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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.

Objective: 

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

Methods: 

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.

Results: 

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.

Conclusion: 

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
Subject:
Location: Oxford, UK
Presentation type:
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