Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2024

Increasing incidence of Acanthamoeba keratitis at a referral eye hospital in Sydney, Australia (#81)

Binod Rayamajhee 1 , Mark Willcox 1 , Fiona L. Henriquenz 2 , Constantinos Petsoglou 3 4 , Amberin Fazal 3 , Hong Chiong 3 , Alexander Chorny 3 , Nicole Carnt 1
  1. School of Optometry and Vision Science , UNSW, Kingsford , New South Wales, Australia
  2. Institute of Biomedical and Environmental Health Research, School of Health and Life Sciences, University of the West of Scotland (UWS), Paisley, Scotland , U.K.
  3. Southeastern Sydney Local Health District, Sydney and Sydney Eye Hospital, Sydney, NSW, Australia
  4. Save Sight Institute, University of Sydney, Sydney, NSW, Australia

Acanthamoeba keratitis (AK) is an increasingly important sight-threatening corneal infection, particularly prevalent among contact lens (CLs) wearers. Approximately 30% of AK patients require surgical interventions due to challenges in early diagnosis and resistance to anti-protozoal treatments. Acanthamoeba spp. have been reported in domestic tap and recreational coastal waters in the greater Sydney area [1, 2]. This study aimed to determine prevalence of AK, evaluate circulating genotypes, and investigate the role of intracellular bacteria harboured by Acanthamoeba in keratitis development using an animal model.

A prospective case series study was conducted at Sydney Eye Hospital between June 2021 and October 2022. Corneal swabs were collected from AK patients and participant’s self-collected domestic tap water samples were assessed to trace the source of infection. Microscopy, PCR, and Sanger sequencing of the amoebal 18S rRNA were performed to confirm the presence of Acanthamoeba in corneal and water samples. Axenic cultures of Acanthamoeba isolates were assessed for intracellular bacteria using 16S rRNA sequencing, fluorescent in situ hybridization, and electron microscopy.

A total of 21 AK patients were recruited in this cohort (mean age 41±12.3 years), and 43% sent their domestic tap water for culture of Acanthamoeba. Among 57% of cases wearing CLs, 38% had a history of water exposure while wearing CLs. Six corneal and four water samples tested positive for Acanthamoeba in culture. All 10 isolates were of genotype T4, with five subclusters belonging to the T4B, T4D, T4F, T4G, and T4H. Among the 10 isolates, one corneal and one water isolate harboured intracellular bacteria, with the water isolate containing Pseudomonas aeruginosa. Intracellular P. aeruginosa was viable and able to replicate in human-macrophage to a greater degree than strain PAO1 (p<0.05). Intra-stromal inoculation of Acanthamoeba containing the intracellular P. aeruginosa in rats’ eyes resulted in a severe keratitis with increased neutrophil response, whereas Acanthamoeba alone induced milder keratitis.

In Sydney, the prevalent Acanthamoeba genotype among AK patients and domestic tap water was T4. This study indicates a higher annual AK incidence than previously reported. Our findings suggest the presence of live intracellular bacteria in Acanthamoeba can increase the severity of keratitis in vivo.

  1. 1. Carnt NA, Subedi D, Lim AW, Lee R, Mistry P, Badenoch PR, Kilvington S, Dutta D. Prevalence and seasonal variation of Acanthamoeba in domestic tap water in greater Sydney, Australia. Clinical and Experimental Optometry. 2020 Nov 1;103(6):782-6.
  2. 2. Rayamajhee B, Williams NL, Siboni N, Rodgers K, Willcox M, Henriquez FL, Seymour JR, Potts J, Johnson C, Scanes P, Carnt N. Identification and quantification of Acanthamoeba spp. within seawater at four coastal lagoons on the east coast of Australia. Science of the Total Environment. 2023 Nov 25;901:165862.