Detection of ESBL mediated resistance in Enterobacter spp. by using new VITEK2 AST cards and advanced expert system

Abstract number: p449

Smet  J., Rodriguez-Villalobos  H., Nonhoff  C., Crevecoeur  S., De Mendonça  R., Struelens  M.


VITEK 2 AST-045 and AST-046 cards (BioMerieux) for Gram-negative susceptibility testing include a specific ESBL detection test combining cefotaxime, cefepime and ceftazidime alone and with clavulanate. Because this test has been validated by the manufacturer only for E. coli and Klebsiella spp , the result is reported only for these species. We determined the ability of VITEK 2 and Advanced Expert System (AES) to detect ESBL mediated resistance in Enterobacter clinical isolates using these cards.


A total of 76 Enterobacter isolates : 63 ESBL producing strains (32 E. aerogenes and 31 E. cloacae) and 13 non ESBL producing strains (7 E. aerogenes and 6 E. cloacae) were inoculated into the VITEK 2 AST-045 and AST-046 cards according to the manufacturer recommendations. Production of ESBL was confirmed by double disc synergy test (with ceftazidime, cefotaxime and cefepime), combined disc method (Oxoid) and PCR for bla TEM, bla SHV and bla CTX-M genes. E. cloacae harboured SHV12 in combination with CTX-M9 in 94%. E. aerogenes ESBLs included: TEM enzymes in 59%, SHV in 9% or other combinations of enzymes in 32%. Results were graded as "agreement" when AES inferred ESBL mechanism, "partial agreement" when AES suggested several mechanisms including ESBL and "disagreement" when AES concluded to different mechanism(s).


Results are summarized in the table.

Overall sensitivity was 92% (91% for E. aerogenes and 94% for E. cloacae) and specificity 23.1% (14.3% for E. aerogenes and 33.3% for E. cloacae). The mean time to obtain results was 8.2 h (range 6.25–11).


This study shows that VITEK2 AES provides a rapid and sensitive tool to detect possible ESBL production in Enterobacter spp by using AST-045 or AST-046 cards but confirmatory analysis is frequently necessary. More efficient automated methods should be developed to distinguish ESBL production from AmpC hyperproduction in this genus.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Location: Oxford, UK
Presentation type:
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