Taylorella is a genus comprising Gram-negative, short rod-shaped, chemoorganotrophic bacteria that include species that are the causative agents of contagious equine metritis. The name Taylorella serves as a dedication to C.E.D. Taylor, the scientist who identified the only species originally included in this genus. They are non-motile microaerophiles that are able to be isolated in pure culture on chocolate agar. .

Phylogeny

The genus Taylorella was first identified by C.E.D Taylor in 1978. It was formerly classified under the genus Haemophilus, and there was originally considerable debate on whether it is more closely related to Moraxella. Due to further investigation by DNA: DNA hybridization and genomic characteristics of this genus, Sugimoto et al. 1983 proposed the creation of a new genus that would include two species isolated from the family Equidae. The

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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Taylorella equigenitalis Taylorella is a genus comprising Gram-negative, short rod-shaped, chemoorganotrophic bacteria that include species that are the causative agents of contagious equine metritis. The name Taylorella serves as a dedication to C.E.D. Taylor, the scien ...

'': causes

contagious equine metritis Contagious equine metritis (CEM) is a type of metritis (uterine inflammation) in horses that is caused by a sexually transmitted infection. It is thus an equine venereal disease of the genital tract of horses, brought on by the ''Taylorella equi ...

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...

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Taylorella asinigenitalis ''Taylorella asinigenitalis'' is a Gram-negative, catalase- and oxidase-positive, nonmotile bacterium of the genus '' Taylorella'', isolated from the genital tract of male donkeys ('' Equus asinus'') in California California () is a U ...

'': found in the genital tract of

donkey The donkey or ass is a domesticated equine. It derives from the African wild ass, ''Equus africanus'', and may be classified either as a subspecies thereof, ''Equus africanus asinus'', or as a separate species, ''Equus asinus''. It was domes ...

s, this species is not

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

ic.

Physiology

As a genus, Taylorella spp. lack glycolysis and the hexose monophosphate pathways, but conserve energy from the oxidation of organic molecules via the citric acid cycle (TCA) and oxidative phosphorylation. Taylorella species are predicted to have a complete TCA cycle, however, three key genes or pathways allowing for the conversion of glucose into pyruvate are absent. These include the 6-phosphofructokinase gene, the non-oxidative branch and transaldolase in the pentose phosphate pathway, and the Entner-Doudoroff pathway. Studies show that the organic acids, malate, glutamate, and alpha-ketoglutarate serve as the main carbon sources for Taylorella spp. While both malate and glutamate are TCA cycle intermediates, alpha-ketoglutarate is a product of deamination of glutamate by

glutamate dehydrogenase Glutamate dehydrogenase (GLDH, GDH) is an enzyme observed in both prokaryotes and eukaryotic mitochondria. The aforementioned reaction also yields ammonia, which in eukaryotes is canonically processed as a substrate in the urea cycle. Typic ...

. Furthermore, genes encoding NADH dehydrogenase, succinate dehydrogenase, cytochrome c reductase, ATP synthase, and a terminal oxidase are found in Taylorella species. This oxidase belongs to the cbb3-type cytochrome c oxidase type, which plays a role in microaerobic respiration. It has been speculated that expression of this oxidase is a requirement for colonization of suboxic tissues. Additionally, respiration is stimulated by Kreb's cycle intermediates. Taylorella is unable to ferment carbohydrates. In some experiments, Taylorella was inhibited by the presence of fermentable carbohydrates.

Ecology

The genus Taylorella harbors two species associated with sexually transmitted diseases in horses and donkeys. Taylorella has an optimum growth between 35 and 37 degrees Celsius but is able to grow between 30 and 42 degrees Celsius. The genus Taylorella was first reported in horses as Taylorella equigenitalis in the United Kingdom in 1977. Now, Taylorella is found on 5 of the 7 continents. Due to the prevalence of this genus and its association with CEM, serological and bacteriological screenings are now used to ensure that Equividae does not have CEM before coming into the United States. The largest contributing factor to the worldwide spread of CEM is carriers for Taylorella. Taylorella species can persist in the genitalia of the equine for years where it can still be transmitted to other equines through sexual or artificial insemination. While mares can be asymptomatic, when symptomatic these mares have a low fertility rate and if they become pregnant the likelihood of a miscarriage is high. In some cases, there is also a vertical transmission of CEM from the mare to the fetus through the placenta. This continues the cycle of infection to future mares. This becomes a clinical concern to equine breeding and an economical concern due to infertility. To help prevent infection, good hygiene and use of sterile or disposable equipment when inseminating mare or collecting semen from colts. Furthermore, Taylorella species do not survive long out of the context of reproductive tissues. Taylorella species are also sensitive to high temperatures, humidity, disinfectants, and UV light.

Special Features

One special feature of Taylorella is the fastidious growth conditions. Taylorella growth is dependent on both enriched bacteriological media and microaerophilic incubation conditions. There is no observed growth on ordinary nutrient media under normal growth conditions and very poor growth is observed on blood agar. The organism grows best on chocolate agar.

Biochemical Test Results

, name = ''Biochemical Tests''. , Oxidase = positive , Catalase = positive , Indole = negative , H2S test = negative , Urease = negative , Motility = non-motile , Nitrate =negative , Gram-stain =negative , Gelatin Hydrolysis =negative , Relationship to Oxygen =

microaerophile A microaerophile is a microorganism that requires environments containing lower levels of dioxygen than that are present in the atmosphere (i.e. < 21% O₂; typically 2–10% O₂) for optimal growth. A more r ...

, Cell shape =

coccobacillus Bacterial cellular morphologies are the shapes that are characteristic of various types of bacteria and often key to their identification. Their direct examination under a light microscope enables the classification of these bacteria (and archae ...

References

{{Taxonbar, from=Q309673 Burkholderiales Bacteria genera