Saline-Tolerant Pathogenic Acanthamoeba spp. Isolated from a Geothermal Power Plant

Abstract

Few studies have been conducted in the cooling systems of power plants; they have focused on Naegleria fowleri, leaving a gap in the knowledge of other pathogenic free-living amoebae in this environment. The objective of this study was to determine the occurrence of saline-tolerant pathogenic Acanthamoeba in a geothermal power plant. The identification of isolated amoebae at genus level was carried out, observing their morphological characteristics; the determination of genotype and species of Acanthamoeba was performed via molecular biology (PCR). Water temperature ranged from 18 to 43 °C and conductivity from 4.0 × 10⁴ to 8.7 × 10⁴ μS/cm; this last value was greater than the seawater value. Only five amoeba genera were found. Acanthamoeba was in all the sampling sites, showing high saline tolerance. The high temperature, but mainly high conductivity, were the environmental conditions that determined the presence of pathogenic free-living amoebae in the hot water. All the strains of Acanthamoeba culbertsoni killed the mice, having a mortality of 40 to 100%. Acanthamoeba genotypes T10 and T5 were identified, T10 is rarely isolated from the environment, while T5 is more frequent. This is the first time that genotypes T5 and T10 have been reported in the environment in Mexico.

Keywords: conductivity; cooling system; hot water; pathogenic free-living amoebae; salinity.

Figure 1

Localization of Cerro Prieto Geothermal Power Plant, Baja California, Mexico.

Figure 2

Sampling sites at Cerro Prieto Geothermal Power Plant. Yellow boxes, sampling sites; blue lines, water channels; CPI, CPII, CPIII, and CPIV production units.

Figure 3

Micrographs of Acanthamoeba isolates. A. lenticulata: (a) cyst, (b) trophozoite. A. culbertsoni: (c) cyst, (d) trophozoite. Bar: 10 µm. Phase-contrast microscopy.

Figure 4

Macroscopic aspects of damage caused by Acanthamoeba culbertsoni infection in mouse brain and lung. (A) Observations were made of the inflammatory process of the brain, the loss of integrity of the central sulcus (orange arrow), and areas with the beginnings of hemorrhagic processes (blue arrows) in a dying mouse brain euthanized 4 days after infection. (B) Mouse brain dead 5 days after infection showed hyperemic meninges (red arrows) that stand out in dorsal view oriented from the central sulcus of the brain and towards the posterior region of the cerebellum. (C) Mouse brain recovered 2 to 4 h after mouse death. Observations were made that the integrity of the brain has been totally lost, the bleeding areas and edema are very evident (blue arrows). (D) Mouse lung dead 12 days after infection; there was abundant hyperemic zone in the anterior lobe; the hemorrhage extended to the central area and in the periphery, and presence of small continuous granules was observed (green arrow). (E) Rounded trophozoites of amoebas (yellow arrows) immersed in brain tissue observed in brain imprinting from a dead mouse. Optical microscope at 40×. (F) Amoeba trophozoites (purple arrows) coming out of the brain of a dead mouse (pink arrow) inoculated on NNA, after 24 h of culture at 37 °C. 10× inverted microscope.