Direct reporting cefazolin from VITEK® 2 for E. coli, K. pneumoniae and P. mirabilis isolated from urine cultures using new CLSI interpretations

Background: In recent years, Clinical and Laboratory Standard Institute (CLSI) has recommended a series breakpoint changes for cefazolin, including testing it as a surrogate agent for oral cephalosporins for treating uncomplicated urinary tract infections (uUTIs). Objectives: This study was conducted to evaluate the feasibility of direct reporting the cefazolin results from VITEKO 2 for E. coli, K. pneumoniae, K. oxytoca and P. mirabilis isolated from patients with uUTIs using 2014 CLSI recommendation. Material and Methods: Cefazolin susceptibility results of urine cultures of the above four species generated from January 1, 2013 December 31, 2013, using both GN AST card N208 on VITEKO 2 and cefazolin disk (gold standard) methods, were extracted from SoftMic Laboratory Information System and analyzed for their category agreement using 2014 CLSI interpretations. Results: Cefazolin susceptibilities of 1969 urinary isolates (1869 patients) of E. coli, K. pneumoniae/K. oxytoca and P. mirabilis comparing their VITEKO 2 and disk test results, category agreement for cefazolin tested with both methods was 98%. The linear correlation between sensitive cefazolin and sensitive cephalothin MICs versus cefazolin zone diameters was good, with a predictive value of 99%. Conclusion: It is acceptable to report cefazolin directly from VITEKO 2 for the named species from urine cultures. The susceptibility correlation among cefazolin, cephalothin and cefixime were excellent (excluded non-susceptible), further testing with individual oral cephalosporin agents, in this institute, may not be necessary. Recommendation: Final report accompanied by a comment in accordance with 2014 CLSI guideline is recommended to provide therapeutic guidance to clinicians. Key Word: Cefazolin, Urine Culture, CLSI, Interpretations, VITEKO 2