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KMID : 0376219810180020235
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Chonnam Medical Journal
1981 Volume.18 No. 2 p.235 ~ p.244
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Response of Sulbenicillin-resistant Pseudomonas aeruginosa to the action of two-antibiotc combinations
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Abstract
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Of forty strains of Pseudomonas aeruginosa, which showed a relatively high resistance (MIC≥20μg/ml) to sulbenicillin (SB) among 150 isolates, only 20 organisms were chosen for the present experiment, to make procedures less submitted by the degree of their resistance to carbenicillin(CB), gentamicin (GM), and tobramycin (TM).
The minimum inhibitory concentration (MIC) of two drugs combined in various ratios was measured against each organism by checkerboard dilution method, and synergism was determined by analysing the MIC distribution curve on isobologram and calculating the fractional inhibition concentration index(FICI).
All of the antibiotic combinations (SB.GM, SB.TM, CB.GM, CB.TM) acted synergistically on 9 str·ains (45%), 3 combinations on 4 strains(20%), 2 combinations on 5 strains (25%), and 1 combination on 2 strains (10%). Thus no test organism was found not inhibited synergistically by at least one of the drug combinations employed. Of the 4 antibiotic combinations, SB-GM and SB.TM showed relatively high degree of synergism (SB.GM, 85%;SB TM, 65%).
When the concentration of SB was fixed at 1/2 MIC and GM or TM was added there after variously diluted, a greatly enhanced inhibitory effect was observed in general.
Original resistance degree of test organisms against each antibiotic did not contribute to extrapolating the attitude of the cells to the combined action of the drugs. Only actual testing was necessary to determine the synergism.
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