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Advances in Microbiology, 2012, 2, 201-207
http://dx.doi.org/10.4236/aim.2012.23024 Published Online September 2012 (http://www.SciRP.org/journal/aim)
Specific Antigens to Distinguish M. tuberculosis
from M. avium
Qun Liang1,2*, Lingxia Zhang3*, Zeng Tu1,4*, Jingyu Wang1,2, Tao Hu1, Pengzhi Wang1,
Weili Wu1, Qi Liu5, Yanlin Zhao6, Yan Li7#, Weijun Chen1,5#
1Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics,
Chinese Academy of Sciences, Beijing, China
2Graduate University of the Chinese Academy of Sciences, Beijing, China
3Beijing 309th Hospital of PLA, Beijing, China
4Department of Pathogenic Biology, Chongqing Medical University, Chongqing, China
5Beijing Genomics Institute in Shenzhen, Shenzhen, China
6Beijing Tuberculosis and Thoracic Tumor research Institute, Beijing, China
7The Affiliated Hospital of the Academy of Millitary Medical Sciences, Beijing, China
Email: firstname.lastname@example.org, email@example.com,
Tuz1980@126.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org,
email@example.com, firstname.lastname@example.org, email@example.com, #firstname.lastname@example.org, #email@example.com
Received April 15, 2012; revised May 23, 2012; accepted June 4, 2012
To distinguish Mycobacterium tuberculosis from Mycobacterium avium, specific M. tuberculosis antigens had been
studied for improving the early differential diagnosis effect of tuberculosis caused by different Mycobacterium. The
rabbit anti-M. avium sera and anti-M. tuberculosis sera were analyzed for antibody-based reactivity by matrix-assisted
laser desorption-ionization mass spectrometry (MALDI-TOF Mass) against M. tuberculosis proteins. The immunoreac-
tive spots, which were attributed to the proteins HspX, GroES and CFP-10, were mostly located at 10 - 60 kDa and PI 4 -
6, subsequently Western blotting result proved that HspX and CFP-10 were specific to M. tuberculosis and ELISA test-
ing result of 30 M. a vium positive sera showed that GroES were cross-reactive to M. avium. Lastly, positive and nega-
tive tuberculosis reference sera and based on the mechanism of indirect ELISA, the specificity and the sensitivity of the
methods targeting the antibodies HspX, GroES or CFP-10 were evaluated at 37% and 26%, 12% and 97%, 81% and
98%, respectively. The combination of these three antibody detection methods allowed to reached a specificity of 42%,
and of 39% without taken into account of the method targeting the GroES antibody. Using proteomics approach, we
found three M. tuberculosis specific antigens showed good potential in tuberculosis diagnosis, providing basic study for
serodiagnosis of tuberculosis.
Keywords: Mycobacterium tuberculosis; Mycobacterium avium; Mass Spectrometry; Immunodetection
Tuberculosis (TB) remains a major cause of death in de-
veloping countries. It is also rising throughout the indus-
trialized countries, partly as the cause of human immu-
nodeficiency virus (HIV) infection. Mycobacterium tu-
berculosis complex (MTC) members such as M. tuber-
culosis are the pathogens of TB infection and Nontuber-
culous mycobacteria (NTM) such as Mycobacterium
avium are responsible of mycobacteria [1,2]. Unfortu-
nately, NTM is resistant to many general anti-TB drugs,
leading the patients to suffer a years prolonged course
and finally become chronic or refractory cases of myco-
bacteria [3,4]. However, clinically it is difficult to dis-
tinguish between them, because they are similar in clini-
cal manifestations, imaging study, smear and culture,
tuberculin tests and pathological examination [5-7]. There-
fore, the rapid identification of M. tuberculosis and M.
avium is of extreme importance to diagnosis, effective
chemotherapy and control transmission of TB.
Represented by two-dimensional gel electrophoresis
(2-D) and mass spectrometry (MS) technology, pro-
teomics has provided some encouraging results in TB
research [8-10]. So far, important antigens of M. tuber-
culosis have been identified such as the 38-kDa antigen,
early secreted antigenic target (ESAT-6), antigen 85B,
the proteins encoded by Rv3872 [11,12]. However, the
cross-reaction between M. tuberculosis and M. avium
makes these antigens unable to distinguish these myco-
*These authors contributed equally to this article.
opyright © 2012 SciRes. AiM
Q. LIANG ET AL.
bacterial species and consequently differentiate those
respective infections . Only a few secreted proteins
such as 14-kDa protein and CFP-10 have been further
characterized which was demonstrated by Western blot-
ting in culture filtrates of M. avium but was not detected
in M. tuberculosis . CFP-10, molecular weight of 10
kDa, mainly existed in M. tuberculosis culture filtrate.
Previous data have shown that it is a specific potential
antigen to M. tuberculosis [15,16]. Renshaw et al. 
reported that BCG and NTM were lack of CFP-10 coding.
HspX-14 was predicted to be an important membrane
antigen, which increased expression along with M. tu-
berculosis growing into stable phase from logarithmic
phase  and in anaerobic condition . Some data
also showed HspX-14 could induce humoral immune
response [20,21]. GroES, a molecular chaperone protein,
joints participation in protein folding, assembly, transport
and degradation . The high abundance of GroES
possibly led antigen presenting cells to secrete many
small peptides which could induce the host produced a
strong immunological response . These reports sug-
gested that these proteins may be the M. tuberculosis-
Comparison of immunoblot profiles of rabbit anti-M.
tuberculosis sera and rabbit anti-M. avium sera reacting
with extracts of M. tuberculosis could detect specific
antigens allowing to distinguish easily these two myco-
bacteria species and helped the serodiagnostic test for
Mycobacterium tuberculosis H37Rv, rabbit anti-M. tu-
berculosis sera and rabbit anti-M. avium sera were ob-
tained from Tuberculosis Research Institute of the Peo-
ple’s Liberation Army Hospital 309 (Beijing, China).
300 sera from healthy blood donators were collected
from Beijing Red-cross blood Central which were tested
negatively to TB by Elisa kits (Chengdu Yongan Phar-
maceutical Co. Ltd).
100 sera from M. tuberculosis patients were collected
in 309 Hospital (Beijing, China). Basis of diagnosis: Two
sputum samples examined by smear microscopy-stained
for acid-fast bacilli or AFB are positive and chest X-ray
visualizes the chest shadow caused by tubercular lesion.
Then used COBAS AMPLICOR™ M. tuberculosis Kit
(Roche) to confirm.
30 sera from M. avium patients were collected in 309
Hospital (Beijing, China). Basis of diagnosis: Used
COBAS AMPLICOR™ M. avium Kit (Roche) to detect
M. avium and used COBAS AMPLICOR™ M. tubercu-
losis Kit (Roche) to confirm they were not infected by M.
200 sera from purified protein derivative (PPD)-posi-
tive healthy body-examining people were collected in
Affiliated Hospital of the Academy of Millitary Medical
3.1. Protein Preparation
M. tuberculosis H37Rv was cultured in modified Sauton
medium for 4 weeks and heat-inactivated at 80˚C for 1 hr.
The bacteria were harvested by centrifugation and were
washed three times with 10 mM Tris buffer (pH 7.4),
then suspended in 500 µl lysate (0.3% SDS, 200 mM
DTT, 50 mM Tris, pH 7) and sonicated for 30 min (250
W, 2 sec pulse-on, 4 sec pulse-off intervals), subse-
quently added the Benzonase nuclease (1:20; Novagen,
Merck KgaA, Darmstadt, Germany) and kept at 4˚C for 1
hr, and then centrifuged at 22,300 g for 30 min. Used
2-D Clean-up Kit (GE Healthcare, Fairfield, USA) to
3.2. 2-D PAGE
Samples of 200 μg protein suspended in rehydration
buffer (6 M Carbamide, 0.71 M SDS, 0.375 M Tris pH
8.8, 20% glycerol) were applied on immobilized pH 4 - 7
linear gradient strips (13 cm; GE Healthcare). Focusing
at 20˚C using the following four-step program: a) 50 V, 6
hr; b) 500 V, 1 hr; c) 1000 V, 1 hr; d) 8000 V constant
until 66,000 Vh. The current limit was set at 50 μA/strip.
After isoelectric focusing (IEF), each strip was equili-
brated for 15 min in equilibration buffer I (rehydration
buffer, 0.13 M DTT) followed by equilibration buffer II
(rehydration buffer, 0.14 M iodoacetamide) for 15 min.
The second dimension separation was performed in uni-
form 12.5% SDS-PAGE gels. Then silver stained the
3.3. Western Blotting
Preparing for Western blotting, proteins was electropho-
retically transferred by using TE70 Semi-Dry Transfer
(Amersham Pharmacia Biotech, Uppsala, Sweden) to
0.2-µm-pore-size polyvinylidene difluoride membrane
(Immun-Blot PDVF membrane; Bio-Rad, Hercules, CA),
which was then washed and blocked in Tris-buffered
saline-Tween 20 (TBS-T) containing 1% Tween 20 and
5% non-fat dry milk for 120 min, next incubated in the
rabbit anti-M. tuberculosis and anti-M. avium sera (both
1:250 TBS-T diluted) for 2 hr, then reacted with horse-
radish peroxidase labeled goat anti-rabbit IgG antibody
(Santa Cruz Biotechnology, Santa Cruz, USA) (1:2500
TBS-T diluted) for 1 hr, subsequently washed exten-
sively in TBS-T and then add freshly prepared DAB so-
lution (Beijing Saichi Shengwu Keji, Beijing, China ) for
color. Signal was detected by using UMAX scanner and
Copyright © 2012 SciRes. AiM
Q. LIANG ET AL. 203
analyzed with ImageMaster 2D software for variance.
3.4. MALDI-TOF MASS
The excised protein spots were destained in 50 mM am-
monium bicarbonate/acetonitrile (1:1) until colorless,
dehydrated with acetonitrile, reduced in 25 mM ammo-
nium bicarbonate/acetonitrile (1:1). The gel pieces were
dried white by acetonitrile and speedvac. Then incubated
at 37˚C overnight with 25 mM ammonium bicarbonate
diluted trypsin. The reaction was stopped by adding 1%
triflouracetic acid (final concentrations 0.1%), Peptide
mixtures were applied to AnchorChip (Bruker Daltonics
Inc. Billerica, USA) and analyzed by MALDI-TOF (Bru-
ker Daltonik) using a-4-hydroxycinnamic acid as matrix
with positive ion detection mode.
For peptide mass fingerprinting (PMF) analysis, MAS-
COT service provided by the Matrixscience Company
(www.matrixscience.com) was used.
3.5. Cloning, Expression, Purification and
Immunization Verification of the
Obtained from M. tuberculosis H37Rv genomic DNA,
HspX antigen gene was prepared by amplification using
appropriate primers (forward: 5’-CGCAATTCATATG-
GCCACCACCCTTCCCGTTC-3’ and reverse: 5’-GCC-
ried Nde I and Hind Ⅲ sites (underlined sequences).
GroES antigen gene used forward: 5’-GGGAATC-
CATATGGTGGCGAAGGTGAACATC-3’ and reverse:
ried the same sites (underlined sequences). While CPF-
10 antigen gene used forward: 5’-CGTAGCTAGC-
CCGAAGCCCATTTGCGAGGACA-3’ carried Nhe I
and EcoR I sites.
The gel-purified PCR products were digested by ap-
propriate restriction enzyme, and ligated to pET-28a(+)
vector (HspX and GroES PCR products) or pET-30a(+)
vector (CFP-10 PCR product) (Novagen).
Escherichia coli BL21 (DE3) harboring recombinant
plasmids were grown in LB medium containing 50 mol/l
of Kanamycin overnight at 37˚C, then induced with iso-
propyl thiogalactoside (1 mmol/l) at 37˚C for 4 hr. The
harvested cells were resuspended in phosphate-buffered
saline (PBS) containing DNAase, and then lysed by
sonication (the same model setted above, 20 min). The
proteins with His-6 label were further purified by anion
Western blots of three proteins were all probed with
rabbit anti-M. tuberculosis sera (1:1000) and rabbit
anti-M. avium sera (1:1000) at 37˚C for 2 hr, followed
reacted with Horseradish peroxidase (HRP)-conjugated
goat anti-rabbit IgG (1:3500, BGI-GBI Biotech, Beijing,
China) at 37˚C for 1 hr. The band density was calculated
by image software.
3.6. Immunological Assessment
The reactivity of each protein was tested with 100 pa-
tients infected by M. tuberculosis, 30 patients infected by
M. avium and 200 PPD-positive healthy subjects. First,
100 μl of each protein (The optimum concentration after
contrast were HspX-14: 0.2 μg/ml, GroES: 5 μg/ml,
CFP-10: 2.5 μg/ml) diluted in blocking buffer (0.05%
Tween-20, 1% BSA, 0.01 M PBS, pH 7.4) was added to
wells of streptavidin coated ELISA plates and incubated
at 37˚C for 1 hr. Subsequently, 100 μl of diluted sera
(1:50 in PBST, containing 0.1% BSA) from healthy sub-
jects and patients was added and incubated at 37˚C for 1
hr (triplicates). After five times washes with PBST, 100
μl of mixture of HRP-conjugated goat anti-Human IgG
(1:40,000, BGI) was added to each well and incubated at
37˚C for 1 hr. After six times washes with PBST, the
optical density (OD) value was measured at 450 nm/630
nm. Concerning the sera collected by the Beijing Red-
cross Blood Central from 300 blood donators, the cutoff
value determining the positive responses was the mean
optical density plus two standard deviations.
4.1. MS Identification of M. tuberculosis
The proteins separated by 2-D PAGE gel (Figure 1)
were transferred to PVDF membrane and reacted with
Figure 1. 2-D PAGE gel of Mycobacterium tuberculosis
Copyright © 2012 SciRes. AiM
Q. LIANG ET AL.
anti-M. tuberculosis and anti-M. avium sera respectively.
Most immunoreactive spots located at PI 4 - 6 and 10 -
60 kDa in molecular mass. Ten spots were recognized
exclusively by anti-M. tuberculosis sera and identified as
GroES, HspX and CFP-10 by PMF using MALDI-TOF
MASS (Table 1), the protein corresponding to spots 6-10
were not detected in 2-D PAGE gel, while spots in areas
(E-I) were reacted with both anti-M. tuberculosis and
anti-M. avium sera (Figure 2, Table 1). Spots in areas A -
D only reacted with anti-M. avium sera.
Copyright © 2012 SciRes.
4.2. Expression, Purification and
Immunogenicity of HspX, GroES and
The purified HspX protein, appeared as a 17 kDa band
on SDS-polyacrylamide gel (Figure 3). GroES and CPF-
10 were approximately 14 kDa, which were similar to the
theoretical molecular weight.
Using Western blotting analysis, rabbit anti-M. tuber-
culosis sera showed strong reactivity with HspX, GroES
and CFP-10, whereas rabbit anti-M. avium sera did not
react with HspX and CFP-10, and showed tenuous reac-
tivity with GroES (Figure 4), checking that HspX, CFP-
10 and GroES were specific to M. tuberculosis compared
to avium species.
4.3. Immunological Assessment
The cutoff values for IgG were 0.14 to HspX, 0.12 to
GroES and 0.1 to CFP-10. HspX, GroES and CFP-10
proteins were detected in 37% (37 of 100), 26% (26 of
Table 1. List of antigens that reacted only with anti-M. tuberculosis sera (spots 1 - 5) and antigens that reacted both with
anti-M. tuberculosis and anti-M. avium sera (areas E - H).
Location Protein Name NCBInr Accession no. Mr pI Sequence Coverage
Spot 1 GroES gi|16796865 10499 4.5159% 68
Spot 2 CFP-10 gi|15611010 10787 4.5964% 71
Spot 3/4/5 HspX-14 gi|15609168 1621766795.0029% 100
Area E protein dnaK gi|15607491 0 4.8539% 166
Area F 60 KDa chaperonin gi|1449370 56692 4.8546% 211
Area G L Elongation factor Tu gi|15607825 43566 5.2887% 267
Area H 35 KDa protein gi|57117019 29240 5.7152% 151
a The scores greater than 63 are significant (P < 0.05).
Figure 2. Screening of antigens in M. tuberculosis with anti-M. avium sera (A) and anti-M. tuberculosis sera (B) by 2-D PAG E.
Areas E-I react ed with both sera. Spots 1 - 10 showed reactivit y with anti-M. tuberculosis sera ex clusively, while areas A-D only
reacted with anti-M. avium sera.
Q. LIANG ET AL. 205
Figure 3. Expression of HspX, GroES and CFP-10 antigens
Figure 4. Validation of the antigens specific to M. tuberculo-
sis. Western blotting analysis of the equal amount expressed
HspX, GroES and CFP-10 proteins separated by SDS-
PAGE, were performed with either anti-M. tuberculosis or
anti-M. avium sera for 3 times.
100) and 12% (12 of 100) of M. tuberculosis patients
sera respectively (Table 2). Moreover, two sera of the
samples were tested positive with CFP-10 but negative
with the other two proteins and another three sera were
positive with GroES protein solely. While only GroES
Table 2. Serological reactivity of CFP-10, GroES and
HspX-14 in M. tuberculosis patients, M. avium patients and
healthy PPD+ individuals.
No. of samples positive by ELISA for:
Status No. of
persons CaGbHc C+G C+H G+HC+G+H
tuberculosis+100 122637 28 39 4042
M. avium+30 070 7 0 7 7
PPD+ 200 3355 36 6 3738
aC: CFP-10; bG: GroES; cH: HspX-14.
protein (7 of 30) was detected in sera of M. avium pa-
To evaluate the specificity, two hundred of sera from
PPD-positive health body-examining people were tested.
The specificity of HspX, GroES and CFP-10 were 97.5%
(195 of 200), 82.5% (165 of 200) and 98.5% (197 of
200), respectively (Table 2). Similarly, 1 sera was tested
positive only with CFP-10, while 2 sera only with HspX-
At present, TB remains a serious threat to human health.
A rapid diagnostic method of early stage of TB infection
will undoubtedly play a decisive role in TB control ,
yet various similar pathological manifestations make
them difficult to distinguish [5-7]. Recently, more and
more M. avium infection has been reported [25-28].
However, the research about the distinction between M.
tuberculosis and M. avium is rare .
Using a serological proteomic approach to detect spe-
cifically by identifying candidate antigen has been re-
ported by previous research [8-10]. Due to high lipid
content of M. tuberculosis, we chose 2-D Clean-up kit to
purify the crude protein and optimized some other pro-
teomics experimental condition of M. tuberculosis, in-
cluding the IEF voltage settings, staining method, trans-
fer membrane current and time settings. Three proteins
(CFP-10, GroES, HspX-14) were identified as potentially
specific antigen of anti-M. tuberculosis by 2-D PAGE,
Western blotting and MALDI-TOF methods in our study.
CFP10, one of the antigens selected by our method was
consistent with what was reported , which suggested
the approach could screen out specific antigens.
The reuslt of Immunoblotting assays showed that
CFP-10 and HspX-14 only reacted with the anti-M. tu-
berculosis sera while the GroES protein cross-reacted
with the anti-M. avium sera slightly (Figure 4).
The result of testing for specificity of these recombi-
nant proteins showed that the specific response to protein
GroES was relatively lower. M. tuberculosis GroES,
Copyright © 2012 SciRes. AiM
Q. LIANG ET AL.
having a part homology sequence with human homolo-
gous protein, often causes the emergence of spontaneous
autoimmune diseases such as rheumatoid arthritis, sys-
temic sclerosis, psoriasis, and ankylosing spondylitis [28,
29]. It may be the causes of lower specificity.
The result of evaluating the sensitivity of theses re-
combinant proteins showed a low sensitivity (37%, 26%,
12%). This was consitent with the previous M. tubercu-
losis antibody detection studies [16,30,31]. Nonetheless,
CFP-10, GroES and HspX-14 proteins as test antigens
were complementary in detecting M. tuberculosis spe-
cific antibodies and could effectively improve the detec-
tion of M. tuberculosis antibodies (42%). Ignoring the
contribution of GroES, the detection ratio of CFP-10 and
HspX-14 proteins as a test antigen could reach 39%.
In summary, we detected three M. tuberculosis spe-
cific antigens, which could be used in order to distin-
guish M. tuberculosis from M. avium. By system re-
search of HspX-14, GroES and CFP-10, we found that
HspX-14 and CFP-10 showed better potentiality in TB
The work was supported by the research funding from
Infectious Diseases Special Project, Minister of Health of
China (2008ZX10003—009) and Beijing Science and
Technology Program (Z08050703080801).
I certify that all my affiliations with or financial in-
volvement in, within the past 5 years and foreseeable
future, any organization or entity with a financial interest
in or financial conflict with the subject matter or materi-
als discussed in the manuscript are completely disclosed.
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