TABLE 6.

BMD and DD discrepancy rates for three antimicrobial agents when testing a fixed ratio versus a fixed concentration of β-lactamase inhibitor

Antimicrobial agent or expt conditionbnNo. (%) of discrepancies% Susceptible isolatesa
Very majorMajorMinor
Ampicillin-sulbactam
    Fixed ratio (2:1)19125 (13.1)028 (14.7)52.9
    Fixed concentration (8 μg/ml)18663 (33.9)015 (8.1)46.0
Piperacillin-tazobactam
    Fixed ratio (2:1)1936 (3.1)042 (21.9)48.2
    Fixed concentration (4 μg/ml)19225 (13.0)048 (24.9)37.6
Ticarcillin-clavulanate
    Fixed ratio (2:1)1920036 (18.8)51.3
    Fixed concentration (2 μg/ml)1925 (2.6)021 (10.9)51.8
  • a According to the NCCLS breakpoint for the β-lactam agent.

  • b NCCLS conditions are shown in bold.