Distribution and Current State of Molecular Genetic Characterization in Pathogenic Free-Living Amoebae

Abstract

Free-living amoebae (FLA) are protozoa widely distributed in the environment, found in a great diversity of terrestrial biomes. Some genera of FLA are linked to human infections. The genus Acanthamoeba is currently classified into 23 genotypes (T1-T23), and of these some (T1, T2, T4, T5, T10, T12, and T18) are known to be capable of causing granulomatous amoebic encephalitis (GAE) mainly in immunocompromised patients while other genotypes (T2, T3, T4, T5, T6, T10, T11, T12, and T15) cause Acanthamoeba keratitis mainly in otherwise healthy patients. Meanwhile, Naegleria fowleri is the causative agent of an acute infection called primary amoebic meningoencephalitis (PAM), while Balamuthia mandrillaris, like some Acanthamoeba genotypes, causes GAE, differing from the latter in the description of numerous cases in patients immunocompetent. Finally, other FLA related to the pathologies mentioned above have been reported; Sappinia sp. is responsible for one case of amoebic encephalitis; Vermamoeba vermiformis has been found in cases of ocular damage, and its extraordinary capacity as endocytobiont for microorganisms of public health importance such as Legionella pneumophila, Bacillus anthracis, and Pseudomonas aeruginosa, among others. This review addressed issues related to epidemiology, updating their geographic distribution and cases reported in recent years for pathogenic FLA.

Acanthamoeba Sequence Types and Allelic Variations in Isolates from Clinical and Different Environmental Sources in Italy

“…The first case of keratitis associated with this genotype was identified in Italy [ 11 ], thus enlarging the spectrum of Acanthamoeba sequence types capable of causing pathogenic effects in humans. Currently, the T15 genotype represents the third most involved genotype in keratitis cases after T4 and T3 [ 25 ] and has a notable worldwide environmental presence, as recently reviewed [ 26 ]. Remarkably, the majority of T15 Acanthamoeba isolates occurred in Italy in both clinical and environmental isolates from Apulia and shared the identical allele sequence T15/01.…”

Pathogenic free-living amoebic encephalitis from 48 cases in China: A systematic review

“…The genus Acanthamoeba is currently classified into 23 genotypes (T1–T23), and of these some are known to be capable of causing GAE mainly in immunocompromised patients while other genotypes cause Acanthamoeba keratitis (AK) mainly in otherwise healthy patients. There are partial genotypes known to cause both AK and GAE (T2, T4, T5, T10, and T12) ( 49 ). Whether ocular symptoms can be indicative of GAE is a question that needs to be further explored in future studies.…”

“…But B. mandrillaris is the only pathogenic species without genotypic classification. It has been reported the variable length of the rps3 type II intron (region of the mitochondrial genome) between the different strains of B. mandrillaris suggesting that it may be promising for the development of molecular genotyping ( 49 ). More B. mandrillaris from different geographical locations need to be sequenced for molecular genotyping.…”

Modelling dynamics between free‐living amoebae and bacteria

“…However, by modelling the within‐amoebae bacterial dynamics, they developed a hierarchical model, which necessitated some simplifying assumptions, for example, that only one bacterium is engulfed by each amoeba. Nevertheless, the model provides a framework for investigating transmission dynamics using realistic ambient temperature fluctuations affecting growth and encystment (Hundt & Ruffolo, 2005; Koshel' et al, 2015; Otero‐Ruiz et al, 2022).…”