Development of Antimicrobial Resistance in Bacterial Isolates

Abstract

Disc-agar diffusion antimicrobial susceptibility results obtained October 1, 1989 to September 30, 1990 were studied to identify organisms and antimicrobial agents exhibiting development of resistance. There were 88 instances (14 antimicrobial agents in 14 species) in which results changed from susceptible to resistant in 50 patients. The 50 patients had 58 cultures (sputa, 25; urine, 23; miscellaneous, 8; and blood, 2) with organisms developing resistance. The most common antimicrobial agents exhibiting development of resistance were piperacillin (20 instances), cefoperazone (18), and cephalothin (10). The most common organisms were Pseudomonas aeruginosa (23), Escherichia coli (18), and Klebsiella pneumoniae (11). The most common antimicrobial agent–organism combinations were P aeruginosa -mezlocillin (7), P aeruginosa -piperacillin (6), K pneumomae -cephalothin (5), and Enterobacter aerogenes -cefoperazone (6). These results suggest that certain organisms and antimicrobial agents should be monitored for development of resistance in our institution.