Related Experiment Videos
Alternate forms of the resistance factor R1 in Proteus mirabilis
Abstract:
The resistance factor R1 may exist in either of two stable physical states in Proteus mirabilis PM-1. In one case, the R1 deoxyribonucleic acid (DNA) has a buoyant density of 1.711 g/cm(3) and replicates under stringent control. Cells harboring R1 in this form may transfer drug resistance by conjugation. In the other case, R1 DNA shows two buoyant density classes at 1.707 and 1.714 g/cm(3). The 1.714 g/cm(3) component is replicated under a degree of relaxed control, and strains carrying this form generally cannot transfer drug resistance by conjugation. Intracellular amounts of the R factor-coded enzyme, chloramphenicol acetyltransferase, did not correspond to amounts of plasmid DNA in Proteus, and the enzyme was present in lower amounts than in Escherichia coli. It is proposed that the two states of R1 in Proteus may represent stable associated and dissociated forms of the plasmid.
Insights
The R1 resistance factor in Proteus mirabilis exists in two states, affecting deoxyribonucleic acid (DNA) density and replication control. These states influence the transfer of drug resistance, suggesting stable associated and dissociated plasmid forms.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- The R1 resistance factor in Proteus mirabilis exhibits distinct physical states.
- Understanding these states is crucial for comprehending drug resistance mechanisms and plasmid behavior.
Purpose of the Study:
- To investigate the two stable physical states of the R1 resistance factor in Proteus mirabilis.
- To correlate these states with deoxyribonucleic acid (DNA) properties, replication control, and drug resistance transfer.
Main Methods:
- Analysis of R1 deoxyribonucleic acid (DNA) buoyant density.
- Assessment of replication control stringency.
- Evaluation of drug resistance transfer via conjugation.
- Quantification of chloramphenicol acetyltransferase activity.
Main Results:
- R1 DNA exists in two states: a single density (1.711 g/cm(3)) with stringent replication and conjugal transfer, or two densities (1.707 and 1.714 g/cm(3)) with relaxed replication and impaired transfer.
- Chloramphenicol acetyltransferase levels did not correlate with plasmid DNA amounts and were lower than in Escherichia coli.
Conclusions:
- The two physical states of R1 in Proteus mirabilis likely represent stable associated and dissociated forms of the plasmid.
- These distinct plasmid forms influence the bacterium's ability to transfer drug resistance.