OCCURRENCE OF BACTERIAL ENDOSYMBIONTS IN ACANTHAMOEBA SPP ISOLATED FROM CORNEAL AND ENVIRONMENTAL SPECIMENS AND CONTACT-LENSES

Free-living and parasitic protozoa are known to harbor a variety of en dosymbiotic bacteria, although the roles such endosymbionts play in ho st survival, infectivity, and invasiveness are unclear. We have identi fied the presence of intracellular bacteria in 14 of 57 (24%) axenical ly grown Acanthamoeba isolates examined. These organisms are gram nega tive and non-acid fast, and they cannot be cultured by routine methodo logies, although electron microscopy reveals evidence for multiplicati on within the amoebic cytoplasm. Examination for Legionella spp. with culture and nucleic acid probes has proven unsuccessful. We conclude t hat these bacteria are endosymbionts which have an obligate need to mu ltiply within their amoebic hosts. Rod-shaped bacteria were identified in 5 of 23 clinical Acanthamoeba isolates (3 of 19 corneal isolates a nd 2 of 4 contact lens isolates), 4 of 25 environmental Acanthamoeba i solates, and 2 of 9 American Type Culture Collection Acanthamoeba isol ates (ATCC 30868 and ATCC 30871) previously unrecognized as having end osymbionts. Coccus-shaped bacteria were present in one clinical (corne al) isolate and two environmental isolates. There was no statistical d ifference (P > 0.8) between the numbers of endosymbiont strains origin ating from clinical (26% positive) and environmental (24% positive) am oebic isolates, suggesting that the presence alone of these bacteria d oes not enhance amoebic infectivity. Rods and cocci were found in both clinical and environmental isolates from different geographical areas (Seattle, Wash., and Portland, Oreg.), demonstrating their widespread occurrence in nature. Our findings suggest that endosymbiosis occurs commonly among members of the family Acanthamoebidae and that the endo symbionts comprise a diverse taxonomic assemblage. The role such endos ymbionts may play in pathogenesis remains unknown, although a variety of exogenous bacteria have been implicated in the development of amoeb ic keratitis, warranting further evaluation.