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Decrease in ribosomal density of Proteus mirabilis exposed to subinhibitory concentrations of ampicillin or
Abstract:
The finding of reduced ribosomal densities at lower concentrations than those required to stop growth or cause visible defects in the cell wall is in contrast to the current view that the initial lesion produced by penicillins or cephalosporins is a defect in murein synthesis (11). This reduction in ribosomal density could be a primary or secondary effect and might be due to a decreased rate of growth, which has been shown to be associated with a lower ribosome frequency (12, 13) or to less stable ribosomes which disintegrated either spontaneously or as a result of the fixation procedures. The possibility that the decrease in ribosomal frequency was due to dilution (influx of liquid through a defective cell wall and/or cytoplasmic membrane, or efflux of ribosomes) remains, but no gross defect in cell wall was seen in more than 50 sections of cells showing reductions in ribosomal frequency. These findings suggest that an effect on ribosomes may antecede an effect on the cell wall.
Insights
Antibiotics like penicillin reduce bacterial ribosome density before causing cell wall defects. This challenges the view that cell wall synthesis is the primary target, suggesting ribosomes may be affected first.
Area of Science:
- Microbiology
- Molecular Biology
- Cell Biology
Background:
- Current understanding posits that penicillins and cephalosporins primarily target bacterial murein (cell wall) synthesis.
- Antibiotic-induced cellular damage is typically characterized by defects in cell wall integrity.
Purpose of the Study:
- To investigate the initial cellular targets of penicillin and cephalosporin antibiotics.
- To determine if ribosomal density changes precede cell wall defects.
Main Methods:
- Microscopic examination of bacterial cell sections.
- Quantitative analysis of ribosomal density in response to antibiotic treatment.
Main Results:
- Reduced ribosomal densities were observed at antibiotic concentrations lower than those causing visible cell wall defects.
- No gross cell wall defects were evident in cells exhibiting decreased ribosomal frequency.
Conclusions:
- Antibiotic-induced reduction in ribosomal density may precede cell wall damage.
- This finding challenges the established model of antibiotic action, suggesting a potential primary effect on bacterial ribosomes.