Biology of M. paratuberculosis

Relationship to other mycobacteria, taxonomy and nomenclature

M. paratuberculosis is virtually identical to Mycobacterium avium genetically. Phenotypic characteristics of M. paratuberculosis are, however, different from those of M. avium: M. paratuberculosis grows slower, requires addition of an iron-transport chemical known as mycobactin for in vitro growth, forms a rough colonies when grown on solid agar media, and infects mammals instead of birds. Consequently, there is debate about what the most appropriate taxonomic classification and proper name for M. paratuberculosis should be. A popular opinion is that M. paratuberculosis should be reclassified as a subspecies of M. avium and thus renamed M. avium subspecies paratuberculosis (abbreviated M. avium ss paratuberculosis). This subspecies designation appears in many recent publications concerning the organism. For simplicity, the name M. paratuberculosis is used throughout this web site. Similarities and differences between M. paratuberculosis and M. avium will be discussed throughout this section on the biology of M. paratuberculosis.

M. paratuberculosis is not as closely genetically related to pathogenic mycobacteria in the TB complex: Mycobacterium tuberculosis, the cause of tuberculosis in humans, and Mycobacterium bovis, the cause of tuberculosis in cattle and other animals. M. paratuberculosis also is not closely related to the cause of leprosy in humans, Mycobacterium leprae. The organism, M. paratuberculosis, and the disease, Johne's disease do share certain characteristics in common with these other mycobacterial pathogens. Scientists often draw parallels between these organisms to try and understand basic mechanisms of how they cause disease.

Top of Page
Back to FYI Home Page

Environmental distribution

M. paratuberculosis bacteria are not thought to be free living in the environment. Because of its unique inability to produce mycobactin, M. paratuberculosis can only grow inside animal cells, most often macrophages. Thus, it is an obligate parasite of mammals meaning infected animals are the only place in nature where growth and multiplication of M. paratuberculosis can occur. If found in soil or water samples, it can be assumed that M. paratuberculosis is simply persisting in those places (not multiplying) after being deposited there through fecal contamination from an infected animal.

Environmental distribution of M. paratuberculosis is markedly different from that of M. avium which can produce mycobactin and thereby acquire iron, essential for growth and survival, from the environment. Mycobactin production allows M. avium to grow and multiply outside a host animal. M. avium is found commonly in lakes, streams and even domestic water supplies. Certain soil types, notably peat bogs, appear to have higher than average numbers of M. avium. A tenuous association between the occurrence of Johne's disease and geographical regions with acidic soils has been reported. The strength of this association and the biological basis of this association remain to be determined.

Top of Page
Back to FYI Home Page

Host range

M. paratuberculosis has a broad host range. Ruminants are the type of animal most commonly infected. These include: cattle, sheep, goats, deer, elk, antelope, camels, llamas, and alpacas. There are also sporadic reports of M. paratuberculosis infections in horses, pigs, chickens, nonhuman primates and people with Crohn's disease.

Top of Page
Back to FYI Home Page

Virulence factors

Like other mycobacteria, M. paratuberculosis has the capacity to thrive inside white blood cells known as macrophages. Macrophages are capable of destroying a wide variety of bacterial pathogens. Mycobacteria, however, are one of the few types of bacteria that not only can survive the anti-bacterial effects of macrophages, but can grow and multiply inside these cells. Bacteria capable of growing inside macrophages and causing disease are referred to as facultative intracellular bacterial pathogens.

Considerable research has been done to try and understand how mycobacteria thrive in what is thought to be a very hostile intracellular environment of macrophages. However, no specific mechanisms have been found to adequately explain this mycobacterial characteristic. In general terms, two properties of mycobacteria explain their resistance to killing by macrophages: 1) the chemically unique mycobacterial cell wall that is resistant to destruction or penetration, and 2) factors produced by mycobacteria that can neutralize the anti-bacterial chemicals produced inside macrophages. For detailed information the reader should obtain the references listed at the end of this section on the biology of M. paratuberculosis.

Survival and multiplication in the host animal is a prerequisite to causing disease. As with mechanisms of intracellular survival, mechanisms by which mycobacteria cause disease are also not well understood. Pathology due to mycobacterial infections results in part from the direct action of toxic chemical components of the cell wall of these bacteria. However, the host animal's response to the presence of M. paratuberculosis also contributes to the pathology and organ dysfunction resulting from the infection.

Top of Page
Back to FYI Home Page

Resistance to physical factors (heat, etc)

M. paratuberculosis bacterial cells, like other mycobacteria, are more resistant to the effects of heat, cold, sunlight, drying etc. than are most common bacteria. Research suggests that M. paratuberculosis may be more resistant to these physical factors than other mycobacteria. In ponds, streams, and lakes M. paratuberculosis may survive as long as a year, depending on water chemistry. In feces or fecal contaminated soil M. paratuberculosis may also survive a year or longer. Survival of M. paratuberculosis in urine is relatively short: roughly 7 days.

Thermal tolerance of M. paratuberculosis, specifically the capacity to survive pasteurization, is the subject of considerable concern. Two published reports indicate M. paratuberculosis can survive pasteurization. Thermal tolerance curves indicate that M. paratuberculosis is comparable in heat resistance to M. avium and far more heat resistant than Listeria, another facultative intracellular bacteria found in raw milk. Thermal tolerance studies in the author's laboratory support the conclusions of published reports that M. paratuberculosis, if present in sufficient numbers in raw milk, could survive high temperature short time (HTST) pasteurization. M. paratuberculosis survives freezing for over a year.

M. paratuberculosis survives less well in acidic solutions (pH less than 6) than at a neutral pH, 7.0. The organism also is killed faster in salt-containing solutions than in water free of salt. Acidification and addition of salt are two things used to kill bacterial pathogens like Listeria that potentially contaminate milk used to make cheese.

Top of Page
Back to FYI Home Page

Resistance to chemical factors: antibiotics and disinfectants

Mycobacteria are notorious for their resistance to antibiotics that kill most other bacteria. Only a select few antibiotics can be used to treat mycobacterial infections. M. paratuberculosis, like its close relative M. avium, is even resistant to antibiotics that normally are efficacious against M. tuberculosis, the cause of tuberculosis. Antimicrobial therapy for Johne's disease is not often attempted, the cost of the drugs and the duration of treatment required make it cost-prohibitive for livestock.

M. paratuberculosis, like other mycobacteria, are resistant to common disinfectants. However, phenolic and cresylic disinfectants are effective. Commercial disinfectant products that have the label claim of being tuberculocidal should generally be effective against M. paratuberculosis. Research in this area was done in the 1950s and there is little current information to substantiate these observations or make more specific recommendations regarding products, concentrations or required contact times. One-Stroke is a product commonly used by veterinarians that is effective at killing M. paratuberculosis.

Top of Page
Back to FYI Home Page

Colonial morphology

The size, color, and texture of a colony of M. paratuberculosis is dependent in part on the type of bacteriologic medium on which it is cultivated. On Herrold's egg yolk agar medium, one of the most commonly used culture mediums in veterinary diagnostic laboratories, the colonies appear small, somewhat rough and off-white to yellow in color. On Middlebrook agar medium without Tween 80 the colonies are very rough in appearance and resemble those of M. tuberculosis. With addition of Tween 80 the growth of M. paratuberculosis changes to a smooth colony form resembling that of M. avium.

Top of Page
Back to FYI Home Page

Cellular morphology

M. paratuberculosis is a small (0.5 x 1.5 micron) rod-shaped bacterium, roughly the size of the common intestinal bacterium called E. coli, that grows in clumps. It can be seen using a light microscope with 40x or greater power objectives. When stained by the Gram stain, it is blue and so called Gram-positive. When stained by acid-fast stains like the Ziel-Neelsen or Kinyoun's stain, M. paratuberculosis stains red and so is called acid-fast positive. Scanning electron microscopy reveals the rough cell wall of M. paratuberculosis. Transmission electron microscopy also shows the rough nature of the waxy cell wall plus the trilaminar structure of the cell wall and intracellular vacuoles or inclusions common to mycobacteria.

Top of Page
Back to FYI Home Page

Biochemical characteristics

Biochemical tests used to distinguish among other species of mycobacteria are not used to identify M. paratuberculosis. The tests are difficult to perform due to the extremely slow growth rate of the organism, and test results are vary among strains of M. paratuberculosis. Thorel, however, successfully used biochemical tests and numerical taxonomy methods to differentiate among subtypes of M. paratuberculosis-like bacteria.

Top of Page
Back to FYI Home Page

Cell wall chemistry

The cell wall of mycobacteria is composed of a thick waxy mixture of unique lipids and polysaccharides. The cell wall of M. paratuberculosis, although not well studied, seems similar in most respects to that of other mycobacteria. One feature is notable, however. While most strains of M. avium produce a surface glycolipid that allows strains to be serotyped (distinguished using antibodies specific for each glycolipid subtype), M. paratuberculosis strains lack such glycolipid antigens on their surface.

Top of Page
Back to FYI Home Page

Molecular genetics

The DNA of M. paratuberculosis is >99% identical with that of M. avium: the reason that many characteristics of the two bacteria are similar. The genetic feature of M. paratuberculosis that distinguishes it from M. avium is the presence of multiple copies of a short DNA element called an insertion sequence (IS). Insertion sequences of various types have been reported in mycobacteria. The first to be discovered was the one unique to M. paratuberculosis and named IS900. Genetic probes used for detection of M. paratuberculosis in clinical specimens or identification of M. paratuberculosis in cultures are based on detection of IS900.

A second insertion sequence, named IS901, that is approximately 60% similar in DNA sequence to IS900, was recently found in some strains of M. avium. How these insertion elements affect the biology and pathogenic capacity of M. paratuberculosis or M. avium is not understood. Evidence suggests, however, that they play a major role.

Top of Page
Back to FYI Home Page

Selected references

  1. Adúriz, J.J., R. A. Juste, and N. Cortabarria. 1995. Lack of mycobactin dependence of mycobacteria isolated on Middlebrook 7H11 from clinical cases of ovine paratuberculosis. Vet.Microbiol. 45:211-217.

  2. Camphausen, R.T., R. L. Jones, and P. J. Brennan. 1988. Antigenic relationship between Mycobacterium paratuberculosis and Mycobacterium avium. Am.J.Vet.Res. 49:1307-1310.

  3. Chiodini, R.J. 1986. Biochemical characteristics of various strains of Mycobacterium paratuberculosis. Am.J.Vet.Res. 47:1442-1445.

  4. Chiodini, R.J. 1990. Characterization of Mycobacterium paratuberculosis and organisms of the Mycobacterium avium complex by restriction polymorphism of the rRNA gene region. J.Clin.Microbiol. 28:489-494.

  5. Chiodini, R.J. and J. Hermon-Taylor. 1993. The thermal resistance of Mycobacterium paratuberculosis in raw milk under conditions simulating pasteurization. J.Vet.Diagn.Invest. 5:629-631.

  6. Collins, D.M. and G. W. de Lisle. 1986. Restriction endonuclease analysis of various strains of Mycobacterium paratuberculosis isolated from cattle. Am.J.Vet.Res. 47:2226-2229.

  7. Collins, D.M., D. M. Gabric, and G. W. de Lisle. 1989. Identification of a repetitive DNA sequence specific to Mycobacterium paratuberculosis. FEMS Microbiol Lett 60:175-178.

  8. Collins, D.M., D. M. Gabric, and G. W. de Lisle. 1990. Identification of two groups of Mycobacterium paratuberculosis strains by restriction endonuclease analysis and DNA hybridization. J.Clin.Microbiol. 28:1591-1596.

  9. Collins, M.T., S. E. Glickman, and J. O. Kilburn. 1995. Identification of Mycobacterium paratuberculosis by high pressure liquid chromatography analysis of mycolic acid extracts, p.292-(Abstract). In R.J. Chiodini, M.T. Collins, and E.O.E. Bassey (ed.), Proceedings of the Fourth International Colloquium on Paratuberculosis, International Association for Paratuberculosis, Rehoboth, MA.

  10. Collins, M.T., N. Hřiby, J. B. Jorgensen, H. Bercovier, R. S. Lambrecht, and E. Jorgensen. 1991. Crossed immunoelectrophoretic analysis of Mycobacterium paratuberculosis. APMIS 99:83-92.

  11. Foley-Thomas, E.M., D. L. Whipple, L. E. Bermudez, and R. G. Barletta. 1995. Phage infection, transfection and transformation of Mycobacterium avium complex and Mycobacterium paratuberculosis. Microbiol. 141:1173-1181.

  12. Garin-Bastuiji, B., B. Perrin, M. F. Thorel, and J. L. Martel. 1990. Evaluation of ç-ray irradiation of cows' colostrum for Brucella abortus, Escherichia coli K99, Salmonella dublin and Mycobacterium paratuberculosis decontamination. Letters Appl.Microbiol. 11:163-166.

  13. Grant, I.R., H. J. Ball, S. D. Neill, and M. T. Rowe. 1996. Inactivation of Mycobacterium paratuberculosis in cows' milk at pasteurization temperatures. Appl.Env.Microbiol. 62:631-636.

  14. Green, E.P., M. L. V. Tizzard, M. T. Moss, J. Thompson, J. J. Winterbourne, J. J. McFadden, and J. Hermon-Taylor. 1989. Sequence and characteristics of IS900, and insertion element identified in a human Crohn's disease isolate of M. paratuberculosis. Nucleic Acids Res. 17:9063-9072.

  15. Hines II, M.E., J. M. Jaynes, S. A. Barker, J. C. Newton, F. M. Enright, and T. G. Snider III. 1993. Isolation and partial characterization of glycolipid fractions from Mycobacterium avium serovar 2 (Mycobacterium paratuberculosis 18) that inhibit activated macrophages. Infect.Immun. 61:1-7.

  16. Hurley, S.S., G. A. Splitter, and R. A. Welch. 1988. Deoxyribonucleic acid relatedness of Mycobacterium paratuberculosis to other members of the family Mycobacteriaceae. Int.J.Syst.Bacteriol. 38:143-146.

  17. Kopecky, K.E. 1977. Distribution of paratuberculosis in Wisconsin, by soil regions. J.Am.Vet.Med.Assoc. 170:320-324.

  18. Kunze, Z.M., F. Portaels, and J. J. McFadden. 1992. Biologically distinct subtypes of Mycobacterium avium differ in possession of insertion sequence IS901. J.Clin.Microbiol. 30:2366-2372.

  19. Lambrecht, R.S. and M. T. Collins. 1992. Mycobacterium paratuberculosis: Factors which influence mycobactin-dependence. Diagn.Microbiol.Infect.Dis. 15:239-246.

  20. Larsen, A.B., R. S. Merkal, and T. H. Vardaman. 1956. Survival time of Mycobacterium paratuberculosis. Am.J.Vet.Res. July:549-551.

  21. McIntyre, G. and J. L Stanford. 1986. Immunodiffusion analysis shows that Mycobacterium paratuberculosis and other mycobactin-dependent mycobacteria are variants of Mycobacterium avium. J.Appl.Bacteriol. 61:295-298.

  22. Moss, M.T., E. P. Green, M. L. Tizard, Z. P. Malik, and J. Hermon-Taylor. 1991. Specific detection of Mycobacterium paratuberculosis by DNA hybridisation with a fragment of the insertion element IS900. Gut 32:395-398.

  23. Pavlík, I., L. Bejcková, M. Pavlas, Z. Rozsypalová, and S. Kosková. 1995. Characterization by restriction endonuclease analysis and DNA hybridization using IS900 of bovine, ovine, caprine and human dependent strains of Mycobacterium paratuberculosis isolated in various localities. Vet.Microbiol. 45:311-318.

  24. Rankin, J.D. 1953. Isoniazid: its effects on Mycobacterium paratuberculosis in vitro and its failure to cure Johne's disease in cattle. Vet.Rec. 65:649-651.

  25. Rastogi, N., K. S. Goh, and V. Labrousse. 1992. Activity of clarithromycin compared with those of other drugs against Mycobacterium paratuberculosis and further enhancement of its extracelullar and intracellular activities by ethambutol. Antimicrob.Agents Chemother. 36:2843-2846.

  26. Saxegaard, F. and I. Baess. 1988. Relationship between Mycobacterium avium, Mycobacterium paratuberculosis and "wood pigeon mycobacteria". Determinations by DNA-DNA hybridization. APMIS 96:37-42.

  27. St-Jean, G. and A. D. Jernigan. 1991. Treatment of Mycobacterium paratuberculosis infection in ruminant8-js. Vet.Clin.North Am.Food Anim.Pract. 7:793-804.

  28. Thorel, M.-F., M. Krichevsky, and V. V. Levy-Frebault. 1990. Numerical taxonomy of mycobactin-dependent mycobacteria, emended description of Mycobacterium avium, and description of Mycobacterium avium subsp. avium subsp. nov., Mycobacterium avium subsp. paratuberculosis subsp. nov., and Mycobacterium avium subsp. silvaticum subsp. nov. Int.J.Syst.Bacteriol. 40:254-260.

  29. Thorel, M.F., M. -C. Blom-Potar, and N. Rastogi. 1990. Characterization of Mycobacterium paratuberculosis and "wood-pigeon" mycobacteria by isoenzyme profile and selective staining of immunoprecipitates. Res.Microbiol. 141:551-561.

  30. Thoresen, O.F. and I. Olsaker. 1994. Distribution and hybridization patterns of the insertion element IS900 in clinical isolates of Mycobacterium paratuberculosis. Vet.Microbiol. 40:293-303.

  31. Thoresen, O.F. and F. Saxegaard. 1991. Gen-Probe rapid diagnostic system for the Mycoabcterium avium complex does not distinguish between Mycobacterium avium and Mycobacterium paratuberculosis. J.Clin.Microbiol. 29:625-626.

  32. Tizard, M.L.V., M. T. Moss, J. D. Sanderson, B. M. Austen, and J. Hermon-Taylor. 1992. p43, the protein product of the atypical insertion sequence IS900, is expressed in Mycobacterium paratuberculosis. J.Gen.Microbiol. 138:1729-1736.

  33. Van Boxtel, R.M., R. S. Lambrecht, and M. T. Collins. 1990. Effect of polyoxyethylene sorbate compounds (Tweens) on colonial morphology, growth rate, and ultrastructure of Mycobacterium paratuberculosis. APMIS 98:901-908.

  34. Van Boxtel, R.M., R. S. Lambrecht, and M. T. Collins. 1990. Effects of colonial morphology and Tween 80 on antimicrobial susceptibility of Mycobacterium paratuberculosis. Antimicrob.Agents Chemother. 34:2300-2303.

  35. van der Giessen, J.W.B., A. Eger, J. Haagsma, R. M. Haring, W. Gaastra, and B. A. M. van der Zeijst. 1992. Amplification of 16S rRNA sequences to detect Mycobacterium paratuberculosis. J.Med.Microbiol. 36:255-263.

  36. van der Giessen, J.W.B., R. M. Harring, and B. A. M. van der Zeijst. 1994. Comparison of the 23S ribosomal RNA genes and the spacer region between 16S and 23S rRNA genes of the closely related Mycobacterium avium and Mycobacterium paratuberculosis and the fast-growing Mycobacterium phlei. Microbiol. 140:1103-1108.

  37. Whipple, D., P. Kapke, and C. Vary. 1990. Identification of restriction fragment length polymorphisms in DNA from Mycobacterium paratuberculosis. J.Clin.Microbiol. 28:2561-2564.

  38. White, W.B., D. L. Whipple, J. R. Stabel, and C. A. Bolin. 1994. Comparison of cellular and extracellular proteins expressed by various isolates of Mycobacterium paratuberculosis and other mycobacterial species. Am.J.Vet.Res. 55:1399-1405.

  39. Zurbrick, B.C. and C. J. Czuprynski. 1987. Ingestion and intracellular growth of Mycobacterium paratuberculosis within bovine monocytes and monocyte-derived macrophages. Infect.Immun. 55:1588-1593.

Top of Page
Back to FYI Home Page





Last revised February 19, 1997.
URL is http://www.vetmed.wisc.edu/pbs/johnes/biology.html.html.
Web Designer can be contacted at mcdonal7@facstaff.wisc.edu
All material Copyright © 1996 by the Board of Regents of the University of Wisconsin System. School of Veterinary Medicine, all rights reserved. If you have questions or comments about this page email us at: mcollin5@facstaff.wisc.edu