An outbreak of methicillin-resistant Staphylococcus aureus (MRSA) involving 27 patients and 14 health-care workers (HCW) was studied. The outbreak started in the hematology unit of the University Hospital Rotterdam, Dijkzigt, The Netherlands, and spread to the surgical unit. Twenty-one patients (77.8%) developed clinical disease, and five died. Subsequently, MRSA was detected in food and in the throat of one of the HCW who prepared food for hematology patients. Food contaminated by an HCW most likely caused the first case of MRSA septicemia. This route of transmission has not been described before. The outbreak strain was probably transmitted to the surgical unit by a colonized nurse, where it caused an explosive outbreak. Airborne MRSA transmission played an important role in disseminating the organism. The outbreak was controlled within 6 months by intensifying surveillance, temporarily closing the affected wards, treating carriers, and instituting an MRSA ward outside the hospital. Phage typing, insertion sequence probing, protein A gene typing, and DNA fingerprinting by PCR revealed that all outbreak-related isolates were identical. By pulsedfield gel electrophoresis, all but one of the outbreak-related isolates were determined to be identical. Protein A gene typing identified numerous (11) repeat units in all outbreak-related isolates, which supports the suggestion that the outbreak strain may have been more virulent and more transmissible than other MRSA strains. Pheno-and genotyping studies underlined the value of DNA fingerprinting methods for investigation of MRSA epidemiology. Optimal discriminatory power was achieved by combining the results of four genotyping methods.

The transferability of plasmid pRI405 between various streptococci of groups A, B, and D, Streptococcus pneumoniae, and Staphylococcus aureus is described. pRI405 originated from Streptococcus faecalis and encodes for resistance to macrolides, lincomycin, and streptogramin B (MLS resistance). The host range of the well-documented streptococcal plasmid pAM/i1 was found to be similar to that of pRI405. Cleavage with restriction enzymes suggests that pRI405 belongs to a related family of MLS resistance plasmids.It is now generally accepted that resistance to various antimicrobial drugs in streptococci is mediated by plasmids. Many of these plasmids have been shown to be self-transferable (8,12,13,16,20,23,32,34) by a process that needs cellto-cell contact between donor and recipient and which resembles in several aspects conjugation (16). Non-self-transferable plasmids can be mobilized by self-transferable ones. The first reports on conjugal transfer of streptococcal plasmids involved intraspecific matings between isolates of group D streptococci (8,16,25). Later, interspecific plasmid transfer between the serogroups B and D was also reported (11, 13, 34). The plasmids used in these studies originated from group B and group D streptococci, and they encoded for resistance to macrolide antibiotics, lincomycin, and streptogramins of group B, the so-called MLS resistance phenotype (37). The host range of one particular plasmid, pAM/i1 (originating from Streptococcus faecalis), has been the subject of several studies. Le Blanc et al. (20) introduced this plasmid into a group F streptococcus by transformation and then retransferred it by mating to the oral streptococci, S. mutans, S. sanguis, and S. salivarius. Furthermore, pAM,B1 could also be transferred to members of the family of Lactobacillaceae (10). Recently, Malke (23) reported the conjugal transferability of MLS resistance plasmids originating from group A and B streptococci between streptococcal strains of groups A, D, and H. Transformation of plasmids has been demonstrated for group H and group F streptococci (11,18,19), and transduction has been reported for group A, C, and G streptococci (15,22, 29).In a preliminary study we reported intergroup transfer of an MLS resistance plasmid between streptococci of groups A, B, and D (35). This plasmid, pRI405, originated from S. faecalis. In this study we extend the earlier observations on the host range of this plasmid and show that conjugal transfer is possible also to strains of Streptococcus pneumoniae and Staphylococcus aureus.MATERIALS AND METHODS Strains. All bacterial strains used in this study are listed in Table 1. Staphylococcal phage 80 (NCTC 9788) was used in transduction experiments.Media. Streptococci, Staphylococcus aureus, and Bacillus subtilis were grown in nutrient broth or on nutrient agar as previously described (34). The media for growth of S. pneumoniae were supplemented with inactivated horse serum to a final concentration of 5%. Haemophilus influenzae was grown in nutrient broth and on nutrie...

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A site-specific restriction endonuclease has been isolated from Staphylococcus aureus PS 96. This enzyme, Sau96 I, recognizes the DNA sequence 5'--G-G-N-C-C--3' and cleaves as indicated by the arrows. The enzyme 3'--C-C-N-G-G--5' cleaves adenovirus type 5 and lambda DNA many times, SV40 DNA 10 times and 0X174 RF DNA 2 times. Evidence is presented that the enzyme is involved in biological restriction-modification.

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No major differences have been found in series of Staphylococcus aureus strains which reverted from 'L'-phase, either by pyrolysis mass spectrometry or by phage-typing or sensitivity testing. In 'L'-phase they have been subcultured for a long time or transformed/reverted many times into/from 'L'-phase. Plasmids were lost during transformations/reversions, but there was some difference between the tetracycline-connected plasmids on the one hand and the erythromycin-connected ones on the other.