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Journal of Clinical Microbiology, September 1999, p. 3078-3079, Vol. 37, No. 9
0095-1137/99/$04.00+0
LETTERS TO THE EDITOR
Stability of IS6110 Restriction Fragment Length
Polymorphism Patterns of Multidrug-Resistant Mycobacterium
tuberculosis Strains
 |
LETTER |
We read with interest the recently published study by Alito et al.
(1) concerning the stability of IS6110
restriction fragment length polymorphism (RFLP) patterns of
multidrug-resistant (MDR) Mycobacterium tuberculosis
strains. The authors analyzed the IS6110 RFLP patterns and
spoligotypes of two groups of MDR M. tuberculosis strains
which they discuss to represent two tuberculosis (TB) outbreaks. Within
the first group, both IS6110 fingerprint patterns and
spoligotypes of the MDR strains have been found to be identical, whereas among the strains of the second group spoligotypes were identical but the IS6110 patterns showed variations. Based
on this, the authors conclude that the rate of change of
IS6110 RFLP patterns in particular MDR M. tuberculosis strains may be too fast for a reliable interpretation
of strain typing results over a period of a few years.
In our recent paper (3), we also elucidated the stability of
IS6110 patterns of drug-resistant M. tuberculosis
strains by analyzing 165 serial isolates obtained from 56 patients with drug-resistant TB. We did not observe a higher level of instability of
IS6110 patterns in these isolates in comparison with the
rates of changes described in other studies comprising mainly
drug-susceptible isolates (e.g., references 2,
4, and 6). In addition, no particular
M. tuberculosis genotypes showing a higher rate of
IS6110 changes have been identified. From these data we
conclude that the stability of IS6110 patterns in
drug-resistant M. tuberculosis strains does not seem to
differ from that of drug-susceptible isolates. The IS6110
changes observed, however, occurred only in MDR isolates (37 of the 56 patients were infected with MDR strains), which is likely to be due to
the longer time intervals between the times of retrieval of the serial
isolates in the patient group with MDR TB (a mean of 300 days for the
MDR isolates compared to a mean of 60 days for the resistant but not
MDR isolates). Moreover, we have not found a higher instability of
IS6110 patterns in several cases of recent transmission of
MDR strains.
It is well known that the IS6110 patterns of unrelated
M. tuberculosis strains generally show a high degree of
variability. However, some M. tuberculosis strain families
displaying similar IS6110 fingerprint patterns and identical
spoligotypes have been described, e.g., the "Beijing family"
(5). Hence, the differences in IS6110 patterns
among the strains of the second MDR group observed by Alito et al.
(1) may be due not to a recent outbreak of a MDR strain
showing a higher rate of IS6110 change but to false clustering of strains of an M. tuberculosis family in one
fingerprint group. This notion is further supported by the fact that in
our German strain collection we found two M. tuberculosis
isolates showing the same spoligotype as and an IS6110
pattern similar to those of the strains of the second group of MDR
strains described by Alito et al. (1) (Fig.
1).
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FIG. 1.
IS6110 RFLP patterns and spoligotypes of two
M. tuberculosis strains obtained from two patients living in
Germany.
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|
In conclusion, we believe that the data presented by Alito
et al. (1) do not give evidence to confirm higher
instability of IS6110 patterns among particular MDR M. tuberculosis strains. On the contrary, our results indicate that
the evolutionary clock of IS6110 RFLP seems to be identical
among drug-susceptible and drug-resistant M. tuberculosis isolates.
| |
FOOTNOTES |
*
Phone: (49) 4537-188658
Fax: (49) 4537-188311
E-mail: sniemann{at}fz-borstel.de
| |
REFERENCES |
| 1.
|
Alito, A.,
N. Morcillo,
S. Scipioni,
A. Dolmann,
M. I. Romano,
A. Cataldi, and D. van Soolingen.
1999.
The IS6110 restriction fragment length polymorphism in particular multidrug-resistant Mycobacterium tuberculosis strains may evolve too fast for reliable use in outbreak investigation.
J. Clin. Microbiol.
37:788-791[Abstract/Free Full Text].
|
| 2.
|
Cave, M. D.,
K. D. Eisenach,
G. Templeton,
M. Salfinger,
G. Mazurek,
J. H. Bates, and J. T. Crawford.
1994.
Stability of DNA fingerprint pattern produced with IS6110 in strains of Mycobacterium tuberculosis.
J. Clin. Microbiol.
32:262-266[Abstract/Free Full Text].
|
| 3.
|
Niemann, S.,
E. Richter, and S. Rusch-Gerdes.
1999.
Stability of Mycobacterium tuberculosis IS6110 restriction fragment length polymorphism patterns and spoligotypes determined by analyzing serial isolates from patients with drug-resistant tuberculosis.
J. Clin. Microbiol.
37:409-412[Abstract/Free Full Text].
|
| 4.
|
Van Soolingen, D.,
P. W. M. Hermans,
P. E. W. de Haas,
D. R. Soll, and J. D. A. van Embden.
1991.
Occurrence and stability of insertion sequences in Mycobacterium tuberculosis complex strains: evaluation of an insertion sequence-dependent DNA polymorphism as a tool in the epidemiology of tuberculosis.
J. Clin. Microbiol.
29:2578-2586[Abstract/Free Full Text].
|
| 5.
|
Van Soolingen, D.,
L. Qian,
P. E. de Haas,
J. T. Douglas,
H. Traore,
F. Portaels,
H. Z. Qing,
D. Enkhsaikan,
P. Nymadawa, and J. D. A. van Embden.
1995.
Predominance of a single genotype of Mycobacterium tuberculosis in countries of east Asia.
J. Clin. Microbiol.
33:3234-3238[Abstract].
|
| 6.
|
Yeh, R. W.,
A. Ponce de Leon,
C. B. Agasino,
J. A. Hahn,
C. L. Daley,
P. C. Hopewell, and P. M. Small.
1998.
Stability of Mycobacterium tuberculosis DNA genotypes.
J. Infect. Dis.
177:1107-1111[Medline].
|
| | | | |
Stefan Niemann*
Elvira Richter
Sabine Rüsch-Gerdes
Forschungszentrum Borstel
National Reference Center for Mycobacteria
Parkallee 18
D-23845 Borstel, Germany
|
| |
AUTHORS' REPLY |
In response to the letter by Niemann et al. commenting on our recent
publication (1), we have the following remarks. Niemann et
al. stated that they did not find a higher rate of change in IS6110 RFLP patterns of serial isolates from patients with
drug-resistant tuberculosis in comparison with the rate of change found
in isolates from patients with mainly drug-susceptible tuberculosis in
other studies. They conclude that instability of the
IS6110 RFLP pattern is not associated with drug
resistance. At face value, this seems to be true. In an extended
study of serial isolates from 546 patients in The Netherlands
(2), we also found that changes in the
IS6110-based RFLP pattern of M. tuberculosis
occurred as often in drug-resistant as in susceptible strains. Yet,
Niemann et al. state in their letter that all changes they observed in
IS6110 RFLP patterns in their recent study (3)
were found in MDR strains. Their explanation for this phenomenon is
that the time intervals at which their serial MDR strains were isolated
were longer than the ones for isolates resistant to only one drug.
However, their findings may also indicate that instability of the
IS6110 RFLP pattern is higher in particular (MDR) strains.
In our laboratory we have recently observed an overrepresentation of
changing RFLP patterns in drug-resistant M. tuberculosis
strains. We hope to present these results within a few months.
The second issue Niemann et al. raise is that the minor
differences in the IS6110 RFLP pattern of the
second-outbreak strain may be due not to the instability of
IS6110 RFLP but to the predominance of a conserved genotype
family in the area of Buenos Aires. As no others, we are aware that
there are predominant M. tuberculosis genotypes
circulating in particular areas and that this may interfere with
the interpretation of strain typing results in molecular epidemiology.
However, our conclusions are not based solely on strain typing results.
As stated in our paper (1), based on conventional contact
tracing we are quite sure that all of the isolates from the patients
involved in the second outbreak were derived from a common ancestor
within a period of 4 years. Nosocomial outbreaks caused by other
M. tuberculosis strains have been recorded several
times in Buenos Aires in the past years (4). Therefore, it
is highly unlikely that the second outbreak described in our paper is a
coincidental combination of circumstances resulting in the isolation of
MDR strains with identical spoligopatterns and highly similar
IS6110 RFLP types from patients with overlapping hospitalization dates.
In conclusion, we agree that our study (1) provides only an
indication that the instability of IS6110 RFLP may be higher in resistant strains. Yet, our statement that the IS6110
RFLP may evolve too fast in particular MDR strains is based on a solid observation. Particular M. tuberculosis genotypes may well
have different molecular clocks.
| |
FOOTNOTES |
*
Phone: 31-2742363
Fax: 31-2744418
E-mail: d.van.soolingen{at}rivm.nl
| |
REFERENCES |
| 1.
|
Alito, A.,
N. Morcillo,
S. Scipioni,
A. Dolmann,
M. I. Romano,
A. Cataldi, and D. van Soolingen.
1999.
The IS6110 restriction fragment length polymorphism in particular multidrug-resistant Mycobacterium tuberculosis strains may evolve too fast for reliable use in outbreak investigation.
J. Clin. Microbiol.
37:788-791.
|
| 2.
| De Boer, A. S., M. W. Borgdorff, P. E. W. de Haas, N. Nagelkerke, J. D. A. van Embden, and
D. van Soolingen. 1999. Rate of change of IS6110
genotypes of Mycobacterium tuberculosis based on serial
patient isolates. J. Infect. Dis., in press.
|
| 3.
|
Niemann, S.,
E. Richter, and S. Rusch-Gerdes.
1999.
Stability of Mycobacterium tuberculosis IS6110 restriction fragment length polymorphism patterns and spoligotypes determined by analyzing serial isolates from patients with drug-resistant tuberculosis.
J. Clin. Microbiol.
37:409-412.
|
| 4.
|
Ritacco, V.,
M. Di Lonardo,
A. Reniero,
M. Ambroggi,
L. Barrera,
A. Dambrosi,
B. Lopez,
N. Isola, and I. N. de Kantor.
1997.
Nosocomial spread of human immunodeficiency virus-related multidrug-resistant tuberculosis in Buenos Aires.
J. Infect. Dis.
176:637-642[Medline].
|
| | | | |
Dick van Soolingen*
Annette S. de Boer
National Institute of Public Health and the Environment
3720 BA Bilthoven, The Netherlands
|
| | | | |
Alicia Alito
Pathobiology Institute CICV/INTA
1708 Morón, Argentina
|
| | | | |
Nora Morcillo
Cetrángolo Hospital
Vicente Lopez, Argentina
|
Journal of Clinical Microbiology, September 1999, p. 3078-3079, Vol. 37, No. 9
0095-1137/99/$04.00+0
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