During a 14-month period beginning in July 1986, three distinct clinical isolates of Streptococcus (Enterococcus) faecium demonstrating high-level resistance (MIC, greater than 2,000 micrograms/ml) to gentamicin, kanamycin, tobramycin, and streptomycin were recovered from individual patients at one institution. Combinations of ampicillin with any of these agents failed to show bactericidal synergism. By filter-mating techniques, high-level gentamicin resistance could be transferred into a susceptible recipient of the same species at frequencies as high as 1 x 10(-4); transfer into Streptococcus faecalis JH2-7 occurred at lower frequencies (less than 2 x 10(-7). Aminoglycoside substrate profile analysis of clinical isolates as well as of laboratory-derived cured strains and transconjugants revealed 2"-aminoglycoside phosphotransferase and 3'-aminoglycoside phosphotransferase (III) phosphorylating enzymes, AAC-6' acetylating activity above that attributable to the intrinsic activity characteristic of S. faecium, and a streptomycin adenylylating enzyme. All three isolates carried a 51-megadalton plasmid. Curing of this plasmid or conjugative transfer into susceptible recipients was associated with the loss or acquisition of high-level gentamicin resistance, respectively. Loss of high-level gentamicin resistance was also observed when curing techniques resulted in a decrease in the size of this plasmid equivalent to a 10-megadalton deletion. Transferable, high-level resistance to gentamicin and other aminoglycosides, which was previously recognized in S. faecalis, has now emerged in clinical isolates of S. faecium, with the attendant concerns for possible spread.

Penicillin-"virgin" strains of Enterococcus faecalis collected from a population of individuals with no previous antibiotic exposure were subjected in vitro to penicillin delivered as repeated pulses, stepwise increasing concentrations, or sustained levels of a single concentration. Changes in resistance to penicillin were assessed by determination of MICs, and time-kill studies were performed to evaluate changes in tolerance to the bactericidal effects of penicillin. Isogenic clones, derived from various exposure regimens, which exhibited changes in either resistance or tolerance were further examined for changes in penicillin-binding proteins. Exposure to repeated pulses of penicillin resulted in the development of tolerance to penicillin without changes in the level of resistance. Clones derived from a regimen of stepwise increases in the penicillin concentration acquired both increased penicillin resistance and tolerance. Clones selected after prolonged continuous exposure to a fixed concentration of penicillin displayed minimally increased resistance to penicillin, but they retained the lytic, nontolerant response to the bactericidal effect of penicillin. Clones which acquired tolerance to the bactericidal effect of penicillin without changes in penicillin resistance exhibited a penicillin-binding protein pattern identical to that of the parental strain. Increased labeling of several penicillin-binding proteins accompanied the development of increased penicillin resistance in both penicillin-tolerant and nontolerant strains. Exposure of E. faecalis to penicillin in repeated pulses of brief duration, for prolonged periods at a constant concentration, or in stepwise graded concentrations can result in the selection of clones with increased resistance to the inhibitory or bactericidal effects of penicillin, or both. These observations may be relevant to the selection of dosing regimens for penicillin in the treatment of enterococcal infections, when bactericidal synergism cannot be achieved with penicillin-aminoglycoside combinations.

Two hemolytic phenotypes of Vibrio damsela, isolated from the tissue of a patient with a fatal wound infection, were characterized. The patient had underlying disease, and the wound was associated with an injury inflicted during the handling of a catfish. The phenotypes were morphologically and biochemically similar except for their lecithinase, lipase, and hemolytic activities. When grown on rabbit blood agar, one phenotype (LZ) produced a large zone of hemolysis (10 mm) around the colony, whereas the other type (SZ) produced only a small zone (1 to 2 mm). On sheep blood agar, the differences in hemolytic activity were more subtle. By a modified CAMP test in which V. damsela was streaked perpendicularly to Staphylococcus aureus, it was determined that a factor elaborated by the LZ phenotype (but not the SZ phenotype) protected sheep erythrocytes from the hemolysis normally caused by S. aureus toxins. Cell-free filtrates of broth cultures of each phenotype had the same effects on erythrocytes as did the organisms themselves.