W. C. Noble

Diversity of staphylococci exhibiting high-level resistance to mupirocin

Plasmids mediating high-level resistance to mupirocin (MIC greater than 1000 mg/L) in staphylococci from various sources were studied by restriction endonuclease cleavage. Several patterns were obtained but six plasmids isolated from various Staphylococcus aureus and S. epidermidis strains were indistinguishable. The diversity and spread of these plasmids is illustrated.

An investigation of plasmids from Staphylococcus aureus that mediate resistance to mupirocin and tetracycline.

Plasmids conferring mupirocin resistance were prepared from isolates of Staphylococcus aureus obtained from four patients in the same ward. The plasmids are related and in all of them the gene conferring mupirocin resistance (mupA) is flanked by copies of IS257 in direct repeat. In two plasmids mupA and IS257 have been duplicated and in one of these plasmids (pJ3358) a small pT181-like plasmid conferring tetracycline resistance is present flanked by copies of IS257. Filter mating with a strain containing pJ3358 as donor and selection on tetracycline sometimes resulted in transfer of the pT181-like plasmid containing a copy of IS257. Analysis showed that the pT181-like plasmid with the insertion of IS257 is present in high copy number and that the IS257 element is inserted in the copy number control region of the plasmid.

Mupirocin resistance in coagulase-negative staphylococci

High-level mupirocin resistance in coagulase-negative staphylococci isolated from patients undergoing peritoneal dialysis was investigated by transfer of the resistance determinants, usually in the form of a plasmid, to Staphylococcus aureus strains, cleavage of the plasmid by restriction endonuclease and hybridisation with a probe comprising a 4.05 kb EcoRI fragment of a plasmid from a S. aureus strain. In most instances the mupirocin-resistant staphylococci isolated from each patient were different according to the species, antibiogram and plasmid profile data. The mupirocin resistance determinant was carried on various plasmids as judged by EcoRI restriction fragment length polymorphisms. All hybridised at about 4 kb with the S. aureus probe.

Probes for the study of mupirocin resistance in staphylococci

Probes constructed from a 4.05-kb EcoRI digest fragment of a mupirocin resistance plasmid and a 751-bp internal part of this fragment hybridised with DNA from all of 36 independent high-level mupirocin-resistant staphylococci tested from seven centres; most were Staphylococcus aureus. In most instances the probes detected an EcoRI digest fragment of approximately 4 kb. Probes did not hybridise to DNA from low-level resistant strains, nor from strains sensitive to mupirocin.

Plasmid profiling of epidemic staphylococci from around 1960: a comparison of epidemiological techniques.

Plasmid profiles have been established for 68 isolates of Staphylococcus aureus from 13 episodes of epidemic spread in hospital wards between 1958 and 1962. Despite the original lack of care in preservation of strains the profiles give, in general, the same epidemiological patterns as were established originally on the basis of phage type, antibiotic sensitivity, ward and date of isolation.