Bordetella avium
Bordetella avium is a gram-negative, rod-shaped, obligate aerobic bacterium of the genus Bordetella. It is of veterinary importance as pathogens in poultry, it came to designing the species name avium ( genitive plural of Latin avis " bird "). The disease mainly affects turkeys and is referred to as turkey coryza. Bordetella avium is characterized by a lack of splitting of urea and nitrate reduction, making it indistinguishable from Bordetella bronchiseptica. The genome of the bacterial strain Bordetella avium 197N was completely sequenced in 2006.
- 3.1 Outer systematics
- 3.2 Internal systematics
- 3.3 Etymology
- 5.1 Literature
- 5.2 Notes and references
Features
Appearance
The cells of Bordetella avium are short rods. They are gram- negative. The cells are 1.0-2.0 microns long and 0.4-0.5 microns wide. The type is - as Bordetella bronchiseptica - motile, they can move independently with the help of five to eight peritrichous flagella arranged. The formation of flagella is dependent on the growth temperature, cultures incubated at 20 ° C contain more than flagellated cells cultures, which were grown at 35 ° C. This effect does not occur in B. bronchiseptica. Endospores are not formed. The cells carry pili ( fimbriae ) on their surface and are surrounded by a capsule. They appear in the light microscopic image stored individually or in pairs.
On solid media, the cells grow to very small colonies, they are transparent. Its diameter is less than 1.0 mm. Found on blood agar - unlike the classical Bordetella species - no hemolysis instead. Colonies of B. avium to peptone -containing culture media that do not contain blood, brown pigment, but the pigment is less common than that of B. parapertussis, so that the characteristic of the kind is given as a variable. Similar to B. bronchiseptica, there is a SR- modulation even in colonies of B. avium. The abbreviations S and R stand for the appearance of colonies, English smooth, "smooth" and English rough, " rough" (see Griffiths experiment). This behavior is most likely to on blood agar, while the rough colonies are larger. A change of the S- to R-form may occur spontaneously, but it was observed in the study of 28 strains of bacteria in only three strains.
Growth and metabolism
The metabolism of Bordetella avium is based on the breathing, the species is strictly aerobic, that requires oxygen to grow. The catalase test and oxidase test was positive. Furthermore, the metabolism is marked as chemoorganotroph and heterotrophic, B. avium uses organic compounds as an energy source as well as for the construction of cellular materials. In this case, it is asaccharolytisch, i.e. they can not sugars (eg glucose ) use, instead, include amino acids to the substrates which are degraded. This must be considered when choosing the appropriate culture medium for the cultivation, with B. avium is not as sophisticated as B. pertussis.
The optimum temperature for growth is 37 ° C. Is suitable for the cultivation of B. parapertussis also (see below) used Bordet - Gengou blood agar. Even simple nutrient media are suitable if they contain amino acids or peptone. Furthermore, the cultivation on MacConkey agar and Salmonella - Shigella agar possible. After incubation for 1-2 days at 37 ° C, colonies can be recognized. The grown-up on the culture media bacterial culture can then be examined biochemically, to distinguish them from the related Bordetella species.
Biochemical characteristics, such as the enzymes present and the resulting metabolic properties can be used in a colorful series for the identification of B. avium. Besides the positive catalase and oxidase test, the following features can be used: you does not conduct nitrate reduction, ie nitrate is not reduced to nitrite. The urease test is negative, the type is not capable of degrading urea. Nor can gelatin are degraded by hydrolysis, there is also no Äskulinhydrolyse instead. Of the indole test is negative. Since no carbohydrates are broken down, there is also no acid formation, thus the methyl red test is also negative. It can degrade the amino acids L- aspartic acid, L- glutamic acid and L -proline. Other organic compounds which may be utilized as an energy source for setting up of cellular materials are citrate, pyruvate, succinate, fumarate, glutarate and. B. avium can be distinguished on the basis of some characteristics of the other species (see table).
Genetics
The genome of the bacterial strain Bordetella avium 197N ( out under the number ATCC BAA -1003 ) was completely sequenced in 2006. This is a strain that was in the early 1980s isolated from a diseased turkey from a poultry farm in Ohio in the United States. The genome has a size of 3732 kilobase pairs (kb ), which is in about 80 % of the genome size of Escherichia coli. There is a circular bacterial chromosome. There are 3381 proteins annotated. The GC content (the proportion of guanine and cytosine nucleobases ) in the bacterial DNA is about 62 mole percent, while the GC content of the classical Bordetella species is 68 mole percent somewhat higher.
The comparison with the 2003 determined genome size of B. bronchiseptica ( 5339 kb ), B. parapertussis ( 4774 kb) and B. pertussis ( 4086 kb) shows that the genome of B. avium smallest fails. One possible explanation is the adaptation to a host, in this case, poultry, while B. bronchiseptica can infect many mammals as host. By host restriction are no longer " needed " genes lost. It is more than 1100 genes have been identified in the genome which do not occur in B. bronchiseptica which is placed in connection with the host adaptation. Relates primarily to the genes that encode for proteins that are suitable as surface proteins or secretory proteins, to adapt to the respiratory tract of birds and not of mammals.
Pathogenicity
If also occur opportunistic infections, Bordetella avium is generally regarded as non-pathogenic (not " pathogenic " ) for humans. By Biostoffverordnung in connection with the TRBA (Technical Rules for Biological Agents ) 466 it is assigned to risk group 2, thus it is found that it can cause human disease. However, this is explained by a note further: it is pathogenic for vertebrates, the human being is not affected under natural conditions. After the protection concept of biological substances for employees who work with biological agents, is taken into account by doing this, that when dealing with high pathogen concentrations may be given a risk of infection.
The genetic study (2006 ) aimed to learn more about the virulence factors of B. avium. The best-studied type Bordetella pertussis (causative agent of whooping cough ) has numerous virulence factors, such as the filamentous hemagglutinin ( FHA ) and pertussis toxin ( PT), while it is a protein that acts as exotoxin and adhesin. In comparison to the classical Bordetella found in B. avium only some of these factors. This includes the filamentous hemagglutinin ( FHA ), which act as antigens fimbriae, the tracheal cytotoxin (TCT ) and the heat-labile toxin. The latter is attributed to a hautnekrotisierende effect, it is therefore also called dermanekrotisches toxin ( dermonecrotic toxin English, DNT) respectively. In contrast, pertussis toxin and the hemolysin formed by the adenylate cyclase are ( CyaA ) from B. avium can not be found, they seem to play no role, so that the genes encoding them have been lost in the infection of birds.
Occurrence
The investigations that led to the discovery of Bordetella avium, included 28 strains of bacteria. These were mainly isolated from turkeys. The turkey is also called Haustruthuhn, it is the domesticated form of the Truthuhns. In addition, strains were also of a chicken, a duck, a goose and a bronze figure ( a genus of the family of finches ) isolated. The isolates from different geographical areas, such as the USA, Spain, France, the United Kingdom (UK), Germany, Israel and Japan. In serological studies on a wide variety of birds over the period from 1998 to 2000 B. avium was detected in 41 of the 61 species studied, including at the Mallard, the Canada goose and the wild form of the Truthuhns. Similar to B. bronchiseptica and B. avium can long periods in the environment survive and was also found in the water.
System
Outer systematics
Bordetella avium is one of several species of the genus Bordetella in the family of Alcaligenaceae, this will be provided to the order of the Burkholderiales in the class of the Betaproteobacteria. One of the bacterial strains that were assigned in the original description of the species, was previously expected to Alcaligenes faecalis type ( type species of the genus Alcaligenes ). Actually, the phylogenetic analyzes of Kersters et al showed a close relationship of B. avium with Alcaligenes denitrificans (now referred to as Achromobacter denitrificans ) and Achromobacter xylosoxidans (now a subspecies of Achromobacter denitrificans viewed ).
Inside systematics
From the genus Bordetella are the species B. bronchiseptica, B. pertussis and B. parapertussis from the first half of the 20th century known. They are also referred to as "classical " Bordetella species and resemble strikingly, so that a classification is discussed as a subspecies. Bordetella avium was founded in 1984 by Karel Kersters et al. discovered as a fourth Bordetella species and first described. As mentioned above, was also a bacterial strain Alcaligenes faecalis of the type previously assigned, identified as B. avium. However, this is based on the earlier, erroneous assignment of the trunk, thus provides Alcaligenes faecalis no synonym dar.
In addition to the phylogenetic analysis ( especially in the 16S rRNA, a typical representative for prokaryotes, the ribosomal RNA) and phenotypic characteristics are compared and made a polyacrylamide gel electrophoresis of the bacterial proteins. This showed that B. avium belongs to the genus Bordetella, as more in common with the species known at that time exist as with the representatives of related genera Alcaligenes or Achromobacter. Further genetic studies of 2006, however, confirm that B. avium is phylogenetically relatively well classified by the classical Bordetella. The strain B. avium ATCC 35086 is the type strain of the type now ( 2014) only the genome of the strain B. avium 197N been fully investigated. We do several bacterial strains in various collections of microorganisms.
Etymology
The genus name was chosen in honor of the Belgian microbiologist Jules Bordet. The specific epithet refers to the occurrence and importance as pathogens in poultry, avium ( genitive plural of Latin avis, " bird" ) means "the birds " ( genitive ).
Veterinary Importance
Bordetella avium is of veterinary importance as the causative agent of an infectious disease in poultry. Infection with B. avium is - just like an infection with B. bronchiseptica in mammals - in veterinary medicine as Bordetellose referred (English bordetellosis ). Even the name avian Bordetellose is used. The infectious disease often occurring in turkeys is then called turkey coryza (English turkey coryza ), with coryza is a synonym for rhinitis ( " runny nose "). On the basis of symptoms, they can not be of the Putenrhinotracheitis (caused by a pneumovirus ) distinguished.
Similar to the classical species B. pertussis and B. parapertussis or B. bronchiseptica in humans in a variety of mammals, the ciliated epithelial cells of the respiratory tract, the point of the pathogen. In B. avium mainly the upper respiratory tract ( respiratory tract) is affected by the medi hiss technical terms for disease of the nose and trachea, this is called rhinotracheitis. The disease is similar to the corresponding infections with other hosts in poultry by the related species. Since B. avium may take longer time in the environment, for example, in water and dilute salt solutions survive, it is assumed that a smear infection is possible than infection. Most often it is the disease spreading by droplets (droplet infection), the diseased animals leave by sneezing.
B. avium infected numerous domesticated poultry species, as well as their living as wild animals relatives. Especially turkeys ( Haustruthühner ) on poultry farms are very sensitive, but also the wild form of the Truthuhns (Meleagris gallopavo ) is affected. The infection is highly contagious and occurs except in turkeys also in chickens, geese and ducks. Especially when poults during the first month of life, there is a complex of rhinitis, sinusitis, conjunctivitis, inflammation of the trachea and bronchi and sometimes even pneumonia. The incubation period is 7-11 days. In an affected stock can be 80-100 % morbidity. Avian Bordetellose is an economic problem in the turkey production in the United States. Infection with B. avium is often exacerbated by secondary infections with other bacteria or viruses. The diseased birds not adequately gaining weight, even deaths do occur.
Live vaccines have been tested for the prevention already in Germany but is still no approved drug available. For the therapy of different antibiotics can be used, for example, from the group of tetracyclines. A 2013 study published in the USA more than 20 isolates that were obtained for a long period of diseased turkeys, showing a resistance of B. avium to several antibiotics, and to tetracyclines. Most isolates are resistant to erythromycin, ampicillin more. All analyzed isolates are resistant against aztreonam, hence this antibiotic is recommended as an additive in the culture medium to selectively grow as avium. The microbiological studies by antibiogram or the determination of the minimum inhibitory concentration, however, have the sensitivity of B. avium to aminoglycoside antibiotics ( amikacin, gentamicin ) result, cephalosporins, such as cefoperazone, ceftazidime and cefepime, and piperacillin.