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Nosocomial infection or colonization due to enterococci with high-level resistance to vancomycin (minimal inhibitory concentrations [MICs] between 64 and greater than 2000 mg/L) has occurred in 41 patients with renal disease. These vancomycin-resistant enterococci were cultured from many sources including blood. All but one strain contained one or more plasmids ranging in molecular weight from 1.0 to 40 Megadaltons (MDa). Vancomycin resistance was transferable by conjugation to a susceptible recipient strain of Enterococcus faecalis but this was not always associated with plasmid DNA. The emergence of transferable high-level vancomycin resistance in enterococci causing significant clinical infections is of particular importance since vancomycin is widely regarded as a reserve drug for the management of infections with multi-resistant Gram-positive organisms.

Summary. Three electrophoretic methods of typing methicillin-resistant Staphylococcus aureus (MRSA) strains-plasmid profiles (PP), whole-cell protein profiles (WCPP) and immunoblotting profiles (1P)-were evaluated and compared with phage typing. The results obtained with isolates from 12 outbreaks were compared both within the outbreaks, to determine the consistency of results, and between outbreaks. There was generally good agreement between the typing methods but in only six outbreaks did all four methods indicate the same relationship between isolates. WCPP comprised more than 50 bands; when differences occurred, they were seen in only a few bands. In contrast, IP comprised only one or two major bands and the differences were much easier to interpret. The PPs of many of the isolates were similar; many isolates contained a plasmid of mol. wt (18-25) x lo6. In several outbreaks both WCPP and IP showed minor differences between isolates that were not apparent with phage typing. When comparisons were made between the 12 index strains and an isolate representing the London epidemic MRSA strain, phage typing and WCPP were the most discriminatory methods ; both gave nine distinct patterns, whereas there were eight IPS and only six PPs amongst the 13 strains. It was concluded that both WCPP and IP could provide valuable epidemiological data on MRSA and that IP was the easiest of the three methods to interpret.

This paper reports the characterisation of a bacteriocin-like inhibitory substance (BLIS), zoocin A, produced by Streptococcus zooepidemicus strain 4881 that exhibits inhibitory activity against strains of S. mutans, S. sobrinus and S. cricetus. A study of the inhibitory activity of strain 4881 against 98 bacterial strains using a deferred antagonism procedure showed that S. mutans strains were relatively more sensitive than were strains of S. salivarius and S. sanguis. Zoocin A was purified from the supernate fluid of chemically defined medium cultures of strain 4881. Purified zoocin A (a protein of estimated MW 30 000) retained biological activity over a wide pH range (410), was sensitive to several proteolytic enzymes and was relatively stable at 37°C but not at 60°C. A triple-species (S. mutans, S. sanguis and Actinomyces viscosus) plaque model was used to test the ability of zoocin A to modify plaque composition. Brief (2min) exposure of preformed plaque to zoocin A resulted in a significant decrease in the proportion of S. mutans and this effect persisted for up to 20 h after treatment.