Peptostreptococcus is a genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of anaerobic
Anaerobic organism
An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present...

, Gram-positive
Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...

, non-spore
An endospore is a dormant, tough, and temporarily non-reproductive structure produced by certain bacteria from the Firmicute phylum. The name "endospore" is suggestive of a spore or seed-like form , but it is not a true spore . It is a stripped-down, dormant form to which the bacterium can reduce...

 forming bacteria. The cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

 are small, spherical, and can occur in short chains, in pairs or individually. Peptostreptococcus are slow-growing bacteria with increasing resistance to antimicrobial
An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes...


The most frequently identified species of Peptostreptococcus is P. magnus.


Peptostreptococcus species are commensal organisms in humans, living predominantly in the mouth, skin, gastrointestinal
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

, vagina and urinary tracts, and compose a portion of the bacterial gut flora
Gut flora
Gut flora consists of microorganisms that live in the digestive tracts of animals and is the largest reservoir of human flora. In this context, gut is synonymous with intestinal, and flora with microbiota and microflora....

. Under immunosuppressed or traumatic
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...

 conditions these organisms can become pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

ic, as well as septicemic
Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...

, harming their host. Peptostreptococcus can cause brain, liver, breast, and lung abscess
An abscess is a collection of pus that has accumulated in a cavity formed by the tissue in which the pus resides due to an infectious process or other foreign materials...

es, as well as generalized necrotizing
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...

 soft tissue infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

s. They participate in mixed anaerobic infection
Anaerobic infection
Anaerobic infections are caused by anaerobic bacteria. Anaerobic bacteria do not grow on solid media in room air ; facultative anaerobic bacteria can grow in the presence as well as in the absence of air. Microaerophilic bacteria do not grow at all aerobically or grow poorly, but grow better under...

s, a term which is used to describe infections that are caused by multiple bacteria that do not require or may even be harmed by oxygen.

Peptostreptococcus species are susceptible to beta-lactam antibiotics
Beta-lactam antibiotic
β-Lactam antibiotics are a broad class of antibiotics, consisting of all antibiotic agents that contains a β-lactam nucleus in its molecular structure. This includes penicillin derivatives , cephalosporins , monobactams, and carbapenems...


They are isolated with high frequency from all specimen sources. Anaerobic gram-positive cocci such as Peptostreptococcus are the second most frequently recovered anaerobes and account for approximately one quarter of anaerobic isolates found. Most often Anaerobic gram-positive cocci are usually recovered mixed in with other anaerobic or aerobic bacteria from various infections at different sites of the human body. This contributes to the difficulty of isolating Peptostreptococcus organisms.


Peptostreptococcus species that are found in clinical infections were once part of the genus formerly known as Peptococcus. Peptostreptococcus is the only genus among anaerobic gram-positive cocci that is encountered in clinical infections. As such, Peptostreptococcus species are viewed as being clinically significant anaerobic cocci. Other similar clinically significant anaerobic cocci include Veillonella
Veillonella are gram-negative anaerobic cocci. This bacterium is well known for its lactate fermenting abilities. They are a normal bacterium in the intestines and oral mucosa of mammals...

species (gram-negative cocci), and microaerophilic streptococci (aerotolerant). Anaerobic gram-positive cocci include various clinically significant species of the genus Peptostreptococcus.

Some clinically significant Peptostreptococcus species are, Gaffkya anaerobia, which was renamed Peptostreptococcus tetradius. The species of anaerobic gram-positive cocci isolated most commonly include Peptostreptococcus magnus, Peptostreptococcus asaccharolyticus, Peptostreptococcus anaerobius, Peptostreptococcus prevotii, and Peptostreptococcus micros.

Anaerobic gram-positive cocci that produce large amounts of lactic acid during the process of carbohydrate fermentation were reclassified as Streptococcus parvulus and Streptococcus morbillorum from Peptococcus or Peptostreptococcus. Most of these organisms are anaerobic, but some are microaerophilic.

Due to a large amount of new research done on the human microbe and more information on bacteria, many species of bacteria have been renamed and re classified. Based on DNA homology and whole-cell polypeptide-pattern study findings supported by phenotypic characteristics, the DNA homology group of microaerobic streptococci that was formerly known as Streptococcus anginosus or Streptococcus milleri is now composed of 3 distinct species: S anginosus, Streptococcus constellatus, and Streptococcus intermedius. The microaerobic species S morbillorum was transferred into the genus Gemella. A new species within the genus Peptostreptococcus is Peptostreptococcus hydrogenalis; it contains the indole-positive, saccharolytic strains of the genus.

Peptostreptococcus infections occur in/on all body sites, including the CNS, head, neck, chest, abdomen, pelvis, skin, bone, joint, and soft tissues. Adequate therapy must be taken against infections, or it could result in clinical failures.
Peptostreptoccocci are often overlooked and they are very difficult to isolate. In order to isolate peptostreptococci, appropriate specimen collection is required. Peptostreptococci grow slowly, and due to this slow growth they are increasingly resistant to antimicrobrials.

The most common Peptostreptococcus species found in infections are P. magnus (18% of all anaerobic gram-positive cocci and microaerophilic streptococci), P asaccharolyticus (17%), P anaerobius (16%), P prevotii (13%), P micros (4%), Peptostreptococcus saccharolyticus (3%), and Peptostreptococcus intermedius (2%).

P magnus were highly recovered in bone and chest infections. P asaccharolyticus and P anaerobius and the highest recovery rate in obstetrical/gynecological and respiratory tract infections and wounds. When anaerobic and facultative cocci were recovered most of the infection were polymicrobial. Most patients from whom microaerophilic streptococci were recovered in pure culture had abscesses (eg, dental, intracranial, pulmonary), bacteremia, meningitis, or conjunctivitis. P. Magnus is the most commonly isolated anaerobic cocci. It is often recovered in pure culture. Other common peptostreptococci in the different infectious sites are P anaerobius which occurs in oral infections; P micros in respiratory tract infection.s, P magnus, P micros, P asaccharolyticus, Peptostreptococcus vaginalis, and P anaerobius in skin and soft tissue infections; P magnus and P micros in deep organ abscesses; P magnus, P micros, and P anaerobius in gastrointestinal tract–associated infections; P magnus, P micros, P asaccharolyticus, P vaginalis, P tetradius, and P anaerobius in female genitourinary infections; and P magnus, P asaccharolyticus, P vaginalis, and P anaerobius in bone and joint infections and leg and foot ulcers.

Many infections caused by peptostreptococcus bacteria are synergistic. Bacterial synergy, the presence of which is determined by mutual induction of sepsis enhancement, increased mortality, increased ability to induce abscesses, and enhancement of the growth of the bacterial components in mixed infections, is found between anaerobic gram-positive cocci and their aerobic and anaerobic counterparts. The ability of anaerobic gram-positive cocci and microaerophilic streptococci to produce capsular material is an important virulence mechanism, but other factors may also influence the interaction of these organisms in mixed infections.

Although anaerobic cocci can be isolated from infections at all body sites, a predisposition for certain sites has been observed. In general, Peptostreptococcus species, particularly P magnus, have been recovered more often from subcutaneous and soft tissue abscesses and diabetes-related foot ulcers than from intra-abdominal infections. Peptostreptococcus infections occur more often in chronic infections.

Frequency of Infections

In the United States it is difficult to determine the exact frequency of peptostreptococcus infections because of inappropriate collection methods, transportation and cultivation of specimen. Peptostreptococcus infections are most commonly found in patients who have had or have chronic infections. Patients who have predisposing conditions are shown to have 5% higher recovery rate of the bacteria in blood cultures.

Of all anaerobic bacteria recovered at hospitals from 1973-1985, anaerobic gram-positive cocci accounted for 26% of it. The infected sited where these organisms were found in the greatest abundance were obstetrical and gynecological sites (35%), bones (39%) cysts (40%), and ears (53%). Occasionally found in other places such as abdomen, lymph nodes, bile, and eyes.

Frequency of infections is greater in developing countries because treatment is often slow, or it is impossible to get the adequate treatment, but mortality due to peptostreptococcus infections have decreased in the last 30 years and will continue to do so due to better treatment.

All ages are susceptible to peptostreptococcus infections, however children are more likely to get head and neck infections.

Skin and soft tissue infections

Anaerobic gram-positive cocci and microaerophilic streptococci are often recovered in polymicrobial skin and soft tissue infections, such as gangrene, fasciitis, ulcers, diabetes-related foot infections, burns, human or animal bites, infected cysts, abcesse of the breast, rectum, and anus. Anaerobic gram-positive cocci and microaerophilic streptococci are generally found mixed with other aerobic and anaerobic florae that originate from the mucosal surface adjacent to the infected site or that have been inoculated into the infected site.

Gastrointestinal florae can cause infections such as gluteal decubitus ulcers, diabetes-related foot infections, and rectal abscesses.
Anaerobic gram-positive cocci and microaerophilic streptococci are part of the normal skin florae, so it is hard to avoid contamination by these florae when obtaining specimens.

CNS infections

CNS infections can be isolated from subdural empyema and brain abscesses which are a result of chronic infections. Also isolated from sinuses, teeth and mastoid. 46% of 39 brain abscesses in one study showed anaerobic gram-positive cocci and microaerophilic streptococci.

Upper respiratory tract and dental infections

There is a high rate of anaerobic cocci colonization which accounts for the organisms significance in these infections. Anaerboci gram positive cocci and micraerophilic streptococci are often recovered in these infections. They have been recovered in 15% of patients with chronic mastoiditis, When peptostreptococci and other anaerobes predominate, aggressive treatment of acute infection can prevent chronic infection. When the risk of anaerobic infection is high, as with intra-abdominal and post surgical infections, proper antimicrobial prophylaxis may reduce the risk
90% of the time, other organisms were mixed in with the anaerobic gram-positive cocci and microaerophilic streptococci. This includes streptococcus species, and staphylococcus aureus.

Bacteremia and endocarditis

Peptostreptococci can cause fatal endocarditis, paravalvular abscess, and pericarditis. The most frequent source of bacteremia due to Peptostreptococcus are infections of the oropharynx, lower respiratory tract, female genital tract, abdomen, skin, and soft tissues. Recent gynecological surgery, immunosuppression, dental procedures, infections of the female genital tract, abdominal and soft tissue along with gastrointestinal surgery are predisposing factors for bacermia due to peptostreptococcus.

Microaerophilic streptococci typically account for 5-10% of cases of endocarditis; however, peptostreptococci have only rarely been isolated.

Anaerobic pleuropulmonary infections

Anaerobic gram-positive cocci and microaerophilic streptococci are most frequently found in aspiration pneumonia, empyema, lung abscesses, and mediastinitis. These bacteria account for 10-20% of anaerobic isolated recovered from pulmonary infections.
It is difficult to obtain appropriate culture specimens. It requires a direct lung puncture, or the use of trans-tracheal aspiration.

Abdominal infections

Anaerobic gram-positive cocci are part of the normal gastrointestinal florae. They are isolated in approximately 20% of specimens from intra-abdominal infections, such as peritonitis. Found in abcesses of the liver, spleen, and abdomen. Like in upper respiratory tract and dental infections, anaerobic gram-positive cocci are recovered mixed with other bacteria. In this case they are mixed with organisms of intestinal origin such as E coli, bacteroides fragilis group, and clostridium species.

Female pelvic infections

The anaerobic gram-positive cocci most often found are P asaccacharolyticus, P anaerobis, and P prevotii. Anaerobic gram-positive cocci and microaerophilic streptococci can be isolated in 25-50% of patients with endometritis, pyoderma, pelvic abscess, Bartholin gland abscess, postsurgical pelvic infections, or pelvic inflammatory disease. The origin of these organisms is probably the vaginal and cervical florae. Anaerobic gram-positive cocci are generally found mixed with Prevotella bivia and Prevotella disiens.
Osteomyelitis and arthritis:

Anaerobic gram-positive cocci are frequently isolated from anaerobically infected bones and joints., they accounted for 40% of anaerobic isolates of osteomyelitis caused by anaerobic bacteria and 20% of anaerobic isolates of arthritis caused by anaerobic bacteria. P magnus and P prevotii are the predominant bone and joint isolates. Management of these infections requires prolonged courses of antimicrobials and is enhanced by removal of the foreign material.

Causes of Infection

Infections with anaerobic gram-positive cocci and microaerophilic streptococci are often caused by:
  • Trauma
  • Immunodeficiency
  • Steroid therapy
  • Vascular disease
  • Malignancy
  • Reduced blood supply
  • Previous surgery
  • Presence of a foreign body
  • Sickle cell anemia
  • Diabetes


When peptostreptococci and other anaerobes predominate, aggressive treatment of acute infection can prevent chronic infection. When the risk of anaerobic infection is high, as with intra-abdominal and post-surgical infections, proper antimicrobial prophylaxis may reduce the risk.
Therapy with antimicrobials (eg, aminoglycosides, trimethoprim-sulfamethazine, older quinolones) often does not eradicate anaerobes.

External links

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