Comparative study between mics determined by dynatech mic 2000 system and by standard agar dilution method (On mh and hi medium)

Minimal inhibitory concentrations (MICs) of antibiotics including ABPC, SBPC, PIPC, CFS, GM, DKB, AMK, CEZ, CMZ,CTM,CZX, CPZ and LMOX against 7 species of bacteria(S. aureus, S.epidermidis, P. aeruginosa, E. coli, K. pneumoniae, K. oxytoca and S. liquefaciens) were determined by a broth dilution method and by an agar dilution method (standard method of Japan Chemotherapy Society), on heart infusion (HI) medium and Mueller Hinton (MH) medium. For the broth dilution method Dynatech MIC 2000 system was used and the inoculum size of bacteria was 0.0015 ml of 10 th dilation of an overnight culture. For the agar dilution method, microplanter was used and the inoculum size of bacteria was 0.005 ml of 100 th dilution of an overnight culture. Neither statistical difference between means of MICs determined by HIB and MHB, nor between means of MICs by MHA and HIA was observed in all of the bacterial species tested. No statistical difference between mean MICs determined by the broth dilution method (MHB) and by the agar dilution method (MHA) was observed in almost all of the bacterial species tested, except that mean MICs of AGs against P. aeruginosa determined by the broth dilution method were statistically lower than that by the agar dilution method. On S. aureus, MICs of ABPC, PIPC, GM, DKB and AMK for fresh isolates were statistically higher than that for the stocked strains. On S. epidermidis, MICs of ABPC, PIPC, DKB and CZX for fresh isolates were statistically higher than that for the stocked. On P. aeruginosa, MICs of GM, AMK, CPZ, and LMOX for fresh isolates were statistically higher than that for the stocked. Also, statistically higher MICs for the fresh isolates in comparison with that for the stocked strains were observed for E. coli of AMK, for K. pneumoniae of LMOX, and for S. liquefaciens of CZX and CPZ.