Transduction and Elimination of Resistance Determinants in Methicillin-Resistant Staphylococcus aureus

Abstract

Elimination and transduction of drug resistance was examined in methicillinresistant strains of Staphylococcus aureus. Irreversible spontaneous loss and "curing" by aging of cultures and by treatment with ethidium bromide indicated that the determinants for penicillinase production and chloramphenicol resistance, and probably also for neomycin resistance, were located extrachromosomally. On the other hand, the determinants of resistance to erythromycin, streptomycin, tetracycline, and methicillin could not be eliminated by acridines, ethidium bromide, rifampin, sodium dodecyl sulfate, ultraviolet (UV) irradiation, growth at 43.5 C, aging of cultures, or combinations of these treatments. The stimulation of transduction frequency by UV irradiation of phage in the case of the stable markers, but not in the case of the unstable ones, supported further the hypothesis of chromosomal location of the markers of methicillin, erythromycin, tetracycline, and streptomycin resistance and extrachromosomal location of the determinants for penicillinase production and chloramphenicol resistance. Neomycin resistance could not be transduced. Joint elimination and co-transduction of the determinants for penicillinase production and resistance to chloramphenicol and neomycin were not observed, indicating the location of these markers on separate, mutually compatible plasmids. Co-transduction of chromosomal resistance determinants was usually less than 1 %, which makes the location of these genes in a circumscribed area of the chromosome improbable.

Genetic Analysis of Methicillin-Resistant Strains of Staphylococcus Aureus; Evidence for Their Evolution From a Single Clone

“…Some rnethicillin-resistant strains lose their resistance in vitro (Dornbusch et al, 1969; Lacey, 1972~; Al Salihy and James, 1972; Grubb and h e a r , 1972; h e a r and Grubb, 1973); this evidence implies an extrachromosomal locus for the relevant genes. But Cohen and Sweeney (1970) and Kayser, Wust, and Corrodi (1972) reported that methicillin resistance is stable, suggesting a chromosomal locus for the genes. But stability, although a necessary condition, is not sufficient evidence for this conclusion; for instance, tetracycline resistance in strain no.…”

Effect of Plasmid Carriage on the Virulence of Staphylococcus Aureus

“…This could occur by the selection of strains capable of maintaining stably a large amount of extrachromosomal DNA, or by integration into the chromosome of regions of plasmid DNA specifying antibiotic resistance and virulence. This process has probably already occurred for the genes coding for tetracycline resistance (Kayser, Wust and Corrodi, 1972;Chopra et al, 1974).…”

Methicillin-resistant staphylococci

“…Evidence for a plasmid location was indirect and based on characteristics of elimination of mec from resistant strains (51,52,73,98). However, some conditions associated with the elimination, transduction, and transformation of mec suggested that the determinant was chromosomal (38,90,91,151). Transformation of mec by chromosomal but not plasmid DNA (143) and elucidation of its map location to the pur-nov-his gene cluster (97) have conclusively demonstrated that the determinant is chromosomal.…”