Chemical Inhibition of Alpha-Toxin, a Key Corneal Virulence Factor of Staphylococcus aureus

• Published in: Investigative ophthalmology & visual science Vol. 50; no. 6; pp. 2848 - 2854
• Main Authors: McCormick, Clare C, Caballero, Armando R, Balzli, Charles L, Tang, Aihua, O'Callaghan, Richard J
• Format: Journal Article
• Language: English
• Published: Rockville, MD ARVO 01.06.2009; Association for Research in Vision and Ophtalmology
• Subjects: Animals; Bacterial Toxins - antagonists & inhibitors; beta-Cyclodextrins - pharmacology; Biological and medical sciences; Cholesterol - pharmacology; Cornea - microbiology; Corneal Ulcer - microbiology; Corneal Ulcer - pathology; Corneal Ulcer - prevention & control; Disease Models, Animal; Drug Therapy, Combination; Erythrocytes - drug effects; Exotoxins - antagonists & inhibitors; Eye and associated structures. Visual pathways and centers. Vision; Eye Infections, Bacterial - microbiology; Eye Infections, Bacterial - pathology; Eye Infections, Bacterial - prevention & control; Fundamental and applied biological sciences. Psychology; Hemolysin Proteins - antagonists & inhibitors; Hemolysis; Medical sciences; Ophthalmology; Rabbits; Sodium Chloride - pharmacology; Staphylococcal Infections - microbiology; Staphylococcal Infections - pathology; Staphylococcal Infections - prevention & control; Staphylococcal Toxoid - antagonists & inhibitors; Staphylococcus aureus - physiology; Vertebrates: nervous system and sense organs; Virulence - physiology; Virulence Factors - antagonists & inhibitors; Toxin; Cornea; Virulence; Bacteria; Micrococcales; Micrococcaceae; Inhibition; Ophthalmology; Staphylococcus aureus
• ISSN: 0146-0404; 1552-5783
• DOI: 10.1167/iovs.08-3157

alpha-Toxin mediates extreme corneal damage during Staphylococcus aureus keratitis. Chemical inhibition of this toxin was sought to provide relief from toxin-mediated pathology. Inhibition of alpha-toxin by phosphate-buffered saline (PBS), 0.1% methyl-beta-cyclodextrin (CD), or CD plus cholesterol (0.1%, CD-cholesterol) was assayed by hemolysis of rabbit erythrocytes. Pathologic changes in rabbit corneas injected with 12 hemolytic units of alpha-toxin suspended in PBS, 1% CD, or 1% CD-cholesterol were compared over time. Rabbit corneas injected with 10(2) colony forming units (CFU) of S. aureus were treated from 7 to 13 hours postinfection (PI) with a total of 15 drops of CD-cholesterol, CD, or PBS. Slit lamp examination (SLE) and measurement of erosions were performed at 13 hours PI and bacteria were quantified at 14 hours PI. Toxin-mediated lysis of erythrocytes was inhibited up to 16,000-fold in the presence of CD-cholesterol compared with CD or PBS. Eyes injected with alpha-toxin mixed with CD-cholesterol had, at 7 hours postinjection, significantly smaller erosions than eyes injected with alpha-toxin in PBS or alpha-toxin mixed with CD (P = 0.0090 and P = 0.0035, respectively). Eyes infected with S. aureus and treated with CD-cholesterol had significantly lower SLE scores than eyes treated with CD or PBS (P <or= 0.0103 and P <or= 0.0017, respectively); however, there were no differences in the number of bacteria present (P >or= 0.0648). CD-cholesterol is a potent inhibitor of alpha-toxin activity in vitro and an effective means to arrest corneal damage during S. aureus keratitis.