Enterobacter aerogenes strains misidentified as Klebsiella pneumoniae and correct identification by sequencing of the QRDR region of the gyrA gene

Abstract number: 1734_97

Agüero J., Conejo M.C., Sáez A., de Cueto M., Martínez-Martínez L., Pascual A.

Objective: To verify by genotypic methods the identification of four clinical isolates initially identified as Klebsiella pneumoniae showing unusual phenotypic characteristics for this species.

Methods: Four isolates from the same patient were obtained from two blood cultures (isolates 1, 2 and 3, 4) performed within 8 days, during which the patient was treated with imipenem. Initial identification and susceptibility testing was done with the VITEK 2 system. Subsequent identification was performed with the WalkAway System and API 20E.

Carbapenem activity was also determined with Etest. The presence of plasmid-mediated AmpC b-lactamases (pACBL) was analysed by multiplex PCR. Sequences from segments of the16S rRNA, rpoB and gyrA (QRDR region) genes were analysed by GenBank database.

Results: The four isolates were identified as K. pneumoniae by the VITEK 2. API 20E identified K. terrigena (isolates 1, 3, 4) or Enterobacter aerogenes (isolate 2). The WalkAway identified isolates 1 and 3 as K. pneumoniae, isolate 2 as E. aerogenes and isolate 4 as uncommon phenotype. MICs for isolates 1, 2, 3, 4 were: 16, ≤1, 16, >16 (ceftazidime); 8, ≤1, 32, >32 (cefotaxime); ≤1, ≤1, ≤1, 8 (cefepime); ≤1, ≤1, 8, >8 (imipenem); ≤1, ≤1, >4, >4 (ertapenem) and >2, 1, >2, >2 (ciprofloxacin). All were resistant to both amoxicillin-clavulanate and cefoxitin. MICs of oxyimino-cephalosporins did not decrease with clavulanate. pACBL were not detected. The AmpC induction test positive in all 4 isolates. Isolates 1, 3 and 4 presented the same REP-PCR type; isolate 2 showed a different one. Isolates 3 and 4 expressed only an OmpA-like outer memprane protein (OMP). Isolate 1 presented an additional OMP of ca.36 Kda, and isolate 2 two OMPs of ca.35 and 36 Kda. One single b-lactamase band of pI 8.1–8.2 was observed in all 4 isolates. 16S rDNA and rpoB sequences did not differentiate Klebsiella sp from Enterobacter sp. The gyrA-QRDR sequences of test isolates was highly similar to that of E. aerogenes (98%) but not that of Klebsiella sp. (≤95%).

Conclusions: Two strains identified as K. pneumoniae/terrigena following conventional methods caused bacteraemia in a single patient treated with imipenem. The more resistant strain was later isolated presenting resistance to carbapenems. Additional phenotypic tests and gyrA sequencing demonstrated that the isolates were actually E. aerogenes which developed carbapenems resistance after porin loss.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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