Difference between revisions of "Chlamydophila pecorum"
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Latest revision as of 03:15, 20 August 2010
A Microbial Biorealm page on the genus Chlamydophila pecorum
Higher order taxa
Domain: Bacteria; Phylum: Chlamydiae; Class: Chlamydiales; Order:Chlamydiaceae; Family: Chlamydophila; Genus: Chlamydophila; species: pecorum
Genus species: Chlamydophila pecorum
Description and significance
Chlamydophila pecorum, previously known as Chlamydia pecorum, is an small, obligate intracellular gram negative bacteria that grows in eukaryotic cells. It is intracellular because no Chalmydophila so far has been observed to grow extracellularly, either in nature or in the lab. It has many characteristics of a gram negative bacteria but it differs in that it lacks peptidoglycan. C. pecorum infects certain mammalian hosts like goats, koalas, sheep, swines and cattles. Because C. pecorum grows slowly within the natural host, actual disease syndromes are not as evident until later in the infectious process.
Before the discovery of C.pecorum, all mammalian Chlamydia diseases were classified as C. psittaci. However, in 1992, Fukusi and Hirai reclassified this species and reclassified them to Chlamydophila pecorum, a subset of C. psittaci. The taxonomy of phylum Chlamydiae has also been revised and the family Chlamydiaceae now has two separate genera: Chlamydia and Chlamydophila, containing three and six recognized chalmydial species respectively.
C. pecorum was first associated with diseases in cattle when Mcnutt and Waller (1940) first isolated this organism from cattles with sporadic bovine encephalomyelitis. In 1955, chicken embryo and cell culture methods for Chlamydiales became widely used, and it was believed that chlamydial agents caused diseases in cattles. Chalamydophila pecorum is continuously being studied through the isolation of cell culture from many organisms. Techniques like polymerase chain reaction (PCR) and ELISA are being used to further study this organism.
The complete genome of six Chlamydiaceae species have already been made, but the genome sequence of Chlamydophila pecorum is not yet known because there are significant barriers is using the genetic approach to understand its genome structure. One of the most significant barriers is its lack of a stable gene transfer system. However, recently a chlamydiaphage (Chp3) was detected in C.pecorum, a chlamydial species not previously known to carry bacteriophages. The discovery of Chp3 has helped develop a genetic transfer system and thus contributes to finding the whole genome sequence of C. pecorum. Chp3 belongs to the microviridae, and members of this virus family are known for their circular, single stranded DNA genome and small T = 1 icosahedral capsids. The double stranded replicative form Chp3 and DNA was purified from EB and used as a template to find the complete genome sequence.
The genome of Chp3 is 4,554 base pairs and it encodes eight open reading frames that are organized in the same genome structure as other chlamydiphages. Chp3 was found to share 97.1% nucleotide sequence identity with Chp2, a bacteriophage isolated from C. abortus. Since Chp2 and Chp3 are highly conserved, with only two amino acids different from each other, Chp2 phages can also infect C. pecorum. All chlamydiphages share similar features: they are small icosahedral particles, containing circular, single stranded DNA genome.
The family of Chlamydiaceae genomes are fairly conserved. Thus the chromosome of C. pecorum is most likely circular and the size and content of the genome is yet to be found. Another important characteristic of the genus Chlamydophila are their proteins in the outer membrane- disulfide bond cross linking of the 40 kDa major outer membrane protein, cysteine rich proteins (Omp2) and cysteine rich lipoprotein (Omp3), forming a supramaromolecular lattice. While there are major proteins in the outer membrane, there are also uncharacterized proteins that have been identified to have major functional roles.
Cell structure and metabolism
Structurally Chlamydophila pecorum are very small cells, about 0.1 to 0.2 um in diameter. Its cell membrane contains both a lipopolysaccharide (LPS) and a cytoplasmic membrane bilayer, suggesting that it is a gram negative bacteria. However, its cell envelope differs from those of a typical gram negative bacteria because it doesn’t have peptidoglycan. Though it lacks a peptidoglycan bilayer, C. pecorum is still able to synthesize penicillin binding proteins and is sensitive to pencillin.
It also has a genus specific LPS that is present at all time in the developmental cycle. Its LPS reveal at least three antigenic domains, two of which are shared with the LPS of some free living gram negative organism and one of which is unique to the LPS of C. pecorum. Though C. pecorum does not have pili or flagella, it does possess unique patches of hexagonally arrayed cylindrical projects on its outer membrane of EB. The cylinders extend all the way through the outer membrane and help connect the interior of the cell with the external environment.
C. pecorum is an ATP energy parasite because it obtains its ATP entirely from their host cells. They contain the cellular machinery for making their own DNA, RNA and proteins, but lack the ability to make ATP or other forms of energy. They make glutamate, glucose and pyruvate to a limited extend but without producing useful energy. So the RB moves ATP in and ADP out of their intracellular space by ATP-ADP exchange system. Then C. pecorum uses the ATP from the host to make proteins.
Chlamydophila pecorum infects mammals like sheep, goats(ruminant), cattle, pigs, koala, swine and pregnant ewe. Chlamydophila pecorum can cause a wide range of pathologies including polyarthritis, conjunctivitis, pneumonia, metritis, encephalomyelitis and subclinical enteric infections. Although transmission from animals to humans is extremely rare, there have been some reports of this infection. For instance, women exposed to infected sheep during lambing had placentitis, intravascular coagulation and spontaneous abortion. There is no direct effect on the environment since it can’t live outside its host cell.
Chlamydophila pecorum is pathogenic and is highly adapted for infection within certain mammalian hosts. Its mechanism of infecting the host is termed the developmental cycle, which consists of infection, growth, maturation, release and reinfection. They cycle begins with the elementary bodies (EB) attaching into the host cells. The EB are small, rigid particles that are osmotically stable, but metabolically inert and thus unable to grow and divide. They also exist in the extracellular environment until a host cell is available for intracellular growth. After its entry into the host cell, EB converts to reticulate body (RB) that grow and divide by binary fission with the inclusion, which are intracellular, membrane enclosed organelle that help the growth of Chlamydophila pecorum. RBs are larger, osmotically unstable and unable to attach to the host cell so they are not infectious. RB eventually converts back to infectious EB in order to release EB into the environment and infect other neighboring host cells.
C. pecorum is found mostly in mammals like cattle, sheep, goats, koalas and swine. In koalas, it causes urinary tract disease, infertility, and reproductive diseases. In other mammals, it is associated with abortion, conjunctivitis, encephalomyelitis, pneumonia, polyarthritis and enteritis. Symptoms are either absent or indolent so it is hard to diagnose. C. pecorum can be transmitted from animals to humans, but it is very rare.
Application to Biotechnology
Chlamydophila pecorum is a harmful pathogen so proper vaccine against this bacteria is needed. It is not known to produce any useful enzymes or compounds. Studies are continuously being conducted to develop effective chlamydial vaccines.
March 2007- The first experiment shows how the rrn-nqrF intergenic segments across 45 Chlamydiaceae strains have diverse geographical and pathological origins. In the Chlamydiaceae, the nucleotide sequence between the 5S rRNA gene and the gene for subunit F of the Na+ translocating NADH quinine reductase (nqrF or dmpP) has different lengths and gene contents. C. pecorum has multiple octamer repeats at the rrn-nqrF site, and this is unique only to C. pecorum. However, its function of multiple octamer repeats are not yet known. Although the underlying mechanism of the genomic plasticity of the rrn-nqrF segments in the Chlamydiaceae is still not clear, data supports the notion that this site can be useful in determining gene recombinations in the Chlamydiaceae.
July 2007- The second study was aimed at evaluating functional and inflammatory consequences of persistent chylamdial infections (ChI+) on the lungs in calves aged 2-7 months. Thirteen calves infected with C. pecorum or C. abortus were compared to 12 calves without chylamdial infections (ChI-). In order to study the lungs, 36 non invasive impulse oscillometry tests were done per animal within 6 months. Higher concentrations of total protein and 8-iso-prostane (8-IP), as well as higher activities of matrix metalloprotease 2 were measured in the broncho alveolar lavage fluids of Chl+ calves. In addition, bronchus associated lymphoid tissue causing partial obstruction of bronchiolar lumina in lungs was found in ChI+ calves. At the age of seven months all the calves were examined by PCR and chlamydial DNA was detected in the lungs of 7 out of 13 ChI+ calves. In conclusion, this showed that respiratory chlamydial infection is associated with chronic inflammation of the lungs and airways. It provided new insight into the impact of chlamydial infections on the respiratory system.
March 2006- The third study was aimed at studying the most common infectious diseases of koalas which are chlamydiosis and cryptococcosis. Chlamydiosis is caused by two chlamydial bacteria- C. pecorum and C. pneumoniae- which involve the bladder, kidneys, eyes and reproductive organs of koalas. Cryptococcosis is caused by the fungus, Cryptococcus gatti, which can cause koala illness and death through infecting the lungs, sinuses and brain. Tests were done on koalas that are infected but show no symptoms of the disease. In order to detect these animals, PCR was used, which helped detected Chlamydial DNA present in the eyes and reproductive tract of koalas. Studies are still being held to find a cure for this disease and firm conclusions can’t yet be drawn. However at this stage, there is evidence that the bursal cysts present at the start of treatment didn’t cure any of the treated animals. In addition, when the koalas were treated with enrofloxacin and marbofloxacin, antibiotics that can lead to loss of appetite, they didn’t lose any weight.
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Edited by KLB