Assessment of Phenotypic Tools for Detection of OXA-48, KPC and NDM in <i>Klebsiella pneumoniae</i> in Oman

Background: For judicious use of reserve drugs, timely detection of carbapenemases is essential. While molecular tools are gold standard for detection of these enzymes, many laboratories have limited access to them. This study focused on evaluating in-house and commercial phenotypic tests for detection of OXA-48 in particular, KPC and NDM in general in K. pneumoniae, the predominant extremely drug-resistant pathogen in Oman. Methods: Eighty GeneXpert/PCR confirmed (40 OXA-48, twenty KPC and NDM each) and 37 whole-genome-sequenced (25 OXA-232, 6 KPC-2 plus NDM-1 and NDM-5 each) K. pneumoniae were subjected to screening by temocillin (30 μg disk MAST Diagnostica, Germany) and D71C (MASTDISCS®). Isolates resistant to temocillin (<11mm) and D71C were subjected to four tests -one in-house (OXA-48 disk test) and three commercial phenotypic tests (i) The MASTDISCS® Combi (D72C) (MAST Group Ltd., UK). (ii) The MASTDISCS® Combi (D73C) (MAST Group Ltd., UK) and (iii) Immunochromatographic assay (ICT); KPC/IMP/NDM/VIM/OXA-48 Combo test kit (Medomics, China for detection of OXA-48 like, KPC and NDM carbapenemases. Results: Temocillin exhibited good sensitivity and specificity (100% and 97.50%) compared to D71C (70% and 100%). Among the confirmatory tests, the in-house OXA-48 disk test had 92.50% sensitivity and 100% specificity, while the commercial MAST DISC tests D72C D73C and ICT had 97.50%, 95.00% and 100% sensitivity and 100%, 91.67% and 95% specificity respectively. Conclusion: Temocillin disc test is a good screening tool. With high sensitivity and specificity, ease of performance, short turnaround time and low cost, we recommend ICT for routine diagnostic use. In resource constrained centres, OXA-48 disk test is an excellent alternative with high sensitivity and specificity.