title: Diverse virulence of Staphylococcus aureus strains for the conjunctiva.
abstract: OBJECTIVE
  To determine the virulence of Staphylococcus aureus strains in the rabbit conjunctiva.
  
  
  METHODS
  Three strains of methicillin-sensitive S. aureus (8325-4, Newman, and UMCR1) and two strains of methicillin-resistant S. aureus (70490 and MW2) were analyzed. Rabbit bulbar conjunctivas (n ≥ 6 per group) were injected with 10(5) colony forming units (CFU) in 10 µl. Eyes were photographed and analyzed for pathology at 20 hr postinfection (PI) using slit lamp examination (SLE) to measure five parameters on a scale from 0 (normal) to 4 (severe): injection, chemosis, iritis, corneal edema, and pinpoint conjunctival hemorrhages. The parameter grades were added to produce a SLE score. Bacteria were enumerated and histopathological analysis was done at 20 hr PI. Myeloperoxidase assays were performed on conjunctival swabs (n ≥ 3 per strain) at 0 and 20 hr PI.
  
  
  RESULTS
  Conjunctivas injected with 8325-4 or Newman had SLE scores of 1.67 ± 0.12 and 0.81 ± 0.16, respectively. Strain 70490 produced an average SLE score of 2.94 ± 0.47, whereas MW2 produced a score of 5.04 ± 0.73. UMCR1 produced severe conjunctivitis having a SLE score of 13.25 ± 0.80. Only strain UMCR1 grew in the conjunctiva showing a 2.7 log increase in CFU; all other strains remained near the inoculated numbers or decreased as much as 1.85 logs. Myeloperoxidase activity was greatest in the tear film of UMCR1 infected eyes with over one million PMN present at 20 hr PI.
  
  
  CONCLUSIONS
  Only one S. aureus strain, UMCR1, was able to cause a reproducible severe conjunctivitis. This conjunctival infection could be used to test new antimicrobials and to help understand the pathogenesis of conjunctivitis, especially in terms of overcoming the host defenses.
authors.affiliation: Department of Microbiology, University of Mississippi Medical Center, 2500 N. State St., Jackson, MS 39216, USA.
authors.forename: Clare C
authors.initials: CC
authors.lastname: McCormick
authors.forename: Armando R
authors.initials: AR
authors.lastname: Caballero
authors.forename: Charles L
authors.initials: CL
authors.lastname: Balzli
authors.forename: Aihua
authors.initials: A
authors.lastname: Tang
authors.forename: Anastasia
authors.initials: A
authors.lastname: Weeks
authors.forename: Richard J
authors.initials: RJ
authors.lastname: O'Callaghan
mesh_terms: D000818:Animals; D015169:Colony Count, Microbial; D003234:Conjunctivitis, Bacterial / Q000382:microbiology*; D004195:Disease Models, Animal; D008712:Methicillin / Q000494:pharmacology; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification / Q000472:pathogenicity*; D009504:Neutrophils / Q000201:enzymology; D009195:Peroxidase / Q000378:metabolism; D011817:Rabbits; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000472:pathogenicity; D014774:Virulence
chemical_list: D009195:Peroxidase; D008712:Methicillin