Effects of photodynamic therapy on rapidly growing nontuberculous mycobacteria keratitis.
OBJECTIVE
The authors investigated the antimicrobial effect of methylene blue (MB)-mediated photodynamic therapy (PDT) on Mycobacterium fortuitum keratitis.


METHODS
In the in vitro study, the mycobacterial suspension and colonies were treated with the following: no MB, no light (normal control); MB and no light (dye control); light and no MB (light control); MB and light (PDT). Morphologic characteristics were examined by transmission electron microscopy. The bactericidal effects of combined PDT and antibiotic therapy (ciprofloxacin, moxifloxacin, and amikacin) were determined using the broth microdilution technique. Twenty-one rabbits with Mycobacterium keratitis were randomly divided into three groups (no treatment, topical amikacin treatment, and PDT combined with amikacin treatment). The clinical features of keratitis were scored and graded before treatment and before euthanatization. The diseased corneas were trephined for quantitative bacteriologic analysis to determine the antibacterial efficacy of the treatment.


RESULTS
In the in vitro tests, the bacterial count had a 2-log reduction immediately after PDT treatment at 100 J/cm(2) with 10(-3)% MB. After PDT at 100 J/cm(2) with 10(-2)% MB, almost no viable bacteria were detected. PDT had a synergistic antimicrobial effect in combination with antibiotics. The phototoxicity occurred in the cytoplasm first and then disrupted the mycobacterial cell walls by lysis. In the rabbit keratitis model, combined PDT resulted in significantly less bacterial burden (P < 0.01) than in the amikacin group.


CONCLUSIONS
This study demonstrated the effectiveness of MB-mediated PDT against Mycobacterium fortuitum. PDT could be a potential alternative treatment for nontuberculous mycobacterial corneal infections.
Shih
Min-Hsiu
MH
Department of Ophthalmology, National Cheng Kung University Hospital, Tainan, Taiwan.
Huang
Fu-Chin
FC
D000583:Amikacin / Q000627:therapeutic use; D000818:Animals; D000890:Anti-Infective Agents / Q000627:therapeutic use*; D001372:Aza Compounds / Q000627:therapeutic use; D002939:Ciprofloxacin / Q000627:therapeutic use; D015169:Colony Count, Microbial; D003320:Corneal Ulcer / Q000188:drug therapy* / Q000382:microbiology; D004357:Drug Synergism; D015818:Eye Infections, Bacterial / Q000188:drug therapy* / Q000382:microbiology; D024841:Fluoroquinolones; D008751:Methylene Blue / Q000627:therapeutic use*; D008826:Microbial Sensitivity Tests; D000077266:Moxifloxacin; D009165:Mycobacterium Infections, Nontuberculous / Q000188:drug therapy* / Q000382:microbiology; D019907:Mycobacterium fortuitum / Q000302:isolation & purification*; D010778:Photochemotherapy; D011804:Quinolines / Q000627:therapeutic use; D011817:Rabbits
D000890:Anti-Infective Agents; D001372:Aza Compounds; D024841:Fluoroquinolones; D011804:Quinolines; D002939:Ciprofloxacin; D000583:Amikacin; D008751:Methylene Blue; D000077266:Moxifloxacin