Transfer of resistance plasmids from Staphylococcus epidermidis to Staphylococcus aureus: evidence for conjugative exchange of resistance

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, RN45ORF, 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°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,1. This represents a novel mechanism for gene exchange among staphylococci.

SCCmecin staphylococci: genes on the move

“…Conjugation and conjugative mobilization have been described among staphylococcal isolates (Forbes & Schaberg, 1983;Projan & Archer, 1989;Archer & Scott, 1991;Thomas & Archer, 1992). Broad-host range conjugative plasmids with aminoglycoside resistance have been shown to transfer at low frequencies from streptococci to staphylococci (Macrina & Archer, 1993) and a self-transmissible plasmid transfers between CoNS and Staphylococcus aureus (Archer & Johnston, 1983).…”

Control of genes for conjugative transfer of plasmids and other mobile elements

“…Some Staphylococcal plasmids are 40^60 kb in size and transfer with low frequency (10 R^1 0 T transconjugants per donor) on solid surfaces [174,175]. pGO1 (52 kb) which encodes resistance to aminoglycosides, trimethoprim and quaternary ammonium compounds serves as a model for study of genetic organisation of the transfer region of such plasmids [176,177].…”

Emergence of teicoplanin-resistant coagulase-negative staphylococci

“…This is a cause of clinical concern, since CoNS may be a reservoir for antibiotic resistance genes in the hospital environment and may spread these resistance factors among other hospital pathogens (4,23). In fact, the conjugative transfer of resistance to gentamicin and other antimicrobial agents from CoNS to S. aureus has been demonstrated (10,13,25).…”