Conjugational transfer of gentamicin resistance plasmids intra- and interspecifically in Staphylococcus aureus and Staphylococcus epidermidis

Abstract

We have previously reported the transfer of gentamicin resistance (Gmr) plasmids in a mixed culture inter-and intraspecifically between strains of Staphylococcus aureus and Staphylococcus epidermidis isolated at Michael Reese Hospital (Jaffe et al., Antimicrob. Agents Chemother. 21:773-779, 1982). We have now shown that representatives of these plasmids were transferred between apparently nonlysogenic strains of S. aureus either in mixed culture in broth or by filter-mating on agar medium. The mechanism of transfer appeared to be conjugation. A transferable Gmr plasmid (pSH8) mobilized or cotransferred a tetracycline R-plasmid and a chloramphenicol R-plasmid that were not independently transferable. The transfer of Gmr plasmids was accompanied by a high incidence of deletion mutations with varied loss of plasmid resistance determinants and, with some mutants, loss of the ability to effect self-transfer. Restriction endonuclease digestion of pSH8 and its deletion mutants made it possible to assign the property of self-transfer to a specific segment of the pSH8 genome and provided the basis for a physical and genetic map of that plasmid. Similar Gmr plasmids from S. aureus strains isolated in locations remote from Michael Reese Hospital had resistance determinants and transfer properties comparable to those of pSH8. Our observations provide evidence for the conjugal transfer of some staphylococcal plasmids, apparently independent of the presence of phage. This mechanism may be of significance in the intra-and interspecific dissemination of resistance to aminoglycosides and other antibiotics in Staphylococcus spp.We have reported the recovery of five classes of closely related gentamicin resistance (Gm) plasmids from Staphylococcus aureus and Staphylococcus epidermidis (13,14). Each plasmid class was defined by its spectrum of antibiotic resistance markers, molecular mass, and restriction endonuclease digestion pattern. Apparently identical Gmr plasmids of each class were present in epidemiologically related isolates of S. aureus and S. epidermidis (35). Similar results have recently been reported by others (2). Evidence of identity between tetracycline resistance plasmids in isolates of S. aureus and S. epidermidis has also been published recently (10,12,34). These findings support the hypothesis that the transfer of plasmids between S. aureus and S. epidermidis occurs in nature.Transduction has been favored as the principal mechanism of genetic exchange between S.

Antibiotic susceptibilities and plasmid profiles of nosocomial methicillin-resistant Staphylococcus aureus: A retrospective study

“…In addition to GTKR, these transformants also acquired ethidium bromide resistance (EbR), a character that has been reported to be encoded on some gentamicin-resistance plasmids (Jaffe et al, 1982;McDonnell et al, 1983). In contrast to these GTKR-EbR transformants that carried pSK 1, GTKR transformants were obtained that lacked pSKl and failed to gain EbR.…”

“…aureus has most frequently been reported to be plasmid-mediated (Soussy et al, 1975;Wood, Carter and Best, 1977;Cohen et al, 1982;Jaffe et al, 1982;McDonnell et al, 1983), although chromosomally-encoded resistance has recently been observed in Australia (Lyon et al, 1983;Townsend, et al, 1983) and elsewhere (Kayser, Homberger and Devaud, 1981;Dowd, Cafferkey and Dougan, 1983). Among the strains isolated at this hospital, aminoglycoside resistance was suspected to be chromosomally encoded in the majority of isolates before 1980.…”

“…Mixed culture transfer was performed as described by McDonnell, Sweeney and Cohen (1983) with strain SK982 as a recipient. Transformation was performed by a modification of the procedures of Lindberg and Novick (1973) and Lederberg and Cohen (1974).…”

Trimethoprim resistance determinants encoding a dihydrofolate reductase in clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci

“…The methods used for testing sensitivity to other antimicrobial agents, for transformation of plasmid DNA, and for plasmid elimination, were as described previously (Lyon et al, 1983;Gillespie et al, 1984). The transfer of plasmid DNA in mixed culture was performed as described by McDonnell et al (1983).…”

Antibiotic Resistance in Staphylococcus Aureus Isolated at an Australian Hospital between 1946 and 1981

“…Resistance to the quaternary ammonium compounds benzalkonium chloride (Sigma Chemical Company, St Louis, MO 63 178 USA) and cetyltrimethylammonium bromide (BDH Chemicals Ltd, Poole, England) was tested in L-agar at concentrations of 4 and 2 mg/L, respectively. Mixed culture transfer by the method of McDonnell, Sweeney and Cohen (1983) was used to transfer resistance to strain SK982.…”