A 5-Year Review of Coinfections in Acanthamoeba keratitis From South India

Abstract

Purpose: To ascertain the frequency of coinfections in Acanthamoeba keratitis, the nature of copathogens involved, and to analyze the implications in the context of current research on amoebic interactions. Methods: A retrospective case review from a Tertiary Care Eye Hospital in South India. Smear and culture data for coinfections in Acanthamoeba corneal ulcers were collected from records over a 5-year period. The significance and relevance of our findings in the light of current research on Acanthamoeba interactions were analyzed. Results: Eighty-five cases of culture-positive Acanthamoeba keratitis were identified over a 5-year period (43 of them being coinfections). Fusarium was most commonly identified species, followed by Aspergillus and the dematiaceous fungi. Pseudomonas spp was the commonest bacterial isolate. Conclusion: Coinfections with Acanthamoeba are common at our centre, and account for 50% of Acanthamoeba keratitis. The diverse nature of the organisms involved in coinfections suggest that such amoebic interactions with other organisms are probably more widespread than recognized. To the best of our knowledge, this is the first documentation from a long-term study of pathogen diversity in Acanthamoeba coinfections. It is possible that Acanthamoeba itself may be virulence enhanced and secondary to the co-organism, breaching the ocular surface defenses in an already compromised cornea. However, observations from the existing literature on Acanthamoeba interactions with bacteria and certain fungi are based mainly on nonocular or nonclinical isolates. It would be illuminating if such studies are performed on Acanthamoeba and coinfectors from corneal ulcers—to ascertain whether interactions are endosymbiotic or virulence enhanced through amoebic passage.

Application of Metagenomic Next-Generation Sequencing in the Diagnosis of Infectious Keratitis

“…Acanthamoeba keratitis is difficult to diagnose, and effective treatment options are limited [ 44 ]. Rammohan et al [ 45 ] showed that over a 5 year period, 85 cases of culture-positive Acanthamoeba keratitis were identified (43 of them being co-infections); Fusarium was the most commonly identified species, followed by Aspergillus , and Pseudomonas was the most common bacterial isolate, which was in accordance with our results. Recent studies have used sequencing, fluorescence in situ hybridization (FISH), and corneal scrape microbiology and found that most clinical isolates of Acanthamoeba contain intracellular microorganisms (such as P. aeruginosa ), which may affect the clinical characteristics of Acanthamoeba keratitis [ 46 , 47 ].…”

Zooming in on the intracellular microbiome composition of bacterivorous Acanthamoeba isolates

“…According to a retrospective study conducted in the USA using corneal scrape cultures [ 62 ], co-infection rates among AK cases were 23.6% with bacteria, 7.3% with fungi, and 4.5% with herpes simplex virus. Similarly, in a recent study conducted in South India [ 31 ], over 50% of AK patients were found to have coinfections with various microbes, including Fusarium spp., Aspergillus spp., Pseudomonas spp., Stenotrophomonas spp., Streptococcus spp., among others. The wide array of organisms involved in coinfections suggests that Acanthamoeba interactions with other organisms are likely more prevalent than currently acknowledged.…”

“…Although a retrospective study of AK versus keratitis from which Acanthamoeba and bacteria were cultured showed no significant differences in the disease at presentation or final outcome, this could be due to the use of broad-spectrum antimicrobials for treatment [ 29 ], and it was not certain whether the co-infecting microbes had originally been part of the Acanthamoeba ’s microbiome. Co-infection is often observed among AK patients with multiple bacterial, viral, and fungal species [ 30 , 31 ].…”

The role of naturally acquired intracellular Pseudomonas aeruginosa in the development of Acanthamoeba keratitis in an animal model

“…Hence, we propose that the simultaneous infection of Acanthamoeba along with released intracellular bacteria could be a major contributing factor to the progression of severe AK [ 26 ]. With the increasing prevalence of coinfections among AK patients [ 18 , 19 , 21 ], which often lead to severe outcomes, this study contributes to our understating of the role of intracellular bacteria and potential bacterial endosymbionts in the development of acute Acanthamoeba keratitis. The findings presented in this study showed that coinfections in Acanthamoeba keratitis are potentially attributed to the carriage of bacteria by Acanthamoeba .…”

“…Surprisingly, high proportions of isolated bacteria and fungi were able to produce biofilms [ 19 ]. According to a recent review conducted in South India, coinfections were found in over 50% of AK cases, with fungal coinfection observed in 34% of cases and bacterial coinfection in 14% of cases [ 18 ].…”