Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) N 133 was intranasally inoculated to mice. Three hours after inoculation with 106 CFU of S.aureus N 133, 105CFU of the bacteria was detected in the caecum. The viable cell count in the caecum decreased to 102CFU three days after inoculation but increased again to approximately 103CFU five days after inoculation. And the cell level was maintained for at least ten days. Ampicillin increased the viable cell count slightly when administered subcutaneously at a dose of 10 or 20mg/kg twice a day for four days starting on the day before inoculation, whereas cefotiam suppressed growth slightly, and cefozopran inhibited it completely. When mice underwent abdominal surgery to provide stress or were administered 200mg/kg of cyclophosphamide or dexamethasone in order to supress immunity, the growth of MRSA in the caecum was enhanced significantly. On the other hand, oral administration of Enterococcus faecium before inoculation suppressed the excessive growth of MRSA induced by abdominal surgery. These results suggest that immunosuppression and stress by abdominal surgery play more important roles than antibiotics in the growth of MRSA in the caecum.
