No abstract

Clinical isolates of Escherichia coli were examined for the presence of hydroxamate siderophore (aerobactin). The incidence of aerobactin-positive strains of E. coli from the blood was greater than the incidence of these strains isolated from other sites. The presence of aerobactin and the virulence of strains of E. coli in urinary tract infection were also examined in mice. The presence of aerobactin in the strains of E. coli correlated with virulence as measured by proportion of deaths but not with renal infection. These results suggest that the presence of aerobactin may be a significant factor in the invasion of the blood stream.

Minimum inhibitory and bactericidal concentrations of four antibiotics and their combinations were determined for 38 strains of enterococci by a microtitration tube dilution technique. The drugs were ampicillin, vancomycin, gentamicin, and streptomycin; the combinations were ampicillin-gentamicin, ampicillin-streptomycin, vancomycin-gentamicin, and vancomycin-streptomycin. At achievable serum concentrations, ampicillin alone killed 60% of strains, whereas combination with streptomycin increased this to 90% and with gentamicin to 100%. Vancomycin alone showed striking inhibitory activity, but very poor bactericidal activity at achievable concentrations. Combination with one of the aminoglycosides increased the bactericidal activity substantially. When combined with ampicillin, gentamicin was both more active and showed synergistic bactericidal activity significantly more often (P < 0.01) than streptomycin.

Certain technical considerations which affected the status of methicillin tolerance in Staphylococcus aureus strains were studied. Methods which consistently demonstrated tolerance or intolerance of a given strain were avoidance of inoculum splashing, use of stationary-phase inoculum, 24-h tube incubation, and minimization of antibiotic carry-over. These studies suggested a need for the establishment of a standardized reference for the determination of tolerance.