[Comparison of three microbiological methods for detection of expanded-spectrum betalactamases in Enterobacteriaceae isolated in Santa Fe (Argentina)]

Abstract

Introduction: Expanded-spectrum betalactamases (ESBLs) are the main source of resistance to oxyimino cephalosporins and monobactams in Enterobacteriaceae. Most of them derive from TEM or SHV, however the incidence of other families like CTX-M, OXA and PER has increased. In Argentina, the most frequent ESBL in Enterobacteriaceae is CTX-M-2. This specific circumstance, which differs from the situation in the Northern Hemisphere, motivated us to study new diagnostic strategies for the detection of ESBLs in our region.

Method: Microbiological ESBL detection was performed by double-disk synergy tests, cefotaxime and ceftazidime disks with and without clavulanic acid (NCCLS), and cefotaxime and ceftazidime disks in Müeller-Hinton agar supplemented with lithium clavulanate (MH-cla). Betalactamases were characterized by isoelectric focusing, hydrolysis profile and PCR amplification.

Results: Among 575 clinical isolates of Enterobacteriaceae, 14% were oxyimino cephalosporin-resistant. Two different ESBLs were detected in 31 resistant strains: CTX-M-2 (28) and PER-2 groups (3). The double-disk synergy test was the least sensitive method for ESBL detection. ESBLs were detected by the other two methods in all isolates with the use of cefotaxime disks, but not with ceftazidime disks.

Conclusion: The microbiological method employing MH-cla with cefotaxime disks had a sensitivity and specificity comparable to the referral test using the same antibiotic proposed by the NCCLS for the detection of ESBLs.