Chlamydophila pneumoniae

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Chlamydophila pneumoniae
Scientific classification
Kingdom: Bacteria
Phylum: Chlamydiae
Order: Chlamydiales
Family: Chlamydiaceae
Genus: Chlamydophila
Species: C. pneumoniae[1]

Chlamydophila pneumoniae is a species of Chlamydophila, an obligate intracellular bacterium[2] that infects humans and is a major cause of pneumonia. It was known as the Taiwan acute respiratory agent (TWAR) from the names of the two original isolates – Taiwan (TW-183) and an acute respiratory isolate designated AR-39.[3] Until recently, it was known as Chlamydia pneumoniae, and that name is used as an alternate in some sources.[4] In some cases, to avoid confusion, both names are given.[5]

C. pneumoniae has a complex life cycle and must infect another cell to reproduce; thus, it is classified as an obligate intracellular pathogen. The full genome sequence for C. pneumoniae was published in 1999. It also infects and causes disease in koalas, emerald tree boas (Corallus caninus), iguanas, chameleons, frogs, and turtles.

The first known case of infection with C. pneumoniae was a case of sinusitis in Taiwan. This atypical bacterium commonly causes pharyngitis, bronchitis and atypical pneumonia,[6] mainly in elderly and debilitated patients, but in healthy adults, also.[7]

Micrograph ofChlamydophila (Chlamydia) pneumoniae in an epithelial cell in acute bronchitis: 1 – infected epitheliocyte, 2 – uninfected epitheliocytes, 3 – chlamydial inclusion bodies in cell, 4 – cell nuclei

Life cycle and method of infection

Life cycle of Chlamydophila pneumoniae. A — Chlamydophila elementary body. B — Lung cell. 2 — Chlamydophila enters the cell. 3 — Elementary body becomes a reticulate body. 4 — Replication. 5 — Reticulate bodies become elementary bodies and are released to infect other cells.

Chlamydophila pneumoniae is a small gram negative bacterium (0.2 to 1 μm) that undergoes several transformations during its life cycle. It exists as an elementary body (EB) between hosts. The EB is not biologically active, but is resistant to environmental stresses and can survive outside a host for a limited time. The EB travels from an infected person to the lungs of an uninfected person in small droplets and is responsible for infection. Once in the lungs, the EB is taken up by cells in a pouch called an endosome by a process called phagocytosis. However, the EB is not destroyed by fusion with lysosomes, as is typical for phagocytosed material. Instead, it transforms into a reticulate body (RB) and begins to replicate within the endosome. The reticulate bodies must use some of the host's cellular metabolism to complete its replication. The reticulate bodies then convert back to elementary bodies and are released back into the lung, often after causing the death of the host cell. The EBs are thereafter able to infect new cells, either in the same organism or in a new host. Thus, the lifecycle of C. pneumoniae is divided between the elementary body, which is able to infect new hosts but cannot replicate, and the reticulate body, which replicates but is not able to cause new infection.

Diseases

C. pneumoniae is a common cause of pneumonia around the world; it is typically acquired by otherwise-healthy people and is a form of community-acquired pneumonia. Because its treatment and diagnosis are different from historically recognized causes, such as Streptococcus pneumoniae, pneumonia caused by C. pneumoniae is categorized as an "atypical pneumonia" .[8]

In addition to pneumonia, C. pneumoniae less commonly causes several other illnesses. Among these are meningoencephalitis (infection and inflammation of the brain and meninges), arthritis, myocarditis (inflammation of the heart), and Guillain-Barré syndrome.[citation needed]

Multiple studies have evaluated prior C. pneumoniae infection and a possible connection to lung cancer. One meta-analysis of serological data comparing prior C. pneumoniae infection in patients with and without lung cancer found results suggesting prior infection was associated with a slightly increased risk of developing lung cancer.[9]

In research into the association between C. pneumoniae infection and atherosclerosis and coronary artery disease, serological testing, direct pathologic analysis of plaques, and in vitro testing suggest chronic infection with C. pneumoniae may be a risk factor for development of atherosclerotic plaques. C. pneumoniae infection increases adherence of macrophages to endothelial cells in vitro and aortas ex vivo.[10] However, the current data do not define how often C. pneumoniae is found in atherosclerotic or normal vascular tissue, nor does it allow for determining whether C. pneumoniae infection has a causative effect on atheroma formation or is merely an "innocent passenger" in these plaques. The largest trials that studied the use of antibiotics as a prevention for diseases associated with atherosclerosis, such as heart attacks and strokes, did not show any significant difference between antibiotics and placebo.[11]

C. pneumoniae has been found in the cerebrospinal fluid of some patients diagnosed with multiple sclerosis.[12]

Serological evidence for possible chronic C. pneumoniae infection was first associated with wheezing, asthmatic bronchitis, and adult-onset asthma in 1991.[13] Subsequent studies of bronchoalveolar lavage fluid from pediatric patients with severe chronic respiratory illnesses including asthma have demonstrated that over half had evidence of C. pneumoniae by direct organism identification.[14][15] The only prospective study of new-onset adult asthma carried out in a primary-care clinic diagnosed acute C. pneumoniae infection serologically in 5/5 patients with acute wheezing that became chronic and that was later diagnosed as asthma, and in another patient who developed new-onset chronic bronchitis who had the organism cultured from his sputum 6 months after illness onset.[16] These observations suggest that acute C. pneumoniae infection is capable of causing protean manifestations of chronic respiratory illness, some of which diagnosed as asthma.

That these associations are clinically relevant in the primary-care setting is suggested by the results of two observational trials[17][18] and two randomized controlled trials[19][20] of azithromycin treatment for asthma. One of these RCTs[20] and another macrolide trial[21] suggest that the treatment effect may be greatest in patients with severe, refractory asthma. These clinical results correlate with epidemiological evidence that C. pneumoniae is positively associated with asthma severity[22] and laboratory evidence that C. pneumoniae infection creates steroid-resistance.[23] Currently available asthma guidelines do not address this evidence.

Vaccine research

There is no vaccine to protect against Chlamydophila pneumoniae. Research is on-going. Identification of highly immunogenic antigens is critical for the construction of an efficacious subunit vaccine against C. pneumoniae infections.

References

  1. ↑ Everett, K. D. E.; Bush, R. M.; Andersen, A. A. (1999). "Emended description of the order Chlamydiales, proposal of Parachlamydiaceae fam. nov. and Simkaniaceae fam. nov., each containing one monotypic genus, revised taxonomy of the family Chlamydiaceae, including a new genus and five new species, and standards for the identification of organisms". International Journal of Systematic Bacteriology 49 (2): 415–440. doi:10.1099/00207713-49-2-415. ISSN 0020-7713. PMID 10319462. 
  2. ↑ Chlamydophila pneumoniae at the US National Library of Medicine Medical Subject Headings (MeSH)
  3. ↑ http://pathmicro.med.sc.edu/mayer/chlamyd.htm
  4. ↑ "www.ncbi.nlm.nih.gov". Retrieved 2009-01-27. 
  5. ↑ Appelt DM, Roupas MR, Way DS, et al. (2008). "Inhibition of apoptosis in neuronal cells infected with Chlamydophila (Chlamydia) pneumoniae". BMC Neurosci 9: 13. doi:10.1186/1471-2202-9-13. PMC 2266938. PMID 18218130. 
  6. ↑ Lang, B. R., Chlamydia pneumonia as a differential diagnosis? Follow-up to a case report on progressive pneumonitis in an adolescent, Patient Care, Sept. 15, 1991
  7. ↑ Little, Linda, Elusive pneumonia strain frustrates many clinicians, Medical Tribune, p. 6, September 19, 1991
  8. ↑ Pignanelli S, Shurdhi A, Delucca F, et al. (2009). "Simultaneous use of direct and indirect diagnostic techniques in atypical respiratory infections from Chlamydophila pneumoniae and Mycoplasma pneumoniae.". J Clin Lab Anal. 23 (4): 206–9. doi:10.1002/jcla.20332. PMID 19623657. 
  9. ↑ Zhan P, Suo LJ, Qian Q, et al. (March 2011). "Chlamydia pneumoniae infection and lung cancer risk: A meta-analysis". Eur. J. Cancer 47 (5): 742–7. doi:10.1016/j.ejca.2010.11.003. PMID 21194924. 
  10. ↑ Takaoka N, Campbell LA, Lee A, Rosenfeld ME, Kuo CC (February 2008). "Chlamydia pneumoniae infection increases adherence of mouse macrophages to mouse endothelial cells in vitro and to aortas ex vivo.". Infection and Immunity 76 (2): 510–4. doi:10.1128/IAI.01267-07. PMID 18070891. 
  11. ↑ Mussa FF, Chai H, Wang X, Yao Q, Lumsden AB, Chen C (June 2006). "Chlamydia pneumoniae and vascular disease: an update". J. Vasc. Surg. 43 (6): 1301–7. doi:10.1016/j.jvs.2006.02.050. PMID 16765261. 
  12. ↑ Sriram S, Stratton CW, Yao S, et al. (1999). "Chlamydia pneumoniae infection of the central nervous system in multiple sclerosis". Annals of Neurology 46 (1): 6–14. doi:10.1002/1531-8249(199907)46:1<6::AID-ANA4>3.0.CO;2-M. PMID 10401775. 
  13. ↑ Hahn DL, Dodge R, Golubjatnikov R (1991). "Association of Chlamydia pneumoniae (strain TWAR) infection with wheezing, asthmatic bronchitis and adult-onset asthma". JAMA. 266: 225–230. doi:10.1001/jama.266.2.225. PMID 2056624. 
  14. ↑ Schmidt SM, Muller CE, Bruns R, et al. (2001). "Bronchial Chlamydia pneumoniae infection, markers of allergic inflammation and lung function in children". Pediatr Allergy Immunol. 12 (5): 257–265. PMID 11737672. 
  15. ↑ Webley WC, Salva PS, Andrzejewski C, et al. (2005). "The bronchial lavage of pediatric patients with asthma contains infectious Chlamydia". Am J Respir Crit Care Med. 171: 1083–1088. doi:10.1164/rccm.200407-917OC. PMID 15735056. 
  16. ↑ Hahn DL, McDonald R (1998). "Can acute Chlamydia pneumoniae infection initiate chronic asthma?". Ann Allergy Asthma Immunol. 81: 339–344. doi:10.1016/S1081-1206(10)63126-2. PMID 9809498. 
  17. ↑ Hahn DL (1995). "Treatment of Chlamydia pneumoniae infection in adult asthma: a before-after trial". J Fam Pract. 41 (4): 345–351. PMID 7561707. 
  18. ↑ Hahn DL, Schure A, Patel K, et al. (2012). "Chlamydia pneumoniae-specific IgE is prevalent in asthma and is associated with disease severity". PLOS ONE 7: e35945. doi:10.1371/journal.pone.0035945. PMC 3335830. PMID 22545149. 
  19. ↑ Hahn DL, Plane MB, Mahdi OS, et al. (2006). "Secondary outcomes of a pilot randomized trial of azithromycin treatment for asthma". PLoS Clin Trials. 1: e11. doi:10.1371/journal.pctr.0010011. PMC 1488900. PMID 16871333. 
  20. ↑ 20.0 20.1 Hahn DL, Grasmick M, Hetzel S, et al. (2012). "Azithromycin for bronchial asthma in adults: An effectiveness trial". J Am Bd Fam Med. 25: 442–459. doi:10.3122/jabfm.2012.04.110309. PMID 22773713. 
  21. ↑ Simpson JL, Powell H, Boyle MJ, et al. (2008). "Clarithromycin targets neutrophilic airway inflammation in refractory asthma". Am J Respir Crit Care Med. 177: 148–155. doi:10.1164/rccm.200707-1134OC. PMID 17947611. 
  22. ↑ von Hertzen L, Vasankari T, Liippo K, et al. (2002). "Chlamydia pneumoniae and severity of asthma". Scand J Infect Dis. 34 (1): 22–27. PMID 11874160. 
  23. ↑ Cho YS, Kim TB, Lee TH, et al. (2005). "Chlamydia pneumoniae infection enhances cellular proliferation and reduces steroid responsiveness of human peripheral blood mononuclear cells via a tumor necrosis factor-alpha-dependent pathway". Clinical & Experimental Allergy. 35: 1625–1631. doi:10.1111/j.1365-2222.2005.02391.x. PMID 16393329. 

External links

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