Abstract

In 2010, the Clinical Laboratory and Standards Institute (CLSI) revised disc diffusion (except cefazolin) and minimal inhibitory concentration (MIC) breakpoints of some cephalosporins and emphasized that it is no longer necessary in routine extended spectrum beta lactamases (ESBL) screening, except for epidemiological research or infection control purposes. The aim of this study was to evaluate the MIC breakpoints of cefazolin, cefotaxime, ceftizoxime and ceftriaxone according to 2009, 2010 and 2011 CLSI criteria, and to discuss the importance of ESBL screening tests. ESBL positive 182Escherichia coli and 18 Klebsiella pneumoniae strains were enrolled in this study. Susceptibility was determined by broth microdilution method. Utilizing the new breakpoints, the susceptibility rates of E. coli strains to ceftriaxone, cefazolin and ceftizoxime were 0.5, 0.5 and 2%, respectively and all E. coli strains were resistant to cefotaxime. However the susceptibility of K. pneumoniae strains was resistant to all antibiotics mentioned above. As a conclusion, according to the CLSI criteria, six strains (3%) were reported as sensitive and five (2.5%) as intermediate. Although the CLSI emphasized that the results reported according to the new criteria are more compatible with clinical outcomes, ESBLs are still a major problem especially between hospitalized patients. According to the results of our study it might be possible to say that the screening methods for ESBL detection are still important.

Key words: ESBL, CLSI, E. coli, Klebsiella