Beschreibung:
<jats:title>ABSTRACT</jats:title>
<jats:p>
We investigated the mechanisms involved in imipenem resistance in 23 clinical strains of
<jats:italic>Acinetobacter baumannii</jats:italic>
. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed the presence of a 30-kDa protein in imipenem-intermediate
<jats:italic>A. baumannii</jats:italic>
(IIAB) and imipenem-resistant
<jats:italic>A. baumannii</jats:italic>
(IRAB) strains; this protein was almost undetectable in imipenem-susceptible
<jats:italic>A. baumannii</jats:italic>
(ISAB) strains. The 30-kDa protein was identified as an OXA-51-like carbapenemase using two-dimensional gel electrophoresis and mass spectrometry. Similar to other recent findings,
<jats:italic>bla</jats:italic>
<jats:sub>OXA-51-like</jats:sub>
genes were found to exist in all 23 clinical strains; however, the transcript levels of
<jats:italic>bla</jats:italic>
<jats:sub>OXA-51-like</jats:sub>
in the IIAB and IRAB were higher than in the ISAB strains using reverse transcriptase PCR (RT-PCR) and real-time RT-PCR assays. This change was due to the presence of an insertion sequence, IS
<jats:italic>Aba1</jats:italic>
, upstream of
<jats:italic>bla</jats:italic>
<jats:sub>OXA-51-like</jats:sub>
in the IIAB and IRAB strains that was not present in the ISAB strains. The introduction of
<jats:italic>bla</jats:italic>
<jats:sub>OXA-66</jats:sub>
(a
<jats:italic>bla</jats:italic>
<jats:sub>OXA-51</jats:sub>
<jats:sub>-like</jats:sub>
gene), identified in ISAB ab1254 and IRAB ab1266, into
<jats:italic>Escherichia coli</jats:italic>
TOP10 cells resulted in 3.95-fold and 7.90-fold elevations in resistance to imipenem, respectively. Furthermore, when ISAB ab8 and ISAB ab1254 and their in vitro-selected imipenem-resistant mutants ISAB ab8(r) and ISAB ab1254(r) were compared, the results showed no change in the
<jats:italic>bla</jats:italic>
<jats:sub>OXA-66</jats:sub>
/
<jats:italic>bla</jats:italic>
<jats:sub>OXA-51-like</jats:sub>
gene sequences, in expression of the gene, and in the outer membrane protein profiles. However, there was a four- to eightfold reduction in imipenem resistance upon adding carbonyl cyanide
<jats:italic>m</jats:italic>
-chlorophenylhydrazone. Taken together, these results suggest that the OXA-66/OXA-51-like carbapenemase contributes to intrinsic resistance to imipenem; however, drug export by an efflux pump may be more important and/or occur more frequently in imipenem-resistant
<jats:italic>A. baumannii</jats:italic>
. Furthermore, this is the first report of a Taiwanese strain of an OXA-66/OXA-51-like carbapenemase that confers imipenem resistance in
<jats:italic>A. baumannii</jats:italic>
.
</jats:p>