Peptostreptococcus Infection

Updated: Apr 30, 2021
  • Author: Itzhak Brook, MD, MSc; Chief Editor: Michael Stuart Bronze, MD  more...
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Clinically significant anaerobic cocci include Peptostreptococcus species, Veillonella species (gram-negative cocci), and microaerophilic streptococci (aerotolerant). Anaerobic gram-positive cocci include various clinically significant species of the genus Peptostreptococcus. [1]

Peptostreptococcus infections can occur in all body sites, including the CNS, head, neck, chest, abdomen, pelvis, skin, bone, joint, and soft tissues. Inadequate therapy against these anaerobic bacteria may lead to clinical failures. Because of their fastidiousness, peptostreptococci are difficult to isolate and are often overlooked. Isolating them requires appropriate methods of specimen collection, transportation, and cultivation. Their slow growth and increasing resistance to antimicrobials, in addition to the polymicrobial nature of the infection, complicate treatment. [2]

Peptostreptococcus is the only genus among anaerobic gram-positive cocci encountered in clinical infections. This group also includes species within the genus formerly known as Peptococcus, with the exception of Peptococcus niger. This change in taxonomy was based on the results of a guanine-plus-cytosine content analysis. Additionally, Gaffkya anaerobia was renamed Peptostreptococcus tetradius. The species of anaerobic gram-positive cocci isolated most commonly include Peptostreptococcus magnus, [3]  Fingoldia magna, [4]  Peptostreptococcus asaccharolyticus, Peptostreptococcus anaerobius, Peptostreptococcus prevotii, and Peptostreptococcus micros. [5, 6, 7, 8]

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.

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. [9] 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. [10]



Peptostreptococcus organisms are part of the normal florae of human mucocutaneous surfaces, including the mouth, intestinal tract, vagina, urethra, and skin. [2] They are isolated with high frequency from all specimen sources. Anaerobic gram-positive cocci are the second most frequently recovered anaerobes and account for approximately one quarter of anaerobic isolates. Anaerobic gram-positive cocci are usually recovered mixed with other anaerobic or aerobic bacteria from infections at different sites of the body.

Many of these infections 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. [11] 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. [12]




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The exact frequency of Peptostreptococcus infections is difficult to calculate because of inappropriate methods of collection, transportation, and cultivation of specimens. These infections are found more commonly in patients with chronic infections. Recovery rates in blood cultures are 2-5% and are higher in patients who have predisposing conditions. Martin reported that anaerobic cocci were isolated in 8.5-31% of clinical specimens that yielded any anaerobic bacteria at the Mayo Clinic. [7]

Park et al reviewed 1070 anaerobic infections in several Hospital in Seoul, South Korea and reported that Peptostreptococcus accounted for 8.4% of these infections. [13]

In 2 studies published in 1988 and 1989, Brook reported that anaerobic gram-positive cocci accounted for 26% of all anaerobic bacteria recovered at Bethesda Navy Hospital and Walter Reed Army Hospital from 1973-1985. The infected sites where the organisms predominated were ears (53% of all anaerobic isolates), cysts (40%), bones (39%), and obstetrical and gynecological sites (35%). They were occasionally found in the CNS, abdomen, lymph nodes, bile, and eyes. Most isolates were found in abscesses, wounds, and obstetrical and gynecological infections.

The recovery rates differed for the different anaerobic gram-positive cocci. In descending order of frequency, the most common anaerobic gram-positive cocci were 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%). [6, 14]

The highest recovery rates of P magnus were in bone and chest infections. The highest recovery rate of P asaccharolyticus and P anaerobius were with obstetrical/gynecological and respiratory tract infections and wounds. Isolates of each of the most frequently recovered anaerobic gram-positive cocci were recovered from abscesses, wounds, and obstetrical and gynecological infections. [6]

Although most of the infections were polymicrobial when anaerobic and facultative cocci were recovered, these organisms were isolated in pure culture in 45 (8%) of 559 patients who had infections involving anaerobic gram-positive cocci, in 12 (10%) of 121 individuals who had infections due to microaerophilic streptococci, and in 15 (9%) of 176 patients who had P magnus infection. [8] The most frequent types of infections from which anaerobic gram-positive cocci were isolated in pure culture were soft tissue infections, osteomyelitis, arthritis (especially in the presence of a prosthetic implant), and bacteremia. 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. [3] It is most often recovered in pure culture. The most common peptostreptococci in the different infectious sites are Fingoldia magna and P. anaerobius in infectious endocarditis,( Brook I. Infective endocarditis caused by anaerobic bacteria.Arch Cardiovasc Dis. 2008 ;101:665-76,) P anaerobius in oral infections; P magnus and P micros in respiratory tract infections; 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, Fingoldia magna,  and P anaerobius in bone and joint infections and leg and foot ulcers. [9]


The frequency of these infections appears to be higher in developing countries, where therapy is often inadequate or delayed. However, because of difficulties in isolation of these and other anaerobic bacteria, their role is underestimated.


Mortality has decreased over the past 4 decades because of early recognition, medical and surgical intervention, and the initiation of proper prophylactic and therapeutic antimicrobial therapies.


Peptostreptococcus infections can occur in patients of all ages; however, upper respiratory tract and head and neck infections occur more frequently in children than in adults. [1]