OCCURRENCE, ISOLATION, AND MORPHOLOGICAL CHARACTERIZATION OF FREE-LIVING AMOEBAE IN DIFFERENT DRINKING WATER SOURCES: IMPLICATIONS FOR PUBLIC HEALTH

Abstract

Free-living amoebae (FLA) are ubiquitous protozoan microorganisms widely distributed in natural and engineered aquatic environments, including surface water, groundwater, drinking water treatment plants, distribution systems, household plumbing, and storage reservoirs. Although many FLA are non-pathogenic, several genera, particularly Acanthamoeba, Naegleria, Balamuthia, and Sappinia, are recognized as opportunistic pathogens capable of causing severe human diseases, including Acanthamoeba keratitis, granulomatous amoebic encephalitis, and primary amoebic meningoencephalitis. Moreover, FLA act as environmental reservoirs and intracellular hosts for numerous amoeba-resistant microorganisms, enhancing the persistence, survival, and dissemination of clinically important bacterial pathogens in drinking water systems. This review comprehensively examines the occurrence, ecology, isolation, and morphological characterization of FLA in different drinking water sources, emphasizing their public health significance and current control strategies. Conventional culture-based techniques and microscopic examination remain valuable for preliminary detection; however, their limited taxonomic resolution necessitates integration with molecular approaches, including polymerase chain reaction (PCR), 18S rRNA gene sequencing, and phylogenetic analysis, to achieve accurate species identification and genotype characterization. The review also highlights the ecological role of FLA in biofilm formation and the "Trojan horse" phenomenon, whereby intracellular pathogens are protected from environmental stress and conventional disinfection.Current evidence indicates that FLA represent an emerging challenge for drinking water safety because their resistant cysts and biofilm-associated populations frequently survive conventional treatment processes. Therefore, effective risk management requires integrated surveillance, optimized treatment technologies, biofilm control, advanced molecular diagnostics, and public health awareness.  Continued multidisciplinary research and internationally standardized monitoring protocols are essential to improve drinking water quality and reduce the global health risks associated with free-living amoebae.