Nontuberculous Mycobacteria as Sapronoses: A Review

Abstract

Mycobacteria are a unique group of microorganisms. They are characterised by exceptional adaptability and durability. They are capable of colonisation and survival even in very unfavourable conditions. In addition to the well-known obligate human pathogens, Mycobacterium tuberculosis and M. leprae, more than 200 other species have been described. Most of them form a natural part of the microflora of the external environment and thrive in aquatic and soil environments especially. For many of the mycobacterial species associated with human disease, their natural source has not yet been identified. From an ecological point of view, mycobacteria are saprophytes, and their application in human and animal diseases is opportunistic. Most cases of human disease from saprophytic mycobacteria occur in immunocompromised individuals. This adaptability and resilience to environmental pressures makes treatment of mycobacterial diseases (most often sapronoses and less often zoonoses) and permanent eradication of mycobacteria from the environment very difficult. Saprophytic mycobacterial diseases (sapronoses) are chronic and recurrent due to the fact of repeated endogenous or exogenous re-exposure. Therefore, knowledge regarding their occurrence in soil and dust would aid in the prevention of saprophytic mycobacterioses. In conjunction, their presence and ecological significance in the environment can be revealed.

Keywords: PICA practices; antidiarrheal; earth-eating; environmental saprophytic mycobacteria; feeding and eating disorders; geochemistry; geophagia; mud; potentially pathogenic mycobacteria; saprophytic mycobacteria; saprozoic mycobacteria; soil consumption; soil exposure; trace elements deficiency.

Figure 1

Dust in spiders’ nests (left) is often contaminated by mycobacteria (right); after the fluorescent staining of the dust sample (magnified 1000 times) yellow-coloured, rod-shaped mycobacterial cells were observed in this microscopic field of view. This sample was culture-positive for M. triviale.

Figure 2

Soil (left) is often contaminated by mycobacteria; after Ziehl–Neelsen staining of the soil sample (magnified 1000 times) numerous acid-resistant, red-coloured polymorphic acid-fast rod-shaped mycobacterial cells were observed in this microscopic field of view (right). This sample was culture-positive for M. terrae and M. avium ssp. hominissuis.

Figure 3

Kaolin extraction by surface mining (left) and direct microscopy after the Ziehl–Neelsen staining of the kaolin used as feed supplement (right; magnified 800 times). This sample was culture-positive for M. avium ssp. hominissuis (Photo I. Pavlik and V. Beran).

Figure 4

Tuberculous lesions in the mesenteric lymph (left) and head (right) nodes of domestic pig (Sus scrofa f. domestica) caused by M. avium ssp. hominissuis from peat used as feed supplements (Photo I. Pavlik).