Antimicrobial Resistance Rates of Enterobacter spp.: A Seven-Year Surveillance Study

Objective: The aim of the study was to evaluate the trends of antimicrobial resistance of Enterobacter spp. over time in a Saudi Arabian hospital. Materials and Methods: This is an in vitro surveillance study of the antibiotic susceptibility pattern among Enterobacter spp. recovered from outpatient andnosocomial isolates over a 7-year period from 2000 to 2006. Only a single isolate per patient was included. Results: A total of 1,394 nonrepetitive isolates were analyzed during the study period. Enterobacter cloacae and Enterobacter aerogenes constituted 60 and 33% of the isolates, respectively. Overall, there was no statistically significant increase in the resistance rates over time for the outpatient and nosocomial isolates of Enterobacter . For E. cloacae, nosocomial isolates were statistically more resistant than outpatient isolates to ceftriaxone (17.5 vs. 5.5%), ciprofloxacin (9.5 vs. 4.7%), ticarcillin (42.8 vs. 25.4%) and ticarcillin-clavulanic acid (23 vs. 9.3%). For E. aerogenes, the nosocomial isolates were also more resistant to ceftriaxone and ciprofloxacin than the outpatientisolates (9.2 vs. 2.4% and 9.6 vs. 3%, respectively). In addition, nosocomial isolates of E. aerogenes were more resistant to piperacillin (25 vs. 15.6%) and ticarcillin-clavulanic acid (32 vs. 10.2%) than outpatient isolates. The most active antimicrobial agents were imipenem, amikacin and gentamicin against Enterobacter . Resistance rate to 6 3 classes of antibiotics was present in 2.5% of nosocomial and 1.7% of outpatient isolates (p = 0.78). Conclusion: The resistance rate for the outpatient and nosocomial isolates of Enterobacter had remained relatively stable over the study period. The most active antimicrobial agents were imipenem, amikacin and gentamicin.