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[Electron microscopic study of the effect of methicillin on phagocytized Staphylococcus aureus cells]
Abstract:
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.
Insights
Methicillin alters Staphylococcus aureus morphology, affecting cell walls and cytoplasm. Higher doses cause cell death, with concentrations exceeding in vitro minimum inhibitory concentrations.
Area of Science:
- Microbiology
- Pharmacology
- Cell Biology
Background:
- Staphylococcus aureus is a common pathogen.
- Methicillin is an antibiotic used to treat Staphylococcal infections.
- Understanding antibiotic mechanisms of action is crucial for combating resistance.
Purpose of the Study:
- To investigate the ultrastructural changes in Staphylococcus aureus cells phagocytized by mouse macrophages following methicillin administration.
- To correlate methicillin dosage with observed morphological alterations in bacteria.
- To compare in vivo methicillin concentrations with in vitro minimum inhibitory concentrations (MIC).
Main Methods:
- Electron microscopy of ultrathin sections was used to examine phagocytized Staphylococcus aureus cells.
- Mouse peritoneal macrophages were infected with Staphylococcus aureus and treated with varying doses of methicillin (2.5, 5, 25, 50 mg/kg).
- Methicillin concentration in peritoneal exudate was measured and compared to in vitro MIC.
Main Results:
- Low methicillin doses (2.5, 5 mg/kg) affected division septa and cell walls, leading to cell enlargement and cytoplasmic changes, but no lysis.
- High methicillin doses (25, 50 mg/kg) induced more severe damage, including cell wall perforations and granular cytoplasm indicative of cell death.
- In vivo methicillin concentrations in peritoneal exudate were 2-4 times higher than the in vitro MIC.
Conclusions:
- Methicillin induces dose-dependent morphological changes in phagocytized Staphylococcus aureus.
- The observed in vivo concentrations suggest methicillin efficacy against Staphylococcus aureus within the peritoneal cavity.
- These findings provide ultrastructural insights into methicillin's bactericidal effects on Staphylococcus aureus.