STUDY ON DRUG SENSITIVITY OF MULTIPLE DRUG RESISTANT STAPHYLOCOCCUS AUREUS

Of clinically isolated Staphylococcus aureus showing resistance to multiple drugs among penicillins (PCs), cephem antibiotics (CEPs), aminoglycosides (AGs), minocycline (MINO) and fosfomycin (FOM), 64 strains were selected for the determination of MIC. Twenty-one drugs were used for the determination of MIC, with ampicillin (ABPC), cloxacillin (MCIPC), cephalothin (CET), cefazolin (CEZ), cefotiam (CTM), cefuroxime(CXM), cefamandole (CMD), cefotaxime (CTX), ceftizoxime (CZX), cefmenoxime (CMX), cefmetazole (CMZ), cefoxitin (CFX), latamoxef (LMOX), cefotetan (CTT), cefoperazone (CPZ), gentamicin (GM), dibekacin (DKB), tobramycin (TOB), amikacin (AMK), MINO, and FOM. 1. MIC80 of each drug at 106 CFU/ml were: ABPC, MCIPC, CEZ, CTM, CXM, CTX, CZX, CMX, CFX, LMOX, CTT, CPZ, GM, DKB and TOB 100 μg/ml; CET 50 μg/ml; CMD and AMK 25 μg/ml; CMZ 12.5 μg/ml; FOM 6.25 μg/ml; and MINO 0.78 μg/ml. 2. The ratio of highly resistant strains with MIC 100 μg/ml at 10 CFU/ml varied according to drug, and a difference tended to be seen in the degree of influence by resistant factors reflected upon MIC, e. g. drugs for which a high resistance of more than 50% was confirmed were ABPC, CXM, CZX, LMOX and TOB, and 20-30% MCIPC, CTM, CTX, CMX and CFX. 3. MIC on MCIPC which has a correlation of structural activity with methicillin correlated with cephems (CEPs) resistance to a high degree, but many of the so-called new CEPs showed resistance even to the strains with a low MIC on MCIPC. 4. It was assumed that CEPs resistant strains have multiple drug resistant factors based on the fact that such strains showed multiple drug resistance. 5. Among CEPs, CMZ and CMD were found to have comparatively stabilized antibacterial potency, and it is expected that this mechanisms, will be elucidated. 6. Strains which show a high resistance of 10.9% to FOM and strains whose sensitivity decreased somewhat with MIC of 3.13-6.25 μg/ml to MINO in 4.7% were confirmed.