fusobacterium

''Fusobacterium'' is a genus of obligate anaerobic, Gram-negative, non-sporeforming bacteria belonging to Gracilicutes. Individual cells are slender, rod-shaped bacilli with pointed ends. ''Fusobacterium'' was discovered in 1900 by Courmont and Cade and is common in the flora of humans.

Strains of ''Fusobacterium'' can cause several human diseases and infections, including periodontal diseases,
Lemierre's syndrome, oral, head, and neck infections, as well as colorectal cancer and topical skin ulcers.

It has been tied to HIV infection and suboptimal immune recovery. Detection of ''Fusobacterium'' is typically through surgical retrieval of tissue, fecal tests, or blood tests in patients showing symptoms. Early detection is preferred and helps to prevent further disease progression.

Although older sources state that ''Fusobacterium'' is part of the normal flora of the human oropharynx, the current consensus is that ''Fusobacterium'' should always be treated as a pathogen. There are thirteen described ''Fusobacterium'' strains; the predominant one affecting humans is '' F. nucleatum'', followed by '' F. necrophorum'', which also affects animals, mainly cattle.

Background

History

Although the genus was not discovered until 1900 by Courmont and Cade, the first documented ''Fusobacterium'' infection was reported in 1898 by Veillon and Zuber, who described a case of systemic infection in a young child. The genus was proposed by Knorr in 1923. ''Fusobacterium'' has been classically considered a normal part of the human oral, gastrointestinal, and female genital flora, which is why infections are not commonly seen.

Clinical relevance

''Fusobacterium'' is often associated with ulcerative colitis. Research of colon cancer has also shown an overrepresentation of ''Fusobacterium'', both in feces of patients and tumor tissue itself. ''Fusobacterium'' has also been seen increased in individuals infected with HIV as well as in individuals with suboptimal immune recovery as compared to patients who were not infected and had optimal responses.

Prevalent pathogenic species

'' F. nucleatum'' is found in humans more so than any other species of ''Fusobacterium''. It is commonly found in the oral cavity as well as in the intestinal tract. Some of its pathogenic ties include its extraction from amniotic fluid sourced from spontaneous premature labor without reason/a given source. A few additional sources of its pathogenic nature include its association with oral inflammation diseases, cancers such as pancreatic, oral, and colorectal, as well as infections of the head and neck. This association is due to the high increase in the prevalence of '' F. nucleatum'' in those infected areas. '' F. nucleatum'' can worsen or initiate colorectal cancer by stimulating other bacteria such as '' Streptococcus, Campylobacter spp.'' and ''Leptotrichia'' as well as cancerous gene expression from Beta-catenin signaling. '' F. nucleatum'' can be detected in tissues, genomic DNA, and feces using methods such as (FQ, q, and dd) polymerase chain reaction and fluorescence in situ hybridization. However, these are limited because tissues can only be tested after surgery and fecal matter can return false positive results.

'' F. necrophorum'' has been found as a common pathogen in the diagnostic of peritonsillar abscess and is more prevalent than other bacteria regarding this infection. It is also the most frequent leading cause associated with Lemierre Syndrome and is not proven to be a normal part of the human oral bacterium population. '' F. necrophorum'' commonly infects animals, causing liver abscesses and necrodic diseases, and can combine with other pathogenic bacteria to cause various infections such as foot rot and uterine infections.

Sources of other species of ''Fusobacterium''

Source:

* ''F. ulcerans'' is very similar to ''F. varium'' and is commonly extracted from tropical ulcers.
* ''F. necrogenes'' is also closely related to ''F. ulcerans'' and ''F. varium'' and has been found in chickens and ducks.
* ''F. perfoetans'' is sourced from fecal matter. (''F. perfoetans'' and ''F. necrogenes'' have not been sourced from any infections in humans or animals)
* ''F. gonidiaformans'' is typically found in the intestines of humans and is not found orally like the other ''Fusobacterium.''
* ''F. russi'' is a common bacteria in canine and feline oral cavities and can lead to the infection of puncture wounds if transferred to humans from bites.
* ''F. simae'' which can be sourced from monkeys.

Symptoms and treatment

''Fusobacterium'' infections often cause clinical symptoms such as a fever, inflammation, and a diseased appearance. Further diagnosis can confirm suspicions of ''Fusobacterium'' infection through blood testing or culturing the tissue. Upon diagnosing the infection, action to treat it involves the application of antibiotics over a 2-week period which could be in the form of penicillin or other variants as well as using anaerobic antibiotics like clindamycin and metronidazole which work when the ''Fusobacterium'' can break down the Beta-lactams. Leaving ''Fusobacterium'' untreated could lead to more severe developments of the infection and early testing is recommended. By testing early, fatal diseases such as Lemierre syndrome can be avoided. However, this requires the family physician to be conscious of the danger as infections such as Lemierre syndrome affects younger populations and especially those of male gender. The bacterium is a big anchor for biofilms. It is usually susceptible to clindamycin, while approximately 20% of the clinical strains are resistant to penicillin. In contrast to ''Bacteroides'' spp., ''Fusobacterium'' has a potent lipopolysaccharide.

Taxonomy

Current species

''Fusobacterium'' is divided into 13 different species, two of which each have their own set of subspecies ('' F. nucleatum'' and '' F. necrophorum'').

Reclassified species

Other previously declared species of Fusobacterium such as ''F. symbiosum, F. praecutum, F. plauti,'' ''F. alocis, F. sulci,'' and ''F. prausnitzii'' have since been reclassified due to containing different characteristics from the other ''Fusobacterium'' members. ''F. alocis'' has been reclassified into '' Filifactor alocis'' while ''F. sulci'' has been reclassified as ''Eubacterium sulci. F. prausnitzii'' is a part of the '' Clostridium leptum'' subgroup under '' Eubacterium-''like organisms. A few strains ''F. prausnitzii'', a gut commensal associated with healthy patients, was completely reclassified as '' Faecalibacterium'' (''Clostridiales'':''Ruminococcaceae'') in 2002.

Phylogenic tree

See also

* Altered Schaedler flora
* List of bacteria genera
* List of bacterial orders

References

External links

''Anaerobic Gram-Negative Bacilli'' chapter
in Baron's ''Medical Microbiology'' (online at the NCBIbr>bookshelf
.

''Fusobacterium''
From MicrobeWiki, the student-edited microbiology resource

{{Authority control
Gut flora bacteria
Fusobacteriota
Bacteria genera