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Conjugative mobilization of the rolling-circle plasmid pIP823 from Listeria monocytogenes BM4293 among gram-positive
E Charpentier1, G Gerbaud, P Courvalin
1Unité des Agents Antibactériens, Institut Pasteur, 75724 Paris Cedex 15, France.
Abstract:
We determined the sequence and genetic organization of plasmid pIP823, which contains the dfrD gene; dfrD confers high-level trimethoprim resistance to Listeria monocytogenes BM4293 by synthesis of dihydrofolate reductase type S2. pIP823 possessed all the features of the pUB110/pC194 plasmid family, whose members replicate by the rolling-circle mechanism. The rep gene encoded a protein identical to RepU, the protein required for initiation of the replication of plasmids pTB913 from a thermophilic Bacillus sp. and pUB110 from Staphylococcus aureus. The mob gene encoded a protein with a high degree of amino acid identity with the Mob proteins involved in conjugative mobilization and interplasmidic recombination of pTB913 and pUB110. The host range of pIP823 was broad and included L. monocytogenes, Enterococcus faecalis, S. aureus, Bacillus subtilis, and Escherichia coli. In all these species, pIP823 replicated by generating single-stranded DNA and was stable. Conjugative mobilization of pIP823 was obtained by self-transferable plasmids between L. monocytogenes and E. faecalis, between L. monocytogenes and E. coli, and between strains of E. coli, and by the streptococcal conjugative transposon Tn1545 from L. monocytogenes to E. faecalis, and from L. monocytogenes and E. faecalis to E. coli. These data indicate that the gene flux observed in nature from gram-positive to gram-negative bacteria can occur by conjugative mobilization. Our results suggest that dissemination of trimethoprim resistance in Listeria spp. and acquisition of other antibiotic resistance determinants in this species can be anticipated.
Insights
Plasmid pIP823 confers trimethoprim resistance to Listeria monocytogenes by carrying the dfrD gene. This plasmid can transfer between various bacteria, suggesting a mechanism for antibiotic resistance gene spread.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Trimethoprim resistance in Listeria monocytogenes is a growing concern.
- Understanding the genetic elements responsible for antibiotic resistance is crucial for public health.
Purpose of the Study:
- To determine the sequence and genetic organization of plasmid pIP823.
- To investigate the replication and transfer mechanisms of pIP823.
- To assess the potential for pIP823 to contribute to antibiotic resistance dissemination.
Main Methods:
- Plasmid sequencing and genetic analysis.
- Replication and stability assays in various bacterial hosts.
- Conjugative mobilization experiments using self-transferable plasmids and transposons.
Main Results:
- Plasmid pIP823 contains the dfrD gene, conferring high-level trimethoprim resistance.
- pIP823 shares features with the pUB110/pC194 family, replicating via a rolling-circle mechanism.
- The plasmid demonstrated a broad host range, replicating stably in Listeria, Enterococcus, Staphylococcus, Bacillus, and Escherichia species.
- Conjugative mobilization of pIP823 was observed between different bacterial species, including gram-positive to gram-negative transfer.
Conclusions:
- Plasmid pIP823 is a mobile genetic element capable of conferring trimethoprim resistance.
- Its broad host range and conjugative transferability facilitate the spread of antibiotic resistance genes.
- These findings highlight the potential for increased dissemination of trimethoprim resistance in Listeria and acquisition of other resistance determinants.