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Transfer of resistance plasmids from Staphylococcus epidermidis to Staphylococcus aureus: evidence for conjugative
Abstract:
The ability of Staphylococcus epidermidis to transfer antimicrobial resistance to Staphylococcus aureus was tested by mixed culture on filter membranes. Two of six clinical isolates examined were able to transfer resistance to S. aureus strains 879R4RF, RN450RF, and UM1385RF. Subsequent S.aureus transconjugants resulting from matings with S. epidermidis donors were able to serve as donors to other S. aureus strains at similar frequencies. Cell-free and mitomycin C-induced filtrates of donors and transconjugants showed no plaque-forming ability. Addition of DNase I, citrate, EDTA, calcium chloride, and human sera to mating mixes and agar showed no effect on transfer. Nonviable donor cells were unable to transfer resistance and transfer did not occur at 4 degrees C. Cell-to-cell contact was required since transfer did not occur in broth or when filters of donor and recipient, respectively, were placed back-to-back so cells were not in direct contact. Analysis of DNA from S. epidermidis isolate UM899, its subsequent S. aureus transconjugants, and cured derivatives demonstrated that all resistance markers which transferred resided on plasmids. Mating experiments suggested a central role for the gentamicin plasmid pAM899-1 in the transfer process. It is concluded that our results are consistent with a conjugative transfer of resistance from S. epidermidis to S. aureus analogous to plasmid transfer demonstrated in streptococcal species for plasmids such as pAM beta 1. This represents a novel mechanism for gene exchange among staphylococci.
Insights
Antimicrobial resistance transfer from Staphylococcus epidermidis to Staphylococcus aureus was observed via cell-to-cell contact. This study identified plasmid-mediated conjugation as the mechanism for this novel gene exchange.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Staphylococcus epidermidis and Staphylococcus aureus are significant human pathogens.
- Antimicrobial resistance in staphylococci poses a major public health threat.
- Understanding gene transfer mechanisms is crucial for combating resistance.
Purpose of the Study:
- To investigate the potential of Staphylococcus epidermidis to transfer antimicrobial resistance to Staphylococcus aureus.
- To elucidate the mechanism of antimicrobial resistance transfer between these staphylococcal species.
Main Methods:
- Mixed cultures of Staphylococcus epidermidis and Staphylococcus aureus on filter membranes.
- Analysis of transconjugants for resistance markers.
- Plasmid DNA analysis and mating experiments.
- Testing effects of various compounds and conditions on transfer efficiency.
Main Results:
- Two of six clinical Staphylococcus epidermidis isolates transferred antimicrobial resistance to Staphylococcus aureus.
- Transconjugants could subsequently act as donors.
- Transfer required direct cell-to-cell contact and was temperature-dependent.
- Resistance markers were located on plasmids, with pAM899-1 playing a central role.
Conclusions:
- A novel mechanism of conjugative transfer of antimicrobial resistance from Staphylococcus epidermidis to Staphylococcus aureus was demonstrated.
- This process is analogous to plasmid transfer mechanisms observed in streptococci.
- This finding highlights a new pathway for staphylococcal gene exchange and resistance dissemination.