Review article
Understanding clinical and immunological features associated with Pseudomonas and Staphylococcus keratitis

https://doi.org/10.1016/j.clae.2020.11.014Get rights and content

Abstract

Pseudomonas aeruginosa and Staphylococcus aureus are the two dominant Gram-negative and -positive species, respectively, isolated from patients with contact lens-related bacterial keratitis. The clinical features of bacterial keratitis vary, such that timely differential diagnosis can be challenging, which may cause a delay in diagnosis resulting in poorer outcome. This review aims to explore the current understanding of clinical and immunological features associated with contact lens-related P. aeruginosa and S. aureus keratitis based on currently available evidence.

Firstly, the review characterises contact lens-related P. aeruginosa and S. aureus keratitis, based on clinical features and prognostic factors. Secondly, the review describes the primary immune response associated with a bacterial infection in in-vivo non-scratch contact lens-wearing animal models, colonised by bacteria on contact lens and topical administration of bacteria on the cornea. Finally, the review discusses the role of macrophage inflammatory protein-2 (MIP-2) and intercellular adhesion molecule (ICAM-1) in neutrophil recruitment based on both in-vivo scratch models of bacterial keratitis and bacterial challenged in cell culture models.

Section snippets

Background

Contact lens wear (CLW) is a significant risk factor associated with bacterial keratitis, which accounts for 22–65 % of cases of bacterial keratitis in hospital or casualty-based studies [[1], [2], [3], [4], [5], [6], [7], [8]]. Bacteria is present in 69–95 % of the culture-positive cases of contact lens-related microbial keratitis [3,[9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]]. Pseudomonas aeruginosa [3,9,10,13,[19], [20], [21], [22]] and Staphylococcus aureus [2,[9], [10]

Clinical features of Pseudomonas aeruginosa and Staphylococcus aureus keratitis

The diagnosis of bacterial keratitis in patients is based on presenting symptoms, history, presenting risk factors, clinical examination and the smear and culture of the corneal scrape.

Pathology of contact lens-related bacterial keratitis in animal models

Animal models have provided invaluable insight into the host-response in contact lens-related bacterial keratitis [25,27,72]. Chiefly, two variants of mice (C57BL/6 and BALB/c) have commonly been compared with wild-type mice in both scratch and non-scratch models of both contact lens-related and non-contact lens-related bacterial keratitis. C57BL/6 (or B6) mice are common inbred strains of laboratory mice and are susceptible Th1 responders while BALB/c mice are immunodeficient laboratory-bred

Neutrophils are primary immune mediators in early bacterial keratitis in mice models

Corneal infiltrates in bacterial keratitis are aggregations of neutrophils which accumulate to clear invading pathogens and their antigens. Principally, intercellular communication between infiltrating leukocytes, corneal tissues, and the limbal vascular endothelium determines neutrophil recruitment [74]. In animal studies, rapid neutrophil recruitment drives the host's innate immune response by activating Th1 cells at the site of infection [74,[99], [100], [101]]. Prolonged neutrophil

Summary and future directions

Contact lens-related bacterial keratitis is rapidly progressing acute clinical condition, which requires urgent diagnosis and treatment. In the early stage, contact lens-related bacterial keratitis can be challenging to differentiate from symptomatic sterile infiltrates like CLPU. Certain features may be more suggestive of a specific causative agent. However, confirmed diagnosis of a causative organism requires culture or molecular techniques from corneal scrapes or corneal biopsy.

P. aeruginosa

Acknowledgement

The Scientia PhD Scholarship, UNSW Sydney. We are thankful to Mr Suresh Sharma and Mr Hira Nath Dahal, BP Koirala Lions Centre for Ophthalmic Studies, Institute of Medicine, Kathmandu for providing a clinical photo.

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