Occurrence of bacterial endosymbionts in Acanthamoeba spp. isolated from corneal and environmental specimens and contact lenses

Abstract

Free-living and parasitic protozoa are known to harbor a variety of endosymbiotic bacteria, although the roles such endosymbionts play in host survival, infectivity, and invasiveness are unclear. We have identified the presence of intracellular bacteria in 14 of 57 (24%) axenically grown Acanthamoeba isolates examined. These organisms are gram negative and non-acid fast, and they cannot be cultured by routine methodologies, although electron microscopy reveals evidence for multiplication within the amoebic cytoplasm. Examination for Legionella spp. with culture and nucleic acid probes has proven unsuccessful. We conclude that these bacteria are endosymbionts which have an obligate need to multiply within their amoebic hosts. Rod-shaped bacteria were identified in 5 of 23 clinical Acanthamoeba isolates (3 of 19 corneal isolates and 2 of 4 contact lens isolates), 4 of 25 environmental Acanthamoeba isolates, and 2 of 9 American Type Culture Collection Acanthamoeba isolates (ATCC 30868 and ATCC 30871) previously unrecognized as having endosymbionts. Coccus-shaped bacteria were present in one clinical (corneal) isolate and two environmental isolates. There was no statistical difference (P > 0.8) between the numbers of endosymbiont strains originating from clinical (26% positive) and environmental (24% positive) amoebic isolates, suggesting that the presence alone of these * Corresponding author.

Novel bacterial endosymbionts of Acanthamoeba spp. related to the Paramecium caudatum symbiont Caedibacter caryophilus

“…Acanthamoeba sp. UWC9 was isolated from a contact lens case (Fritsche et al, 1993); Acanthamoeba polyphaga HN-3 was isolated from a human nasal swab and was obtained from the American Type Culture Collection (ATCC 30173); and Acanthamoeba sp. UWE39 was recovered from a soil sample collected in Clearwater County, MN, USA.…”

“…In addition, we isolated and studied an environmental Acanthamoeba specimen (UWE39) bearing a morphologically similar endosymbiont. Previous attempts to culture these bacteria using different media and conditions have not been successful (Fritsche et al, 1993). Although cultivation failure does not necessarily exclude the existence of a free-living stage of these bacteria, we provisionally consider them as being obligate endosymbionts.…”

“…Such interactions might be of clinical relevance, especially as multiplication of Legionella pneumophila and Mycobacterium avium within the amoeba host cell increases bacterial virulence (Cirillo et al, 1994;Cirillo et al, 1997). In contrast to these transient interrelationships, which result in lysis of the infected amoebae, the presence of stably infecting, obligate bacterial endosymbionts has been reported for about 25% of all Acanthamoeba isolates (Fritsche et al, 1993). Using the rRNA approach, the relationship of some of these endosymbionts to the genera Rickettsia and Chlamydia has been demonstrated Fritsche et al, 1999;T.…”

“…In this study, we analysed two clinical Acanthamoeba spp. isolates (HN-3 and UWC9), which have been reported to contain Gram-negative, rod-shaped bacterial endosymbionts (Fritsche et al, 1993;Hall and Voelz, 1985). In addition, we isolated and studied an environmental Acanthamoeba specimen (UWE39) bearing a morphologically similar endosymbiont.…”

Members of the Cytophaga–Flavobacterium–Bacteroides phylum as intracellular bacteria of acanthamoebae: proposal of ‘Candidatus Amoebophilus asiaticus’

“…Several types of interactions between acanthamoebae and bacteria leading to transient, as well as long-term, associations have been reported (e.g. Fritsche et al, 1993;Barker and Brown, 1994). Besides being a food source for amoebae, some bacteria survive phagocytosis and are able to multiply as parasites within free-living amoebae.…”