-negative bacteria, with greater activity against both types of organism than third-generation agents. A 2007 meta-analysis suggested when data of trials were combined, mortality was increased in people treated with cefepime compared with other β-lactam antibiotics. In response, the U.S. Food and Drug Administration (FDA) performed their own meta-analysis which found no mortality difference.

Sultamicillin chemical compound

Sultamicillin, sold under the brand name Unasyn among others, is an oral form of the antibiotic combination ampicillin/sulbactam. It contains esterified ampicillin and sulbactam.

Virulence factors are molecules produced by bacteria, viruses, fungi, and protozoa that add to their effectiveness and enable them to achieve the following:

Hospital-acquired pneumonia (HAP) or nosocomial pneumonia refers to any pneumonia contracted by a patient in a hospital at least 48–72 hours after being admitted. It is thus distinguished from community-acquired pneumonia. It is usually caused by a bacterial infection, rather than a virus.

Orbital cellulitis Human disease

Orbital cellulitis is inflammation of eye tissues behind the orbital septum. It is most commonly caused by an acute spread of infection into the eye socket from either the adjacent sinuses or through the blood. It may also occur after trauma. When it affects the rear of the eye, it is known as retro-orbital cellulitis.

Liver abscess collection of pus within the liver as a result of infection by bacteria, protozoa, or other agents

A liver abscess is a mass filled with pus inside the liver. Common causes are abdominal conditions such as appendicitis or diverticulitis due to haematogenous spread through the portal vein. It can also develop as a complication of a liver injury.

Cefodizime chemical compound

Cefodizime is a 3rd generation cephalosporin antibiotic with broad spectrum activity against aerobic gram positive and gram negative bacteria. Clinically, it has been shown to be effective against upper and lower respiratory tract infections, urinary tract infections, and gonorrhea. Cefodizime is a bactericidal antibiotic that targets penicillin-binding proteins (PBPs) 1A/B, 2, and 3 resulting in the eventual death of the bacterial cell. In vivo experimental models of infection showed that bacterial clearance by this drug is at least as effective compared with other 3rd generation cephalosporins. It has similar adverse effect profile to other 3rd generation cephalosporins as well, mainly being limited to gastrointestinal or dermatological side effects.

Ecthyma gangrenosum skin lesion

Ecthyma gangrenosum is a type of skin lesion characterized by vesicles or blisters which rapidly evolve into pustules and necrotic ulcers with undermined tender erythematous border. "Ecthyma" means a pus forming infection of the skin with an ulcer, "gangrenosum" refers to the accompanying gangrene or necrosis. It is pathognomonic of Pseudomonas aeruginosa bacteremia. Pseudomonas aeruginosa is a gram negative, aerobic bacillus.

Pyogenic liver abscess areas of pus from bacterial infection in the hepatic parenchyma

A pyogenic liver abscess is a type of liver abscess caused by bacteria.

Pancreatic abscess is a late complication of acute necrotizing pancreatitis, occurring more than 4 weeks after the initial attack. A pancreatic abscess is a collection of pus resulting from tissue necrosis, liquefaction, and infection. It is estimated that approximately 3% of the patients suffering from acute pancreatitis will develop an abscess.

ESKAPE is an acronym encompassing the names of six bacterial pathogens commonly associated with antimicrobial resistance: ESKAPE is an acronym for their names and a reference to their ability to escape the effects of commonly used antibiotics through evolutionarily developed mechanisms, and also because it is a acronym made from the first letters of their scientific names:

An innate immune defect is a defect in the innate immune response that blunts the response to infection. These defects may occur in monocytes, neutrophils, natural killer cells, basophils, mast cells or complement proteins.


  1. "Pus". dictionary.reference.com. Retrieved 2008-08-18.
  2. "Pus – What Is Pus?". medicalnewstoday.com. Retrieved 2016-08-19.
  3. British Medical Journal. British Medical Association. 1917. pp. 751–754.
  4. Society, Louisiana State Medical (1846). Journal. p. 251.
  5. Barer, M.R. (2012). "The natural history of infection". Medical Microbiology. Elsevier. pp. 168–173. doi:10.1016/b978-0-7020-4089-4.00029-9. ISBN   978-0-7020-4089-4.
  6. 1 2 Madigan, Michael T. and Martin, John M. Brock Biology of Microorganisms 11th ed. Pearson Prentice Hall. US. 2006: 734
  7. " pyogenic " at Dorland's Medical Dictionary
  8. Topazian RG, Goldberg MH, Hupp JR (2002). Oral and maxillofacial infections (4 ed.). Philadelphia: W.B. Saunders. ISBN   978-0721692715.
  9. "Infections Caused by Common Pyogenic Bacteria", Dermatopathology, Berlin Heidelberg: Springer, 2006, pp. 83–85, doi:10.1007/3-540-30244-1_12, ISBN   978-3-540-30245-2
  10. Thompson, Alexis; Miles, Alexander (1921). "Pyogenic Bacteria". Manual of Surgery (6th ed.). Oxford Medical Publications. OCLC   335390813.
  11. 1 2 3 Nuland, Sherwin B. (2011). Doctors: The Biography of Medicine. Knopf Doubleday. ISBN   978-0-307-80789-2. Closed Access logo transparent.svg
  12. Van Hoosen, Bertha (Autumn 1947). "A Woman's Medical Training in the Eighties". Quarterly Review of the Michigan Alumnus: A Journal of University Perspectives. University of Michigan Libraries: 77–81. UOM:39015006945235. Open Access logo PLoS transparent.svg
  13. Scott, William (1922). An indexed system of veterinary treatment. Chicago: Eger. p. 603. Open Access logo PLoS transparent.svg
  14. 1 2 3 Schneider, Albert (1920). Pharmaceutical bacteriology (2nd ed.). P. Blakiston. p. 247.
  15. Williams, Charles J. B. (1848). Principles of Medicine: Comprising General Pathology and Therapeutics, and a Brief General View of Etiology, Nosology, Semeiology, Diagnosis, and Prognosis: With Additions and Notes by Meredith Clymer. Churchill. p. 306. Open Access logo PLoS transparent.svg