Tolerance of Naked Amoebae to Low Oxygen Levels with an Emphasis on the Genus Acanthamoeba

Amoebae feed on attached bacteria within, and below, bacterial biofilms where they experience reduced oxygen levels. The implications of this were examined by comparing the migration (an index of growth) of thirteen strains of Acanthamoeba and five species of naked amoebae grown under microaerophilic and aerobic conditions. All amoebae replicated well under both conditions and twelve isolates migrated significantly faster under low oxygen. Only one isolate, Vannella sp., migrated further (presumably grew faster) under aerobic conditions. The data show most amoebae prefer low oxygen as befits the biofilm habitat. Interestingly, the eleven acanthamoeba strains that replicated faster under microaerophilic conditions were all T4 genotypes and included four strains isolated from patients with amoeba keratitis (AK) infections. This genotype is most frequently found in AK cases and it is suggested that strains of Acanthamoeba capable rapid growth in a biofilm of a poorly cleansed contact lens may be an important factor in the development of an effective infective dose when placed on the cornea.