Emergence of bacterial resistance to imipenem and ciprofloxacin in a university hospital

We have continuously monitored the in-vitro activities of imipenem and ciprofloxacin against large numbers of non-fastidious clinical isolates. After eight years of use, 97-100% of Enterobacteriaceae and Acinetobacter baumannii remained susceptible to imipenem, but susceptibility of Pseudomonas aeruginosa declined from 100% to 91%. After six years of use, 94%-100% of Enterobacteriaceae (except Providencia stuartii) remained susceptible to ciprofloxacin but susceptibility of P. stuartii, A. baumannii and P. aeruginosa declined from 100% to 46%, 66% and 84%, respectively. Oxacillin-resistant staphylococci were considered to be resistant to imipenem and all beta-lactams. There were no quinolone-resistant staphylococci observed in 1986, but susceptibilities of Staphylococcus aureus, Staphylococcus epidermidis and Staphylococcus haemolyticus to ciprofloxacin decreased to 85-93% for oxacillin-susceptible strains and to 7-39% for oxacillin-resistant strains. Enterococcus faecalis has remained susceptible to imipenem and the modal MIC of ciprofloxacin has remained 1 mg/L; however, susceptibility to ciprofloxacin 2 mg/L decreased from 94% to 64%. Imipenem-quinolone cross-resistance was observed for staphylococci but not for P. aeruginosa.