Overview

Arcobacter is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of Gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

, spiral-shaped bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 in the epsilonproteobacteria

Epsilonproteobacteria

Epsilonproteobacteria is a class of Proteobacteria. All species of this class are, like all Proteobacteria, gram-negative.The Epsilonproteobacteria consist of few known genera, mainly the curved to spirilloid Wolinella spp., Helicobacter spp., and Campylobacter spp...

 class. It shows an unusually wide range of habitats, and some species can be human and animal pathogens. Species of the genus Arcobacter are found in both animal and environmental sources, making it unique among the epsilonproteobacteria. This genus currently consists of five species: A. butzleri, A. cryaerophilus, A. skirrowii, A. nitrofigilis, and A. sulfidicus, although several other potential novel species have recently been described from varying environments. Three of these five known species are pathogenic. Members of this genus were first isolated in 1977 from aborted bovine fetuses. They are aerotolerant Campylobacter

Campylobacter

Campylobacter is a genus of bacteria that are Gram-negative, spiral, and microaerophilic. Motile, with either unipolar or bipolar flagella, the organisms have a characteristic spiral/corkscrew appearance and are oxidase-positive. Campylobacter jejuni is now recognized as one of the main causes...

-like organisms, previously classified as Campylobacter. The Arcobacter genus, in fact, was created as recently as 1992. Although they are similar to this other genus, Arcobacter species can grow at lower temperatures than Campylobacter as well as in the air, which Campylobacter cannot.

Pathogenicity

Arcobacter species have been discovered as both animal and human pathogens within the past decade, thanks to improvements in isolation techniques. Up to now, little is known about the mechanisms of pathogenicity or potential virulence factors of Arcobacter spp. Since no routine diagnostic of these bacteria has been performed, the global prevalence of Arcobacter infection is rather underestimated and the exact routes of transmission are unknown. There is evidence that livestock animals may be a significant reservoir of Arcobacter, and over the last few years, the presence of these organisms in raw meat products as well as in surface and ground water has received increasing attention. In humans, A. butzleri and, less commonly, A. cryaerophilus have been linked to enteritis

Enteritis

In medicine, enteritis, from Greek words enteron and suffix -itis , refers to inflammation of the small intestine. It is most commonly caused by the ingestion of substances contaminated with pathogenic microorganisms. Symptoms include abdominal pain, cramping, diarrhea, dehydration and fever...

 and occasionally bacteremia

Bacteremia

Bacteremia is the presence of bacteria in the blood. The blood is normally a sterile environment, so the detection of bacteria in the blood is always abnormal....

. Symptoms of A. butzleri infections include diarrhea associated with abdominal pain, nausea, and vomiting or fever. Studies of patients infected with A. butzleri have demonstrated that without treatment, symptoms endured for a very variable amount of time, from two days to several weeks. When antimicrobial therapies were administered, the infection was eradicated within a few days, and all strains in the study were found to be susceptible to the antibiotics given. A third species, A. skirrowii, has also recently been isolated from a patient with chronic diarrhea. Although the microbiological and clinical features of Arcobacter are not yet well defined, initial studies of A. butzleri suggest that these bacteria display similar microbiological and clinical features as C. jejuni, but are more associated with a persistent, watery diarrhea than with the bloody diarrhea associated with C. jejuni. Recent studies suggest that A. butzleri induces epithelial barrier dysfunction by changes in tight junction

Tight junction

Tight junctions, or zonula occludens, are the closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid. It is a type of junctional complex present only in vertebrates...

 proteins and induction of epithelial apoptosis

Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...

. Based on this model, the virulence of A. butzleri seems to have two phases. An initial effect on tight junctions was observed first, followed by a late effect on cytotoxicity because of necrosis

Necrosis

Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...

 and induction of apoptosis.

Non-Pathogenic Strains

A. nitrofigilis is a nitrogen-fixing bacterium that has been isolated from the roots of the salt marsh plant Spartina alterniflora

Spartina alterniflora

Spartina alterniflora is a perennial deciduous grass which is found in intertidal wetlands, especially estuarine salt marshes. It grows 1-1.5 m tall, and has smooth, hollow stems which bear leaves up to 20-60 cm long and 1.5 cm wide at their base, which are sharply tapered and bend down...

. A. sulfidicus is an obligate microaerophile that oxidizes sulfides and is an autotrophic producer of filamentous sulfur

Sulfur

Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

. Large populations of this bacteria produce mats of this solid, white sulfur filament. These mats are useful in anchoring the bacteria to rocky surfaces in the face of flowing subsurface hydrothermal fluids as well as providing important carpeting around hydrothermal vents that attracts other animals to that site and encourages them to settle and grow. One interesting potential novel Arcobacter species, designated LA31BT, was isolated from water collected from a hypersaline lagoon. Preliminary characterization based on 16S rRNA gene sequence analysis showed that LA31BT shared 94 % identity with Arcobacter nitrofigilis, the type species

Type species

In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 of the genus, and taxonomic studies confirmed the phylogenetic affiliation of strain LA31BT to the genus Arcobacter. Other analytical methods, however, showed that LA31BT was distinct from all recognized Arcobacter species. Most notably and of interest, LA31BT was found to be an obligate halophile

Halophile

Halophiles are extremophile organisms that thrive in environments with very high concentrations of salt. The name comes from the Greek for "salt-loving". While the term is perhaps most often applied to some halophiles classified into the Archaea domain, there are also bacterial halophiles and some...

, a trait not found among recognized Arcobacter species.