Infections caused by anaerobic bacteria are common, and may be serious and life-threatening. Anaerobes predominant in the bacterial flora of normal human skin and mucous membranes, and are a common cause of bacterial infections of endogenous origin. Infections due to anaerobes can evolve all body systems and sites. The predominate ones include: abdominal, pelvic, respiratory, and skin and soft tissues infections. Because of their fastidious nature, they are difficult to isolate and are often overlooked. Failure to direct therapy against these organisms often leads to clinical failures. Their isolation requires appropriate methods of collection, transportation and cultivation of specimens. Treatment of anaerobic bacterial infection is complicated by the slow growth of these organisms, which makes diagnosis in the laboratory only possible after several days, by their often polymicrobial nature and by the growing resistance of anaerobic bacteria to antimicrobial agents.

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Bite Wound, and Infected tumor Infections

Human and animal bites and other orally contaminated wounds are relatively common. 1 Bite wounds include scratches, punctures, lacerations, and evulsions. Although these wounds may look innocuous initially, they frequently lead to serious infection and complications.

A variety of organisms can be recovered from bite wounds that generally originate from the aerobic and anaerobic microbial oral cavity flora of the biter, rather than the victim's own skin flora.

Most infections are polymicrobial. (TABLE 1) A higher number of isolates/wound is found in human bites, compared to animal bites (5.4 versus 2.8 isolates per specimen) mostly due to the presence of more Gram negative anaerobic bacilli (3.0 versus 1.0). Anaerobes were isolated from over 2/3 of human and  animal bite wound infections, especially those associated with abscess forma­tion.1,2  The predominant ones are Gram negative bacilli ( pigmented Prevotella and Porphynomonas spp., Fusobacterium nucleatum and anaerobic Gram-positive cocci. 3 Streptococcus pyogenes is generally found in human bites, Pasteurella multocida in animal bites, Eikenella corrodens in both animal and human bites (mostly with the latter), Capnocytophaga canimorsus (formerly called CDC group DF-2), Capnocytophaga cynodegmiNeisseria weaveri (formerly M-5), Weeksella zoohelcum (formerly IIj), Neisseria canisStaphylococcus intermedius, NO-1, and EO-2 in dog bites, A Flavobacterium group (IIb-like organism) in infected pig bite, and Actinobacillus species in horse and sheep bite wounds.
Vibrio species, Plesiomonas shigeloidesAeromonas hydrophila, and Pseudomonas spp., cause infections in bites from marine settings.

Tularemia can be transmitted from cats, herpes B virus from monkeys, rat bite fever and sodoku from rats, hepatitis B virus from humans, and rabies virus and leptospirosis from dogs and rodents.
Clenched-fist injury


The potential for infection of human or animal bites is great. The average dog mouth harbors more than 64 and the human over 400 species of bacteria. The polymicrobial aerobic and anaerobic flora, is a synergistic infection that is hard to eradicate.


The symptoms following a bite depend on the animal species inflicting the injury. The signs of infection can include redness, swelling, and clear or pussy discharge. The adjacent lymph nodes may be enlarged, and reduction in range of movement of an extremity can be present. In severe cases, there may be a peripheral leukocytosis. Bites of the hand are at high risk of deep damage and severe infection because sharp teeth may penetrate tendon sheaths or the midpalmar space.

Human bites generally are more severe than animal bites. This is particularly true in clenched-fist injury when the skin over the knuckles is penetrated after striking the teeth of another person. The teeth may cause a deep laceration that implant oral and skin organisms into the joint capsules or dorsal tendons, thus causing septic arthritis or osteomyelitis. Radiographs of hands injured by teeth are recommended.

About 5% of all dog bite wounds become infected. Cultured for both aerobic and anaerobic bacteria and Gram stain should be obtained from wounds. In wounds contaminated by soil or vegetative debris, culture for mycobacteria and fungi should be done.

Dog bite injury


Management includes local care wound approximation, administration of antimicrobials and tetanus and rabies (when indicated) immunization,  Herpes B virus evaluation (in monkey bites),  and re-examination at 24 and 48 hours. The incidence should be reported to the local health department when indicated.

The rules governing the management of any laceration also apply to animal bites: cleanse, explore, irrigate, debride, drain, and possibly suture. Bite wounds should be washed vigorously with soap or a quaternary ammonium compound and water. The site  should be explored for damage to, tendons, blood vessels, joints, and bones. Devitalized tissues should be debrided.  Whether bite wounds that are clinically uninfected and are seen within 24 hours should be surgically closed, remains controversial.

Bites to the face require meticulous management. Early treatment of all human bites, especially of the hand, must be thorough and aggressive. Clenched-fist injuries require more intensive care, preferably by a hand surgeon.

Antimicrobial therapy is not usually prophylactic, but therapeutic and is administered to all patients with deep wounds. These include puncture wounds, facial bites and any wound over a tendon or bone. The exception are patients who present 24 hours or more after injury without clinical signs of infection.

Penicillin or ampicillin are the most active agents against P. multocida and the other oral flora but are inactive against beta-lactamase producers. The combination of amoxicillin and clavulanic acid is effective against most wound pathogens. Clindamycin and the penicillinase-resistant penicillins should not be administered without penicillin because of their poorer activity against P. multocida. Azithromycin and clarithromycin are only modestly effective against E. corrodens and Peptostreptococcus spp. Cefoxitin, the combination of ticarcillin and clavulanic acid, the newer quinolones (moxifloxacin and trovafloxacin ) are active against all major pathogens.4

E. corrodens, is susceptible to penicillin, ampicillin, and the quinolones, but resistant to oxacillin, clindamycin, and sometimes to cephalosporins.4

Duration and route of antibiotic therapy should be individualized based on the site involved, the culture results, and the response to treatment. A 7- to 14-day course is usually adequate for soft tissue infections and a minimum of 3 weeks is required for those evolving joints or bones.

Complications include lymphangitis, local abscess, septic arthritis, tenosynovitis, and osteomyelitis. Rare complications include endocarditis, meningitis, brain abscess, and sepsis with disseminated intravascular coagulation,2,3 especially in immunocompromised individuals. Rabies must also be considered.






 1.  Goldstein EJC. New horizons in the bacteriology, antimicrobial susceptibility and therapy of
       animal bite wounds. J Med Microbiol 1998;47:95‑97.
2.Brook, I.: Microbiology of human and animal bite wounds in children. J. Pediatr. Infect. Dis6:29-   32, 1987.
3.Talan, D.A., Citron, D.M., Abrahamian, F.M., Moran, G.J., Goldstein, E.J.: Bacteriological analysis of infected dog and cat bites. Emergency Medicine Animal Bite Infection Study Group. N Engl J Med 14;340:85–92, 1999.
4.  Goldstein, E.J., Citron, D.M., Merriam, C.V., Tyrrell, K, Warren, Y.: Activity of gatifloxacin    compared to those of five other quinolones versus aerobic and anaerobic isolates from skin and soft tissue samples of human and animal bite wound infections. Antimicrob Agents Chemother 43:1475–9, 1999.

Table 1: Common bacterial isolates from dog and cat bite wounds

Pasteurella multocida subsp. multocida
Pasteurella multocida subsp. septica
Pasteurella dagmatis
Pasteurella canis
Pasteurella stomatis
Pasteurella haemolytica
Capnocytophaga cynodegmi
Capnocytophaga canimorus
Alpha‑hemolytic streptococci
Beta‑hemolytic streptococci
Enterococcus spp.
Staphylococcus aureus
Staphylococcus intermedius
Staphylococcus epidermidis
Haemophilus felis
Haemophilus aphrophilus
Corynebacterium species
Micrococcus luteus
Moraxella species
Neisseria canis
Neisseria weaveri
Acinetobacter calcoaceticus
Actinobacillus actinomycetemcomitans
Eikenella corrodens
Weeksella zoohelcum
Bacteroides tectum
Fusobacterium nucleatum
Fusobacterium russii
Prevotella melaninogenica
Prevotella heparinolytica
Prevotella intermedia
Prevotella brevia
Prevotella buccae
Prevotella denticola
Prevotella zoogleoformans
Porphyromonas cangingivalis
Porphyromonas canoris
Porphyromonas circumdentaria
Porphyromonas salivosa
Porphyromonas sulci
Porphyromonas asaccharolytica
Veillonella parvula
Leptotrichia buccalis


Aerobic and anaerobic bacteria of endogenous source can cause infections in necrotic tumor, especially when they occur in proximity to a site where these bacteria reside as part of the normal flora.

Several case reports described the polymicrobial microbiology of infected solid tumors (1-5).  Three studies investigated the microbiology of infected tumors (6-8).  Rotimi and Durosinmi-Etti (6) studied 70 patients with infected ulcers; 30 of the underlying lesions in these patients were carcinoma of the breast, and 19 were a variety of skin cancers. Most infections were mixed, yielding both anaerobes and aerobes. Anaerobes were the predominant organisms isolated from individual ulcers. There were 282 bacteria isolates, and anaerobic bacteria accounted for 179 (63%). Of the 179 anaerobes isolated, 37 were Porpyromonas asaccharolytica, 31 each were Prevotella. melaninogenica and anaerobic streptococci, 29 Bacteroides fragilis, and 17 Bacteroides ureolyticus. Among the facultative organisms Escherichia coli was the commonest and was isolated mainly from patients with carcinoma of the breast.

Brusis and  Luckhaupt (7) reported the microbiology of 15  patients with tumors of the oral cavity, the oropharynx and with recurrent tumors of the hypopharynx and larynx that were infected with anaerobic bacteria. P. melaninogenica, Prevotella oralis, Prevotella bivia, Peptostreptococcus spp. and Fusobacterium spp. were most frequently represented. Five cases showed mixed aerobic-anaerobic infections.

 A large unresectable infected desmoid tumor 

Brook (8) reviewed his experience in culturing necrotic tumors from 91 patients. Bacterial growth was present in 63 (69%) specimens. Of these tumors, 14 were abdominal, 5 pelvic, 23 head and neck, 4 lung, 4 mediastinum, 2 lymphatic, 3 breast, and 8 miscellaneous. Aerobic or facultative anaerobic bacteria only were present in 12 (19%) specimens, anaerobes only in 10 (16%), and mixed aerobic and anaerobic bacteria in 41 (65%). The average number of isolates was 2.1/ infected tumor. A total of 84 anaerobic and 46 aerobic and facultative anaerobic bacteria were recovered. The predominant anaerobic bacteria were Bacteroides spp., anaerobic cocci, and Propionibacterium acnes. The most frequently isolated aerobic and facultative bacteria were Staphylococcus aureus, alpha-hemolytic streptococci, Escerichia coliStaphylococcus epidermidis, Klebsiella pneumoniae, and Pseudomonas aeruginosa .

The aerobic and anaerobes recovered from the infected tumors originated most probably from the mucous membranes adjacent to the tumor site ( oral, gastrointestinal, and vaginal flora ). Organisms can also infect the tumor by dissemination through bacteremia. ( 9, 10 ) Insufficient blood supply of rapidly growing solid tumors can lead to the presence of tissue hypoxia that can favor the growth of anaerobic bacteria (11).


1. Rolston K.V.I., Bodey G. P., Safdar A. Polymicrobial infection in patients with cancer: an unappreciated and underreported entity. Clin. Infect. Dis. 45:228-233, 2007.
2. Braverman J., Adachi A., Lev-Gur M., Fallen S., Rosenzweig M., Greston W.M., Kleiner GJ. Spontaneous clostridia gas gangrene of uterus associated with endometrial malignancy. Am J Obstetrics Gynecolog 156, 1205-1207, 1987.
3. Graham B.S., Johnson A.C., Sawyers J.L. Clostridial infection of renal cell carcinoma. J Urology   ;135:354-355, 1986.
4. Lenkey J.L., Reece G.J., Herbert D.L. Gas abscess transformation of a huge hypernephroma. Am J  Roentgenol.  133:1174-1176, 1979.
5. Trump D.L., Fahnestock R., Cloutier C.T., Dickman MD. Anaerobic liver abscess and intrahepatic metastases: a case report and review of the literature.  Cancer. 41:682-686, 1978.
6.Rotimi V.O., Durosinmi-Etti F.A. The bacteriology of infected malignant ulcers. J . Clin  Pathol. 37:592-595, 1984.
7. Brusis T., Luckhaupt H.  Anaerobic infections in ulcerating tumors of the head and neck. A contribution to the problem of odors. Laryngology Rhinology Otology (Stuttg);65:65-68, 1986.
9. Brook I. Bacterial Infection Associated with Malignancy in Children. Internat J Pediatr Hematology Oncology.  5, 379-386,1999.
10. Felner J.M., Dowell VR Jr. "Bacteroides" bacteremia. Am J Medicine. 50:787-96. 1971.
11. Vaupel P. Oxygen transport in tumors: characteristics and clinical implications.  Advances in  Experimental Medicine and  BiologyAdv Exper Med  Biol. 388:341-351. 1996.

Colonic cancer with abscess