Diversity of microbial species implicated in keratitis: a review

Abstract

Background: Microbial keratitis is an infectious disease of the cornea characterised by inflammation and is considered an ophthalmic emergency requiring immediate attention. While a variety of pathogenic microbes associated with microbial keratitis have been identified, a comprehensive review identifying the diversity of species has not been completed.

Methods: A search of peer-reviewed publications including case reports and research articles reporting microorganims implicated in keratitis was conducted. Search engines including PubMed, Scopus and Web of Science with years ranging from 1950-2012 were used.

Results: 232 different species from 142 genera, representing 80 families were found to be implicated in microbial keratitis. Fungi exhibited the largest diversity with 144 species from 92 genera. In comparison, 77 species of bacteria from 42 genera, 12 species of protozoa from 4 genera and 4 types of virus were identified as the infectious agents. A comparison of their aetiologies shows reports of similarities between genera.

Conclusions: The diversity of microbial species implicated in keratitis has not previously been reported and is considerably greater than suggested by incidence studies. Effective treatment is heavily reliant upon correct identification of the responsible microorganisms. Species identification, the risk factors associated with, and pathogenesis of microbial keratitis will allow the development of improved therapies. This review provides a resource for clinicians and researchers to assist in identification and readily source treatment information.

Keywords: Acanthamoeba; Amoebic Keratitis; Candida; Fusarium; HSV-1.; Herpetic keratitis; Microbial Keratitis; Mycotic keratitis; Staphylococcus.

Fig. (1)

Distribution of microorganisms associated with keratitis, at the family, genera and species levels based on the literature, amoebic ■, bacterial ■, viral and fungal keratitis .

Fig. (2)

Mycotic keratitis following corneal grafting with (a) filamentary, Aspergillus, Insert: higher magnification showing the irregular feathery margins, and (b) unicellular, Candida spp.

Fig. (3)

Bacterial keratitis due to Pseudomonas spp.

Fig. (4)

Acanthamoeba keratitis, Insert: higher magnification showing epithelial irregularity in early acanthamoeba keratitis.

Fig. (5)

A dendritic ulcer from herpes simplex keratitis stained with fluorescein and viewed with a cobalt blue light. Insert: appearance in natural light.