[Comparison of three microbiological methods for detection of expanded-spectrum betalactamases in Enterobacteriaceae isolated in Santa Fe (Argentina)]. / Comparación de tres métodos microbiológicos para la detección de betalactamasas de espectro extendido en enterobacterias aisladas en Santa Fe (Argentina).

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.

Comparación de tres métodos microbiológicos para la detección de betalactamasas de espectro extendido en enterobacterias aisladas en Santa Fe (Argentina) / Comparison of three microbiological methods for detection of expanded-spectrum betalactamases in Enterobacteriaceae isolated in Santa Fe (Argentina)

Introducción. Las betalactamasas de espectro extendido (BLEE) son la principal causa de resistencia a las oxiiminocefalosporinas y monobactamas en enterobacterias. La mayoría de las BLEE derivan de TEM o SHV, sin embargo se ha incrementado la incidencia de otras familias como CTX-M, OXA y PER. En Argentina, CTX-M-2 es la BLEE más frecuente en enterobacterias. Esta situación particular, diferente a la del hemisferio norte, ha motivado el estudio de nuevas estrategias diagnósticas que permitan detectar la mayor parte de las BLEE de nuestra región. Métodos. La detección microbiológica de las BLEE se realizó comparando los métodos de sinergia de doble disco, discos de cefotaxima y ceftazidima con y sin el agregado de ácido clavulánico (National Committee for Clinical Laboratory Standards, NCCLS) y discos de cefotaxima y ceftazidima en placas de agar Müeller-Hinton suplementado con clavulanato de litio (MH-cla). Las betalactamasas fueron caracterizadas mediante isoelectroenfoque, perfil de hidrólisis y amplificación por reacción en cadena de la polimerasa. Resultados. Sobre 575 enterobacterias, el 14% fueron resistentes a oxiiminocefalosporinas. En 31 aislados resistentes se detectaron dos tipos diferentes de BLEE: grupo CTX-M-2 (28) y PER-2 (3). El método de sinergia presentó menor sensibilidad en la detección de BLEE que los otros dos métodos. Con ellos se detectó la presencia de BLEE en todos los aislados empleando discos de cefotaxima, sin embargo no ocurrió lo mismo al emplear discos de ceftazidima. Conclusión. El método microbiológico que emplea MH-cla con disco de cefotaxima tuvo una sensibilidad y especificidad equivalentes a la técnica de confirmación propuesta por el NCCLS para la detección de las BLEE empleando el mismo antibiótico (AU)

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 Müeller­Hinton 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 (AU)