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Kim, Kang, Park, and Choi: Evaluation of ChromID MRSA for the Detection of Methicillin-resistant Staphylococcus aureus
Original Article

Korean J Clin Microbiol 2009;12(4):169-173.

Published online: 22 December 2009

DOI: https://doi.org/10.5145/KJCM.2009.12.4.169

Evaluation of ChromID MRSA for the Detection of Methicillin-resistant Staphylococcus aureus

Min Jung Kim, Dae Hyuk Kang, Jae Im Park, Tae Yeal Choi

Department of Laboratory Medicine, Hanyang University Hospital, Seoul, Korea

Correspondence: Tae Yeal Choi, Department of Laboratory Medicine, Hanyang University Hospital, 17, Haegdang-dong, Seongdong-gu, Seoul 133-792, Korea. (Tel) 82-2-2290-8974, (Fax) 82-2-2298-1735, (E-mail) tychoi@hanyang.ac.kr

Received 22 June 200926 October 2009       Accepted 20 November 2009

Copyright © 2009 Korean Journal of Clinical Microbiology

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen in both nosocomial and community settings, and screening for a carrier is an important infection control practice in many hospitals. We evaluated the sensitivity and specificity of the ChromID MRSA assay (bioMérieux, Marcy I'Etoile, France).

Methods

A total of 190 clinical samples were collected from the anterior nares of premature infants in a newborn intensive care unit (N-ICU). Equal volumes (100μL) of the samples were inoculated on mannitol salt agar with oxacillin 6 mg/L (MSAO) and ChromID MRSA after emulsifying the screening swab in brain-heart Infusion broth with oxacillin 6 mg/L (BE). The specimens in BE were subcultured on ChromID MRSA after an overnight incubation.

Results

Twenty-one of 190 samples (11%) was positive for MRSA by BE. After a 24 h incubation, the sensitivity/specificity of MSAO was 52%/98% and that of ChromID MRSA was 62%/100%, and at 48 h, the sensitivity/specificity of MSAO was 62%/92% and that of ChromID MRSA was 81%/99%.

Conclusion

ChromID MRSA is a useful selective medium for the rapid isolation and identification of MRSA.

Keywords: Methicillin-resistant Staphylococcus aureus (MRSA), Detection, Performance, Culture medium

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Table 1.
Sensitivity and specificity of mannitol salt agar containing oxacillin 6 mg/mL (MSAO) and ChromID MRSA (ChromID) for detection of MRSA from anterior nare of patients in a newborn intensive care unit (N=190)
Incubation Medium TP∗ FP† TN‡ FN§ Sensitivity (%) Specificity (%) PPV (%) NPV (%)
24 h MSAO 11 4 165 10 52 98 73 94
ChromID 13 0 169 8 62 100 100 95
48 h MSAO 13 14 155 8 62 92 48 95
ChromID 17 1 168 4 81 99 94 98

∗ A true positive (TP) is defined as a green colony on ChromID or yellow change of medium on MSAO that was identified as MRSA by identification;

† A false positive (FP) is defined as an isolate that exhibited green color on ChromID or yellow change of medium on MSAO but was not identified as MRSA;

‡ A true negative (TN) is defined as the lack of MRSA on solid medium and broth enrichment;

§ A false negative (FN) is defined as an isolates that was confirmed as a MRSA on broth enrichment but did not grown on solid medium.

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