Photodynamic therapy against resistant bacteria from cystic fibrosis patients

Abstract number: P582

Torun O., Ak S., Sener B.

Objectives: Photodynamic therapy (PDT) combines a photosensitizer dye with visible light to generate reactive oxygen radicals toxic to cells. High rate of antibiotic resistance in cystic fibrosis (CF) isolates highlights the need for new treatment strategies. This study is aimed to evaluate the in-vitro effect of PDT alone and in the presence of antibiotics on MRSA, Pseudomonas aeruginosa (PA), Stenotrophomonas maltophilia (SM) and Burkholderia cepacia complex (BCc) isolated from CF patients.

Methods: Four MRSA, 4 PA, 8 SM and 2 BCc isolates were initially tested for susceptibility by microdilution method. PDT was applied by using toluidine blue at a light dose of 54 J/cm2 with a light emitting diode on microtiter plates and killing was determined by viable cell counts. PDT was also applied on antibiotic containing MIC trays and effect on MIC values were tested. MBC values were determined by direct plate count for MIC and MIC+PDT trays.

Results: All PA, Sm and Bcc strains were resistant to ceftazidim (CAZ), meropenem (MEM), ciprofloxacin (CIP) and amikacin (AK), except for two PA strains susceptible to AK and CIP. All MRSA strains were also resistant to AK and CIP. Overall PDT alone exhibited 4 log killing in 8, 2 log in 4, 1 log in 5 and no effect in one strain. PDT application in presence of antibiotics lowered the MIC values in all bacteria except for two PA strains, at least for 4 folds for all the antibiotics tested to susceptible levels. PDT application in the presence of antibiotics decreased viable cell counts at least 3 logs for all the MRSA, SM, BCc strains. PDT+CAZ and PDT+MEM achieved no bactericidal activity in 3 PA strains while AK and CIP exhibited bactericidal activity in the presence of PDT for all PA strains.

Conclusions: Although PDT alone was not able to achieve bactericidal activity for all the tested strains, a significant bactericidal effect was detected when PDT was applied in the presence of antibiotics for all bacteria except for PA. Resistance to antibiotics in CF isolates may be overcome by the synergistic activity of PDT which should further be improved for in-vivo application.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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