R2146 Detection of extended-spectrum β-lactamases, including the CTX-M-type enzymes, among Enterobacteriaceae using VITEK 2 system and the Advanced Expert system

Abstract

Objectives: The aims of the present study were to assess if the VITEK 2 AES could accurately detect ESBL in Enterobacteriaceae isolates, comparing the final data report with the results of phenotypic and genotypic based methods. The susceptibility of ESBL producers to Ertapenem was also investigated. A special relevance was given to a new emergent CTX-M-type ESBL. Methods: From April 2006 to October 2006, 35 isolates of Enterobacteriaceae were recovered from 35 inpatients of different wards of the Hospital Infante D. Pedro de Aveiro, Portugal, and identified as extended-spectrum βlactamases (ESBL) producers by the automatic VITEK 2 system and Advanced Expert System (VITEK 2 AES) (BioMerieux, Marcy L'Etoile, France). The antibiotic susceptibilities were determined by VITEK 2 and the susceptibilities reports were edited after interpretation by AES of the inferred resistance phenotype. ESBL were also detected by Etest ® (AB Biodisk) ESBL with Cefotaxime/Cefotaxime + Clavulanic acid and Ceftazidime/Ceftazidime + Clavulanic acid strips, according to manufacturer's instructions. Susceptibility to Ertapenem was tested using disc diffusion method (DDM) (10 ug, Oxoid). PCR, sequencing and sequence analysis was used to assess β-lactamase encoding sequences. Sequences obtained were compared with others deposited in the GeneBank database. Results: VITEK 2 determined that: for CAZ, 32 isolates were resistant and 3 were susceptible, for CTX, the same result was obtained. AES edited these data as resistance phenotypes, suggesting the production of ESBL. Using the Etest, 34 isolates presumable produced ESBL. One isolate was indeterminate, according to the manufacturer's guidelines. All the isolates identified as ESBL producers were sensitive to Ertapenem. PCR specific for CTX-M encoding sequences showed the presence of this gene in 14.3% of the isolates bearing an ESBL. Conclusion: This study demonstrated the capacity of VITEK 2 AES to detect and interpret resistance mechanisms, inferring with a high level of confidence the presence of isolates ESBL producers. Also shows that Ertapenem is effective against ESBL producers. CTX-M-1 and CTX-M-15 were the CTX-M-type enzymes found among the Enterobacteriaceae population studied.