A comparison of the early inflammatory effects of an agr(-)/sar(-) versus a wild type strain of Staphylococcus aureus in a rat model of endophthalmitis

Purpose. We examined the;ability of a wild type and an isogenic mutant stra in of Staphylococcus aureus, deficient in the production of hemolysins and lipase (agr (-)/sar (-)), to induce endophthalmitis and inflammatory cell i nfiltration into the eye at 6, 24 and 48 hours after injection in a rat mod el of endophthalmitis. Methods. Rat eyes were injected with 25 mu l of viable S. aureus or sterile saline. Eyes were graded for clinical signs of inflammation daily, removed and processed for standard histologic analysis 6, 24 and 48 hours after in jections. Comparisons of clinical scores and mean inflammatory cell numbers were made between S. aureus and control injected eyes. Results. Both experimental groups developed clinical signs of endophthalmit is and demonstrated infiltration of inflammatory cells at 24 and 48 hours. Clinical inflammation in the Mutant I group was less than the wild type gro up at these times and significantly less at 48 hours (p<0.05). No statistic ally significant difference in the number of inflammatory cells was detecte d between the wild type and Mutant I injected eyes at 24 hours. At 48 hours , inflammatory cells increased by 75.0% in the wild type group and decrease d by 19.0% in the Mutant I group and a statistically significant difference was seen between these two groups (p<0.05). At all times, the majority of inflammatory cells were neutrophils. By 48 hours, an increase in monocytes- macrophages was noted. Conclusion. Both strains of S. aureus induced clinical signs of inflammatio n and inflammatory cell infiltration. Clinical inflammation and inflammator y cell numbers were less in rats injected with the Mutant I strain. These r esults suggest that hemolysins and lipase may be important in the early ind uction phase of the inflammatory response.