Essay: Mycobacteria

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  • Subject area(s): Science essays
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  • Published on: July 28, 2019
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More than 150 species of mycobacteria are validly described, and most of them are opportunistic pathogens. All mycobacteria cause risk for human and animal health. Human infections due to environmental mycobacteria are increasing in both industrial and developing countries. The most susceptible risk groups are children, seniors and people or animals with immunosuppressive conditions. Drug therapy of mycobacteriosis is difficult and not always successful. Infections caused by drug-resistant mycobacteria can be life-threatening also for healthy adults and thus they are a relevant risk for humans. In pigs, environmental mycobacterial infections are usually without clinical signs and the lesions are mainly detected at slaughter. Mycobacterium-infected pork can pass for human consumption due to the poor specificity of visual meat control at slaughterhouses and mycobacteria in pigs also cause economical losses due to condemnation of carcasses. The main challenge is the evaluation of the hygienic risk due to the use of mycobacteria contaminated pork.

The majority of environmental mycobacteria species have been isolated from various sources, such as water, swimming-pools, soil, plants and bedding material. In our study mycobacterial growth in piggeries were found in all bedding materials, sawdust, straw, peat and wood chips in most cases, water and food samples in many cases, and only occasionally in dust and on wall surfaces. We found mycobacteria maximum almost 1x10exp9 per gram of used bedding materials, which are close of the maximum bacterial concentration in any growth media. Mycobacteria can multiply in piggeries and contaminate feed and water. Isolation of mycobacteria from pig faeces should be considered as indication of an infection risk to humans.
Environmental mycobacteriosis in humans and pigs are mainly caused by M. avium subsp. hominissuis. There is little evidence of direct transmission from animals to humans, but certain strain types can be recovered from both humans and pigs. In our studies identical mycobacteria RFLP and MIRU-VNTR fingerprints of porcine and human origins were found. Interspecies clusters were more common than intraspecies clusters with both methods. Therefore, we concluded that pigs may be as a reservoir of virulent M. avium strains and the vector for transmission of infections towards humans and vice versa or humans and pigs may have an identical infection source.

Culturing of mycobacteria is the gold standard for diagnosis, but detection of environmental mycobacteria based on cultivation and biochemical methods may take several weeks. Culture-independent rapid and accurate techniques for the detection of mycobacteria in food and feed chains are urgently needed. In this work we developed a rapid and accurate real-time quantitative PCR for detection of environmental mycobacteria in bedding materials and pig organs.

Conclusion: Mycobacteria can multiply in bedding materials and the heavy load mycobacterial contamination caused simultaneous infections of pigs. Mycobacterial DNA was found in pig organ samples also without lesions and similar strains was found from humans and pig organ samples. It cannot be ruled out, that mycobacteria are transmitted between pigs and humans.

List of Original Publications

I. Pakarinen J, Nieminen T, Tirkkonen T, Tsitko I, Ali-Vehmas T, Neubauer P, Salkinoja-Salonen M, 2007: Proliferation of mycobacteria in a piggery environment
revealed by Mycobacterium-specific real-time quantitative PCR and 16S rRNA sandwich hybridization. Veterinary Microbiology 120, 105-112.

II. Tirkkonen T, Pakarinen J, Moisander A-M, Mäkinen J, Soini H, Ali-Vehmas T, 2007: High genetic relatedness among Mycobacterium avium strains isolated from pigs and humans revealed by comparative IS 1245 RFLP analysis. Veterinary Microbiology 125, 175-181.

III. Tirkkonen T, Pakarinen J, Rintala E, Ali-Vehmas T, Marttila H, Peltoniemi O, Mäkinen J, 2010: Comparison of Variable-Number Tandem-Repeat Markers typing and IS 1245 Restriction Fragment Length Polymorphism fingerprinting of Mycobacterium avium subsp. hominissuis from human and porcine origins. Acta Veterinaria Scandinavica 52:21.

IV. Tirkkonen T, Nieminen T, Ali-Vehmas T, Peltoniemi O, Wellenberg G, Pakarinen J, 2013. Quantification of Mycobacterium avium subspecies in pig tissues by real-time quantitative PCR. Acta Veterinaria Scandinavica 2013, 55:26.

The author’s contribution

Paper I: TT planned and performed the relevant sampling procedure and participated in the writing of the paper especially regarding veterinary medicine and zoonotic aspects.

Paper II: TT performed strain selection for the porcine originating strains for the RFLP typing, interpreted the results and wrote the paper together with the co-authors.

Paper III: TT participated in the study design, sampling, analysis and interpretation of the results, TT wrote the paper and was the corresponding author.

Paper IV: TT participated in the study design, sampling, analysis and interpretation of the results, TT wrote the paper and was the corresponding author.

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