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Journal of Clinical Microbiology, June 2002, p. 2282-2284, Vol. 40, No. 6
0095-1137/02/$04.00+0     DOI: 10.1128/JCM.40.6.2282-2284.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Evaluation of Etest Strips for Rapid Susceptibility Testing of Mycobacterium tuberculosis

I. M. Freixo,1 P. C. S. Caldas,2 F. Martins,2 R. C. Brito,3 R. M. C. Ferreira,1 L. S. Fonseca,1 and M. H. F. Saad4*

Microbiology Institute, Rio de Janeiro Federal University (UFRJ),1 Helio Fraga National Reference Center,2 Pedro Ernesto University Hospital, Rio de Janeiro State University (UERJ),3 Leprosy Laboratory, FIOCRUZ, Rio de Janeiro, Brazil4

Received 14 December 2001/ Returned for modification 1 February 2002/ Accepted 1 March 2002

In this study, our objective was to evaluate Etest strips containing exponential gradients of isoniazid (INH), rifampin (RIF), and streptomycin (STR) for susceptibility testing of Mycobacterium tuberculosis. M. tuberculosis isolates were tested for antimicrobial susceptibilities by the standard proportion method using Löwenstein-Jensen (LJ) medium and by the Etest. The MICs determined by the Etest were obtained at 5, 7, or 10 days. In some strains with Etest-discrepant results, radiometric susceptibility testing (BACTEC) was performed to determine a consensus result. M. tuberculosis concordance between the two methods was 97% (86 of 89 isolates) for RIF, 96% for INH (84 of 87 isolates), and 80% (61 of 76 isolates) for STR. Most of the MICs determined by the Etest were easy to interpret and readable within 5 days. Results correlated well with those obtained by the LJ proportion and BACTEC methods for INH and RIF. However, a high proportion of false-sensitive and false-resistant results were observed, most often for STR. We also observed that variations in the inoculum size of M. tuberculosis isolates affected the MICs to a substantial degree. These discrepancies, along with the expense of the media, the Etest strips, and the specialized equipment required (CO2 incubator), make this method less useful in developing countries.

* Corresponding author. Mailing address: Fundação Oswaldo Cruz, Instituto Oswaldo Cruz, Laboratório de Hanseníase, Av. Brasil 4365, Rio de Janeiro RJ21045-900, Brazil. Phone: 55.21.25984288. Fax: 55.21.22709997. E-mail: saad{at}ioc.fiocruz.br.

Journal of Clinical Microbiology, June 2002, p. 2282-2284, Vol. 40, No. 6
0095-1137/02/$04.00+0     DOI: 10.1128/JCM.40.6.2282-2284.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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