[Bactericidal activity of ampicillin, chloramphenicol and gentamicin, alone or in combinations against susceptible and resistant "Haemophilus influenzae" (author's transl)].

Bactericidal activity of three antibiotics, ampicillin, chloramphenicol and gentamicin, alone or in combinations, was determined against susceptible and resistant strains of Haemophilus influenzae. The various antibiotic combinations were studied for the determination of a synergistic or antagonistic effect. The study was done by the checkerboard method. A percentage of survivors inferior or equal to 0.01% of the inoculum represents the bactericidal activity. Ampicillin and chloramphenicol are bactericidal antibiotics against H. influenzae at concentrations of 1 microgram/ml and 4 microgram/ml, respectively. The combination of ampicillin and gentamicin exhibited a synergistic effect against strains sensitive and resistant to ampicillin. The combination of chloramphenicol and gentamicin was synergistic against all strains. Ampicillin and chloramphenicol, when combined, were antagonistic against two strains using a bacteriostatic concentration of chloramphenicol; and against the remaining strains the effects of the combination were indifferent.