Mycobacteriosis (Fish Tuberculosis): Difference between revisions
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[[Image:PHIL_1181_lores.jpg|thumb|300px|right|Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.]] | [[Image:PHIL_1181_lores.jpg|thumb|300px|right|Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.]] | ||
<br>By Sally Moseley<br> | <br>By Sally Moseley<br> | ||
<br>IMycobacteria are a class of rod-shaped bacteria that are infamous for the difficulty they pose in detecting and isolating the cells within their host organisms. This is due to the fact that mycobacteria (including Myobacterium marinum), are acid-fast. For these species, procedures such as Ziiehl-Neelsen staining and biopsy culture are necessary for detection instead of using traditional means of staining and examining. The organism is difficult to isolate by a normal swab procedure. For effective analysis of specific species of mycobacteria, polymerase chain reaction (PCR) for the 65-kDa protein (the protein with a highly conserved genetic code amongst the mycobacterial species, particularly notable between M. marinum and M. tuberculosis) and analysis the PCR products using restriction enzyme analysis are used. These methods prove most effective with the touch cell type to isolate. Many products are analyzed using BACTEC technology, which detects microbial growth from blood specimens, which is useful in mycobacterial species that inhabit macrophages.<br> | |||
==Fish Tuberculosis== | ==Fish Tuberculosis== | ||
Revision as of 01:18, 26 April 2011
Introduction
By Sally Moseley
IMycobacteria are a class of rod-shaped bacteria that are infamous for the difficulty they pose in detecting and isolating the cells within their host organisms. This is due to the fact that mycobacteria (including Myobacterium marinum), are acid-fast. For these species, procedures such as Ziiehl-Neelsen staining and biopsy culture are necessary for detection instead of using traditional means of staining and examining. The organism is difficult to isolate by a normal swab procedure. For effective analysis of specific species of mycobacteria, polymerase chain reaction (PCR) for the 65-kDa protein (the protein with a highly conserved genetic code amongst the mycobacterial species, particularly notable between M. marinum and M. tuberculosis) and analysis the PCR products using restriction enzyme analysis are used. These methods prove most effective with the touch cell type to isolate. Many products are analyzed using BACTEC technology, which detects microbial growth from blood specimens, which is useful in mycobacterial species that inhabit macrophages.
Fish Tuberculosis
Several species of mycobacteria infect fish with fish tuberculosis, including M. fortuitum, M. flavescens, M. chelonae, M. gordonae, M. terrae, M. triviale, M. diernhoferi, M. celatum, M. kansasii ,M. intracellulare, and M. marinum. Because of the wide range of fish found to be infected with different Mycobacterium, it is assumed that all fish are susceptible to fish tuberculosis.
Different strains of mycobacteria are found worldwide and certain strains have been fairly ubiquitous around the world. Tropical aquarium fish appear to be the most susceptible, though certain strains grow in the fish of other environments more readily. Because of the ideal temperature range (25-35 ̊C), mycobacteriosis is not as commonly found in fish in cold temperature zones. Like human tuberculosis, it is a progressive condition that may not show signs until years after the infection begins. In many fish, it is not apparent that they are infected until much later in the disease. The first sign of infection are seen in abnormal growth on the liver and spleen. Later in the disease, typical signs can be seen externally in unusual wear on the scales and skin of the fish, which may include lesions. Infected species are often emaciated and lethargic.
Human Pathogenicity
M. fortuitum, M. chelonae and M. marinum, among others, are known to be zootonic and are therefore the subject of most studies for both health and economic reasons. The zootonic strains are conditionally pathogenic mycobacteria, or CPM. M. marinum has proved to be the most prevalent cause of disease transfer. It is the primary pathogenic mycobacteria and earlier studies only mention M. fotuitum and M. chelonae as present in affected humans as opposed to the causative agent. Effects on the human population usually result in hand lesions from handling infected fish. The infection tends to stay at the extremities of the human body because of the cooler temperatures they provide as opposed to the internal temperatures. Fortunately, even though the bacterium prove fatal to fish, it usually only results in a cutaneous infection for humans.
These infections, however, can be chronic. Lesions tend to be noticed two to four weeks after exposure to the mycobacterium. They may be completely painless, irritating, or give discomfort. The lesions swell and develop into ulcerations, often leading to granuloma. In some instances, infection spreading to the lymphatics lead to a sporotrichoid pattern of infection. Some long-term effects of lesions are tenosynovitis, osteomyelitis, arthritis, and a compromised immune system. The skin, kidney, and liver are the main body parts affected in both fish and humans. Fish tuberculosis is especially characterized by causing granulomatous in its host organism. When a granuloma is formed, the mycobacteria form epithelioid layers as they pack together. The nodules of each granuloma is usually covered by a thin capsule. The presence of mycobacteria is prolific; The pathogens can be found within cells and spread throughout the tissues of infected organs. When growing within eukaryotic cells, the replication of the bacteria, though slower than many pathogens, eventually reaches critical levels that kill the cells before lysing the membranes It appears that mycobacteria cells, both CPM cells and non-pathogenic mycobacteria, can be internalized by macrophages and epithelial cells readily, though mycobacteria has been found in several other cell types. Interestingly, pathogenic cells can be internalized by and survive and reproduce in HeLa cells, which is not normally the case for non-pathogenic cells.
The fish pathogen M. fortuitum has also been associated with masses found in cows and sheep, abscesses in dogs, granulomas in cats, and “spinning disease” (a neurological disorder) in mice, but the relation between these ailments is still unclear. M. fortuitum is particularly potent if the host organism already has an open would and is known to easily infect these wounds.
Pathogenic strains of different mycobacteria, though associated with different animals, have been known to infect a range of animals. In studying the pathogenicity of certain strains, the control mycobacteria used also ended up affecting the host organism. Usually, the newly pathogenic strain of mycobacteria is not as potent as the strain previously known to affect the particular host, but these experience describe the range with which mycobacterium can survive. Talaat et al. demonstrated that an environmental mycobacterium, M. smegmatis, (normally found in soil environments and found as the source of an infection in many wounds of several species of animals) caused more massive granulomatous in goldfish (Carassius auratus) than the known fish pathogen M. fortuitum.
One factor that has led to a greater portion of the human population is the survival of CPM outside of the host (the fish). The CPM can be found in the water, on other organisms, on plant matter, and on abiotic substances. The location or environment of the mycobacteria does not play as much of a role in the survival of any of the species as much as the temperature. CPM grow ideally above 18-20 ̊C, but also survive below these temperatures for months. Environmental infestations have proved to cause many of the cases of disease transfer to humans. The disease can be transferred by the touching or ingesting of any infected object or organism. The mycobacteria have even been found on clinically healthy fish at low concentrations, but it is unclear whether this concentration has the ability to infect humans or not.
The concern with the range of substances mycobacteria inhabit has to do with the fact that water used for drinking and facilities have been contaminated in the past with infectious species.
M. marinum as a Study Tool
M. marinum is a useful tool in tuberculosis studies because of its close association with M. tuberculosis, the pathogen that causes tuberculosis and its relatively short generation time. The generation time of M. tuberculosis is about twenty hours and the generation time of M. marinum is about four hours. The shorter generation time allows for further studies to work faster and be more productive. M. marinum also, even though it is closely associated to M. tuberculosis, does not have the potency of M. tuberculosis in humans. The pathogen tends to stay in the extremities of the body and there have been no reported cases of a breakdown in the organs of affected humans, even in cases of immunocompromised symptoms. This makes the handling of the bacteria easier
The growth rate of mycobacteria depends on the species. Even though M. marinum has a generation time of four hours, this is not true for all species of mycobacteria. Species of mycobacteria can be defined by their rate of isolation. Fast-growing mycobacteria take a couple of days to isolate and slow-growing mycobacteria take weeks or months to isolate.
Conclusion
Overall text length at least 3,000 words, with at least 3 figures.
References
Edited by student of Joan Slonczewski for BIOL 238 Microbiology, 2011, Kenyon College.
