**11.** *Acanthamoeba* **spp. and coinfections**

*Acanthamoeba* spp., a protozoon, is a free-living amoeba that can live in diverse environments. It has been isolated from soil, water for domestic use, salt or freshwater sewage, estuaries, hot springs, and swimming pools, among others, which highlight the microorganism's ability to live in extreme heat and pH conditions. Schuster and Visvesvara described *Acanthamoeba* spp. producing keratitis as non-opportunistic and thus occur in immunocompetent humans [28]. Galarza *et. al*., described this amoeba as *amphizoic* due to its ability to live in the environment and parasitize humans [29].

The life cycle of *Acanthamoeba* spp. includes two stages: the cyst, a form of resistance to adverse environmental conditions, and the trophozoite, the amoeboid free-living stage. Due to the organism's phagocytic condition, *Acanthamoeba* spp. can feed of bacteria, algae, yeast, fungi, etc [30]; but some of these microorganisms have developed mechanisms to avoid intracellular death and take advantage of the amoeba (endosymbiosis). These circumstances make *Acanthamoeba* spp. a vector of almost any type of microorganism; Barket *et. al*., in studies of the host-parasite relationship, called it a "Trojan horse" [31, 32].
