The research focus of the Ocular Microbiology lab is aimed at understanding the pathogenesis of ocular infections and host pathogen interactions. We employ various phenotypic and genotypic approaches to characterize the ocular pathogens like methicillin resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Acanthamoeba and Trematodes. Access to a large repository of ocular isolates enables us to probe into the virulence and antibiotic resistance mechanisms of the pathogens in the context of ocular infections. Based on the antimicrobial susceptibility testing, the resistant isolates are selected and subjected to further analysis to identify the molecular mechanisms underlying resistance. Correlates of protective immune response are being studied by analyzing the host pathogen interactions using exvivo and invitro models of infection and corneal tissue samples obtained from patients.
Infectious keratitis is a major cause of blindness, next to cataract and majority of cases are caused by either fungi or bacteria in developing countries. Bacterial keratitis develops very quickly because of its rapid progression and increased corneal destruction and it may lead to blindness, if left untreated. In our lab, we utilize the ocular isolates of P. aeruginosa and methicillin resistant S. aureus (MRSA) to delineate their virulence and antibiotic resistance mechanisms.
The pathogenesis of P. aeruginosa is mediated through the production of several cell-associated and extracellular virulence factors. We study the involvement of Type 3 secretion system and other virulence factors of P. aeruginosa in causing ocular infection by both phenotypic and genotypic methods. We also analyze the differentially expressed genes by whole genome sequencing and transcriptome analysis of the ocular isolates. Yet another study in our lab focuses on the molecular characterization and epidemiological analysis of MRSA causing ocular infections. We found the community acquired MRSA strains (SCCmec type IV and V) to be more prevalent than hospital acquired MRSA in causing ocular infections. Further studies are done to analyze the expression of toxin genes in association with various ocular infections using advanced molecular methods.
Since corneal ulceration is a leading cause of ocular morbidity and blindness worldwide, it is imperative that the functional and molecular aspects of the disease be well understood to develop an effective treatment plan. An earlier study from our lab reported elevated expression of TLR?s in relation to Microbial keratitis (Karthikeyan et al., 2013). Although much of the focus in the literature has been on the study of protein regulators of inflammation, miRNAs have emerged as important controllers of certain features of the inflammatory process. We propose that miRNAs may play a role in the pathogenesis of microbial keratitis by modulating TLR signaling which has not been previously reported. Our present study attempts to reveal the involvement of miRNAs in the microbial keratitis pathogenesis by expression profiling of miRNAs in corneal scrapings from keratitis and normal controls.
For an effective therapeutic intervention of keratitis without the need for surgery, excessive inflammatory responses need to be curtailed. We analyze the involvement of various host innate defense molecules in ocular inflammation caused by infectious keratitis. Also, we study the usefulness of immunomodulators like Vitamin D in controlling the excessive inflammation in infectious keratitis using invitro and exvivo models of infection.
Pediatric parasitic ocular inflammation is one of the common clinical conditions in South India. We have identified the causative agent of granulomatous uveitis as trematode, Procerovum varium and source of infection as fresh water snails, Melanoid tuberculata. Immunohistochemistry studies are now being done to analyze the inflammatory cellular pattern to understand the disease pathogenesis.
Another vision threatening ocular infection is caused by Acanthamoeba which leads to corneal ulceration, loss of visual acuity, corneal scarring and monocular blindness. The incidence rate of Acanthamoeba is 3.1% in the year 2013, at Aravind Eye Hospital, Madurai, India. Acanthamoeba keratitis is difficult to treat and there is minimal evidence on which to base treatment decisions. We are investigating the microbiological clearance time for Acanthamoeba by Real time quantitative PCR. Also we are determining the Minimum Cysticidal Concentration (MCC) of anti-microbial drugs with a view to evaluate the efficacy of combination therapy by invitro synergy assay.
Etiology and Immunopathogenesis of sub conjunctival and anterior chamber granulomatous uveitis in children of South India. Funding agency: ICMR (2011-2014).
Characterization of the virulence determinants of pseudomonas aeruginosa causing ocular infections.
Genotypic characterization and analysis of virulence factors in Methicillin resistant staphylococcus aureus causing ocular infections. Funding agency: ICMR.
Microbiological clearance time and Sensitivity assay for acanthamoeba keratitis. Funding agency: Proctor Foundation, USA.
Elucidating the role of MicroRNAs in infectious keratitis.
Evaluation of the anti- microbial and anti- inflammatory functions of vitamin D in
Aspergillus flavus study group of India (AFSGI) Epidemiology, pathogenomics, and system biology of A. flavus infections in India - an integrative approach. Funding agency: DBT (2012-2015).
Characterization of the host immune response during corneal infection with pathogenic fungi and bacteria. Funding agency: ICMR (2010-2013).
Molecular insights into the etiology of infectious uveitis. Funding agency: DBT (2008-2011).
Standardization and application of multiplex PCR in the detection of infectious agents in the intraocular fluid of patients with retinochoroiditis. Funding agency: ICMR (2006-2009).