Journal of Clinical Microbiology, November 2004, p. 5053-5057, Vol. 42, No. 11
0095-1137/04/$08.00+0 DOI: 10.1128/JCM.42.11.5053-5057.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Mycobacterium africanum Genotyping Using Novel Spacer Oligonucleotides in the Direct Repeat Locus
Karine Brudey,1
M. Cristina Gutierrez,2
Véronique Vincent,2
Linda M. Parsons,3
Max Salfinger,3,4
Nalin Rastogi,1* and
Christophe Sola1
Unité
de la Tuberculose et des Mycobactéries, Institut Pasteur de
Guadeloupe, Pointe-à-Pitre,
Guadeloupe,1
Centre National de
Référence des Mycobactéries, Institut Pasteur,
Paris, France,2
Clinical Mycobacteriology
Laboratory, Wadsworth Center, New York State Department of
Health,3
Department of Medicine,
Albany Medical College, Albany, New
York4
Received 4 December 2003/
Returned for modification 20 February 2004/
Accepted 23 June 2004
 |
ABSTRACT
|
|---|
This
study involves a first evaluation of 25 novel spacer oligonucleotides
in addition to the 43 routine spacers for molecular characterization of
a panel of 65 isolates of tubercle bacilli from different geographic
origins that were initially classified as Mycobacterium
africanum based on phenotypic characters. The 68-spacer format
defined four additional patterns, and three groups were identified. The
relatively homogeneous groups A1 and A2 included strains from West
Africa, and A3-1 included strains from East Africa. The presence of
deletion region RD9 confirmed the reclassification of the M.
africanum subtype II spoligopattern within group A3-1 as
Mycobacterium tuberculosis. These isolates may represent a
diverging branch of M. tuberculosis in Africa. The use of new
spacers also suggested an undergoing evolution of M. africanum
subtype I in West Africa. Our results showed that the strain
differentiation within the M. tuberculosis complex is improved
by using novel spacers, and extensive studies using new-generation
spoligotyping may be helpful to better understand the evolution of
M.
africanum.
 |
INTRODUCTION
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Many recent studies have used spoligotyping, a commonly used PCR-based
method, for Mycobacterium tuberculosis complex identification
and genotyping (13,
19). Recently,
Viana-Niero et al. showed that a collection of isolates tentatively
identified as Mycobacterium africanum could be successfully
subdivided into three groups, A1 to A3, by spoligotyping,
IS6110-restriction fragment length polymorphism analysis, and
analysis by variable number of tandem DNA repeats and that a specific
spoligotyping signature of M. africanum was the absence of
spacers 8, 9, and 39
(25). This was followed
by a study on isolates from Uganda, which showed that M.
africanum subtype II differed from the classical M.
africanum subtype I isolates by the absence of spacers 33 to 36
and 40 (16,
21).
Although
spoligotyping is easier to perform than IS6110-restriction
fragment length polymorphism analysis, its discriminatory power is not
optimal when it is used in a routine 43-spacer format
(14). Recently, a panel
of novel spacers was used in spoligotyping to improve M.
tuberculosis complex differentiation
(23,
24). As these studies did
not investigate any M. africanum strains, we thought it
desirable to investigate the variability of a set of novel sequences in
addition to the routine spoligotyping spacers with a panel of isolates
of tubercle bacilli from different geographic origins that were
initially classified as M. africanum based on phenotypic
characters. The present study involves a first evaluation of the 25
novel spoligotyping spacers for M. africanum
characterization.
 |
MATERIALS AND METHODS
|
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Mycobacterial strains.
This study used a collection of 65
clinical isolates from Benin, Cameroon, France, Guinea-Bissau, Nigeria,
Senegal, Sierra-Leone, and Uganda and from African patients residing in
the United States. Twenty-nine clinical isolates were from the National
Reference Laboratory for Mycobacteria, Institut Pasteur, Paris, France,
and 36 were from the Clinical Mycobacteriology Laboratory, Wadsworth
Center, Albany, New York. Among the latter, two were M.
africanum American Type Culture Collection strains (ATCC
25420T and ATCC 35711), and six were isolates that were
recently reclassified as variants of M. tuberculosis by
genomic deletion analysis
(3,
17).
Genotyping.
DNA was extracted by a simple
thermolysis method. Spoligotyping using 43 spacers was performed as
previously described by Kamerbeek et al.
(13). The 68-spacer
format with 25 novel spacers was used according to the scheme of van
Embden et al., which numbers the spacers according to their position in
the direct repeat locus
(24). It should be
emphasized that this representation of spacers, although genomically
true, is completely different from the initial arbitrary designation of
Kamerbeek et al. (13);
e.g., spacer 12 in the scheme of van Embden et al. corresponds to
spacer 4 in that of Kamerbeek et al. The hybridization results
(positive or negative) were documented in the form of a binary code for
each spacer and entered in an Excel spreadsheet file. The results were
further analyzed by using the Bionumerics software (Applied Maths, St.
Maarten Latem, Belgium), following the instruction manual for
similarity analysis with the Jaccard index. Dendrograms were built by
the unweighted pair group method of arithmetic averages method. The
relative discriminatory powers of the 43- and 68-spacer spoligotyping
methods were determined by using the Hunter-Gaston discriminatory index
(11). A more exhaustive
analysis, using a full set of deletion regions RD1 to RD11 and TbD1,
was also performed on some isolates for each of the group defined by
68-spacer spoligotyping
(3,
17).
 |
RESULTS AND DISCUSSION
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Characterization of M. africanum by 43-spacer spoligotyping.
Classical spoligotyping showed a total
of 41 different patterns for 65 isolates studied (results not shown).
The results obtained corroborated the typical absence of spacers 8, 9,
and 39 in 57 subtype I isolates
(25). The six subtype II
pattern strains (strains 960096, 960104, 960106, 960107, 960108, and
960109 in Table
1) showed a positive hybridization with these three spacers, which
corroborated their classification as M. tuberculosis
(3,
17). Two other isolates
were also atypical, since one showed positive hybridization signals
with spacers 8 and 9 but not 39 (isolate 960091), whereas the other
(isolate 220476) was positive for spacer 8 but not for spacers 9 and
39.
The spoligotyping patterns were compared to those found in
the international spoligotyping database at the Institut Pasteur de
Guadeloupe (7). Its recent
version (SpolDB4), which is under development, contained patterns from
23,200 clinical isolates, split into 1,340 shared types (STs) and 2,000
unique types, at the time of the comparison. Eighteen unique patterns
and 23 STs (two or more isolates with the same pattern in the SpolDB4
database) were observed. Among the 23 STs, seven clusters containing 2
to 12 isolates were defined: 1 cluster of 12 strains (ST 181), 1 of 5
strains (ST 331), 4 of 3 strains (STs 52, 187, 328, and 438) and 1 of 2
strains (ST 326). Detailed analysis of the patterns (p), and not the
strains, led to the identification of three main groups (Table
1), designated A1 (p-12),
A2 (p- 20), and A3 (p-9). It should be emphasized that the
classification of strains within various groups in the present study
does not follow the scheme of Viana-Niero et al.
(25).
Groups A1 and
A2 were relatively homogeneous, whereas A3 was more heterogeneous and
included isolates that could not be grouped as either A1 or A2. The
group A1 signature appeared to be the absence of spacers 7 to 9 and 39
(Table
2).Group A2 could be divided into three subgroups: A2-1 (p-11), whose
characteristic was the absence of spacers 8 to 12, 21 to 24, and 37 to
39; subgroup A2-2 (p-4), with the absence of spacers 8 to 12 and 37 to
39; and subgroup A2-3 (p-5), which showed no hybridization with spacers
8 to 12, 25 to 33, 35, and 37 to 39 (Table
2). A3 arbitrarily
contained all of the isolates that were not grouped as either A1 or A2.
A tentative profile for some of the A3 strains was the absence of
spacers 33 to 36 with or without spacer 40 (subtype II
[16]). The
absence of spacer 40 in strains from Africa has been reported
(20).
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TABLE 2. Rules
describing specific spoligotyping signatures for strains within each of
the groups or subgroups defined by 68-spacer spoligotyping
|
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Characterization of M. africanum by new-generation spoligotyping.
As summarized in Tables
1 and
2 and Fig.
1, a total of 45 different patterns were obtained for the 65 isolates by
68-spacer spoligotyping. Group A1 (p 14) was characterized by the
absence of spacers 15 to 19 and 53 to 57 (Table
2). Group A2 (p 22) was
divided into three different subgroups (Table
2): A2-1 (p 13),
characterized by the absence of spacers 18 to 22, 31 to 34, and 51 to
60; A2-2 (p 4), characterized by the absence of spacers 18 to 22 and 51
to 60; and A2-3 (p 5), characterized by the absence of spacers 18 to
22, 25, 35 to 43, and 51 to 60. This method also highlighted a new
subgroup (p 4) with a potential signature characterized by the absence
of spacers 5 to 11, 16 to 17, 43 to 50, and 54 to 62 within the
previously defined group A3. It contained the six subtype II pattern
strains that did not show a typical M. africanum signature in
the 43-spacer format (missing spacers 8, 9, and 39) and was designated
A3-1. Nonetheless, five other patterns did not fit any of the
above-described groups and were arbitrarily designated A3-2 (Table
1; Fig.
1).

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FIG. 1. Dendrogram
and schematic representation of spoligotype patterns obtained by using
the new 68-spacer format. The degree of similarity of the spoligotypes
was calculated with the 1-Jaccard index, and the relationship between
patterns was assessed by the unweighted pair group method of arithmetic
averages. For descriptions of the various groups and subgroups and the
STs listed, see the
text.
|
|
Regarding the
geographic variability (Table
1), groups A1 and A2
included strains from West Africa (Benin, Cameroon, African patients in
France, Guinea-Bissau, Ivory Coast, Nigeria, Senegal, and Sierra
Leone), whereas A3-1 included strains that were mostly from East Africa
(five out of six strains).
The addition of novel spacers enhanced
the discriminatory power of the spoligotyping. It increased the number
of patterns identified from 41 to 45, with a Hunter-Gaston
discriminatory index of 0.97, instead of 0.95 for the 43-spacer format.
Indeed, the 20 clinical isolates that clustered in three STs numbered
181, 187, and 331 in the classical 43-bit representation, were further
subdivided by using the 68-bit representation system. The seven
subtypes thus obtained are shown in Table
2. Interestingly, ST 181,
which defines the majority of M. africanum isolates described
so far (25), was
characterized by an increased deletion step (absence of a block of five
spacers). The same phenomenon is also apparent for shared types 187 and
331 (Table 2). These
results corroborate and further extend those of van der Zanden et al.
showing that the strain differentiation of M. bovis, M.
microti, and M. canettii within the M.
tuberculosis complex was improved by using novel spacers
(23), and they suggest
that extensive studies using new-generation spoligotyping may be
helpful to better understand the evolution of M.
africanum.
PCR-deletion region analysis.
Out of 20 variable
regions described for the M. tuberculosis complex
(2,
3,
8), RD9 and RD10 are
particularly useful to differentiate M. africanum, since it
lacks RD9 (and sometimes RD10), regions that are present in M.
tuberculosis (3,
10,
17). Our results showed
that RD9 was present only among the 6 subtype II strains (A3-1
subgroup) and not in the remaining 59 strains. In contrast, the TbD1
region was systematically present in all M. africanum groups
studied with the exception of six isolates in subgroup A3-1, suggesting
that these isolates are "modern" strains of M.
tuberculosis (3).
This finding shows that the latter isolates are clearly different from
other M. africanum strains seen in this and previous studies
(12,
25) and is consistent
with their reclassification as M. tuberculosis
(17). Further analysis
showed that RD11 was absent in all strains belonging to group A1 but
was present in strains in groups A2 and A3, whereas RD10 was variable.
The distribution of the RDs in conjunction with the current knowledge
of M. tuberculosis phylogeny suggests a possible way in which
M. tuberculosis evolution may have proceeded
(3,
10,
15). It seems likely that
M. bovis is the final member of a separate lineage represented
by M. africanum, M. microti, M. caprae, and
M. bovis and that M. africanum may be an offspring of
M. tuberculosis which has lost RD9. This evolutionary
hypothesis regarding M. africanum applies to M.
africanum subtype I but not to M. africanum subtype II,
which may represent a diverging branch of the M. tuberculosis
lineage.
Phylogeographical considerations.
The M.
tuberculosis complex currently encompasses M.
tuberculosis, M. africanum, M. bovis, M.
bovis BCG, M. bovis subsp. caprae, M.
canettii, M. microti, and a recently described species,
M. pinnipedii
(4), with characteristic
animal and/or human epidemiologies
(4,
18). M.
tuberculosis and M. bovis are most commonly isolated in
clinical laboratories and may be easily distinguished by biochemical
tests, phenotypic characters, and several genetic markers
(5). However, the
taxonomical status of M. africanum isolates, which were shown
to introduce substantial phenotypic heterogeneity and genetic diversity
within M. bovis and M. tuberculosis clusters,
remained controversial
(6). A distinction between
West African strains (from Senegal, Mauritania, and Cameroon), which
are more likely to have M. bovis-like phenotypic
characteristics (M. africanum type I), and East African
strains (from Burundi and Rwanda), which are more likely to have M.
tuberculosis-like characteristics (M. africanum type II),
was previously made by David et al.
(6). Our results with the
68-spacer spoligotyping format showed that the patterns for these
strains lacking spacers 33 to 36 and 40, did resemble those previously
labeled as M. tuberculosis
(24). Nonetheless,
spoligotyping alone may not always allow us to gain sufficient
information to establish a likely evolutionary history of M.
tuberculosis; e.g., generation of identical spoligotype patterns
among different strain families may also arise due to
IS6110-mediated deletion polymorphism
(26). For a precise
phylogeographical attribution of the various M. africanum
clades, larger studies using 68-spacer format spoligotyping in
conjunction with other markers, such as mycobacterial interspersed
repetitive units (22),
RDs, and single-nucleotide polymorphisms
(1,
9), may be
rewarding.
 |
ACKNOWLEDGMENTS
|
|---|
This work was supported
through grants from the Réseau International des Instituts
Pasteur et Instituts Associés, Institut Pasteur, Paris, France,
and EU Project QLK2-CT-2000-630, entitled "New generation
genetic markers and techniques for the epidemiology and control of
tuberculosis." K.B. was cofinanced by Institut Pasteur and
European Social Funds provided through the Regional Council of
Guadeloupe.
L.M.P. is grateful to Gisela Bretzel for access to
isolates of M. africanum from African
patients.
 |
FOOTNOTES
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* Corresponding
author. Mailing address: Unité de la Tuberculose et des
Mycobactéries, Institut Pasteur de Guadeloupe, Morne
Jolivière, BP 484, 97165 Pointe-à-Pitre, Cedex, Guadeloupe.
Phone: 590-(590)-893 881. Fax: 590-(590)-893 880. E-mail:
nrastogi{at}pasteur-guadeloupe.fr. 
 |
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Journal of Clinical Microbiology, November 2004, p. 5053-5057, Vol. 42, No. 11
0095-1137/04/$08.00+0 DOI: 10.1128/JCM.42.11.5053-5057.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
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43: 4010-4014
[Abstract]
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