Serotype and susceptibilities to eight antibiotics of fifty strains of Pseudomonas aeruginosa isolated from clinical specimens and changes in susceptibilities of Pseudomonas aeruginosa to various antibiotics during a period between 1983 and 1986

Abstract Efficacies of 8 antibiotics against Pseudomonas aeruginosa in the relation to serotypes and clinical sources were investigated on 50 strains isolated from patients at Nagoya Ekisaikai Hospital between August and September, 1986. Disk sensitivity test was carried out simultaneously for 5 antibiotics including piperacillin (PIPC), cefoperazone (CPZ), cefsulodin (CFS), ceftazidime (CAZ) and amikacin (AMK), using the single-disk method. We also examined changes in susceptibilities of P. aeruginosa to 5 antibiotics including PIPC, CFS, fosfomycin, gentamicin (GM) and AMK during last 4 years (1983-1986). The results are summarized as follows. 1. CAZ and AMK proved to have high antibacterial potencies, and their MIC80's (concentrations to inhibit growth of 80% of objective bacteria) were both 6.25 micrograms/ml. Following these two the order of potencies were; CFS, cefpiramide (CPM), PIPC, CPZ, netilmicin (NTL), and cefmenoxime (CMX). Sixty two percent of the strains of P. aeruginosa showed high resistances (MIC greater than 50 micrograms/ml) to CPM, CPZ, NTL and CFS, 58% to PIPC, and 2% to AMK. 2. With regard to serotypes, strains belonging to type E were less susceptible than those belonging to types G and I. Type E strains showed high resistance to all antibiotics except CAZ and AMK. 3. Strains obtained from pura and secreta were relatively susceptible, while those from urines were resistant, to these antibiotics tested, in general. 4. Good correlation between MIC's obtained with the agar dilution method (MIC less than or equal to 12.5 micrograms/ml) and these with the disk sensitivity test (greater than ? was observed. chi 2 statistical analysis showed that the results obtained with the 2 methods were closely related (P less than 0.01). 5. P. aeruginosa showed fairly high susceptibility to AMK through the recent 4 years (1983-1986). On the other hand, highly resistant strains against CFS, PIPC, FOM and GM increased rapidly during this period.