Corneal pathogenesis of Staphylococcus aureus strain Newman.
OBJECTIVE
To determine the pathogenic role of gamma- and alpha-toxin in a rabbit model of Staphylococcus aureus keratitis.


METHODS
S. aureus strains Newman (expressing gamma-toxin), Newman Delta(hlg) (deficient in gamma-toxin), Newman Delta(hlg)/pCU1 hlg(+) (chromosomal gamma-toxin-deficient mutant rescued by a plasmid encoding gamma-toxin), and Newman Delta(hla) (alpha-toxin-deficient) were intrastromally injected into rabbit corneas. Eyes were scored by slit lamp examination (SLE), and bacterial colony-forming units (CFU) per cornea were determined at 15, 20, and 25 hours after infection. Histologic examination of corneas was performed. Rabbits were immunized against alpha-toxin and subsequently challenged with S. aureus strain Newman. Western blot analyses of culture supernatants were performed to detect alpha-toxin production.


RESULTS
All strains grew equivalently, producing approximately 7 log CFU per cornea at 25 hours after infection. SLE scores at 20 and 25 hours after infection revealed that strains Newman Delta(hlg) and Newman Delta(hla), although virulent, caused significantly less ocular damage and inflammation than their parent or the gamma-toxin genetically rescued strain (P <or= 0.0006). Histologic and SLEs revealed that all strains except Newman Delta(hla) produced corneal erosions. Rabbits immunized actively or passively to alpha-toxin had reduced SLE scores (P <or= 0.0003 and P <or= 0.0033, respectively) and no epithelial erosions when infected with strain Newman. Western blot analysis demonstrated that strains Newman and Newman Delta(hlg), but not Newman Delta(hla), produced alpha-toxin.


CONCLUSIONS
These results illustrate that the virulence of strain Newman involves both alpha- and gamma-toxin, with alpha-toxin mediating corneal epithelial erosions. An additional uncharacterized toxin could also be active in damaging the cornea.
Dajcs
Joseph J
JJ
Department of Microbiology, Immunology, and Parasitology, Louisiana State University (LSU) Health Sciences Center, New Orleans, Louisiana 70112-1393, USA.
Austin
Megan S
MS
Sloop
Gregory D
GD
Moreau
Judy M
JM
Hume
Emma B H
EB
Thompson
Hilary W
HW
McAleese
Fionnuala M
FM
Foster
Timothy J
TJ
O'Callaghan
Richard J
RJ
D000818:Animals; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000235:genetics; D015373:Bacterial Typing Techniques; D015153:Blotting, Western; D015169:Colony Count, Microbial; D003315:Cornea / Q000382:microbiology* / Q000473:pathology; D015818:Eye Infections, Bacterial / Q000382:microbiology* / Q000473:pathology; D006460:Hemolysin Proteins / Q000235:genetics; D007634:Keratitis / Q000382:microbiology* / Q000473:pathology; D011817:Rabbits; D013203:Staphylococcal Infections / Q000382:microbiology* / Q000473:pathology; D013211:Staphylococcus aureus / Q000145:classification / Q000235:genetics / Q000472:pathogenicity*; D014611:Vaccination; D014774:Virulence
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D006460:Hemolysin Proteins; C037956:gamma-hemolysin, Staphylococcus aureus; C021091:staphylococcal alpha-toxin