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[Group of derepressed pKMR plasmids found in wild strains of Shigella]
Abstract:
A group of derepressed (drd) R plasmids was identified in 3 clinical isolates of Shigella, i. e. Sh. flexneri 1b, Sh. flexneri 3c and Sh. sonnei resistant to ampicillin (Ap), streptomycin (Sm), tetracycline (Tc), chloramphenicol (Cm), kanamycin (Km) and sulfathiazole (Su). The plasmids were designated as pKMR 202-2 (Sm, Tc, Cm, Km, Su), pKMR 203-3 (Ap, Tc, Cm, Su), pKMR 204--2 (Sm, Km, Su), pKMR 204-3 (Ap, Sm, Cm, Km, Su), pKMR 204-4 (Ap, Sm, Km, Su), pKMR 204-5 (Km, Su), pKMR 204-6 (Ap, Sm, Tc, Cm, Km, Su) and pKMR 204-7 (Sm, Tc, Cm, Km, Su). All of the plasmids were transferred with the R- -cells of E. coli in 5 minutes at a frequency of 2 . 10(-6) to 4 . 10(-5) and had the Fi+ phenotype. None of them except pKMR 203-2 transferred sensitivity to F- donor-specific phages (f2 and Q beta) to the E. coli cells. The plasmids had neither capacity for maintaining multiplication of phages Ike and PR4 possessing the donor-specific properties with respect to the Inc N-, Inc P- and Inc W-plasmids. Therefore, the pKMR plasmids do not belong to these incompatibility groups. It should be noted that several plasmid variants (2--6) were isolated from every of the Shigella strains studied. Since they were stable in the cells and could be transferred separately on conjugation it was concluded that each combination was presented by the R factors belonging to different Inc-groups.
Insights
Researchers identified derepressed R plasmids in Shigella strains resistant to multiple antibiotics. These plasmids, designated pKMR, were transferable and exhibited the Fi+ phenotype, indicating potential for antibiotic resistance spread.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Clinical isolates of Shigella are a significant source of antibiotic resistance.
- R plasmids contribute to the spread of antimicrobial resistance among bacterial pathogens.
- Understanding plasmid characteristics is crucial for combating infectious diseases.
Purpose of the Study:
- To identify and characterize derepressed R plasmids in clinical Shigella isolates.
- To determine the antibiotic resistance profiles and transferability of these plasmids.
- To investigate the incompatibility (Inc) groups of the identified R plasmids.
Main Methods:
- Isolation and identification of R plasmids from Shigella flexneri and Shigella sonnei.
- Conjugation experiments to assess plasmid transfer frequency and phenotype (Fi+).
- Phage sensitivity assays to determine plasmid incompatibility groups.
Main Results:
- Multiple derepressed R plasmids (pKMR series) were identified in ampicillin, streptomycin, tetracycline, chloramphenicol, kanamycin, and sulfathiazole-resistant Shigella.
- All identified plasmids were transferable to E. coli with high frequency and displayed the Fi+ phenotype.
- The pKMR plasmids did not belong to Inc N, Inc P, or Inc W incompatibility groups and did not confer sensitivity to specific phages.
Conclusions:
- The identified pKMR plasmids represent a significant reservoir of antibiotic resistance in Shigella.
- The diverse Inc groups of these stable, transferable plasmids suggest multiple mechanisms for resistance dissemination.
- Further research into these R plasmids is warranted to understand their role in antimicrobial resistance epidemiology.