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Incompatibility group P-1 bla+ plasmids do not increase penicillin resistance of Pseudomonas acidovorans
Abstract:
Incompatibility group P-1 plasmids with the bla+ genotype were transferred from various Escherichia coli strains to Pseudomonas acidovorans strain 29. When resistance to ampicillin was used as the criterion, none of these plasmids appeared able to express their Bla+ phenotype in this host. When the plasmids were subsequently transferred back from these ampicillin-sensitive P. acdiovorans transcipients to E. coli strains, it was found that the Bla+ phenotype was again expressed. Although beta-lactamase was not detected in cultures of P. acidovorans transcipients, macroiodometric determinations of beta-lactamase activity made on broken cell suspensions revealed that beta-lactamase was indeed synthesized. It was concluded that P. acidovorans strain 29 allows expression of the bla gene within the cell but that this organism is unable to excrete the enzyme.
Insights
Pseudomonas acidovorans strain 29 can synthesize beta-lactamase from P-1 plasmids but cannot excrete it, leading to ampicillin sensitivity. This enzyme activity is restored upon transfer back to Escherichia coli.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Incompatibility group P-1 plasmids carry the bla+ gene conferring ampicillin resistance.
- Escherichia coli and Pseudomonas acidovorans are common bacterial species with distinct genetic mechanisms.
- Understanding plasmid gene expression across different bacterial hosts is crucial for antibiotic resistance research.
Purpose of the Study:
- To investigate the expression of the bla+ gene from P-1 plasmids in Pseudomonas acidovorans.
- To determine the reason for ampicillin sensitivity in P. acidovorans transcipients carrying bla+ plasmids.
- To elucidate the mechanism of beta-lactamase activity and its host-specific expression.
Main Methods:
- Conjugative transfer of P-1 plasmids (bla+) from Escherichia coli to Pseudomonas acidovorans strain 29.
- Assessment of ampicillin resistance in P. acidovorans transcipients.
- Back-transfer of plasmids from P. acidovorans to E. coli to confirm plasmid integrity and phenotype.
- Detection of beta-lactamase activity in whole cells and cell extracts of P. acidovorans.
Main Results:
- P-1 plasmids (bla+) failed to confer ampicillin resistance in Pseudomonas acidovorans.
- The bla+ phenotype was re-expressed when plasmids were transferred back to Escherichia coli.
- Beta-lactamase was synthesized intracellularly in P. acidovorans but not detected extracellularly.
- Enzyme assays on broken cell suspensions confirmed intracellular beta-lactamase synthesis in P. acidovorans.
Conclusions:
- Pseudomonas acidovorans strain 29 permits intracellular expression of the bla gene from P-1 plasmids.
- The inability to excrete beta-lactamase is responsible for the observed ampicillin sensitivity in P. acidovorans.
- Host-specific enzyme export mechanisms influence the phenotypic expression of plasmid-borne antibiotic resistance genes.