[Studies on the antimicrobial activities of gentamicin, amikacin, and tobramycin against Pseudomonas aeruginosa isolated at Hokkaido University Hospital].

Antimicrobial activities of 3 aminoglycoside antibiotics, including gentamicin (GM), amikacin (AMK) and tobramycin (TOB), were determined against 1,714 Pseudomonas aeruginosa strains isolated from clinical specimens in this hospital during 3 years since April of 1976 to March of 1979. From these results, some discussions were made as follows. 1) MIC ranges, to which about 70% of strains tested distributed, were 3.13--6.25 micrograms/ml of GM, 3.13--12.5 micrograms/ml of AMK, and 0.78--3.13 micrograms/ml of TOB in each year. 2) Frequency of drug-resistant strain, which showed 12.5 micrograms/ml or more MIC value in any drug, was highest in AMK and lowest in TOB in each year. 3) Drug-resistant strain-frequency to any one of 3 drugs tested was lowest in 1977, and higher in 1976 than in 1978. It was not supposed that this phenomenon should be undoubtedly caused by the amount of drugs used in each year in this hospital. 4) Frequency of highly TOB-resistant strain increased year by year during the period studied, unlike both cases of other 2 antibiotics. 5) Cross resistance was most frequently observed between GM and TOB, and more between GM and AMK than between TOB and AMK. 6) It was considered that anti- Ps. aeruginosa-activity was highest in TOB followed by GM and by AMK. 7) It was suggested that there seemed to be some qualitative difference between antimicrobial activity of AMK and those of GM and TOB.