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Conjugative mobilization of a vancomycin resistance plasmid by a putative Enterococcus faecium sex pheromone response
1Laboratory of Microbiology, Rockefeller University, New York, New York 10021, USA.
Abstract:
Recent epidemiological evidence suggests that horizontal gene transfer may be an important mechanism for dissemination of vancomycin resistance. A filter mating survey of 21 VanA Enterococcus faecium isolates from The New York Hospital showed that 14 of these isolates transferred vancomycin resistance (Vmr) to the plasmid-free reference strain Enterococcus faecalis JH2-2. One isolate, E. faecium R7, was selected for further study based on its ability to transfer Vmr to strain JH2-2 in liquid culture. Analysis of the plasmid content of transconjugants revealed three general classes. The predominant class (28 of 47 transconjugants) contained two separate plasmids: pHKK702 and pHKK703. pHKK702 is a 41-kb plasmid that contains an element indistinguishable from the Vmr transposon Tn1546 and an element that hybridizes with an ermB probe from the Staphylococcus aureus erythromycin resistance transposon Tn551. pHKK703 is a 55-kb plasmid that hybridizes with probes for the sex pheromone response genes prgA, prgB, and prgX derived from the E. faecalis plasmid pCF10. The second group of transconjugants (18 of 47) contained various recombinant forms of pHKK702 and pHKK703, whereas a third transconjugant class contained only pHKK702 (1 of 47). Transconjugants that contained both pHKK702 and pHKK703 were able to efficiently transfer Vmr to recipient strains in broth or on filters. However, no transfer of Vmr was detected using the donor containing only pHKK702. The transfer of Vmr from the recombination-deficient derivative of E. faecalis JH2-2 [strain UV202(pHKK702, pHKK703)] was reduced 600-fold compared to that of JH2-2(pHKK702, pHKK703). We propose that pHKK703 functions as an E. faecium sex pheromone response plasmid that conjugatively mobilizes pHKK702, and that a major pathway for this mobilization may require donor-mediated recombination proficiency. This report provides the first example in which a plasmid containing a Tn1546-related element is conjugatively mobilized.
Insights
Horizontal gene transfer aids vancomycin resistance spread. A specific Enterococcus faecium plasmid (pHKK703) mobilizes another (pHKK702) carrying resistance genes, requiring donor cell recombination for efficient transfer.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Epidemiological data suggest horizontal gene transfer (HGT) is crucial for vancomycin resistance dissemination.
- Vancomycin resistance in Enterococcus faecium is a significant public health concern.
- Understanding the mechanisms of resistance gene transfer is vital for combating antimicrobial resistance.
Purpose of the Study:
- To investigate the plasmid-mediated transfer of vancomycin resistance (Vmr) from Enterococcus faecium.
- To characterize the plasmids involved in the conjugative mobilization of Vmr.
- To elucidate the role of donor cell recombination in Vmr transfer.
Main Methods:
- Filter mating and liquid culture assays were used to assess Vmr transfer between Enterococcus strains.
- Plasmid content analysis of transconjugants was performed using hybridization techniques.
- Recombination-deficient recipient strains were employed to evaluate the role of recombination in transfer.
Main Results:
- 14 out of 21 VanA Enterococcus faecium isolates transferred Vmr to Enterococcus faecalis JH2-2.
- Two plasmids, pHKK702 (41-kb) and pHKK703 (55-kb), were identified in efficient Vmr transconjugants.
- pHKK702 contains a Tn1546-like element and an ermB-hybridizing element; pHKK703 contains sex pheromone response genes.
- Efficient Vmr transfer required both plasmids; transfer was significantly reduced in recombination-deficient recipients.
Conclusions:
- The plasmid pHKK703 acts as a conjugative mobilizing plasmid for pHKK702, which carries the vancomycin resistance transposon.
- Donor-mediated recombination proficiency appears to be a significant factor in the mobilization of pHKK702 by pHKK703.
- This study demonstrates the conjugative mobilization of a Tn1546-related element by a pheromone-responsive plasmid.