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The in vitro activity of selected defensins against an isolate of Pseudomonas in the presence of human tears
  1. A M McDermott1,
  2. D Rich2,*,
  3. J Cullor2,,
  4. M J Mannis2,
  5. W Smith3,
  6. T Reid2,,
  7. C J Murphy2,
  1. 1University of Houston, College of Optometry, Houston, TX, USA
  2. 2Department of Ophthalmology, University of California, Davis, CA, USA
  3. 3Department of Veterinary Pathology, University of California, Davis, CA, USA
  1. Correspondence to: Mark J Mannis MD, Department of Ophthalmology, UC Davis Medical Center, Ellison Building, 4860 Y Street #2400, Sacramento, CA 95817-2307, USA: mjmannis{at}ucdavis.edu

Abstract

Background/aims:Pseudomonas aeruginosa is a major cause of severe bacterial keratitis and remains a difficult clinical entity to treat successfully with the current arsenal of antimicrobial agents. Defensins are small cationic peptides with broad in vitro antimicrobial activity and are potential ocular therapeutic agents. The authors characterised the in vitro activity of defensins NP-1 and NP-3a against P aeruginosa in the presence of human tears.

Methods: A clinical Pseudomonas isolate was grown to mid-log phase, and 1×106 colony forming units were exposed to the peptides (200 μg/ml) for up to 2 hours in the presence of varying concentrations (10–70%) of human tears.

Results: For both peptides in the presence of 10% tears, >3 log units of killing was achieved within 30 minutes. In 70% tears, NP-1 produced >1 log unit of killing at 2 hours, indicating that, although reduced, its activity remained significant. In 20% tears, NP-3a demonstrated 2 log units of killing at 2 hours; however, the antimicrobial activity of this defensin was completely inhibited in the presence of 70% tears.

Conclusion: These in vitro data suggest that while the microbicidal activity of some defensins may be diminished at the ocular surface in vivo, significant activity is still possible with certain peptides.

  • hBD, human β-defensin
  • HNP, human neutrophil peptide
  • HPLC, high performance liquid chromatography
  • TSA, trypticase soy agar
  • TSB, trypticase soy broth
  • defensin
  • tears
  • Pseudomonas
  • hBD, human β-defensin
  • HNP, human neutrophil peptide
  • HPLC, high performance liquid chromatography
  • TSA, trypticase soy agar
  • TSB, trypticase soy broth
  • defensin
  • tears
  • Pseudomonas

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Footnotes

  • * Currently in private practice, Santa Rosa, CA;

  • currently at Veterinary Medicine Teaching and Research Centre, Tulare, CA;

  • currently at Texas Tech University Health Sciences Centre, Lubbock, TX;

  • currently at the University of Wisconsin-Madison, WI, USA.

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