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. 2017 Jan;24(1):155-161.
doi: 10.1016/j.sjbs.2016.07.004. Epub 2016 Aug 6.

Comparison of phenotypic and PCR methods for detection of carbapenemases production by Enterobacteriaceae

Maryam AlTamimi  1 , Ali AlSalamah  1 , Manal AlKhulaifi  1 , Hisham AlAjlan  2
Affiliations

Comparison of phenotypic and PCR methods for detection of carbapenemases production by Enterobacteriaceae

Maryam AlTamimi et al. Saudi J Biol Sci. 2017 Jan.

Abstract

Dissemination of carbapenem resistance via Enterobacteriaceae, particularly among Klebsiella pneumoniae and Escherichia coli, is a major public health concern. Rapid methods for determining antimicrobial susceptibility are important to ensure adequate and appropriate use of antimicrobial agents and to limit the spread of these bacteria. In the current study, we compared the rapidity, sensitivity and specificity of traditional methods and molecular-based Xpert Carba-R PCR assay to identify sixty isolates, (26 E. coli and 34 K. pneumoniae). The specificity of MicroScan was 100% while sensitivity to ertapenem (ERT), imipenem (IMI), and meropenem (MER) was 93%, 68.9%, and 55.17%, respectively. For the modified Hodge test, the specificity was 96.77% and sensitivity was 89.65%. Although some results of phenotypic assays matched with the definite PCR identification, some results were misleading. Out of the 29 positive PCR samples, three samples of K. pneumoniae were negative for the MHT and one E. coli sample was MHT positive but negative for the PCR. Nine samples were positive for the PCR but were determined as carbapenem sensitive by MicroScan. While MicroScan and MHT requires several hours and multi-steps to obtain results, Xpert Carba-R PCR assay takes less than an hour. Therefore, we recommend using Gene xpert Carba-R assay for the optimal carbapenemnase detection with reducing material, manpower and cost. Also it is important to know the type of carbapenemase is present.

Keywords: Antibiotic resistance; Carbapenemase; E. coli; Gene Xpert Carba-R assay; Klebsiella pneumonia; MicroScan; Modified Hodge test; PCR; Phenotypic.

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Figures

Figure 1
Figure 1
Antibiotic resistance profile of the 60 isolates of E. coli and K. pneumoniae as determined by MicroScan. (R = resistant, I = intermediate, S = sensitive).
Figure 2
Figure 2
Example of E. coli isolates showing a positive and negative results with MHT on Muller Hinton Agar. Symbols; (1) K. pneumoniae negative control ATCC 1706. (2) E. coli 25922. (3) Meropenem disk. (4) K. pneumoniae positive control ATCC1705. (5) Negative MHT result. (6) Positive MHT result.
Figure 3
Figure 3
Gene Xperts Carba-R assay analysis. (A) OXA-48 gene detected in K. pneumoniae isolates, (B) NDM gene detected in E. coli isolates, (C) VIM gene detected in K. pneumoniae isolates, and (D) positive control KPC of K. pneumoniae.
See this image and copyright information in PMC

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