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Journal of Clinical Microbiology, April 2002, p. 1277-1282, Vol. 40, No. 4
0095-1137/02/$04.00+0     DOI: 10.1128/JCM.40.4.1277-1282.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Evolution of the IS6110-Based Restriction Fragment Length Polymorphism Pattern during the Transmission of Mycobacterium tuberculosis

R. M. Warren,1 G. D. van der Spuy,1 M. Richardson,1 N. Beyers,2 C. Booysen,2 M. A. Behr,3 and P. D. van Helden1*

MRC Centre for Molecular and Cellular Biology, Department of Medical Biochemistry,1 Department of Paediatrics and Child Health, Faculty of Health Sciences, University of Stellenbosch, Tygerberg 7505, South Africa ,2 Department of Medicine, McGill University Health Centre, Montreal H3G 1A4, Canada3

Received 25 October 2001/ Returned for modification 4 December 2001/ Accepted 21 January 2002

Interpretation of the molecular epidemiological data of Mycobacterium tuberculosis is dependent on the validity of the assumptions that have been made. It is assumed that the IS6110 banding pattern is sufficiently stable to define epidemiological events representing ongoing transmission. However, molecular epidemiological data also support the observation that the IS6110 banding pattern may change over time. Factors affecting this rate may include the nature and duration of disease in a host and the opportunity to experience different host environments during the transmission cycle. To estimate the rate of IS6110 change occurring during the process of transmission, M. tuberculosis isolates from epidemiologically linked patients were genotypically characterized by restriction fragment length polymorphism (RFLP) analysis. The identification of IS6110 banding pattern changes during ongoing transmission suggested that a rate could be estimated. IS6110 change was significantly associated with strains with >5 IS6110 elements (P = 0.013) and was not observed in low-copy-number isolates. The minimum rate of appearance of variant strains was calculated to be 0.14 variant cases per source-case per year. This data suggest that clustering of isolates based on identical RFLP patterns is expected to underestimate transmission in patients infected with high-copy-number isolates. A model based on the rate of appearance of both variant and invariant strains demonstrates that the genotypically defined population structure may change by 18.6% during the study period of approximately 6.5 years. The implications for the use of RFLP data for epidemiologic study are discussed.

* Corresponding author. Mailing address: MRC Centre for Molecular and Cellular Biology, Department of Medical Biochemistry, University of Stellenbosch, P.O. Box 19063, Tygerberg 7505, South Africa. Phone: 27-21-9389401. Fax: 27-21-9317810 or 9389476. E-mail: PVH{at}SUN.AC.ZA.

Journal of Clinical Microbiology, April 2002, p. 1277-1282, Vol. 40, No. 4
0095-1137/02/$04.00+0     DOI: 10.1128/JCM.40.4.1277-1282.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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