2008 OMIG, Abstract 6

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A New Staphylococcus aureus Rabbit Endophthalmitis Model and the Effectiveness of Fourth Generation Fluoroquinolones
Balzli CL, McCormick CC, Caballero A, Newman E, O’Callaghan RJ
University of Mississippi Medical Center Microbiology Department

Purpose: The ideal prophylactic therapy for cataract and related surgeries has been
difficult to determine because there has been no animal model in which bacteria survive
and replicate in the anterior chamber, causing endophthalmitis. Such a model of
Staphylococcus aureus infection has now been developed and used to compare two
fluoroquinolone therapies.
Methods: The model of endophthalmitis infection was established by injecting either 104 or 106 colony forming units (CFU) of log phase S. aureus strain UMCR1 directly into the anterior chamber. Pathology was recorded at 2, 4, 6, 8, 12, and 16 hours post-infection (PI). Bacteria were quantified at these time points by removing and serially diluting the aqueous humor then plating the dilutions in triplicate to determine CFU ± SEM per eye. To assess the capacity of two fluoroquinolones to prevent endophthalmitis, one drop of either Vigamox (0.5% moxifloxacin) or the most recent fluoroquinolone product Iquix (1.5% levofloxacin) was applied to rabbit eyes. After 5 minutes, each eye was rinsed topically with 5 ml of phosphate buffered saline. Ten minutes following administration of the topical drops, each eye was injected with 106 CFU in 10 µl. The animals were sacrificed at 30 minutes after infection and bacteria in the aqueous humor were quantified.
Results: Strain UMCR1 was able to replicate extensively in the aqueous humor reaching maximal CFU of 107 per ml. Depending on the inoculum, infections were stopped at 8 or 16 hours PI because of the severity of infection as evidenced by severe iritis, fibrin accumulation, corneal edema, and hyperemia. In this S. aureus endophthalmitis model, both groups of fluoroquinolone treated eyes were significantly lower than the untreated control which had 4.80 ± 0.34 CFU per ml (P = 0.0016). Eyes treated prophylactically with Vigamox had 1.12 ± 0.32 log CFU at 30 minutes PI whereas eyes treated with Iquix had 2.46 ± 0.42 log CFU (P = 0.0288).
Conclusions: Strain UMCR1 appears unique in its ability to resist the host defenses of the anterior chamber, an ability that remains undefined. Prophylactic administration of
Vigamox to the cornea was superior to Iquix in providing bacterial killing within the
rabbit anterior chamber.

Disclosure code: F