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Electron microscopic observations of polysaccharide components in polymyxin B treated outer membranes from Serratia
Abstract:
Treatment of outer membranes of Serratia marcescens with polymyxin B results in the formation of blebs. This effect is thought to be due to the action of the antibiotic on the lipopolysaccharides, proteins, phospholipids or a combination thereof. It is unclear whether this effect is dissociative, degradative or due to an inhibition of the assembly of outer membrane components. Prior studies showed that lipopolysaccharides and polymyxin B form complexes, but direct visualization of the in situ action of polymyxin B had not been accomplished. Isolated outer membranes normally exhibit a periodicity of the polysaccharide molecules when stained by the thiosemicarbazide-silver technique. Polymyxin B treated outer membranes display a change in their basic morphology. This effect is very drastic in the sensitive strain as demonstrated by the large gaps in the deposition of the granules in the modified outer membrane structure. Thus it appears that the polysaccharide molecules (probably the lipopolysaccharide) either alone or in association with protein or phospholipids are the primary targets of the antibiotic.
Insights
Polymyxin B antibiotic treatment causes blebbing in Serratia marcescens outer membranes. This study visualizes polymyxin B
Area of Science:
- Microbiology
- Bacterial Outer Membrane Structure
- Antibiotic Action
Background:
- Serratia marcescens outer membranes form blebs upon treatment with polymyxin B.
- The precise mechanism of polymyxin B's effect on outer membrane components (lipopolysaccharides, proteins, phospholipids) remains unclear.
- Previous research indicated lipopolysaccharide-polymyxin B complex formation, but in situ visualization was lacking.
Purpose of the Study:
- To directly visualize the in situ action of polymyxin B on Serratia marcescens outer membranes.
- To elucidate the specific targets and mechanism of polymyxin B-induced outer membrane alterations.
Main Methods:
- Treatment of isolated Serratia marcescens outer membranes with polymyxin B.
- Utilizing the thiosemicarbazide-silver staining technique to visualize outer membrane morphology.
- Comparative analysis of polymyxin B treated and untreated outer membranes.
Main Results:
- Polymyxin B treatment drastically altered the basic morphology of Serratia marcescens outer membranes.
- Significant gaps in granule deposition were observed in polymyxin B treated membranes, especially in sensitive strains.
- The polysaccharide molecules, likely lipopolysaccharides, were identified as the primary targets of polymyxin B.
Conclusions:
- Polymyxin B directly targets polysaccharide molecules, likely lipopolysaccharides, in the Serratia marcescens outer membrane.
- These interactions lead to significant morphological changes, including bleb formation and altered granule deposition.
- The findings suggest that lipopolysaccharides, potentially in association with proteins or phospholipids, are the primary targets of polymyxin B's action.