The following results were obtained from a disk-diffusion test for microbial susceptibility to antibiotics (Table 2). Staphylococcus aureus was the test organism, and the interpretive standards table for the different antibiotics are shown in Table 1.
Table 1. Antibiotic Resistant Intermediate Susceptible
A <9mm 10-11mm >12 mm
B <14mm15-18mm >19mm
C <19mm 20-22mm >23mm
D <11mm 12-14mm > 15mm
Table 2. Antibiotic Zone of Inhibition
In the table, the most effective antibiotic tested was