For testing bacterial susceptibility to PD131628, a 5-micrograms disk and the following tentative interpretive criteria may be used: > or = 19 mm for susceptible (MIC, < or = 1.0 micrograms/ml), 16 to 18 mm for intermediate (MIC, 2.0 micrograms/ml), and < or = 15 mm for resistant (MIC, > or = 4.0 micrograms/ml). For standard quality control strains, the following limits are proposed: for Escherichia coli ATCC 25922, zones of 31 to 41 mm or a MIC of 0.002 to 0.016 micrograms/ml; for Pseudomonas aeruginosa ATCC 27853, zones of 26 to 34 mm or a MIC of 0.12 to 0.5 micrograms/ml; for Staphylococcus aureus ATCC 25923, zones of 27 to 33 mm; for Staphylococcus aureus ATCC 29213, a MIC of 0.03 to 0.12 micrograms/ml; and for Enterococcus faecalis ATCC 29212, a MIC of 0.12 to 0.5 micrograms/ml.