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Structural alterations in the envelope of a gentamicin-resistant rough mutant of Pseudomonas aeruginosa
Abstract:
Comparative studies of a gentamicin-sensitive strain (P28-0) of Pseudomonas aeruginosa and a gentamicin-resistant mutant (P23-800) have been carried out. No aminoglycoside-modifying enzymes were detected in extracts of the mutant. Electron microscopy of thin sections and the loss of O-antigenicity suggested that resistance of the mutant to gentamicin was related to an alteration in the outer membrane. Analysis of the lipopolysaccharide (LPS) components of the cell walls revealed significant differences. The LPS from strain P28-0 was typical of wild-type P. aeruginosa strains of Habs serotype O6, with quinovosamine and aminogalacturonic acid as O-specific aminocomponents. The LPS from the resistant mutant lacked the O-specific polymer, but had a core oligosaccharide similar to that of the parent strain. Both LPS were rich in phosphorus, part of which was present in triphosphate residues. Although the 31P nuclear magnetic resonance spectra of the LPS differed in some respects, these differences did not seem to correlate with the disparity in sensitivity to gentamicin of the two organisms.
Insights
Pseudomonas aeruginosa developed gentamicin resistance due to outer membrane changes, not enzyme modification. Lipopolysaccharide alterations, specifically the loss of O-specific polymer, are key to this resistance.
Area of Science:
- Microbiology
- Bacterial genetics
- Molecular biology
Background:
- Gentamicin resistance in Pseudomonas aeruginosa is a significant clinical concern.
- Mechanisms of antibiotic resistance often involve enzymatic inactivation or target modification.
- Outer membrane alterations can influence bacterial susceptibility to antibiotics.
Purpose of the Study:
- To investigate the mechanism of gentamicin resistance in a specific mutant strain of Pseudomonas aeruginosa.
- To compare the gentamicin-sensitive parent strain (P28-0) with the resistant mutant (P23-800).
- To elucidate the role of outer membrane and lipopolysaccharide (LPS) composition in gentamicin resistance.
Main Methods:
- Comparative analysis of gentamicin-sensitive and resistant Pseudomonas aeruginosa strains.
- Detection of aminoglycoside-modifying enzymes.
- Electron microscopy for outer membrane structural analysis.
- Lipopolysaccharide (LPS) component analysis, including O-specific aminocomponents.
- 31P nuclear magnetic resonance (NMR) spectroscopy of LPS.
Main Results:
- No aminoglycoside-modifying enzymes were detected in the resistant mutant.
- Electron microscopy indicated outer membrane alterations and loss of O-antigenicity in the resistant strain.
- LPS analysis revealed significant differences, with the resistant mutant lacking the O-specific polymer but retaining a similar core oligosaccharide.
- Both strains had LPS rich in phosphorus, including triphosphate residues, but 31P NMR spectra differences did not correlate with gentamicin sensitivity.
Conclusions:
- Gentamicin resistance in this Pseudomonas aeruginosa mutant is associated with alterations in the outer membrane and lipopolysaccharide structure, specifically the absence of the O-specific polymer.
- The findings suggest that changes in LPS composition, rather than enzymatic modification, are responsible for the observed resistance.
- Further research into outer membrane and LPS modifications is warranted for understanding and combating antibiotic resistance in Pseudomonas aeruginosa.