Novel approaches in bacterial keratitis

Sueke, Henri Novel approaches in bacterial keratitis. Doctor of Medicine thesis, University of Liverpool.

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Abstract

Bacterial keratitis is a serious ophthalmic disease with significant visual morbidity. The aims of this thesis are to investigate (1) the prevalence and type of bacterial virulence factors in the two major species causing keratitis; Staphylococcal aureus and Pseudomonas aeruginosa and (2) the pharmacodynamics and pharmacokinetics of meropenem, a potentially novel antimicrobial for use in keratitis. The prevalence, genetic diversity and clinical relevance of the lukSF-PV gene, encoding the bacterial toxin Panton Valentine Leukocidin, were investigated in S. aureus, isolated from cases of bacterial keratitis in the UK. Patients with lukSF-PV+ve S. aureus were found to be associated with a trend to worse clinical outcome and more surgical interventions, with an effect unrelated to minimum inhibitory concentrations (MICs). This suggests that lukSF-PV may be an important virulence factor in S. aureus associated keratitis. The genetic characteristics of P. aeruginosa isolates collected from patients with bacterial keratitis were compared between two time periods; 2003-04 and 2009-10 using an Array Tube genotyping system. 71% of keratitis-associated P. aeruginosa isolates clustered together, with no evidence for major variations in the distribution of clone types between the two time periods. The “core keratitis cluster” was found to be related to the P. aeruginosa eccB clonal complex, which is associated with adaptation to survival in environmental water. This suggests that adaptation to environmental water is a key factor in the ability of P. aeruginosa to cause keratitis. Further analysis of clinical data and studies involving additional sets of patients for verification of this hypothesis will provide a clearer picture. Pharmacodynamic properties of commonly used and potentially novel antimicrobials were determined by calculating MICs against isolates from patients with keratitis. Antimicrobial combinations were investigated for synergy or antagonism against isolates of S. aureus and P. aeruginosa using E-Tests. Meropenem was identified as a potentially novel antimicrobial for use in keratitis, offering broad-spectrum cover against both Gram-positive and -negative microorganisms. Meropenem was also shown to show synergistic properties when used in combination with other commonly used antimicrobials. In light of these results, the antimicrobial meropenem was chosen to undergo further pharmacokinetic studies. MTT and Live Dead toxicity assays were performed on human keratocytes and human corneal epithelial cells treated with meropenem. Meropenem was found to have low toxicity against these cells. Corneal penetration of meropenem was assessed in human cadaver corneo-scleral discs mounted onto artificial anterior chambers. The concentration of meropenem in the aqueous estimated by HPLC and disc diffusion bioassay exceeded the MIC90 of E. coli in all 18 corneas tested after the 45 minutes sample point.

Item Type:	Thesis (Doctor of Medicine)
Additional Information:	Date: 2014-10 (completed)
Depositing User:	Symplectic Admin
Date Deposited:	05 Feb 2015 10:21
Last Modified:	17 Dec 2022 01:27
DOI:	10.17638/02006499
URI:	https://livrepository.liverpool.ac.uk/id/eprint/2006499