eMedicine Specialties > Infectious Diseases > Bacterial Infections

Peptostreptococcus Infection

Author: Itzhak Brook, MD, MSc, Professor, Department of Pediatrics, Georgetown University School of Medicine
Contributor Information and Disclosures

Updated: Jun 17, 2008

Introduction

Background

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 Peptostreptococcus asaccharolyticus, Peptostreptococcus anaerobius, Peptostreptococcus prevotii, and Peptostreptococcus micros.^4,5,6,7

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.⁸ 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.⁹

Pathophysiology

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.¹⁰ 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.¹¹

Frequency

United States

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. In 1974, Martin reported that anaerobic cocci were isolated in 8.5-31% of clinical specimens that yielded any anaerobic bacteria at the Mayo Clinic.⁶

In 2 studies published in 1988 and 1989, Brook reported that anaerobic gram-positive cocci accounted for 26% of all anaerobic bacteria recovered at BethesdaNavyHospital and WalterReedArmyHospital 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%).^5,12

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.⁵

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.⁷ 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 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, and P anaerobius in bone and joint infections and leg and foot ulcers.⁸

International

The frequency of these infections appears to be higher in developing countries, where therapy is often inadequate or delayed.

Mortality/Morbidity

Mortality has decreased over the past 3 decades.

Age

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

Clinical

Physical

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.¹ Peptostreptococcus infections occur more often in chronic infections and in association with the predisposing conditions below.

• CNS infections
  • Anaerobic gram-positive cocci and microaerophilic streptococci can be isolated from subdural empyema and from brain abscesses that develop as sequelae of chronic infections of the ears,¹³ mastoid, sinuses,¹⁴ and teeth.
  • Anaerobic gram-positive cocci and microaerophilic streptococci have been isolated from 18 (46%) of 39 brain abscesses.^2,1
• Upper respiratory tract and dental infections^2,1
  • The high rate of anaerobic cocci colonization of the oropharynx accounts for the organisms' significance in these infections. Anaerobic gram-positive cocci and microaerophilic streptococci are often recovered from acute and chronic upper respiratory tract infections. These organisms have been recovered in 15% of patients with chronic mastoiditis, 30% of patients with chronic sinusitis, 33% of patients with peritonsillar and retropharyngeal abscesses, and 50% of patients with purulent parotitis. They have also accounted for two thirds of isolates from periodontal abscesses.
  • In more than 90% of cases, other organisms also present in the oral florae have been found mixed with anaerobic gram-positive cocci and microaerophilic streptococci. These include Staphylococcus aureus, Streptococcus species, Fusobacterium species, and pigmented Prevotella and Porphyromonas species.
• Anaerobic pleuropulmonary infections^4,2,1
  • Anaerobic gram-positive cocci and microaerophilic streptococci account for 10-20% of anaerobic isolates recovered from properly obtained specimens of pulmonary infections. The pulmonary infections in which these organisms have been found most frequently include aspiration pneumonia, empyema associated with aspiration pneumonia, lung abscesses, and mediastinitis.
  • Obtaining appropriate culture specimens of these organisms requires the use of transtracheal aspiration, aspiration through double-lumen catheterization, or direct lung puncture.
• Intra-abdominal infections^2,1
  • Because anaerobic gram-positive cocci are part of the normal gastrointestinal florae, they can be isolated in approximately 20% of specimens from intra-abdominal infections, such as peritonitis and abscesses of the liver, spleen, and abdomen.
  • Anaerobic gram-positive cocci are generally recovered mixed with other organisms of intestinal origin that include Escherichia coli , Bacteroides fragilis group, and Clostridium species.
• Female pelvic infections^2,1
  • 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.
  • The predominant anaerobic gram-positive cocci are P asaccharolyticus, P anaerobius, and P prevotii.
  • Bacteremias with anaerobic gram-positive cocci and microaerophilic streptococci are often associated with septic abortion.
  • Anaerobic gram-positive cocci are generally found mixed with Prevotella bivia and Prevotella disiens.
• Osteomyelitis and arthritis^2,1
  • Anaerobic gram-positive cocci are frequently isolated from anaerobically infected bones and joints. In studies, 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. In a 1980 study by Bourgault and colleagues, most patients with infections involving these organisms underwent orthopedic surgery and had foreign prosthetic material in place at the time of infection.³ Management of these infections requires prolonged courses of antimicrobials and is enhanced by removal of the foreign material.
• Skin and soft tissue infections^2,1
  • Anaerobic gram-positive cocci and microaerophilic streptococci are often recovered in polymicrobial skin and soft tissue infections (eg, necrotizing synergistic gangrene; necrotizing fasciitis; decubitus ulcers; diabetes-related foot infections; paronychia; burns; human or animal bites; infected cysts; abscesses 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.
  • Vaginal and cervical florae can cause scalp wound infections in newborns after fetal monitoring.
  • Because anaerobic gram-positive cocci and microaerophilic streptococci are part of the normal skin florae, care must be used when obtaining specimens to avoid contamination by these florae.
• Bacteremia and endocarditis^12,15
  • Anaerobic gram-positive cocci and microaerophilic streptococci may be responsible for 4-15% of anaerobic bacteria isolated from blood cultures of patients with clinically significant anaerobic bacteremia. They are often recovered in persons with puerperal sepsis.
  • Peptostreptococci can cause fatal endocarditis, paravalvular abscess, and pericarditis.
  • The most frequent source of bacteremia due to Peptostreptococcus is infections of the oropharynx, lower respiratory tract, female genital tract, abdomen, skin, and soft tissues.
  • Predisposing factors for bacteremia due to Peptostreptococcus include malignancy; recent gastrointestinal, obstetrical, or gynecological surgery; immunosuppression; dental procedures; and oropharyngeal, female genital tract, abdominal, and soft tissue infections.
  • Microaerophilic streptococci typically account for 5-10% of cases of endocarditis; however, peptostreptococci have only rarely been isolated.

Causes

• The following are the major predisposing conditions to infection with anaerobic gram-positive cocci and microaerophilic streptococci:
  • Previous surgery
  • Immunodeficiency
  • Malignancy
  • Trauma
  • Diabetes
  • Steroid therapy
  • Presence of a foreign body
  • Sickle cell anemia
  • Reduced blood supply
  • Vascular disease
• Infection with aerobic bacteria can make the local tissue conditions more favorable for the growth of anaerobes, including anaerobic cocci. Anaerobic conditions and anaerobic bacteria can impair host defenses. Anaerobic infection often manifests as suppuration, thrombophlebitis, abscess formation, and gangrenous destruction of tissue associated with gas. Anaerobes, including peptostreptococci, are common in chronic infections. Therapy with antimicrobials (eg, aminoglycosides, trimethoprim-sulfamethazine, older quinolones) often does not eradicate anaerobes.

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