Synergism with Aminoglycosides of Penicillin, Ampicillin and Vancomycin Against Non-Enterococcal Group-D Streptococci and Viridans Streptococci

Abstract

The antibiotic susceptibility of 10 strains of non-enterococcal group-D streptococci was compared with that of 20 strains of viridans streptococci. The minimal inhibitory concentrations of penicillin, ampicillin, oxacillin, nafcillin, cephalothin, vancomycin, erythromycin and clindamycin for the 2 groups of streptococci were similar in range and median values. Both groups of streptococci were resistant to the aminoglycosides. The effect of the combination of penicillin, ampicillin or vancomycin with streptomycin, kanamycin, gentamicin or tobramycin on the in-vitro killing of the 2 groups of streptococci was compared. For all the antibiotic combinations tested, synergism was demonstrated against all strains of non-enterococcal group-D streptococci after 1 or more of the time-intervals 6, 24 and 48 h. Some or all of the antibiotic combinations were synergistic against all strains of viridans streptococci after one or more of the same time-intervals. The other aminoglycosides (kanamycin, gentamicin and tobramycin) offered no advantage over streptomycin in synergism with penicillin, ampicillin or vancomycin against non-enterococcal group-D streptococci or viridans streptococci. Non-enterococcal group-D streptococcal endocarditis [in humans] may be treated by the same regimen as endocarditis caused by the viridans streptococci.