Table 1

Mechanisms of resistance and MICs for imipenem and ertapenem of 56 isolated imipenem-resistant Gram-negative bacilli

SpeciesNo. of strainsResistance mechanismsaMIC (mg/liter)b
EnzymesOtherImipenemErtapenem
P. aeruginosa19OprD−6–>32ND
6AmpC++OprD−16–>32ND
4OprD− MexAB efflux ++24–>32ND
2AmpC++OprD− MexAB efflux ++24–32ND
1GES-9OprD−>32ND
4VIM-2>32ND
Enterobacteriaceae
    K. pneumoniae2DHA-1OMP−24–32>32
1TEM-1 CTX-M15NP3>32
    E. aerogenes1TEM-24 AmpC++OMP−16>32
    E. cloacae1SHV-12 AmpC++OMP−32>32
    H. alvei1AmpC++NP432
A. baumannii26–12ND
S. maltophilia12Wild typeNDND
  • a OprD−, loss of OprD porin; AmpC++, hyperexpression of AmpC chromosomal cephalosporinase; MexAB efflux ++, hyperexpression of MexAB-OprM system efflux; OMP−, loss or reduced expression of outer membrane protein; NP, OMP analysis not performed.

  • b ND, not determined.