Chlamydophila
Chlamydophila is a genus of gram-negative, aerobic, obligate intracellular parasites characterized by a unique two-phase life cycle consisting of elementary bodies and reticulate bodies. This genus includes several species, among which Chlamydophila pneumoniae and Chlamydophila psittaci are notable for their impact on human health. Chlamydophila pneumoniae is primarily associated with respiratory infections such as bronchitis and pneumonia and has been linked to chronic respiratory diseases. In contrast, Chlamydophila psittaci is primarily found in birds, with humans contracting psittacosis through close contact with infected birds, leading to severe pneumonia.
Chlamydophila species have relatively small genomes and are known for their limited metabolic capabilities, relying heavily on host cells for essential nutrients. Although some strains can be isolated from various hosts, including koalas and cats, not all species are known to infect humans. Treatment for Chlamydophila infections typically involves antibiotics like tetracycline and doxycycline, with specific recommendations based on the species and the severity of the infection. Understanding the characteristics and implications of Chlamydophila infections is important for managing public health, particularly for those who work closely with animals or in environments where these bacteria may be present.
Chlamydophila
- TRANSMISSION ROUTE: Direct contact, inhalation
Definition
Chlamydophila is a gram-negative, aerobic, obligate, intracellular parasite with a reduced genome and a limited metabolism.
Natural Habitat and Features
Until the 1990s, all members of the order Chlamydiales were placed in the single family Chlamydiaceae and the single genus Chlamydia. Studies on the DNA (deoxyribonucleic acid) and rRNA (ribosomal ribonucleic acid) of several species culminated, in 1999, with the publication of a new taxonomy of the order. Chlamydiales is now thought to contain three families: Chlamydiaceae, Parachlamydiaceae, and Simkaniaceae. Members of Chlamydiaceae have been separated into two monophyletic genera Chlamydia and Chlamydophila mainly by differences in their 23s rRNA and genomic DNA. Because of this change, Chlamydophila spp. are often still referred to as Chlamydia spp.
Like Chlamydia spp., all Chlamydophila spp. are obligate intracellular parasites that exist in two phases, the elementary body and the reticulate body. Their cell wall is without a peptidoglycan layer but does contain gram-negative-like lipopolysaccharides and uniquecysteine-rich proteins found only in Chlamydiales. They are usually coccobacilli with diameters of 0.1 to 0.2 micrometers (um). The genomes of Chlamydophila spp. are quite small: approximately 1.1 million to 1.2 million base pairs compared with 0.5 million to 1.0 million in Chlamydia spp. and 4.6 million in Escherichia coli.
The genomes of several Chlamydophila strains have been sequenced, and most strains also contain a large plasmid of about 7,550 base pairs. This plasmid seems to be involved in virulence because avirulent strains have been found to lack this plasmid. The only exception is C. abortus, which has not been found in any strains. Genes coding for enzymes in many metabolic pathways are missing. Because of the lack of various enzymes, metabolism is incomplete. Some electron transport proteins are present, but Chlamydophila spp. have only limited abilities to produce adenosine triphosphate (ATP), usually by substrate-level phosphorylation, and so must obtain most of their ATP from the host cell.
In addition, pathways to produce many amino acids and other cellular building blocks are incomplete or missing, so that these too must be obtained from the host. Some carbohydrates can be broken down by a modified glycolytic pathway, but carbohydrate metabolism is incomplete. Chlamydophila spp. lack an ability to use fats for ATP production or as carbon sources, but these bacteria have extensive lipid biosynthetic pathways that produce their complex cell wall lipopolysaccharides. Unlike Chlamydia spp., they do not produce glycogen.
Pathogenicity and Clinical Significance
Of the six species of Chlamydophila, two, pneumoniae and psittaci, commonly cause human disease. Humans are occasional hosts for two others, abortus and felis, while the final two, pecorum and caviae, are not known to infect humans.
In humans, pneumoniae, as its name implies, is primarily found in the respiratory tract, where it causes bronchitis and pneumonia. It has also been associated with other chronic respiratory diseases, and chronic infections have been implicated in a higher risk of lung cancer. The bacterium had been considered a strictly human parasite, but some strains have been found in koalas, where they are associated with respiratory infections too, and in horses, where they seem to be asymptomatic. Occasionally, strains can also be isolated from the conjunctiva and the urogenital tract.
Although psittaci primarily infects birds, humans can become infected by close contact with infected pet birds or infected poultry. In humans, the infection leads to a severe atypical pneumonia called psittacosis (also known as ornithosis and parrot fever). A pandemic of the disease occurred in 1929-1930 following a shipment of infected parrots to various parts of the world.
Abortus, once considered a subspecies of psittaci, is associated with placental colonization and abortion in ruminants. These bacteria have been associated with respiratory disease in humans who work with infected animals and associated with abortion in women who work with infected sheep.
Felis usually causes conjunctivitis, rhinitis, and pneumonia in domestic cats. Humans who have close contact with infected cats are occasionally infected, showing many of the same symptoms. Caviae is very host specific and is limited to guinea pigs. Pecorum has a broader host range and has been found in koalas, ruminants, and swine. In most organisms, it is associated with abortion, conjunctivitis, and respiratory infections. In koalas, it is also a leading cause of infertility and other reproductive diseases.
Drug Susceptibility
Although Chlamydophila spp. are affected by penicillin, the primary antibiotic of choice for psittaci infections specifically is tetracycline. A course of a minimum of fourteen days is recommended to prevent relapse. Children and pregnant women can be treated with erythromycin. For pneumoniae infections, doxycycline is usually used.
Bibliography
“About Chlamydia Pneumoniae Infection.” CDC, 30 Jan. 2024, www.cdc.gov/cpneumoniae/about/index.html. Accessed 23 Nov. 2024.
Everett, Karen D. E., et al. "Emended Description of the Order Chlamydiales." International Journal of Systematic Bacteriology, vol. 49, 1999, pp. 415-440.
Krieg, Noel R., et al., editors. Bergey's Manual of Systematic Bacteriology. 2nd ed., Springer, 2010.
Romich, Janet A. Understanding Zoonotic Diseases. Thomson Delmar, 2008.
Schlossberg, D. "Chlamydia Psittaci (Psittacosis)." Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, edited by Gerald L. Mandell et al., 7th ed., Churchill Livingstone/Elsevier, 2010.