Photodynamic Antimicrobial Chemotherapy for Methicillin-resistant Staphylococcus aureus Keratitis
Date Issued
2012
Date
2012
Author(s)
Chu, Hsiao-Sang
Abstract
【Background and Study Purpose】
Infectious keratitis is a common ocular emergency and can lead to permanent visual loss. Occasionally, corneal transplant or evisceration is necessary for infection control in severe cases. Among the common pathogens, methicillin-resistant Staphylococcus aureus （MRSA） is one of the most notorious. MRSA has poor response to traditional antibiotics and is usually found in post-operative infections and in patients of chronic diseases. The community acquired MRSA infection rate is increasing. Photodynamic antimicrobial therapy （PACT）uses light of certain wavelength to activate the photosensitizer and produces abundant oxygenated products killing the bacteria. PACT has been proved to be effective in photoinactivation of both gram positive and gram negative bacteria in vitro. Our study aims to prove the possible application of PACT in treating MRSA keratitis.
【Material and Method】
Our studies can be divided in to three parts. First, we have tried to increase the efficiency of PACT in order to find the ideal combination of light source and photosensitizer. We apply PACT on MRSA ATCC 33592 bacterial suspension. We test the different efficacy between free form chlorin e6（Ce6）and micelle encapsulated Ce6. We also test the different photoinactivation ability between 405nm purple laser 663nm red laser. Second, we construct MRSA biofilms, ex vivo bovine eye keratitis model, and in vivo rabbit keratitis models. We titrate the PACT protocol and test the photoinactivation results in different models. Third, we combined PACT with vancomycin and test that whether PACT pre-treatment can have synergestic effect with vancomycin therapy.
【Results】
In the first part of our study, we have proved （1）the light itselt, neither purple laser nor red laser, has photoinactivation effect of MRSA 33592 within 20J/cm2 irradiation.（2） micelle Ce6 and free form Ce6 have no toxicity to MRSA 33592 below 100μM.（3）micelle encapsulation can increase the photoinactivation efficiency of chlorin e6. （4） micelle Ce6 can absorb both 405nm purple laser and 663nm red laser efficiently, but 405nm purple laser may be a better light source due to its stability and slightly higher efficiency. （5） with laser irradiation（purple or red laser）, the photoinactivation effect of micelle Ce6 is significant. We can decrease 5 log MRSA 33592 in suspension with 10J/cm2 irradiation of 2μM micelle Ce6.
In the second part of our study, we have found （1）the photoinactivation ability of our PACT decreases dramatically in MRSA ATCC 33592 biofilm model. With 20J/cm2 irradiation on 100μM micelle Ce6 can only decrease 2 to 3 log bacteria load. （2）using this protocol to treat ex vivo keratitis model of bovine eyes and in vivo rabbit keratitis model, the effecs are both poor without significant difference than the placebo group.
In the third part of our study, we have tried to combine PACT with vancomycin treatment. We have found （1）PACT (10 J/cm2 irradiation on 2μM micelle Ce6）pretreating can not increase the vancomycin therapeutic effect in MRSA ATCC 33592 suspension. （2）PACT （20 J/cm2 irradiation on 100μM micelle Ce6）pretreating can increase the vancomycin therapeutic effect in MRSA ATCC 33592 biofilm. （3）PACT （20 J/cm2 irradiation on 100μM micelle Ce6）effects on MRSA biofilm is temporary and disappears after 24 hours incubation. （4）PACT （40 J/cm2 irradiation on 100μM micelle Ce6） pretreating can mildly incrase the vancomycin therapeutic effect in MRSA keratits in ex vivo bovine eye model.
【Conclusion】
Our PACT uses 405nm purple laser combined with micelle encapsulated chlorine e6. This regimen has significant photoinactivation effect in MRSA bacterial suspension. However, the therapeutic effect decreases in biofilm model and is not significant in either ex vivo bovine keratitis model or in vivo rabbit keratitis model. Combination of PACT and vancomycin treatment can have partial syngestic effect in treating MRSA biofilm and bovine keratitis model. Our study has proved that PACT may be effective in MRSA infection control, but the photoinhibition effect only lasts for less than 24 hours. Therefore, PACT may not be suitable for single treatment or once treatment for MRSA keratitis. Furhter studies are necessary to find the clinical useful regimen of PACT as a new modality for treating MRSA keratitis.
Subjects
photodynamic therapy
photodynamic antimicrobial therapy
methicillin-resistant Staphylococcus aureus
micelle
chlorin e6
biofilm
Type
thesis
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