Cholesterol as treatment for pneumococcal keratitis: cholesterol-specific inhibition of pneumolysin in the cornea.
OBJECTIVE
The purpose of this study was to determine whether cholesterol, the host cell receptor for pneumolysin of Streptococcus pneumoniae, could effectively treat pneumococcal keratitis.


METHODS
New Zealand White rabbits were intrastromally injected with 10(5) colony-forming units (CFUs) of S. pneumoniae D39. Corneas were treated with topical drops of 1% cholesterol every 2 hours beginning 25 hours after infection and were examined by slit lamp microscopy 24, 36, and 48 hours after infection. Rabbits were killed, and CFUs were recovered from the corneas after the final slit lamp examination (SLE). Minimal inhibitory concentration (MIC) assays of cholesterol against bacteria were performed. Specific inhibition of pneumolysin by cholesterol in the rabbit cornea was tested by intrastromal injection of pneumolysin with or without cholesterol and was compared with cholesterol inhibition of pneumolysin in vitro using hemolysis assays with rabbit erythrocytes.


RESULTS
Corneas treated with cholesterol had significantly lower SLE scores 48 hours after infection than corneas treated with vehicle (P = 0.0015). Treated corneas also had significantly less log(10) CFUs than vehicle-treated corneas (P = 0.0006). Cholesterol at a 1% concentration was bactericidal to bacteria in vitro, and lower concentrations of cholesterol were partially inhibitory in a concentration-dependent manner. Cholesterol also specifically inhibited 1 mug pneumolysin in vivo and up to 50 ng pneumolysin in vitro.


CONCLUSIONS
Topical cholesterol is an effective treatment for S. pneumoniae keratitis. Cholesterol not only inhibits pneumolysin, it is also bactericidal.
Marquart
Mary E
ME
Department of Microbiology, University of Mississippi Medical Center, Jackson, Mississippi 39216, USA. mmarquart@microbio.umsmed.edu
Monds
Kathryn S
KS
McCormick
Clare C
CC
Dixon
Sherrina N
SN
Sanders
Melissa E
ME
Reed
Julian M
JM
McDaniel
Larry S
LS
Caballero
Armando R
AR
O'Callaghan
Richard J
RJ
D000818:Animals; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors; D002784:Cholesterol / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D015169:Colony Count, Microbial; D003315:Cornea / Q000187:drug effects / Q000382:microbiology; D003320:Corneal Ulcer / Q000188:drug therapy* / Q000382:microbiology; D015818:Eye Infections, Bacterial / Q000188:drug therapy* / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D009883:Ophthalmic Solutions / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D011008:Pneumococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D011817:Rabbits; D013296:Streptococcus pneumoniae / Q000254:growth & development / Q000302:isolation & purification*; D013301:Streptolysins / Q000037:antagonists & inhibitors*
D001426:Bacterial Proteins; D009883:Ophthalmic Solutions; D013301:Streptolysins; C032290:plY protein, Streptococcus pneumoniae; D002784:Cholesterol