Corneal virulence of Staphylococcus aureus: roles of alpha-toxin and protein A in pathogenesis

Infect Immun. 1994 Jun;62(6):2478-82. doi: 10.1128/iai.62.6.2478-2482.1994.

Abstract

Staphylococcus aureus produces a variety of proteins, including alpha-toxin and protein A, that could contribute to corneal tissue damage during keratitis. We examined corneal infections produced by intrastromal injection of four S. aureus strains--three isogenic mutants, one lacking alpha-toxin (Hly- Spa+), one lacking protein A (Hly+ Spa-), and one lacking both alpha-toxin and protein A (Hly- Spa-), and the wild type (Hly+ Spa+)--in a rabbit model of experimental keratitis. Rabbit corneas were injected intrastromally with 100 CFU of one of the four strains, and the eyes were examined by slit lamp biomicroscopy over a 25-h period. Corneal homogenates were used for determination of CFU and neutrophil myeloperoxidase activity at 5-h intervals. All strains had the same logarithmic growth curve from 0 to 10 h postinfection, after which CFU remained constant at 10(7) CFU per cornea. By 15 h postinfection, slit lamp examination scores were significantly higher for eyes infected with Hly+ strains than for Hly(-)-infected eyes. At this time, distinct epithelial erosions were seen in Hly(+)-infected eyes but not in Hly(-)-infected eyes. Myeloperoxidase activity was significantly greater for Hly(+)-infected corneas than for Hly(-)-infected corneas at both 20 and 25 h postinfection. Spa(+)- and Spa(-)-infected eyes showed no differences in slit lamp examination scores or myeloperoxidase activities. These results suggest that alpha-toxin, but not protein A, is a major virulence factor in staphylococcal keratitis, mediating the destruction of corneal tissue in eyes infected with this bacterial pathogen.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Bacterial Toxins / toxicity*
  • Exotoxins / toxicity*
  • Hemolysin Proteins / toxicity*
  • Keratitis / etiology*
  • Rabbits
  • Staphylococcal Protein A / toxicity*
  • Staphylococcus aureus / pathogenicity*
  • Virulence

Substances

  • Bacterial Toxins
  • Exotoxins
  • Hemolysin Proteins
  • Staphylococcal Protein A
  • staphylococcal alpha-toxin