A highly virulent Staphylococcus aureus: rabbit anterior chamber infection, characterization, and genetic analysis.
OBJECTIVE
To describe and characterize a Staphylococcus aureus strain with unique virulence that overcomes host defenses of the rabbit anterior chamber and mimics clinical cases of postcataract surgery endophthalmitis.


METHODS
Nine isolates of S. aureus were tested to determine their viability in the rabbit anterior chamber. Growth of UMCR1 in the anterior chamber was established and expressed as log colony-forming units per milliliter of aqueous humor. Pathologic changes produced by UMCR1 were documented by photographs, slit lamp examination, histopathologic analysis, and quantification of neutrophils. UMCR1 was characterized by antibiotic susceptibility, biochemical tests, ribotyping, genome restriction mapping, and multilocus sequence typing (MLST).


RESULTS
UMCR1 was the only S. aureus strain that grew within the anterior chamber, reaching log 6.97 ± 0.18 CFU/mL by 16 hours after infection. Pathologic changes included conjunctival injection, chemosis, corneal edema, severe iritis, fibrin accumulation, and a 193-fold increase in neutrophils by 16 hours after infection. UMCR1 was only resistant to sulfamethoxazole and, like other S. aureus isolates, polymyxin B. UMCR1 also had biochemical reactions and a ribotype pattern typical of S. aureus. The genomic reconstruction analysis of UMCR1 was most similar to strains MW2 and MSSA476. MLST revealed a 1 in 3198 nucleotide difference between UMCR1 and strains MW2 and MSSA476.


CONCLUSIONS
This study describes a unique S. aureus strain that overcomes host defenses and replicates in the anterior chamber. The survival and growth of this organism could be used for studies of S. aureus pathogenesis, host defenses, and effectiveness of antibiotics within the anterior chamber.
Balzli
Charles L
CL
Department of Microbiology, University of Mississippi Medical Center, Jackson, Mississippi 39216, USA. cbalzli@umc.edu
Bartell
John
J
Dajcs
Joseph J
JJ
McCormick
Clare C
CC
Caballero
Armando R
AR
Stroman
David
D
O'Callaghan
Richard J
RJ
D000818:Animals; D000867:Anterior Chamber / Q000382:microbiology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001082:Aqueous Humor / Q000276:immunology; D001483:Base Sequence; D015169:Colony Count, Microbial; D015715:Corneal Edema / Q000382:microbiology; D024881:Drug Resistance, Bacterial; D009877:Endophthalmitis / Q000382:microbiology* / Q000473:pathology; D015818:Eye Infections, Bacterial / Q000382:microbiology* / Q000473:pathology; D007500:Iritis / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000276:immunology; D016133:Polymerase Chain Reaction; D011817:Rabbits; D021521:Ribotyping; D013047:Specific Pathogen-Free Organisms; D013203:Staphylococcal Infections / Q000382:microbiology* / Q000473:pathology; D013211:Staphylococcus aureus / Q000235:genetics* / Q000472:pathogenicity*; D014774:Virulence
D000900:Anti-Bacterial Agents