Eleven Staphylococcus aureus clinical isolates were tested for transfer of resistance markers by transduction and filter mating. The resistance markers of six of the strains could be transferred only by transduction; however, the five remaining strains transferred their resistance both by transduction and filter mating. The resistance markers that were cotransferred in filter matings (transfer of resistance to penicillin and streptogramin A was accompanied, in each case, by the transfer of one or more markers, i.e., resistance to aminoglycosides, cadmium, or tetracycline, depending on the donor) were not cotransduced. The ylococcal Diseases, in press). Evidence for the chromosomal location of these genes includes their low frequency of transduction (<1 x 10-9 transductants per PFU) and the absence of extrachromosomal DNA in the transductants. Further evidence was obtained from hybridization experiments with probes consisting of aminoglycoside resistance genes. These probes did not hybridize with the plasmids isolated from the wild-type strains; hybridization with cellular DNA from both the wild-type strains and the plasmid-free transductants supported the hypothesis of the chromosomal location of these genes (13a).Although the transfer by conjugation of the antibiotic resistance genes in the absence of detectable plasmids occurs in various bacterial genera (4,7,18,20,21,23,24,34,36,44,49,50,56), reports of such conjugative transfer in staphylococci have so far been limited to plasmid-borne determinants (2,3,15,19,33,37,53,54).We report in this study the transfer by conjugation of apparently chromosome-borne resistance markers from wild-type S. aureus strains into staphylococcal recipients belonging to different species. MATERIALS AND METHODSBacterial strains. The bacterial strains used in this study are listed in bacterial growth, mating experiments, and the preparation of all of the selective media except those containing trimethoprim. Nutrient broth no. 2 (Oxoid Ltd., London, England) and nutrient broth agar (Oxoid) were used for bacteriophage propagation and transduction experiments. Mueller-Hinton agar (Institut Pasteur Production, Paris, France) was used for disk susceptibility tests and preparation of selective media containing trimethoprim.Mating procedures on agar media. A 0.3-ml portion of a mixture containing 1 x 107 CFU of donors and 10-fold more recipients, both obtained from late-logarithmic-phase broth cultures, was spread either on nitrocellulose filters (type HAEP; pore size, 0.45 ,um; Millipore Corp., Bedford, Mass.), as described by Horodniceanu et al. (20), or directly on agar plates. After 18 h of incubation at 37°C, the cells on each filter were suspended in 1 ml of BHI, and the suspension was spread on BHI agar or Mueller-Hinton agar containing the appropriate selective drug. Controls, consisting of donor or recipient cells alone, were treated similarly. For two crosses, the donor and recipient cultures were separated during incubation (18 h at 37°C) by a nitrocellulose filter: a filter w...

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The incidence of exfoliative toxin-producing strains of Staphylococcus aureus was studied. Samples from hospitalized patients of all ages and samples from infants less than 6 weeks old were screened; out of 2,632 coagulase-positive S. aureus strains tested, 6.2% synthesized exfoliative toxin. The clinical features could be assessed in 86 patients harboring exfoliative toxin-producing staphylococci. Skin lesions (pustules, blisters, and bullous impetigo) could be observed only when the exfoliative toxin-positive strains were isolated from the skin. Phage nongroup II strains seemed less skin pathogenic than phage group II strains. Outbreaks and sporadic cases were observed.

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