Program Schedule

Validation of Rosco Diagnostica Diffusion Discs for Identification of Carbapenem Resistance Mechanisms in a Clinical Laboratory

Session: Poster Abstract Session: Diagnostic Microbiology: Bacterial Infections
Saturday, October 11, 2014
Room: The Pennsylvania Convention Center: IDExpo Hall BC
  • Poster1394_Sarah Kemble_IDWeek2014.pdf (909.6 kB)
  • Background: There is increasing need for clinical laboratories to reliably detect and differentiate carbapenem resistance mechanisms. We evaluated the performance of two methods for the detection of Klebsiella pneumoniae carbapenemase (KPC): the Rosco KPC/Metallo-beta-lactamase and OXA-48 Confirm Kit, a disc diffusion method for in vitro identification of bacteria producing carbapenemases and the modified Hodge test.

    Methods: Bacterial test strains were selected from previously identified beta-lactam and carbapenem resistant clinical isolates, including KPC producing strains confirmed by blaKPC PCR . Carbapenemase detection was performed with Rosco discs using 0.5 McFarland suspension of each isolate on Mueller Hinton agar. Modified Hodge test was performed using 10ug meropenem discs. Plates were incubated overnight at 35°C in ambient air  and read independently by two blinded investigators  When discrepancies in interpretation occurred, the tests were repeated by a third blinded investigator. Test characteristics of the two methods were calculated using PCR as the reference standard.

    Results: Fifty-two bacterial strains (20 KPC positive and 32 KPC negative) were tested. Sensitivity of the Rosco discs and modified Hodge test for identification of KPC was 95%. Specificity of the Rosco discs  (positive synergy test with boronic acid), using the manufacturer’s cutoff of ≥4 mm increase in the zone size was 87.5% for KPC. By increasing the cutoff to ≥5 mm, the specificity of the Rosco kit increased to 93.8% without any decrease in sensitivity. Hodge test specificity for KPC was 71.9%; positive results were also observed for 2 ampC, 1 extended-spectrum beta-lactamase, 3 metallo-beta-lactamase, and 2 OXA-48-like producing strains.

    Conclusion: The Rosco KPC/Metallo-beta-lactamase and OXA-48 Confirm Kit had equivalent sensitivity and superior specificity for identification of KPC compared to the Hodge test. We propose a modification of interpretation of test results to further improve specificity. An added advantage of the Rosco kit is its ability to differentiate between classes of carbapenem resistance mechanisms.

    Sarah Kemble, MD1, Jonathan Claus, MD1, Karen Lolans, BS2, Jennifer Lindsley2 and Kamaljit Singh, MD1, (1)Section of Infectious Diseases, Rush University Medical Center, Chicago, IL, (2)Department of Pathology, Rush University Medical Center, Chicago, IL


    S. Kemble, None

    J. Claus, None

    K. Lolans, None

    J. Lindsley, None

    K. Singh, Quidel Corporation: Scientific Advisor, Consulting fee

    Findings in the abstracts are embargoed until 12:01 a.m. EDT, Oct. 8th with the exception of research findings presented at the IDWeek press conferences.

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