Article

Failure of Coagulase-negative Staphylococci to Transfer Antibiotic Resistance to Staphylococcus aureus 1030 in Mixed Cultures

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Abstract

One hundred and fifty-three isolates of coagulase-negative staphylococci obtained from human skin failed to transfer resistance to either cadmium ions (46 isolates), trimethoprim (37 isolates), erythromycin (25 isolates) or tetracycline (45 isolates) to Staphylococcus aureus strain 1030 or to each of 10 of its lysogenic derivatives in mixed cultures. Thirty-three trimethoprim-resistant coagulase-negative staphylococcal isolates obtained from the human intestine also failed to transfer this resistance to the recipients in mixed cultures.

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... In contrast, phage-mediated conjugation was inhibited on human skin but transferred resistance plasmids in moist conditions in the presence of free Ca"^+ (Townsend et al., 1986). This mechanism would appear to be limited to intraspecies transfer based on the species specificity of staphylococcal phages and previous failure to detect interspecies transfer under conditions that favoured phage-mediated conjugation (Fawcett, Lord and Lacey, 1981). ...
... Other studies had failed to detect interspecies transfer of resistance among staphylococci (Fawcett et aL, 1981). This led to suggestions that similar plasmids in different staphylococcal species arose by convergent evolution or by being descendants of a highly conserved '^primordal" plasmid (Lacey, 1984). ...
... This led to suggestions that similar plasmids in different staphylococcal species arose by convergent evolution or by being descendants of a highly conserved '^primordal" plasmid (Lacey, 1984). However, the failure to detect interspecies transfer between staphylococci was most probably the result of using transfer conditions more suited to phage-mediated conjugation (Fawcett et aL, 1981) as well as the presence of restriction barriers. Plasmids pWG4 and pWG25 serve as an example. ...
Two staphylococcal plasmids, pWG4 and pWG25, encode production of a diffusible pigment and resistance to erythromycin and spectinomycin. The former was found occurring naturally in a clinical isolate of Staphylococcus aureus and the latter in S. epidermidis. Both plasmids are conjugative, capable of high-frequency, interspecies transfer, only isolated in the open-circular form and identical in molecular weight and pattern of restriction-endonuclease fragments. The only difference between the plasmids is in the expression of resistance, pWG4 encoding inducible and pWG25 constitutive erythromycin resistance. The resistance determinants of both plasmids behave as hitch-hiking transposons in cultural conditions that favour phage-mediated or phage-independent conjugation, always inserting a copy of themselves into the recipient's chromosome, except in S. epidermidis in which the chromosomal insertion site may be absent. The resistance determinants have been cloned and located on a 4 X 7 kbp EcoR1/HindIII restriction fragment which has a restriction map similar to that of the right arm of Tn554 (Murphy and Lofdahl, 1984). The hitch-hiking transposon of plasmid pWG25 has been designated Tn3853.
... Surveys of coagulasenegative staphylococci and animal isolates of S. aureus found little or no evidence for transferable resistance to human isolates of S. aureus, raising doubts about these organisms as a source of an ti bio tic resistance. However, the experiments were performed under conditions that allowed transfer by a phage-mediated mechanism only (Lacey, 1980b;Fawcett et al., 1981). ...
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