Time–kill curves as a tool for targeting ceftazidime serum concentration during continuous infusion

1047 cases. Pulsed-field gel electrophoresis of ApaI-digested genomic DNA was performed and banding patterns were compared visually. Nine distinct clones were defined, each containing 3–21 isolates. It is of interest that all but three of the 15 isolates that exhibited an MIC of imipenem of 8 mg/L were indistinguishable, indicating a clonal spread of these acinetobacters. This particular clone was not defined among the remaining low-level carbapenem-resistant isolates or among those that were fully susceptible. Carbapenem-resistant acinetobacters have been reported sporadically from clinical infections after prolonged exposure to carbapenems.2 However, the emergence of strains that exhibit low-level resistance to carbapenems is limited. In a UK burns unit, acinetobacters that exhibit MICs of 2 and 0.5 mg/L of meropenem and imipenem, respectively, have been reported.3 In addition, a USA electronic surveillance programme has recorded a yearly increase in A. baumanni strains with reduced susceptibility to imipenem.4 In our region, acinetobacters are one of the most frequent nosocomial pathogens, and the majority of them are multidrug-resistant, leading to an extensive use of carbapenems.5 The detection in one of the largest Greek hospitals that the vast majority of A. baumannii exhibit low-level resistance to carbapenems is a novel observation, suggesting a potential for wider dissemination. Since the disc diffusion method is not always sensitive in the detection of strains with lowlevel resistance to carbapenems,3 it is important that our diagnostic laboratories use a reference susceptibility method to screen periodically for the presence of such acinetobacters. The continuing spread of low-level carbapenem-resistant A. baumannii clones in our hospital demands more prudent use of antimicrobials and more strict infection control measures. Further studies, to determine if similar clones exist in other hospitals, are important in continuing to monitor this situation.