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NAME: Bacteroides spp. or related genera, formerly considered as Bacteroides

SYNONYM OR CROSS REFERENCE: species associated with sepsis, abscess or surgical infections include B. caccae, B. coagulans, B. coprocola, B. eggerthii, B. fragilis, B. massiliensis, B. nordii, B. ovatus, B. plebeius, B. pyogenes, B. salyersiae, B. stercoris, B. tectus, B. thetaiotaomicron, B. uniformis, B. vulgatus (1,2).

CHARACTERISTICS: The gram-negative Bacteroides spp. or closely related genera are capsulated obligatory anaerobic bacilli that are non-spore forming, pale-staining, and some (B. polypragmatus, B. xylanolyticus) are motile by peritrichous flagella, while other taxa are non-motile(1,3-5). Bacteroides, Parabacteroides, Odoribacter are generally bile resistant, distinguished from genera which are bile sensitive. They are normally commensal, found in the intestinal tract of humans (mouth, colon, urogenital tract) and other animals(1,6). Many cultures of Bacteroides strains display brown to black pigmentation on blood agar media caused by esculin hydrolysis(7).


PATHOGENICITY/TOXICITY: Bacteroides spp. represent an important anaerobic bacterial genus associated with human infections(3). In combination with other facultative/strict anaerobes, they are responsible for the majority of localized abscesses within the cranium, thorax, peritoneum, liver, and female genital tract(4,8). They can cause pulmonary abscesses when naturally-occurring oropharangeal Bacteroides and closely related genera are aspirated into the lung(8). These taxa can lead to many types of diseases, some of which can be fatal, including noma (cancrum oris), human apical periodontitis, endocarditis, pelvic inflammatory disease, suppurative thrombophelebitis, and wound infections(4,6,9). Organisms from oral flora also have a role in dental abscesses and infectivity of human bites.

Bacteroides fragilis is the most common opportunistic pathogen of Bacteroides spp.(1,4). Spread to bloodstream (bacteremia) is more common for B. fragilis than any other anaerobe(4). Deep pain and tenderness below the diaphragm are typical of B. fragilis infection. Widespread intra-abdominal abscesses may be associated with fever and abdominal pain.

EPIDEMIOLOGY: Worldwide - Bacteroides spp. or closely related genera are part of the normal flora of the gastrointestinal and respiratory tract(10), the mouth, and the female genital tract(1,3,4,6,8). Infections are normally endogenous, originating from the patients own intestinal flora(1,4,6). People who consume a considerable amount of meat show higher numbers of Bacteroides spp.(11).

HOST RANGE: Humans, dogs, cats and other animals(1,3,4,12,13).

INFECTIOUS DOSE: Incubation period is variable and depends on the inoculum and the site of involvement but is usually 1 to 5 days(6).

MODE OF TRANSMISSION: Infection results from displacement of Bacteroides spp. or closely related genera from normal mucosal location as a result of trauma such as animal/human bites, burns, cuts, or penetration of foreign objects, including those involved in surgery(1,4,6). There is no evidence that organisms are invasive on their own(4).


COMMUNICABILITY: Low; human-to-human transmission is possible through clenched-fist wounds and skin penetrating human bites(1,12).


RESERVOIR: Present as part of normal flora in of the gastrointestinal tract, the mouth, and the female genital tract of humans and other animals(1,3,4,6,8).

ZOONOSIS: Yes, skin penetrating animal bites could lead to infection(1,13).



DRUG SUSCEPTIBILITY: Susceptible to chloramphenicol, clindamycin, and metronidazole(4). Piperacillin-tazobactam combinations as well as tigecycline are active against most strains of Gram-negative rods(1). Ertapenem, imipenem, and meropenem are consistently active against most anaerobes. Moxifloxacin is moderately active against many strains.

Use of β-lactamase inhibitors (i.e. clavulanate, sulbactam) and β-lactam (i.e. ampicillin, ticarcillin) has been used to circumvent resistance. Cefoxitin or imipenem (β-lactam's) have been used effectively alone for some strains(4).

DRUG RESISTANCE: Resistance against antibiotics is increasingly common(1,4,8), and frequently observed with penicillin, ampicillin, cephalothin, tetracycline, piperacillin, chloramphenicol, kanamycin, colistin, rifampicin, vancomycin, and the aminoglycosides(14-16). The B. fragilis group is commonly resistant to expanded and broad spectrum cephalosporins, including β-lactamase-resistant drugs such as cefoxitin, and clindamycin(1). Strain resistance to imipenem and metronizadole, although it has been detected worldwide, are rarely encountered(17). Resistance to quinolones is increasing. Some members of B. fragilis group have shown resistance to ampicillin-sulbactam and amoxicillin-clavulanante combination therapies. Isolates often produce β-lactamase, often making penicillin based antibiotics ineffective(1,4).

SUSCEPTIBILITY TO DISINFECTANTS: More specific information on Bacteroides spp. is not available, but most bacteria have been shown to be susceptible to low concentration of chlorine, 1% sodium hypochlorite, 70 % ethanol, phenolics such as orthophenylphenol and ortho-benzyl-paua-chlorophenol, 2% aqueous glutaraldehyde, iodine, formaldehyde, and peracetic acid (0.001% to 0.2%)(18-20).

PHYSICAL INACTIVATION: Information specific to Bacteroides and like genera is not available, but most bacteria can be inactivated by moist heat (121°C for 15 min - 30 min) and dry heat (160-170°C for 1-2 hours)(21).

SURVIVAL OUTSIDE HOST: Bacteroides and like genera have been detected in feces infected water by PCR for at least 2 weeks at 4°C; 4 to 5 days at 14°C; 1 to 2 days at 24°C; and 1 day at 30°C(22).


SURVEILLANCE: Monitor for symptoms. The gross appearance (purulence, necrotic tissue) and characteristic odour of a specimen may give a clue to the presence of an anaerobic infection caused by organisms such as Bacteroides spp.(1,6) . The Gram stain is the fastest and simplest method to detect these agents. Molecular methods are becoming a commonly used diagnostic tool.

For wound infections: Identification requires careful sampling to avoid contamination by normal, non-infectious flora(23). Swab samples are frequently misleading. Preferred method is to aspirate purulent lesions with sterile syringe following disinfection of skin surface. Internal purulent discharges or from surgically removed tissue samples can be sampled by biopsy. Samples must be transported from collection site under anaerobic conditions.

Note: All diagnostic methods are not necessarily available in all countries.

FIRST AID/TREATMENT: Administer appropriate drug therapy. Drainage of abscesses and debridement of necrotic tissue are the mainstays of treatment(4,6). Antimicrobial therapy is complicated by the fact that abdominal B. fragilis isolates almost always produce β-lactamase(1,4).

IMMUNISATION: It has been demonstrated that antibodies to capsular polysaccharides facilitate classical complement pathway killing; however, there is no evidence that this confers immunity to reinfection(4). There is evidence that cell-mediated immunity may be protective.

PROPHYLAXIS: Metronidazole, imipenem, and amoxicillin seem to be effective against B. fragitis and B. thetaiotaomicron (16). Studies using a rat model have shown that pretreatment using oral vancomycin/imipenem resulted in undetectable levels of Bacteroides spp.(24).



SOURCES/SPECIMENS: Feces, wound exudates, tissues (intestinal tract, vagina, respiratory tract), and laboratory animal bites(1,3,4,6,23).

PRIMARY HAZARDS: Accidental parenteral inoculation; direct contact of mucous membranes (or wounds, cuts on skin); skin penetrating animal bites(1,4,12,13).



RISK GROUP CLASSIFICATION: Risk Group 2(25). This risk group applies to the genus Bacteroides, and may not apply to every species within the genus or other genera outlined here.

CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures. These containment requirements apply to the genus Bacteroides, and may not apply to each species within that genus or other genera outlined here.

PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes(18).

OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities(18).


SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up.

DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incineration.

STORAGE: Properly labelled and sealed containers.


REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.

UPDATED: November 2010

PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada

Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.

Copyright ©
Public Health Agency of Canada, 2010


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