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 and nosocomial 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. Enterobactercloacae and Enterobacteraerogenes 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 outpatient isolates (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 >or=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.