Infections Caused By Anaerobic Bacteria Accounting Essay

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There are mainly three different bacterial categories based upon gaseous requirement: aerobic bacteria that require oxygen as electron acceptor, facultative anaerobic bacteria that grow either with or without oxygen and anaerobic bacteria that cannot grow in the presence of oxygen though there are some aerotolerant anaerobes. Anaerobic bacteria, unlike the other categories, they lack superoxide dismutase and catalase but the aerotolerant anaerobe has some superoxide dismutase and catalase. This lack of superoxide dismutase and catalase will allow oxygen radicals to form in anaerobic bacteria leading to its death.

Copyright © 1996 The University of Texas Medical Branch at Galveston

Most anaerobic bacteria are part of our normal flora and they exist in areas of the body where the oxygen tension is very low but they are potentially pathogenic if they are removed from their normal habitat. Multiplication of aerobic and facultative bacteria will lead to decrease in the oxygen supply that will support the growth of anaerobic bacteria. Anaerobic bacteria may cause infections in all different parts of the human body and they may exist with other types of bacterial (polymicrobial infection).

Anaerobic bacteria that are clinically important are classified into: gram negative bacilli (Bacteroides fragilis group, Prevotella melaninogenica grp, Fusobacterium), gram-positive bacilli (Actinomyces, Lactobacillus, Propionibacterium, Eubacterium, Bifidobacterium, Arachnia and Clostridium), gram positive cocci (Peptostreptococcus) and gram negative cocci (Veillonella)

Anaerobic infections include Intra-abdominal infections such as peritonitis, pulmonary infections such as aspiration pneumonia, pelvic infections, brain abscesses, skin and soft tissue infections, oral and dental infections and bacteremia.

Copyright © 1996 The University of Texas Medical Branch at Galveston

Treatment is complicated due to polymicrobial nature and the growing resistance to antibiotics. So the choice of antimicrobial agent should provide coverage for both types of pathogens. Inappropriate therapy for anaerobic infections may result in mortality; therefore, routine antibiotic susceptibility testing is very important especially because recent studies are showing increase resistance of anaerobic bacteria to certain antibiotics that were previously susceptible to them.

Special Precautions are needed for appropriate collection and transport of specimens of anaerobic bacteria in order to exclude air. There are mainly three anaerobic isolation procedures: anaerobe jar, the roll tube and glove box but studies have shown that the anaerobic jar is adequate to recover clinically significant anaerobes. The extremely oxygen-sensitive bacteria of the micro flora are not associated with infectious processes. The jar is a medium-sized glass or plastic jar with a tightly fitting lid containing palladium-coated alumina particles, which serve as a catalyst. Achieving anaerobiosis in the jar, it consists of evacuation and replacement. Air is evacuated from the sealed jar containing the culture plates and is replaced with an oxygen-free mixture of 80 percent nitrogen, 10 percent hydrogen, and 10 percent carbon dioxide.

For cultivation of anaerobes, a reliable, nonselective medium consists of Brucella agar supplemented with sheep blood, hemin, cysteine, sodium carbonate, and menadione is used. Identification is based on Gram-staining reactions, cellular and colony morphology, antibiotic sensitivity patterns, carbohydrate fermentation reactions, and other biochemical tests. Analysis of metabolic end products, especially organic acids, provides additional information useful in classifying these organisms.

Copyright © 1996 The University of Texas Medical Branch at Galveston


Anaerobic cocci are opportunistic pathogens that cause a multitude of infections. They are part of the normal microbial flora of a healthy individual, but they can and do cause infections involving traumatized tissue or infections in the compromised host. They are isolated most often from a wide variety of polymicrobic infections indicating a synergistic role in these infections. In certain cases, such as aspiration pneumonia, anaerobic bacteria from a site of normal carriage may move into another area that is normally free of organisms and infect that site. Tissue necrosis and poor blood supply lower the oxidation-reduction potential, thus favoring the growth of anaerobes. Vascular disease, cold, shock, trauma, surgery, foreign bodies, cancer, edema, and gas production by bacteria, significantly predispose individuals to infection with anaerobes, as may prior infection with aerobic or facultative bacteria. Bacteroides, Prevotella, Porphyromonas, and Fusobacterium species produce enzymes that may play a role in pathogenesis. Prevotella melaninogenica is one of the few bacteria that produce collagenase, an enzyme of considerable importance. Gram negative bacilli anaerobes, such as P. melaninogenica, sometimes inhibit phagocytosis and killing of other organisms during mixed infection. Constituents of the cell envelope and cell surface may contribute to pathogenicity. The capsule of organisms such as B. fragilis is an important virulence factor. Pili (fimbriae) and lectinlike adhesins may also be important in the adherence of Bacteroides cells to epithelial surfaces. Butyrate and succinate produced by Bacteroides show a cytotoxic effect. Neuraminidase may be important in the pathogenesis of Bacteroides infection. This enzyme alters neuraminic acid-containing glycoproteins of human plasma.

Conditions Predisposing to Anaerobic Infection are summarized in the following table.

Copyright © 1996 The University of Texas Medical Branch at Galveston

The initial event in tetanus is trauma to host tissue, as with all Clostridial infections, followed by accidental contamination of the wound with C. tetani. Tissue damage is needed to lower the oxidation-reduction potential and provide an environment suitable for anaerobic growth. After growth initiation, the organism is not invasive and remains confined to the necrotic tissue where it elaborates the lethal toxin. The incubation period from the time of wounding to the appearance of symptoms varies from days to weeks, depending on the infectious dose and the site of the wound. C. tetani actually produces two toxins: tetanolysin, a hemolysin that is inactivated by cholesterol and has no role in pathogenesis, and tetanospasmin, a spasmogenic toxin responsible for the classical symptoms of the disease. Toxin enters the nervous system through the neuromuscular junction of alpha motor neurons, and then is transported to the other neurons, most importantly presynaptic inhibitory cells, where it is no longer accessible to be neutralized by antitoxin.

The pathogenicity of C. botulinum depends entirely on neurotoxin production. In humans, these toxins cause disease in three ways: food poisoning resulting from ingestion of toxin in improperly preserved food; wound botulism resulting from C. botulinum growing in the necrotic tissue of a wound; and infant botulism is caused when the organism grows and produces toxin in the intestines of infants. The toxin travels through the blood and lymphatic systems, as it enters the body, and then becomes fixed to cranial and peripheral nerves. The toxin binds to receptor sites at the neuromuscular junctions of parasympathetic nerves, and inhibits the release of acetylcholine at peripheral cholinergic synapses. The result is flaccid muscular paralysis. The cranial nerves are affected first, followed by a descending, symmetric paralysis of motor nerves. Decreased saliva production causes a dryness of the mouth and throat, and swallowing may be painful. An overall weakness arises, followed by descending paralysis. Death usually is caused by respiratory failure, but cardiac failure could be the primary cause.

Antibiotic Susceptibility:

According to a study done by (Wybo et al 2006), four hundred and forty-three anaerobic clinical isolates from various body sites were collected from October 2003 to February 2005 in nine Belgian hospitals and were used for antibiotic susceptibility testing. The results showed that, Gram-negative bacilli except Fusobacterium spp. were resistant to penicillin. Piperacillin/tazobactam, metronidazole, chloramphenicol, meropenem and amoxicillin/clavulanic acid were very active against all groups, but only 86% of Bacteroides fragilis group strains were susceptible to the latter. 62%, 52% and 48% of B. fragilis group strains were susceptible to Cefoxitin, cefotetan and clindamycin respectively. The susceptibility of anaerobic bacteria remains stable in Belgium, except for clindamycin, which shows a continuous decrease in activity. This table shows us the percentage of susceptible isolates for each antimicrobial agent tested during the three surveys and the results are compared with previous surveys.

Wybo et al.2006

Another study concerning antibiotic susceptibility done by (Kommedal, Nystad, Bolstad, & Digranes, 2007), showed that 98.5% of 200 blood culture isolates of anaerobic bacteria were fully susceptible to Metronidazole, imipenem, and piperacillin-tazobactam. Both Bacteroides spp. and Clostridium spp. had reduced susceptibility to clindamycin. All Bacteroides isolates were resistant to penicillin, and only 60% of Prevotella spp. was susceptible to this agent.

A third study done on 100 patients with skin infections (10-60 years old) by (Eslami, Fallah, Goudarzi, & Navidinia, 2005). The specimens that were collected were either aerobic-anaerobic facultative bacteria, aerobic and anaerobic bacteria mixed infection or strictly anaerobic bacteria. (It's illustrated in the following table)

The prevalence of aerobic-anaerobic facultative bacteria isolated from patients with skin infection is distributed as the following:

The prevalence of anaerobic bacteria isolated from patients with skin infection is distributed as the following:

The antibiogram test was done on aerobic-anaerobic facultative bacteria and the susceptibility of those bacteria was: Cefizoxim100%, Ciprofloxcin 98%, Ceftazidim 82%, Tobramycin 47%, and Amikacin 33%. And they were resistance to: Gentamycin (97%), Penicillin (93%), Cloxacillin (86%), and Erythromycin (62%). In anaerobic bacteria, susceptibility to Ciprofloxacin was 100%, Ceftyzoxim 100 100%, Ceftazidim 91% Rifampin 76%, Colistin 67%. Their resistance was: to Penicillin was 95%, Erythromycin 83%, Cloxacillin 85%. Susceptibility of both anaerobic and aerobic bacteria to Ceftizoxim was 100 %, so the authors suggested this drug for treatment of many skin infections.

This figure shows the prevalence of antibiotic susceptibility aerobic bacteria isolated from patients with skin infection.

Eslami et al 2005

This figure shows the prevalence of antibiotic susceptibility anaerobic bacteria isolated from patients with skin infection

Eslami et al 2005

Treatment and Control: Antibiotics that must be used should be based upon the statistical studies that have been done by different authors.

Surgical drainage and debridement is an important aspect of treating most anaerobic infection cases. It is often not necessary to eradicate all of the organisms in order to cure. Appropriate surgical manipulation, the patient's general health status, and the microenvironment at the site of the infection, have a significant impact on the outcome, regardless of whether a particular isolate is susceptible to the antimicrobial. Although appropriate therapy for anaerobic infections has been associated with significant reductions in mortality; most clinical laboratories still do not perform routine anaerobic susceptibility tests. Antibiotics that must be used in treating anaerobic bacteria, should cover both types of bacteria; aerobic and anaerobic bacteria, since most of the time they are coexisting together. In case of Clostridium tetani, the administration of tetanus toxoid is a preventive measure. C. tetani infection is treated with antimicrobial agents and by local wound debridement. Other measures include tetanus immunoglobulin and supportive therapy. In case of C. botulinum, the best control is to eliminate the toxin source via proper food handling. Once the food poisoning is diagnosed, treatment should include an attempt to neutralize unbound toxin. Supportive care is of primary importance.


Infections caused by anaerobic bacteria constitute a real medical threat for the infected patients for many reasons stated above. Anaerobic bacteria exist as polymicrobial infections which make the choice of antibiotic more difficult. Appropriate treatment should be done in order to decrease the rate of mortality. Therefore, set of actions should be taken in order to control anaerobic infections. First, appropriate specimen collection should be done. Second, proper isolation procedure should be applied in order to have a proper identification of the anaerobe. Third, antibiotic susceptibility testing should be done continuously since many studies shown that resistance to some antibiotics is increasing. Last but not least, is the appropriate treatment of such infections through surgical drainage and debridement and with specific antibiotics.