Impact of revised susceptibility breakpoints on bacteremia of Klebsiella pneumoniae: Minimum inhibitory concentration of cefazolin and clinical outcomes

BackgroundThe Clinical and Laboratory Standards Institute (CLSI) revised the susceptibility breakpoints of cephalosporins for Enterobacteriaceae in 2010 and 2011. However, there is a lack of clinical data about the correlation of minimum inhibitory concentrations (MICs) and clinical outcome. Data for the distribution of MICs and clinical outcomes were analyzed in this study to evaluate the impact of changes in the CLSI breakpoints on the treatment of Klebsiella pneumoniae bacteremia.MethodsNinety-seven bacteremic K. pneumoniae isolates from Taichung Veterans General Hospital, Taichung, Taiwan were collected for study during the period 2009-2011. The cefazolin MIC was determined by the broth microdilution method according to the recommendations of the CLSI. The MIC distribution of cefazolin and the clinical responses to definitive cefazolin treatment were analyzed.ResultsThe modal cefazolin MIC among the 97 isolates was 1 μg/mL and accounted for 73 (75.3%) isolates. There were 18 (18.6%) isolates with a cefazolin MIC of 2 μg/mL. The conventional dosage regimens of cefazolin (1 g every 6 hours or 8 hours) achieved a clinical cure in 70 (97.2%) of 72 patients in the group with a cefazolin MIC ≤1 μg/mL and in 14 (87.5%) of 16 patients in the group with a cefazolin MIC of 2 μg/mL. With the conventional dose, the cumulative clinical cure rate for K. pneumoniae bacteremia with cefazolin MIC ≤2 μg/mL was 95.5% (84/88 patients).ConclusionThe conventional cefazolin dose still can result in satisfactory clinical cure rates for bacteremic episodes due to K. pneumoniae with cefazolin MIC ≤2 μg/mL, the revised susceptible breakpoint of CLSI 2011.