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We determined the positive predictive value and specificity of ertapenem resistance for KPC detection in 2, Enterobacteriaceae isolates.
Detection of Klebsiella pneumoniae carbapenemases KPCs can be difficult because carbapenem MICs may be high but still in the susceptible range as defined by Clinical and Laboratory Standards Institute CLSI criteria cldiespecially when an automated susceptibility testing instrument is used 1.
Ertapenem is the least-active carbapenem m1100 KPCs, and the use of this drug in automated or manual susceptibility testing has been found to be a highly sensitive method for the detection of KPCs 1.
One recent European study found that only 2 of ertapenem-resistant Enterobacteriaceae isolates produced carbapenemases, neither of m00 was a KPC 6. We evaluated the performance of ertapenem susceptibility screening for KPCs for all mucoid lactose-positive Enterobacteriaceae regardless of susceptibility profile and for all broad-spectrum-cephalosporin-resistant Enterobacteriaceae isolated in our laboratory during Mucoid lactose-positive bacteria were selected because it was known in that KPCs were present only in Klebsiella pneumoniae at our institution.
Navigating the 2012 Changes to CLSI M100, M02 and M07
In addition, all non-urine source Enterobacteriaceae that underwent susceptibility testing in our laboratory from August to December were included. Use of the GN card allowed broader testing of ertapenem against all Enterobacteriaceae undergoing antimicrobial susceptibility testing. The presence of KPCs was confirmed by both PCR and the modified Hodge test using meropenem as the indicator drug, both performed as previously described 7.
Ertapenem screening was performed with 2, Enterobacteriaceae isolates, including isolates of Enterobacter spp. Of these 85 ertapenem-intermediate or -resistant isolates, 63 were KPC positive, all of which were K. The positive predictive value of ertapenem screening for K.
Ertapenem screening specificity for KPCs was Ertapenem screening was falsely positive for KPCs in all five ertapenem-intermediate or -resistant Enterobacter and E.
The ertapenem disk zone size of inhibition for the KPC-positive ertapenem-intermediate bacteria was 16 mm for all three isolates, versus 17, 17, 18, and 19 mm for the four non-KPC bacteria, indicating that it might be possible to distinguish KPC-positive from KPC-negative bacteria solely by the size of the ertapenem disk zone of inhibition, using 16 mm as the breakpoint.
Roughly half of the isolates screened for ertapenem resistance were tested by Vitek II and half by disk diffusion testing, with equivalent performances for each type of test.
The positive predictive value is high despite a low 2. Both the modified Hodge test and the KPC PCR test performed identically, except for the latter’s advantages of a more rapid turnaround time and less dependence on experience with reading the Hodge tests, which are sometimes difficult to read.
The performance of ertapenem screening is likely to be much different in w18 regions where KPCs are rare and especially if ertapenem-resistant non-KPC bacteria are common. These recommendations use screening breakpoints currently in the susceptible range, using either ertapenem or meropenem disk diffusion testing or broth dilution susceptibility testing using ertapenem, meropenem, or imipenem.
The disk diffusion breakpoints are 19 to 21 mm and 16 cclsi 21 mm for ertapenem and meropenem, respectively.
Navigating the Changes to CLSI M, M02 and M07 – ppt video online download
Modified Hodge testing with either ertapenem or meropenem is recommended for isolates with positive screening test results. Based on our results, these new screening breakpoints would likely detect a small number of KPCs not detected by the methods we used but with clssi even lower positive predictive value than we observed.
It is important to note that the new CLSI MIC breakpoint criteria are for conventional broth dilution methods and are clzi applicable to automated susceptibility instruments, based on our results and those of others, especially for meropenem and imipenem testing 125. National Center for Biotechnology InformationU. Journal List J Clin Microbiol v. Published online Jan Author information Article notes Copyright and License information Disclaimer. This article has been cited by other articles in PMC.
Ertapenem-intermediate or -resistant isolate screen results. Open in a separate window. Evaluation of methods to identify the Klebsiella pneumoniae carbapenemase in Enterobacteriaceae. Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing; 18th informational supplement.
Performance standards for antimicrobial susceptibility testing; 19th informational supplement. Carbapenem resistance in Klebsiella pneumoniae not detected by automated susceptibility testing.