KPC is not equally active against all carbapenems. In general, ertapenem
susceptibility is a more sensitive indicator of KPC-mediated resistance than
either meropenem or imipenem.
It is important to note that nonsusceptibility to carbapenems, can be
mediated by mechanisms other than KPC, e.g., the combination of an AmpC-type β-
lactamase and porin loss. These other mechanisms are clinically important,
but as of today, no documented outbreaks have been attributed to them.
As of September 27, 2007, KPC-producing Klebsiella pneumoniae isolates have
been confirmed by molecular testing in 22 healthcare institutions in New
Jersey and it is likely that many more laboratories will encounter these
organisms in the near future.
Below are recommendations to help clinical microbiologists recognize the
KPC mechanism of resistance in their laboratories.
Microbiologists should look for evidence of carbapenemase-mediated
resistance in Enterobacteriaceae using the following criteria, paying
particular attention to isolates of Klebsiella spp. and E. coli that.
Are resistant to carbapenems by any standardized testing method. These
are very likely KPC-producers. Confirmation of the resistance mechanism in
these organisms is not currently a clinical or public health necessity, since
KPC-producers are already known to exist widely throughout the state..
Test susceptible to carbapenems, but with elevated MICs. These isolates may
also possess the enzyme.. A rule of thumb is to ”flag” isolates with
carbapenem MICs of 2 or 4 μg/ml. Hospitals are evaluating their reporting
protocols for these organisms.
Produce a nonsusceptible ertapenem disk diffusion result (I or R). This is
a sensitive indicator of KPC-production.
nonsusceptibility in this instance refers to carbepenem disc diffusion
results of Intermediate or Resistant or carbepenum MIC results of 2 ug/ml or
greater.
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