Cephalothin clearance of Staphylococcus aureus from two experimental infection sites in the presence and absence of local phagocytic cells

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Abstract
The clearance of Staphylococcus aureus from perforated peritoneal capsules which are accessible to phagocytic cells, and subcutaneous Visking chambers which exclude phagocytes, was studied simultaneously in eight rabbits implanted with both devices. Animals were treated with cephalothin, 100 mg/kg im every 8 h for sixteen doses, beginning 24 h after inoculation of the infection sites with S. aureus (cephalothin MIC 0.125 mg/l, MBC 0.5 mg/l). At the start of cephalothin, subcutaneous chambers contained a higher concentration of S. aureus (8.4 log10 cfu/ml) than peritoneal capsules (6.8 log10 cfu/ml, P < 0.001). There was a significant bactericidal effect in subcutaneous chambers on both the third and sixth day of treatment (P < 0.002), whereas in peritoneal capsules this did not occur until day six. The total reduction in bacterial count in subcutaneous chambers (7.0 log10 cfu/ml) was significantly greater than in capsules (4.4 log10 cfu/ml, P < 0.002). The mean concentration of cephalothin in subcutaneous chambers (10.7 mg/l) was significantly higher than in peritoneal capsules (6.1 mg/l, P < 0.02), but no difference in in-vitro killing of S. aureus was detected at these concentrations. We conclude that cephalothin clearance of S. aureus from a site accessible to phagocytes was delayed when compared to a phagocyte-inaccessible site.