Detection of the presence of extended-spectrum beta-lactamase enzyme in gram-negative bacteria according to CLSI and EUCAST criteria

Abstract

Introduction: Expanded spectrum beta-lactamase is a critical source that is limiting the using areas of beta-lactam antibiotics by hydrolysing them. The method to be used for accurate detection of ESBL production is significant. CLSI and EUCAST are the two most commonly used standards for the determination of antibiotic susceptibility. This study aimed to investigate the sensitivity and specificity of these standards for ESBL detection. Methods: This study includes 76 ESBL producers and 74 ESBL negative strains, which were isolated from urine specimens that sent to the Medical Microbiology Laboratory of Haydarpasa Numune Training and Research Hospital from April to July 2014. For screening tests, ceftazidime (10µg and 30µg), cefotaxime (5µg and 30µg), ceftriaxone (30µg), cefpodoxime (10µg), cefepime (30µg) ve aztreonam (30µg) disks; for confirmation tests double-disk synergy and combination disk method were used. For molecular confirmation tests, CTX-M, TEM and SHV resistance genes were investigated by polymerase chain reaction. Results: ESBL producing isolates were found at 86.8% as CTX-M, 47.4% as TEM and 9.2% as SHV. More than one resistance gene was detected in some isolates. Beta-lactam susceptibilities of ESBL producers with CLSI and EUCAST breakpoints were 29.2% and 19.7% for ceftazidime, 14.5% and 15.8% for cefepime, 2.6% and 13.2% for aztreonam, respectively. Among the screening disks, cefpodoxime (interpreted by EUCAST criteria), showed the highest sensitivity and specificity. This was followed by cefpodoxime (CLSI), cefotaxime and ceftriaxone with similar sensitivity and specificity for both standards. Discussion and Conclusion: There was no significant difference between CLSI and EUCAST in determining ESBL production. The suggestion of EUCAST that using different disks for screening and confirmation tests increases the sensitivity of detecting ESBL, especially in ceftazidime; however, it may cause practical difficulties. For both standards, the use of cefpodoxime, cefotaxime or ceftriaxone disks in screening and; cefotaxime and cefotaxime- clavulanate disks in confirmation tests will provide more accurate results.