Peptostreptococcus Infection 

Updated: Jul 06, 2017
Author: Itzhak Brook, MD, MSc; Chief Editor: Mark R Wallace, MD, FACP, FIDSA 



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]


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]



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

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.[12]

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%).[5, 13]

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]


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]




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,[14] mastoid, sinuses,[15] 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

The high rate of anaerobic cocci colonization of the oropharynx accounts for the organisms' significance in these infections.[2, 1, 7, 16] Anaerobic gram-positive cocci and microaerophilic streptococci are often recovered from acute and chronic upper respiratory tract infections. These organisms have been recovered in 9%-38% of patients with chronic otitis media,[16] 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.[17] They have also accounted for two thirds of isolates from periodontal abscesses and are also found in acute necrotizing gingivitis.

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, 18]

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, 19, 20]

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

Anaerobic gram-positive cocci and microaerophilic streptococci are often recovered in polymicrobial skin and soft tissue infections[2, 1] (eg, necrotizing synergistic gangrene; necrotizing fasciitis; decubitus ulcers; diabetes-related foot infections; paronychia; burns; human or animal bites[21] ). Peptostreptococcus is also commonly found in the tropical infection, acute noma. 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[13, 22]

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.[23]

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.[24] Peptoniphilus species that were formerly classified in the genus Peptostreptococcus have been recovered from blood samples in patients with pneumonia, from patients in preterm delivery, from patients with soft tissue infection, and from patients with colon or bladder disease. Half of these infections were polymicrobial.[25]

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.


The following are the major predisposing conditions to infection with anaerobic gram-positive cocci and microaerophilic streptococci:

  • Previous surgery

  • Rupture of viscous

  • 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.



Laboratory Studies


Anaerobic, microaerophilic, and facultative gram-positive cocci have minor morphological differences. P magnus has a larger diameter than other anaerobic gram-positive cocci. P micros has a smaller diameter than other anaerobic gram-positive cocci and usually forms short chains. P anaerobius and Peptostreptococcus productus are elongated and often appear in pairs or chains.

Gas-liquid chromatography and biochemical tests are required for genus-level identification and separation of most anaerobic gram-positive cocci. These organisms are fastidious, and their complete identification is often difficult. Because of ill-defined differences in the pathogenic potential for the different species, the need for exact specification is controversial.

Anaerobic cocci show slow but adequate growth on all nonselective anaerobic growth media. Vancomycin-containing selective media inhibit their growth.

Recovery in clinical specimens[9]

Anaerobic and facultative gram-positive cocci are often isolated from clinical specimens mixed with other anaerobic or aerobic bacteria and, on rare occasions, are isolated as the sole pathogen. As a group, these organisms are the most frequently recovered anaerobes in cutaneous, oral, respiratory tract, and female genital tract infections.

Collecting anaerobic bacteria specimens is important because documentation of an anaerobic infection is through culture of organisms from the infected site. Documentation requires proper collection of appropriate specimens, expeditious transportation, and careful laboratory processing.

Obtain uncontaminated specimens. Inadequate culture techniques or media can lead to faulty results and the incorrect conclusion that only aerobic organisms are present in a mixed infection. Specimens must be obtained free of contamination. Inadequate techniques or media can lead to missing the presence of anaerobic bacteria or the assumption that only aerobic organisms are present in a mixed infection.

Because anaerobes are present on mucous membranes and skin, even minimal contamination with normal florae can be misleading.

Unacceptable or inappropriate specimens can also yield normal florae and therefore have no diagnostic value. Obtain appropriate specimens using techniques that bypass the normal florae.

Direct-needle aspiration is the best method of obtaining a culture. Direct-needle aspiration is probably the best method of obtaining a culture, and the use of swabs is much less desirable. Specimens obtained from normally sterile sites, such as blood, spinal, joint, or peritoneal fluids, are collected after thorough skin decontamination. Two approaches are used to culture the maxillary sinus by aspiration following sterilization of the canine fossa or the nasal vestibule, either via the canine fossa or via the inferior meatus.

Urine collected is collected by percutaneous suprapubic bladder aspiration.

Other specimens can be collected from abscess contents, from deep aspirates of wounds, and by special techniques, such as transtracheal aspirates or direct lung puncture.

Specimens of the lower respiratory tract are difficult to obtain without contamination with indigenous florae. Double-lumen catheter bronchial brushing and bronchoalveolar lavage, cultured quantitatively, can be useful.

Culdocentesis fluid obtained after decontamination of the vagina is acceptable.

Transportation of specimens should be expeditious. Place specimens into an anaerobic transporter as soon as possible. These devices generally contain oxygen-free environments provided by a mixture of carbon dioxide, hydrogen, and nitrogen plus an aerobic condition indicator.

Liquid or tissue specimens are always preferred to swabs.

Inoculate liquid specimens into an anaerobic transport vial or a syringe. All air bubbles are expelled from the syringe. Insertion of the needle tip into a sterile rubber stopper is no longer recommended. Because air gradually diffuses through the plastic syringe wall, specimens should be processed in less than 30 minutes.

Transport tissue specimens in an anaerobic jar or a sealed plastic bag rendered anaerobic.

If swabs are used, place them in sterilized tubes containing carbon dioxide or prereduced, anaerobically sterile Carey and Blair semisolid media.

Gram stain of a smear of the specimen provides important preliminary information regarding types of organisms present, suggests appropriate initial therapy, and serves as a quality control. Immediately place cultures under anaerobic conditions and incubate for 48 hours or longer. An additional 36-48 hours is usually required for species- or genus-level identification using biochemical tests; kits containing these tests are commercially available.

A rapid enzymatic test enables identification after only 4 hours of aerobic incubation. Gas-liquid chromatography of metabolites is often used. Nucleic acid probers and polymerase chain reaction methods are also being developed for rapid identification.[26] Detailed procedures of laboratory methods can be found in microbiology manuals.

Antimicrobial susceptibility test results of peptostreptococci have become less predictable because of the increasing resistance of peptostreptococci to several antimicrobials.[27] Resistance to metronidazole is common. Routine susceptibility testing is time consuming and often unnecessary; however, testing the susceptibility of isolates recovered from sterile body sites, those that are clinically important and have variable susceptibilities, and especially those isolated in pure cultures from properly collected specimens is important. These include isolates associated with bacteremia; endocarditis; and bone, joint, or skull infections.[28]

Routine susceptibility testing is time-consuming and often unnecessary. Poor quality control of in-vitro susceptibility testing, and the difficulty to obtain results in a reasonable time makes testing less useful. However, testing the susceptibility of isolates recovered from sterile body sites and/or those that are clinically important (ie, blood cultures, bone, CNS, serious infections) and have variable susceptibilities, especially those isolated in pure culture from properly collected specimens, is important. Antimicrobial testing is recommended, however, to monitor local hospital and geographic susceptibility profiles, and to determine the activity of new antimicrobials.

Recommended methods include agar microbroth and macrobroth dilution. Newer methods include the E-test and the spiral gradient end point system. Agents that should be tested include penicillin, broad-spectrum penicillin, penicillin plus a beta-lactamase inhibitor, clindamycin, chloramphenicol, second-generation cephalosporins (eg, cefoxitin), moxifloxacin, tigecycline, metronidazole, and carbapenems.

Imaging Studies

Radiological or imaging studies are helpful. The presence of gas in the infected site is a strong indication of anaerobic infection.



Medical Care

A patient's recovery from anaerobic infection depends on prompt and proper treatment according to the following principles: (1) neutralizing toxins produced by anaerobes, (2) preventing local bacterial proliferation by changing the environment, and (3) limiting the spread of bacteria.

Control the environment by debriding necrotic tissue, draining pus, improving circulation, alleviating obstruction, and increasing tissue oxygenation. Certain types of adjunctive therapy, such as hyperbaric oxygen therapy, may be useful but remain unproven.

In many cases, antimicrobial therapy is the only form of therapy required, but it can also be an adjunct to a surgical approach. Because anaerobic bacteria, including peptostreptococci, are generally recovered mixed with aerobic organisms, choose antimicrobial agents that treat both types of pathogens, taking into consideration their aerobic and anaerobic antibacterial spectrum and their availability in oral or parenteral form.[28, 29]

Penicillin G is most effective for treating anaerobic gram-positive cocci and microaerophilic streptococci. Other effective agents include other penicillins, cephalosporins, chloramphenicol, clindamycin, vancomycin, telithromycin, linezolid, quinupristin/dalfopristin, and carbapenems.

The efficacy of macrolides (eg, erythromycin) and imidazoles (eg, metronidazole) is variable and unpredictable. Imidazoles are ineffective against some anaerobic gram-positive cocci and all aerotolerant strains.

The newer quinolones are effective against more than 90% of anaerobic cocci; ciprofloxacin is less effective.

Occasionally, certain strains are resistant to antimicrobials, especially after administration of these agents.

When mixed with other beta-lactamase–producing bacteria, anaerobic gram-positive cocci and microaerophilic streptococci may survive penicillin or cephalosporin therapy because of the protection provided by the free enzyme. In such instances, antimicrobials with wider spectrums of activity may be more effective.

Surgical Care

In most cases, surgical therapy is critically important. Surgical therapy includes (1) draining abscesses, (2) debriding necrotic tissues, (3) decompressing closed-space infections, and (4) relieving obstructions.[30] If surgical drainage is not used, the infection may persist and serious complications may develop.



Medication Summary

Clinical judgment, personal experience, safety, and expected level of patient compliance should direct the physician in the choice of antimicrobial agents. When choosing antimicrobials for the therapy of mixed infections, their aerobic and anaerobic antibacterial spectrum and their availability in oral or parenteral form should be considered. Some antimicrobials have a limited range of activity.

Aside from susceptibility patterns, other factors influencing the choice of antimicrobial therapy include the pharmacologic characteristics of the various drugs, their toxicity, their effect on the normal florae, and their bactericidal activity. Although identification of the infecting organisms and their antimicrobial susceptibility may be needed for selection of optimal therapy, the clinical setting and gram-stain preparation of the specimen may indicate the types of anaerobes present in the infection and may indicate the nature of the infectious process.

Although the duration of therapy for anaerobic infections is generally longer than for aerobic and facultative infections, the duration must be individualized depending on the patient's response to the therapy. In some cases, the patient may require a 6- to 8-week course. However, therapy may be shortened after proper surgical drainage.[29]

Because peptostreptococci are often mixed with other aerobic and anaerobic bacteria in the infectious process, broader antimicrobial coverage is often necessary. Furthermore, because of the difficulty in recovering other fastidious anaerobic organisms, they may not be recovered even when cultures are taken.

Antimicrobial agents with broader coverage against anaerobic bacteria, including peptostreptococci, include cefoxitin, clindamycin, carbapenem (eg, imipenem, meropenem, ertapenem, doripenem), tigecycline, the combination of a penicillin (eg, ticarcillin) with a beta-lactamase inhibitor (ie, clavulanate), and quinolones with anti-anaerobic activity (ie, moxifloxacin).[29]

An anti–gram-negative enteric agent is generally added to treat Enterobacteriaceae when treating intra-abdominal infections.

Metronidazole has excellent activity against gram-negative anaerobic bacteria and has no activity against aerobic and facultative bacteria. Gram-positive anaerobic bacteria including peptostreptococci, microaerophilic streptococci, Propionibacterium acnes, and Actinomyces species are often resistant; therefore; adding an antimicrobial that is effective against these organisms (eg, penicillin) is often necessary.[28, 29]

Penicillin is added to metronidazole to cover microaerophilic streptococci, peptostreptococci, Actinomyces species, and Arachnia species when treating intracranial and dental infections.

Penicillin is the antimicrobial of choice for bacteremia caused by non–beta-lactamase producers; however, if other organisms may be involved in another site, broader coverage is needed.

Clindamycin is effective against aerobic and anaerobic gram-positive cocci. However, resistance of the B fragilis group in some centers in the United States recently reached about 40%. This agent can therefore not be used as empiric therapy. Antibiotic-associated colitis due to Clostridium difficile, although associated with most antimicrobials, was first described following clindamycin therapy.

A macrolide or amoxicillin is added to metronidazole to treat S aureus and aerobic streptococci in upper respiratory tract infections. The macrolides have moderate-to-good in vitro activity against anaerobic bacteria other than B fragilis group strains and fusobacteria. Macrolides are active against pigmented Prevotella and Porphyromonas species and microaerophilic streptococci, gram-positive non–spore-forming anaerobic bacilli, and certain clostridial organisms. They are less effective against Fusobacterium and Peptostreptococcus species.[31]

Tigecycline has effective in vitro activity against both gram-positive and gram-negative anaerobes, as well as against gram-positive aerobic strains such as methicillin-resistant staphylococci, streptococci, and enterococci. Resistance of members of the B fragilis group varied from 3.3-7.2%.[26] Tigecycline was approved by the US Food and Drug Administration (FDA) for the treatment of complicated skin and skin-structure infections and complicated intra-abdominal infections.

The newer tetracycline analogs doxycycline and minocycline are more active than tetracycline. Because of the significant resistance to these drugs, they are useful only when susceptibility tests can be performed or in less severe infections in which a therapeutic trial is feasible. Doxycycline is effective against chlamydial and mycoplasmal infections and is added to most regimens when treating pelvic infections.

Trovafloxacin, moxifloxacin, and gatifloxacin yield low minimum inhibitory concentrations (MICs) against most groups of anaerobes. Moxifloxacin was approved by the FDA for the treatment of complicated skin and skin-structure infections and complicated intra-abdominal infections. However, up to 40% of Bacteroides species are resistant to moxifloxacin.[32] The use of the quinolones is restricted in growing children and pregnancy because of their possible adverse effects on the cartilage.

Oral therapy for peptostreptococci is often substituted for parenteral therapy. Oral agents include clindamycin, amoxicillin and clavulanate, and chloramphenicol.


Class Summary

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.

Penicillin G (Pfizerpen)

Interferes with synthesis of cell-wall mucopeptide during active multiplication, resulting in bactericidal activity against susceptible microorganisms (beta-lactam).

Cefoxitin (Mefoxin)

Second-generation cephalosporin indicated for gram-positive cocci and gram-negative rod infections. Infections caused by cephalosporin- or penicillin-resistant gram-negative bacteria may respond.

Cefotetan (Cefotan)

Second-generation cephalosporin indicated for management of infections caused by susceptible gram-positive cocci and gram-negative rods.

Clindamycin (Cleocin)

Resistance of Bacteroides fragilis group against lincosamide has increased. However, these agents are effective against peptostreptococci. They are used for treatment of serious skin and soft tissue staphylococcal infections. Effective against aerobic and anaerobic streptococci (except enterococci). Inhibits bacterial growth, possibly by blocking dissociation of peptidyl t-RNA from ribosomes, causing RNA-dependent protein synthesis to arrest.

Amoxicillin and clavulanate (Augmentin)

Treat bacteria resistant to beta-lactam antibiotics.

Ticarcillin and clavulanate potassium (Timentin)

Inhibit biosynthesis of cell-wall mucopeptide and are effective during stage of active growth. Contains 4.7-5 mEq of Na+/g.

Chloramphenicol (Chloromycetin)

Binds to 50S bacterial-ribosomal subunits and inhibits bacterial growth by inhibiting protein synthesis. Effective against gram-negative and gram-positive bacteria.

Imipenem and cilastatin (Primaxin)

For treatment of multiorganism infections in which other agents do not have wide-spectrum coverage or are contraindicated because of potential for toxicity.

Meropenem (Merrem)

Bactericidal broad-spectrum carbapenem antibiotic that inhibits cell-wall synthesis. Effective against most gram-positive and gram-negative bacteria. Has slightly increased activity against gram-negatives and slightly decreased activity against staphylococci and streptococci compared with imipenem.

Ertapenem (Invanz)

Bactericidal activity results from inhibition of cell wall synthesis and is mediated through ertapenem binding to penicillin-binding proteins. Stable against hydrolysis by a variety of beta-lactamases, including penicillinases, cephalosporinases, and extended-spectrum beta-lactamases. Hydrolyzed by metallo-beta-lactamases.

Moxifloxacin (Avelox)

Inhibits the A subunits of DNA gyrase, resulting in inhibition of bacterial DNA replication and transcription.

Tigecycline (Tygacil)

A glycylcycline antibiotic that is structurally similar to tetracycline antibiotics. Inhibits bacterial protein translation by binding to 30S ribosomal subunit, and blocks entry of amino-acyl tRNA molecules in ribosome A site. Complicated intra-abdominal infections caused by C freundii, E cloacae, E coli, K oxytoca, K pneumoniae, E faecalis (vancomycin-susceptible isolates only), S aureus (methicillin-susceptible isolates only), S anginosus group (includes S anginosus, S intermedius, and S constellatus), B fragilis, B thetaiotaomicron, B uniformis, B vulgatus, C perfringens, and P micros.




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 postsurgical infections, proper antimicrobial prophylaxis may reduce the risk.

Preventing oral florae aspiration by improving neurological status, suctioning oral secretions, improving oral hygiene, and maintaining lower stomach pH can reduce the risk of aspiration pneumonia and its complications.

Irrigating wounds, debriding necrotic tissue, draining pus, and improving the blood supply helps prevent skin and soft tissue infections.

Patient Education

For excellent patient education resources, visit eMedicineHealth's Infections Center. Also, see eMedicineHealth's article Antibiotics.