Interpretive criteria and tentative quality control limits for apalcillin disk susceptibility tests

In vitro studies with 661 bacterial isolates were performed to establish interpretive criteria. In addition, a nine-laboratory study was performed to establish quality control limits for tests with 100-micrograms apalcillin disks and to confirm testing criteria for tests with 100-micrograms piperacillin disks. The two drugs were very similar, and nearly identical criteria were recommended for interpretation and for control of the two types of disks. Neither disk is recommended for testing Staphylococcus spp. or Haemophilus spp.; with other microorganisms, zone size limits of less than or equal to 13 mm (resistant) and greater than or equal to 18 mm (susceptible) are proposed for tests with 100-micrograms apalcillin disks.