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Lipopolysaccharide changes in impermeability-type aminoglycoside resistance in Pseudomonas aeruginosa
Abstract:
Clinical isolates of Pseudomonas aeruginosa were examined for the basis of impermeability-type aminoglycoside resistance. Two apparently related burn isolate strains with high-level (strain 8803) and low-level (strain 13934) gentamicin resistance each had a plasmid. Transformation of the plasmid from either strain to P. aeruginosa PAO503 resulted in low-level gentamicin resistance. No mechanism for this resistance could be determined. Low-level gentamicin and streptomycin resistance from strain 8803 (but not 13934) was transduced with phage E79.tv2 to PAO503 without transfer of plasmid DNA. Transductants like strain 8803 showed absence or reduction of the lipopolysaccharide (LPS) "ladder" pattern of PAO503, had a change in chemical composition of LPS, and, like strain 8803, had a reduced capability to accumulate streptomycin. Comparison of the resistant clinical isolates 8803 and P10 with the apparently related but less-resistant strains 13934 and P10R, respectively, showed the latter strains had LPS ladder patterns and the former strains did not. Strain 8803 had normal outer membrane protein profiles, electron transport components, and transmembrane electrical potential relative to PAO503 and has been previously shown to have no detectable gentamicin-modifying enzymes and normal protein synthesis. We conclude that low-level impermeability-type aminoglycoside resistance in P. aeruginosa results from conversion of smooth LPS to superficial or deeper rough LPS phenotypes. High-level resistance apparently results from a plasmid-specified, but as yet unknown, mechanism combined with the preceding change in LPS structure.
Insights
Pseudomonas aeruginosa aminoglycoside resistance involves changes in lipopolysaccharide (LPS) structure. Low-level resistance stems from altered LPS, while high-level resistance combines this with unknown plasmid-mediated mechanisms.
Area of Science:
- Microbiology
- Molecular Biology
- Drug Resistance
Background:
- Aminoglycoside antibiotics are crucial for treating Pseudomonas aeruginosa infections.
- Mechanisms of antibiotic resistance in P. aeruginosa, particularly impermeability-type resistance, require further elucidation.
- Lipopolysaccharide (LPS) alterations are implicated in bacterial outer membrane permeability and antibiotic resistance.
Purpose of the Study:
- To investigate the basis of impermeability-type aminoglycoside resistance in clinical isolates of Pseudomonas aeruginosa.
- To determine the role of plasmids and lipopolysaccharide (LPS) structure in conferring gentamicin and streptomycin resistance.
- To differentiate mechanisms contributing to low-level versus high-level aminoglycoside resistance.
Main Methods:
- Analysis of clinical P. aeruginosa isolates for aminoglycoside resistance.
- Plasmid transformation experiments in P. aeruginosa PAO503.
- Bacteriophage transduction to transfer resistance markers.
- Examination of lipopolysaccharide (LPS) structure using SDS-PAGE (ladder pattern) and chemical analysis.
- Assessment of streptomycin accumulation in bacterial cells.
- Characterization of outer membrane proteins and electron transport components.
Main Results:
- Two related P. aeruginosa strains exhibited high-level (8803) and low-level (13934) gentamicin resistance, each possessing a plasmid.
- Plasmid transformation conferred low-level gentamicin resistance but the exact mechanism remained undetermined.
- Low-level gentamicin and streptomycin resistance was transduced from strain 8803 to PAO503 without plasmid transfer, associated with LPS alterations (reduced ladder pattern, changed composition).
- Resistant strains (8803, P10) showed absence or reduction of the LPS ladder pattern compared to less-resistant strains (13934, P10R).
- Strain 8803 demonstrated reduced streptomycin accumulation, normal outer membrane proteins, and no detectable gentamicin-modifying enzymes.
Conclusions:
- Low-level impermeability-type aminoglycoside resistance in P. aeruginosa is associated with the conversion of smooth LPS to rough LPS phenotypes.
- High-level aminoglycoside resistance appears to result from a combination of plasmid-mediated factors and LPS structural changes.
- Understanding these resistance mechanisms is critical for developing effective therapeutic strategies against P. aeruginosa infections.