Emergence of Enterobacter aerogenes strains resistant to imipenem mediated by the coexistence of metallo-beta-lactamase production and outer membrane permeability

Abstract number: p1246

Biendo  M., Laurans  G., Canarelli  B., Thomas  D., Hamdad Daoudi  F., Rousseau  F., Adjide  C., Eb  F.


We documented the emergence of imipenem resistant (IPM-R) strains after prolonged antibiotic therapy.


22 cases of E. aerogenes colonization or infection were monitored retrospectively (July 2003–May 2005). 62 strains were found in 22 patients consisted of 12 men (54.5%) and 10 women (45.5%) with a mean age of 67.1%. The antibiotic susceptibilities, envelope permeabilities, and molecular typing of all the clinical strains were studied.


Of 62 strains, 22 (35.5%) were imipenem-susceptible (IPM-S) and 40 (64.5%) IPM-R. The following Beta-lactam resistance phenotype [FOX (R) CTX (R + I) FEP (R + I) CPO (R + I) ATM (R + I) IPM (R + I) CAZ (R)] 40/62 (64.5%) was found among the 40 IPM-R strains: The MBL production screened by Etest imipenem + EDTA (IPE) among the 40 IPM-R strains showed that 24 were producers [MICs IP: 16–64 mg/mL versus MICs IPE 4–24 mg/mL] (ratio *IP/IPE > 8 mg/mL). The AmpC enzyme production was investigated in the 40 IPM-R strains in Mueller-Hinton (M.H) + 500 mg of cloxacillin containing Cefotaxime (CTX), Ceftazidime (CAZ), Moxalactam (MOX) and Aztreonam (ATM) disks. Two strains were AmpC producers, 10 were ESBLs producers and 28 were AmpC + ESBL producers (mean diameter inhibition between M.H + cloxacillin and MH >5 mm). SDS-PAGE analysis showed 2 major proteins: 42 and 39 kDa presumed to be OmpC and OmpF like respectively. 25 IPM-R strains (IPM-MICs of 8-32 mg/mL) produced both Omps with the level of 42-kDa thinner than IPM-S strains and E. coli HB101. 15 IPM-R strains (IPM-MICs > 32 mg/mL) produced only a 39-kDa Omp. Pulsed-Field Gel Electrophoresis using XbaI, revealed 6 pulsotypes (A-F). The prevalent epidemiological pulsotype A included 77.4% of strains genetically related; 28 (58.4%) of them were IPM-R and 20 (41.6%) IPM-S.


The emergence of multidrug-resistant E. aerogenes strains involving the coexistence of ESBLs; AmpC Beta-lactamase; alteration of Omps and MBL-production is very disquieting in our hospital.

*IP = imipenem

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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