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Genetic heterogeneity in Mycobacterium tuberculosis isolates reflected in IS6110 restriction fragment length
A S de Boer1, K Kremer, M W Borgdorff
1Department of Infectious Disease Epidemiology, National Institute of Public Health and the Environment (RIVM), 3720 BA Bilthoven, The Netherlands. Annette.de.Boer@rivm.nl
Abstract:
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.
Insights
Multiple low-intensity bands (LIBs) in Mycobacterium tuberculosis IS6110 RFLP patterns were investigated. Findings suggest multiple infections are rare, with LIBs often indicating mixed bacterial populations or genetic adaptation in tuberculosis strains.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Identical IS6110 restriction fragment length polymorphism (RFLP) patterns in Mycobacterium tuberculosis isolates typically indicate ongoing transmission from a common ancestor.
- The presence of multiple low-intensity bands (LIBs) in RFLP patterns may suggest infections involving multiple M. tuberculosis strains.
Purpose of the Study:
- To investigate the occurrence and nature of multiple low-intensity bands (LIBs) in IS6110 RFLP patterns of Mycobacterium tuberculosis isolates.
- To assess the implications of LIBs for understanding tuberculosis transmission dynamics and bacterial population heterogeneity.
Main Methods:
- Analysis of 1,277 IS6110 RFLP patterns from Mycobacterium tuberculosis isolates.
- Investigation of isolates exhibiting LIBs using single-colony cultures to determine the presence of mixed bacterial populations.
- Correlation of LIB occurrence with patient demographics, specifically age.
Main Results:
- No instances of multiple LIBs were detected, suggesting that infections with multiple M. tuberculosis strains are rare in the Netherlands.
- LIBs were observed in 7.4% (94/1277) of patterns and were predominantly attributed to mixed bacterial populations with slightly different RFLP profiles (10-30% DNA contribution).
- A subset of LIBs could not be explained by mixed populations, and their occurrence was associated with increased patient age, potentially indicating bacterial adaptation or population changes over time.
Conclusions:
- Multiple M. tuberculosis infections appear uncommon, with IS6110 RFLP patterns generally reflecting single-strain infections.
- LIBs in RFLP patterns often represent minor components of mixed bacterial populations, rather than distinct co-infections.
- The association of LIBs with patient age suggests potential mechanisms of Mycobacterium tuberculosis adaptation or evolution within the host environment.