Piperacillin susceptibility tests by the single-disk agar diffusion technique
Barry, A.L.; Thornsberry, C.; Badal, R.E.; Baker, C.N.; Jones, R.N.; Gerlach, E.H.
Antimicrobial Agents and Chemotherapy 16(3): 378-385
1979
ISSN/ISBN: 0066-4804 PMID: 507794 Document Number: 151513
Piperacillin is a new semisynthetic penicillin with broader spectrum activity than carbenicillin or ticarcillin. Studies were performed to establish standards for agar diffusion susceptibility tests with piperacillin disks. Tests with 100-, 150- and 200-.mu.g piperacillin disks and with 100-.mu.g carbenicillin disks were evaluated. With both penicillins, 100-.mu.g disks were satisfactory, in spite of the fact that piperacillin is a larger molecule and diffuses at a slower rate. With both carbenicillin and piperacillin disks, resistant strains of Staphylococcus aureus produced zones .ltoreq. 28 mm and susceptible strains gave zones .gtoreq. 29 mm in diameter. When testing other microorganisms , zone standards .ltoreq. 13 mm for resistant (minimal inhibitory concentration, .gtoreq. 256 .mu.g/ml) and .gtoreq. 17 mm for susceptible (minimal inhibitory concentration, .ltoreq. 64 .mu.g/ml) are recommended for tests with 100-.mu.g piperacillin disks. Similar zone standards are currently recommended for carbenicillin and ticarcillin disk tests.