[Electron microscopic study of the effect of methicillin on phagocytized Staphylococcus aureus cells].

Morphological changes in phagocytized cells of Staph. aureus due to methicillin were studied with electron microscopy of ultrathin sections. Peritoneal macrophages of mice obtained by excitation of the abdominal cavity with medium No. 199 followed by infection with 1-milliard staphylococcal suspension were tested. Methicillin was administered in single doses of 2.5, 5, 25 and 50 mg/kg. The doses of 2.5 and 5 mg/kg induced specific changes in some cells. First of all the division septa were affected. After that the cell walls became thinner the cells increased in size, the cytoplasm became electronically less solid. No lysed cells were detected. The use of the doses of 25 and 50 mg/kg entailed polymorphism of the damages. Perforations formed in the bacterial cell wall. The cytoplasm acquired a characteristic granular structure evident of the cell death. With an increase in the dose from 25 to 50 mg/kg no rise in the level of the morphological changes in the bacterial cells was noted. Determination of methicillin concentration in the peritoneal exudate showed that it was 2--4 times higher depending on the dose than the MIC in vitro.