Free-Living Amoebas (FLAs) in Sewage and Sludges: Their Role as a Natural Reservoir of Potentially Pathogenic Bacteria

Free-living amoebae (FLA) are ubiquitous protozoa, present in soils and in natural and artificial aquatic ecosystems. They take part in the purification processes that take place in Wastewater Treatment Plants (WWTPs), thereby turning these plants into ecological niches suitable for proliferation of FLAs, which they colonize and in which they establish their habitat, since they feed on bacteria present in the environment. Biological purification processes are not designed to remove microbiological contamination, although they help to reduce some microbial populations. At present only some genera and species of FLAs have been described as pathogenic, but all of them pose a risk as reservoirs of pathogenic bacteria. Their cystic stage gives them resistance to adverse conditions and common disinfectants, allowing them to withstand water purification processes and colonize artificial water systems. The presence of FLAs in waters and sludges from 5 WWTPs that discharge their waters into the Ebro river basin has been studied in this work. To this end, a total of 20 sample points were analysed by isolating the FLAs and subsequently identifying their genus and species. The same was done for endosymbiotic bacteria, by Polymerase Chain Reaction (PCR). Out of 41 FLAs that were isolated in 85 % of the samples, 21 were genetically identified. Thirteen belonged to the genus Acanthamoeba spp., 6 to Naegleria spp. and 2 were identified as Vermamoeba vermiformis. 53.66 % of FLAs hosted Mycobacterium spp., 29.27 % Legionella pneumophila, and 14.63 % Pseudomonas spp.