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Journal of Clinical Microbiology, December 2000, p. 4478-4484, Vol. 38, No. 12
Department of Infectious Disease
Epidemiology,1 Laboratory for Infectious
Diseases and Perinatal Screening, Department of
Mycobacteriology,2 and Staff Bureau for
Informatics and Methodological Advice,4
National Institute of Public Health and the Environment (RIVM), 3720 BA
Bilthoven, and Royal Netherlands Tuberculosis Association
(KNCV), 2501 CC The Hague,3 The Netherlands
Received 10 April 2000/Returned for modification 28 July
2000/Accepted 24 September 2000
Mycobacterium tuberculosis isolates with identical
IS6110 restriction fragment length polymorphism (RFLP)
patterns are considered to originate from the same ancestral strain and
thus to reflect ongoing transmission. In this study, we investigated
1,277 IS6110 RFLP patterns for the presence of multiple
low-intensity bands (LIBs), which may indicate infections with multiple
M. tuberculosis strains. We did not find any multiple LIBs,
suggesting that multiple infections are rare in the Netherlands.
However, we did observe a few LIBs in 94 patterns (7.4%)
and examined the nature of this phenomenon. With single-colony cultures
it was found that LIBs mostly represent mixed bacterial populations
with slightly different RFLP patterns. Mixtures were expressed in RFLP
patterns as LIBs when 10 to 30% of the DNA analyzed originated from a
bacterial population with another RFLP pattern. Presumably, a part of
the LIBs did not represent mixed bacterial populations, as in some clusters all strains exhibited LIBs in their RFLP patterns. The occurrence of LIBs was associated with increased age in patients. This
may reflect either a gradual change of the bacterial population in the
human body over time or IS6110-mediated genetic adaptation of M. tuberculosis to changes in the environmental
conditions during the dormant state or reactivation thereafter.
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Genetic Heterogeneity in Mycobacterium tuberculosis
Isolates Reflected in IS6110 Restriction Fragment Length
Polymorphism Patterns as Low-Intensity Bands
*
Corresponding author. Mailing address: Department of
Infectious Disease Epidemiology, National Institute of Public Health and the Environment (RIVM), P.O. Box 1, 3720 BA Bilthoven, The Netherlands. Phone: 31 30 274 3691. Fax: 31 30 274 4409. E-mail: Annette.de.Boer{at}rivm.nl.
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