Importance of amoebae as a tool to isolate amoeba‐resisting microorganisms and for their ecology and evolution: the Chlamydia paradigm

Abstract

Free-living amoebae are distributed worldwide and are frequently in contact with humans and animals. As cysts, they can survive in very harsh conditions and resist biocides and most disinfection procedures. Several microorganisms, called amoeba-resisting microorganisms (ARMs), have evolved to survive and multiply within these protozoa. Among them are many important pathogens, such as Legionella and Mycobacteria, and also several newly discovered Chlamydia-related bacteria, such as Parachlamydia acanthamoebae, Estrella lausannensis, Simkania negevensis or Waddlia chondrophila whose pathogenic role towards human or animal is strongly suspected. Amoebae represent an evolutionary crib for their resistant microorganisms since they can exchange genetic material with other ARMs and develop virulence traits that will be further used to infect other professional phagocytes. Moreover, amoebae constitute an ideal tool to isolate strict intracellular microorganisms from complex microbiota, since they will feed on other fast-growing bacteria, such as coliforms potentially present in the investigated samples. The paradigm that ARMs are likely resistant to macrophages, another phagocytic cell, and that they are likely virulent towards humans and animals is only partially true. Indeed, we provide examples of the Chlamydiales order that challenge this assumption and suggest that the ability to multiply in protozoa does not strictly correlate with pathogenicity and that we should rather use the ability to replicate in multiple and diverse eukaryotic cells as an indirect marker of virulence towards mammals. Thus, cell-culture-based microbial culturomics should be used in the future to try to discover new pathogenic bacterial species.

The High Prevalence and Diversity of Chlamydiales DNA within Ixodes ricinus Ticks Suggest a Role for Ticks as Reservoirs and Vectors of Chlamydia-Related Bacteria

“…Even if the transmission from ticks to birds and mammals deserves to be investigated, ticks should be considered potential new vectors and reservoirs for Chlamydiales bacteria. By using tick cell lines and other innovative culture methods (19), further work should be begun to isolate new species from tick samples, as has already been done to isolate Anaplasma and Rickettsia species (38)(39)(40)(41). Moreover, since huge quantities of Chlamydiales DNA have been obtained from some ticks, it should be a unique opportunity to obtain genomic data for some still-uncultivable Chlamydiales, including new family-level lineages, and in this way increase our knowledge of Chlamydiales biology, diversity, and ecology.…”

“…This peculiar ability of most Chlamydia-related bacteria to grow within protozoa has been used to successfully isolate novel Chlamydiae by using amoebae in an innovative cell culture system called amoebal coculture (18,19).…”

Relationships between Free-Living Amoeba and their Intracellular Bacteria

“…Therefore, FLA may be viewed as a "biological gym" where bacterial pathogens are continuously trained to Cavalier-Smith, 2004;Adl et al, 2005; be more resistant on impact with more developed host cells. Since ARB can exchange genetic material with other intracellular bacteria and develop virulence traits, FLA are used as an evolutionary crib, which explains their adaptation for survival within macrophages (Harb et al, 2000;Huws et al, 2008;Kebbi-Beghdadi and Greub, 2014). A selective agent that determines features that are relevant for bacterial survival and evolution is predation (Matz and Kjelleberg, 2005).…”

“…Intracellular bacteria called also amoeba-resisting bacteria (ARB), use the amoeba as a "training ground" for resistance to destruction by macrophages (Greub and Raoul, 2004;Thomas et al, 2006). An effective tool to detect ARB is co-culture with amoeba (Kebbi-Beghdadi and Greub, 2014). Mostly water (cooling towers, hospital water supplies, rivers, lakes, domestic water supplies and others) and soil have been investigated as possible reservoirs of ARB using the co-culture method described by Pagnier et al, 2008.…”

Chlamydiales Bacterial Sequences in Lesional and Healthy Skin of Patients with Parapsoriasis

“…Chlamydia-related bacteria represent a diverse group of bacteria within the order Chlamydiales that have been detected ubiquitously in various environmental samples, such as soil and water, in animals, and also in humans (1)(2)(3)(4)(5)(6). We recently demonstrated the presence of Chlamydiales DNA in human skin (7).…”