Interaction of ciprofloxacin with ampicillin and vancomycin for Streptococcus faecalis

Streptococcus faecalis is known to be resistant to killing by many of the commonly used antimicrobial agents. Ciprofloxacin, a member of the quinolone class of compounds, was studied for its ability to inhibit and to kill S. faecalis. The rate of killing by ciprofloxacin was slow and was comparable to that of ampicillin or vancomycin. The antimicrobial effect of combining ciprofloxacin with ampicillin or with vancomycin was also studied using checkerboard double-dilution and killing kinetics. There was no synergy or antagonism between ciprofloxacin and either cell wall active agent. Unlike the aminoglycosides, the addition of ciprofloxacin did not produce additional killing over that of ampicillin or of vancomycin alone.