Detection of Bacterial Endosymbionts in Clinical Acanthamoeba Isolates

Purpose To determine the presence of 4 clinically relevant bacterial endosymbionts in Acanthamoeba isolates obtained from patients with Acanthamoeba keratitis (AK) and the possible contribution of endosymbionts to the pathogenesis of AK. Design Experimental study. Participants Acanthamoeba isolates (N = 37) recovered from the cornea and contact lens paraphernalia of 23 patients with culture-proven AK and 1 environmental isolate. Methods Acanthamoeba isolates were evaluated for the presence of microbial endosymbionts belonging to the bacterial genera Legionella , Pseudomonas , Mycobacterium , and Chlamydia using molecular techniques (polymerase chain reaction and sequence analysis, fluorescence in situ hybridization) and transmission electron microscopy. Corneal toxicity and virulence of Acanthamoeba isolates with and without endosymbionts were compared using a cytopathic effect (CPE) assay on human corneal epithelial cells in vitro. Initial visual acuity, location and characteristics of the infiltrate, time to detection of the infection, and symptom duration at presentation were evaluated in all patients. Main Outcome Measures Prevalence and potential pathobiology of bacterial endosymbionts detected in Acanthamoeba isolates recovered from AK. Results Twenty-two (59.4%) of the 38 cultures examined contained at least 1 bacterial endosymbiont. One isolate contained 2 endosymbionts, Legionella and Chlamydia , confirmed by fluorescence in situ hybridization. Corneal toxicity (CPE) was significantly higher for Acanthamoeba -hosting endosymbionts compared with isolates without endosymbionts ( P