Defective killing of enterococci: a common property of antimicrobial agents acting on the cell wall.

We tested the ability of antimicrobial agents that act on the cell wall to kill enterococci and found defective killing (a minimal bactericidal concentration/minimal inhibitory concentration ratio of greater than or equal to 32) with both beta-lactams (penicillin G and cephalothin) and non-beta-lactams (vancomycin, cycloserine, and bacitracin). Our results indicate that the resistance of enterococci to antimicrobial killing spans the spectrum of agents known to inhibit cell wall synthesis and suggest that the mechanism responsible for enterococcal resistance to killing by these drugs may be a defective autolytic enzyme system.