Equis ISSN 2398-2977

Fusobacterium spp

Contributor(s): Graham Munroe, Nicola Menzies-Gow

Introduction

Classification

Taxonomy

  • Phylum: Fusobacteria.
  • Order: Fusobacteriales.
  • Family: Fusobacteriaceae.
  • Genus: Fusobacterium.
  • Gram-negative, non-sporulating, anerobic, slender, straight rods often with tapered ends.
  • The most commonly isolated species is Fusobacterium necrophorum Fusobacterium necrophorum.
  • The typical virulent diseases in animals and humans are caused by biovar A, now called F. necrophorum ssp necrophorum; whereas biovar B strains, now called subspecies funduliformis, are less pathogenic.
  •  Its major virulence factor is a leukotoxin. Other important factors include the production of high levels of endotoxin, hemagglutinin production, and dermotoxic activity.
  • A new species that is phenotypically similar to F. necrophorum has been described from the normal oral cavity and oral-associated disease of horses. Phylogenetic analysis of 16S rRNA gene sequences placed the novel strains as distinct members of the genus. The proposed name is F. equinum.
  • The genus Fusobacterium currently includes 13 species:
    • F. nucleatum, the most frequently encountered species in humans, is heterogeneous and currently includes 5 subspecies.
    • Additional molecular studies have characterized F. ulcerans as separate from the phenotypically similar F. mortiferum and F. varium.
    • F. sulci and F. alocis have been reclassified as Eubacterium sulci and Filifactor alocis, respectively.
    • F. prausnitzii is phylogenetically related to the Eubacterium-like organisms and will likely be reclassified in the future.
    • The status of the remaining species is unchanged.

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Clinical Effects

Epidemiology

Habitat

  • Worldwide distribution, but reporting of infections is infrequent.

Pathological effects

  • Infections are often endogenous from normal flora at the anatomical site, or occasionally from wounds contaminated by flora. These anerobes need certain conditions to multiply and this includes the reduction of the redox potential of tissues, which may occur following trauma, necrosis, ischemia, parasitic damage, or concomitant multiplication of facultative anerobes.
  • Part of the normal flora of the oral cavity and pharynx. As such, can be aspirated into the upper and lower respiratory tracts where, if the normal defense mechanisms are overwhelmed or compromised, it can become one of the anerobic organisms leading to infection of the lower airways. It is commonly isolated, often in mixed culture, as one of the anerobic bacteria in cases of pleuropneumonia Lung: pleuropneumonia - bacterial (pleuritis). In general, the presence of anerobes in pneumonia Lung: pneumonia - bacterial or pleuropneumonia cases decreases the overall prognosis.
  • Their presence in the oral and nasal cavities as normal flora allows them opportunities to be involved in problems such as submandibular abscesses, mandibular osteomyelitis Bone: osteitis - septic, paranasal sinus infections Paranasal sinuses: bacterial sinusitis, and dental periapical abscesses Teeth: apical infection.
  • Eighteen cases of septic sialoadenitis have recently been reported and all of those where culture of the infected salivary gland or its secretions was undertaken had a growth of Fusobacterium spp cultured along with other aerobic and anerobic bacteria. The majority of affected animals had dental or other oral abnormalities. Infection resolved in 84% of cases.
  • In one case of infective endocarditis Heart: endocarditis, following previous dental procedures, F. necrophorum was isolated.
  • Occasional cases of peritonitis Abdomen: peritonitis and liver abscesses may have Fusobacterium spp cultured from them, often in mixed cultures. F. necrophorus is a normal inhabitant of the gastrointestinal tract and this may act as the source of some of these infections.
  • Fusobacterium spp and specifically F. necrophorum have been implicated in the etiology of thrush Foot: thrush or bacterial pododermatitis. The same organism/s have also been recorded as a cause of canker Canker: hypertrophic pododermatitis - chronic in the foot. In thrush the collateral and central sulci of the frog is invaded causing degeneration and breakdown of the frog, usually accompanied by a foul-smelling black exudate. Fusobacterium spp are a part of the normal flora of the horse, possibly including the foot, and can also survive in the soil and environment for months. It is therefore likely that other predisposing factors need to be in place before the infection can be established. This may include: traumatic damage; poor blood supply; other anerobic infections; general poor foot health due to lack of exercise, lack of proper trimming and general hoof care, and foot imbalance; and damp environments and poor stable sanitation.
  • Fusobacterium spp can also be involved as opportunists in infections of wounds and surgery sites, muscle abscesses, cellulitis Cellulitis, and mastitis Mammary gland: mastitis.

Control

Control via chemotherapies

  • Debridement of damaged and infected tissue and/or abscess drainage helps increase blood supply and oxygen levels to the infected area, improves immune responses, and increases antibiotic penetration.
  • All infections should be cultured, identified and subjected to antibiotic sensitivity testing but in general, Fusobacterium spp are susceptible to penicillins Penicillin G, cephalosporins Therapeutics: beta-lactam antibacterials, tetracyclines Therapeutics: tetracyclines, chloramphenicol Therapeutics: chloramphenicol, and metronidazole Therapeutics: nitrofurans/nitroimidazoles/quinolones:
    • Antibiotic resistance has been recorded in the first three.
    • Metronidazole Metronidazole is generally regarded as the drug of choice and it can be given orally, by intravenous injection or per rectum. It is well absorbed, giving high MIC levels, and safe.
    • Many infections are polymicrobic and may require the use of combinations of antibiotics to treat them effectively.
  • Fusobacterium spp are susceptible to solutions of 1% sodium hypochlorite, 0.2% chlorhexidine Chlorhexidine, 70% ethanol, 2% glutaraldehyde, 3% hydrogen peroxide Hydrogen peroxide, formaldehyde, phenolics, iodophores, calcium hydroxide, formocresol, and triclosan.

Control via environment

  • Fusobacterium spp can be inactivated by UV light with a wavelength 254 nm.
  • Fusobacterium spp are also susceptible to moist heat of 121°C/249.8°F for at least 15 min, and dry heat of 170°C/338°F for at least 1 h.

Diagnosis

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Kilcoyne I et al (2015) Septic sialoadenitis in equids: a retrospective study of 18 cases (1998-2010). Equine Vet J 47 (1), 54-59 PubMed.
  • Petrov K K & Dicks L M (2013) Fusobacterium necrophorum, and not Dichelobacter nodosus, is associated with equine hoof thrush. Vet Microbiol 161 (3-4), 350-352 VetMedResource.
  • Bank S et al (2010) Fusobacterium necrophorum - detection and identification on a selective agar. APMIS 118 (12), 994-999 PubMed.
  • Tadepalli S et al (2008) Fusobacterium equinum possesses a leukotoxin gene and exhibits leukotoxin activity. Vet Microbiol 127 (1-2), 89-96 PubMed.
  • Racklyeft D J & Love D N (2000) Bacterial infection of the lower respiratory tract in 34 horses. Aust Vet J 78 (8), 549-559 WileyOnline.

Other sources of information

  • Markey B et al (2013) Clinical Veterinary Microbiology. 2nd edn. Elsevier Health Sciences.

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