Prevalence of Porphyromonas gingivalis Four rag Locus Genotypes in Patients of Orthodontic Gingivitis and Periodontitis
Xiao S (2013) Prevalence of Porphyromonas gingivalis Four rag Locus Genotypes in Patients of Orthodontic Gingivitis and
Periodontitis. PLoS ONE 8(4): e61028. doi:10.1371/journal.pone.0061028
Prevalence of Porphyromonas gingivalis Four rag Locus Genotypes in Patients of Orthodontic Gingivitis and Periodontitis
Yi Liu 0
Yujie Zhang 0
Lili Wang 0
Yang Guo 0
Shuiqing Xiao 0
Krzysztof Pyrc, Jagiellonian University, Poland
0 1 Pediatric Research Institute, Qilu Children's Hospital of Shandong University , Ji'nan, Shandong , China , 2 Department of Orthodontic, Jinan Stomatological Hospital , Jinan, Shandong , China , 3 Clinical Laboratory, Jinan Central Hospital of Shandong University , Jinan, Shandong , China
Porphyromonas gingivalis is considered as a major etiological agent in periodontal diseases and implied to result in gingival inflammation under orthodontic appliance. rag locus is a pathogenicity island found in Porphyromonas gingivalis. Four rag locus variants are different in pathogenicity of Porphyromonas gingivalis. Moreover, there are different racial and geographic differences in distribution of rag locus genotypes. In this study, we assessed the prevalence of Porphyromonas gingivalis and rag locus genotypes in 102 gingival crevicular fluid samples from 57 cases of gingivitis patients with orthodontic appliances, 25 cases of periodontitis patients and 20 cases of periodontally healthy people through a 16S rRNA-based PCR and a multiplex PCR. The correlations between Porphyromona.gingivalis/rag locus and clinical indices were analyzed. The prevalence of Porphyromonas gingivalis and rag locus genes in periodontitis group was the highest among three groups and higher in orthodontic gingivitis than healthy people (p,0.01). An obviously positive correlation was observed between the prevalence of Porphyromonas gingivalis/rag locus and gingival index. rag-3 and rag-4 were the predominant genotypes in the patients of orthodontic gingivitis and mild-to-moderate periodontitis in Shandong. Porphyromonas.gingivalis carrying rag-1 has the strong virulence and could be associated with severe periodontitis.
Funding: This work was funded by Jinan Science and Technology Research Project (JK200905034) from Jinan Science and Technology Committee. The funders
had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Malocclusion is one of the most common oral-maxillofacial
diseases that bring some negative effects on facial aesthetics, oral
physical function and health as well. In China, morbidity of
malocclusion in teenagers is as high as 67.82% . Orthodontic
treatment is currently the preferred and most common method for
the reason of solving above the problems, but it also holds some
potentials of harming teeth and periodontal tissues due to plaque
accumulation and gingival inflammation that are induced by the
changes of oral internal environment after wearing fixed
orthodontic appliance, therefore lead to changing of host
physiology and the composition of the oral microflora [2,3]. The
inflammatory reaction of gingival tissue can often be detected in
patients wearing fixed orthodontic appliances. The overall
morbidity of gingivitis was higher as 56.8% and 34.4% in
adolescent group and adult group respectively during fixed
orthodontic treatment in China . Primary pathogenic
microorganisms strongly implicated in gingival inflammation and
posterior periodontal destruction, such as Porphyromonas gingivalis,
Prevotella intermedia/nigrescens, Aggregatibacter actinomycetemcomitans,
Tannerella forsythia, Treponema denticola, and Fusobacterium species
have been found elevated in patients after bracket placement [5
7]. Our previous research showed that the percentage of bacilli,
esp. Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans,
Fusobacterium nucleatum increased significantly after wearing
orthodontic appliance and the increase of those pathogens was
significantly related with the development of gingivitis in
orthodontic treatment .
Porphyromonas gingivalis is a gram-negative oral anaerobe and
considered as a major etiological agent in periodontal diseases by
producing a number of virulence factors and extracellular
proteases, such as lipopolysaccharide, capsule, gingipain, fimbria
and so on, resulting in the destruction of periodontal tissues [10
13]. The pathogenicity of P.gingivalis has been investigated in a
variety of experimental animal models, such as rat , mouse
, rabbit , drosophila , and cell models ,
showing complicated mechanisms of P.gingivalis-host interactions in
development of periodontal diseases. Three gingipains referred to
be the important virulence factors, Arg-x-specific proteinase and
adhesins (RgpA), Arg-x-specific proteinase (RgpB), and a
Lys-xspecific proteinase and adhesins (Kgp) have been well known and
studied in details with properties of activating and/or degrading a
wide range of host proteins through different mechanisms .
Pathogenicity island is a large unstable chromosome DNA
region encoding virulence determinants of pathogenic bacteria
and was first described in human pathogens of the species
Escherichia coli by Hacker et al.. The island has been also
detected in other pathogens, such as Klebsiella pneumoniae,
Enterobacter aerogenes, and Citrobacter koseri isolates with high conservative
property among these species and is in association with the
yersiniabactin determinant . In 1999, Curtis et al  found a
novel pathogenicity island in a proportion of P.gingivalis strains
named rag locus and it was more frequently detected in deep
periodontal pockets in periodontal patients. It was reported that
the rag locus of P.gingivalis might arise from Bacteriodes via horizontal
gene transfer and encodes RagA and RagB. RagA is a 115-kDa
TonB-dependent outer membrane receptor, and RagB is a 55-kDa
lipoprotein constituting an immunodominant outer antigen. Both
proteins of RagA and RagB constitute a membrane transporter
system. Further study demonstrated that four rag locus variants
with different pathogenicity were detected from clinical isolates of
P.gingivalis . A significant correlation was observed between
prevalence of rag-1 allele and a highly virulent phenotype in a
murine model of soft tissue destruction . In addition, there are
different racial and geographic differences in distribution of rag
locus genotypes . Wang et al. investigated the distribution
of rag genotypes in chronic periodontitis patients in Northeast of
China and found P.gingivalis carrying rag-1, rag-3 was more
predominant in chronic periodontitis so that might be associated
with the development of pediodontitis.
There have been reports about the association between
prevalence of P.gingivalis and gingival inflammation during
orthodontic treatment . Our previous research showed
that the prevalence of P. gingivalis was totally higher as 40.62% two
months after orthodontics detected by using traditional anaerobic
culture . While there have been no investigations about the
correlation between P.gingivalis rag locus and periodontal health
status in orthodontic gingivitis patients. Therefore, we assessed the
prevalence of P.gingivalis and rag locus genotypes in gingival
crevicular fluid samples from the gingivitis lesions of orthodontic
patients and compared them with periodontitis patients as well as
periodontally healthy people who showed healthy periodontal
tissues before wearing orthodontic appliances.
Materials and Methods
The study subjects consisted of three groups who visited Jinan
stomatological hospital for orthodontic or periodontitis treatment
from 2010 to 2011. Of three groups, orthodontic group (OG)
included 57 patients, 38 females and 19 males, aged between 10
and 30 years (mean 16.3) who got gingival inflammation during
orthodontic treatment; control group (CG) contained 20
periodontally healthy people, 12 females and 8 males, aged between
10 and 30 years (mean 16.05) before orthodontic treatment;
periodontitis group (PG) was composed of 25 periodontitis
patients, 10 females and 15 males, aged from 20 to 60 years
(mean 25) who came to hospital for periodontitis treatment. The
patients who are having any systemic diseases, antibiotics therapy
within the last 3 months and pregnant or lactating females were
This work was approved by the Medical Ethics Committee of
the Jinan Stomatological Hospital. All patients or their parents
gave their verbal followed by written informed consent before the
examination was performed. The relevant regulations and
institutional polices were followed strictly.
The reference strains of P.gingivalis ATCC33277, F.nucleatum
ATCC25586 and A.actinomycetemcomitans ATCC29522 were from
the West-China Dental School of Sichun University and P.gingivalis
We selected the gingivitis or periodontal sites that exhibited the
deepest pocket depth of every subject. The clinical parameters
included gingival index (GI), plaque index (PI), sulcus bleeding
index (SBI) and probing depth (PD) of each person were examined
and recorded. All clinical examinations were carried out by the
Sample collection and DNA extraction
Gingival crevicular fluid (GCF) was obtained from the two
deepest periodontal pockets in the maxilla according to Ru din et al
. In brief, before collecting, saline solution was used to rinse
out food debris and then each site was cleaned by cotton rolls.
Sterile filter paper strips were placed for 30 seconds into the packet
until a minimum of resistance. The paper points were placed into
a sterile microcentrifuge tube containing 0.5 ml of 16PBS
immediately. The tubes were mixed thoroughly and stored at
220uC until analyzed. The bacterial DNA was extracted by the
boiling method . In short, a 10 ml aliquot of each stored
sample was added to 10 ml of 2 6lysis buffer (2 mM EDTA, 1%
X-100). The mixture was boiled for 10 minutes and then placed on
ice. The supernatant was used as the template for PCR
The 16S rRNA-based PCR and multiplex PCR amplification
The 16S rRNA gene specific primers were used to determine
the prevalence of P.gingivalis in GCF, while four different rag locus
variants primers were utilized to amplify the rag locus variants
genes from GCF samples containing P.gingivalis. The 16S
rRNAbased PCR was first performed on DNA extracts from GCF
samples using primers of 16S rRNA-F (59-AGG CAG CTT GCC
ATA CTG CG-39) and 16S rRNA-R (59-ACT GTT AGC AAC
TAC CGA TGT-39) that amplify a 404-bp region of the 16S
rRNA gene. The specificity of this PCR was confirmed by
sequencing and amplifying P.gingivalis ATCC33277, W83, as well
as unrelated pathogens F.nucleatum ATCC25586 and
A.actinomycetemcomitans ATCC29522. Then the multiplex PCR was utilized to
amplify rag locus genes from the positive P.gingivalis samples.
Amplification reaction was run in a Tetrad Thermal Cycler (MJ
Research, South San Francisco, USA) in a 25 ml reaction mixture
containing 4.5 ml 106PCR buffer (100 mM Tris-HCl, 500 mM
KCl, and 15 mM MgCl2), 0.25 mM of each deoxynucleoside
triphosphate (dNTP), 10 mM of each primers, 5 ml of DNA
extracts from GCF samples, and 1.5 units of Taq DNA
Groups Cases (n)
polymerase (Transgen Biotech, Beijing) for 5 min at 94uC and 33
cycles, with each cycle consisting of denaturation at 94uC for 30
sec, annealing at 57uC for 30 sec, extension at 72uC for 1 min, and
final extension for 10 min. Nucleotide sequences of the forward
and reverse primers for rag locus genes were listed in Table 1 .
The amplified PCR products were then electrophoreses on
1.5% agarose gel in Tris-acetate buffer (40 mM Tris acetate, 1
mM EDTA, pH 8.0). The products were visualized with ethidium
bromide by UV transillumination.
The differences in the prevalence of rag locus genes were
analyzed using the Chi square test. The Spearman Correlation
Test was utilized to analyze the correlation between prevalence of
P.gingivalis/rag locus genes and clinical indices in three research
groups. All statistical analyses were done by using a statistical
software package (SPSS for Windows 13.0).
Detection and confirmation of 16S rRNA-based PCR for
The reference stains were first amplified by the 16S
rRNAbased PCR to evaluate the specificity of it. The positive product
appeared only from P.gingivalis ATCC33277 and W83, not from
F.nucleatum ATCC25586 and A.actinomycetemcomitans ATCC29522.
Sixty-five P.gingivalis was detected in 65 (63.73%) cases of GCF
samples from 102 cases of three groups, thirty-five (61.40%) from
orthodontic group (OG), Seven (35%) from control group (CG),
and 23 (92%) from periodontitis group (PG). Prevalence of
Prevalence of P.gingivalis
Figure 1. Detection and distribution of rag locus genes. a. Detection of rag locus genes in clinical GCF samples. M DNA Marker; Lane1 positive
control of P.gingivalis W83; Lane 27 clinical GCF samples, showing rag-1 (lane 2), rag-2 (lane3), rag-1 combined with rag-4 (lane4), rag-3 (lane5), rag-4
(lane6), and negative (lane 7). b. The prevalence of rag locus genes in clinical GCF samples of three groups. ** P,0.01 between OG/PG and CG
(Chisquared test). c. Distribution of four rag locus genes among three groups.
P.gingivalis was found significantly different in three groups:
P.gingivalis was the highest prevalence in PG (P,0.01) and higher
level in OG than CG (P,0.05) (Table 2). Of 65 P.gingivalis positive
samples, 10 were randomly sequenced by a 3730 DNA sequencer
in Invitrogen Company (Invitrogen, Shanghai) and confirmed the
validity of the 16S rRNA-based PCR for clinical GCF samples
(date were not showed).
The correlation of patients age and prevalence of P.gingivalis
was analyzed. The average age of patients with positive P.gingivalis
in GCF was 25.54 years, while patients with negative P.gingivalis
was 16.19 years, and there was statistical difference between the
patients ages of both positive and negative P.gingivalis (P,0.05).
**P,0.01 between GI 2 and GI 0; * P,0.05 between GI 1 and GI 0,
#P,0.05 between GI 1 and GI 0 (Chi-squared test).
Multiplex-PCR amplification of rag locus genes
Multiplex-PCR was firstly used to detect rag locus genes from
the high virulent P.gingivalis W83 and low virulent P.gingivalis
ATCC33277. It showed that rag-1 gene was amplified from
P.gingivalis W83 and rag-4 was from ATCC33277, which were
consistent with previous documents [40,41].
There were 52 (80%) positive rag locus genes detected from the
65 GCF samples which were P.gingivalis positive, twenty-nine
(82.86%) from those in OG, 22 (95.65%) from those in PG, only
one case (14.29%) from healthy people. The prevalence of rag
locus was significantly higher in PG and OG than in CG (P,0.01),
while no significant difference between PG and OG (P.0.05)
Among P.gingivalis-positive GCF samples from three groups, the
most prevalent rag gene was rag-3 (51.92%), followed by
rag4(38.26%) and rag-1(26.92%). While in those of PG, rag-3
(60.87%), rag-4 (39.13%), rag-1(30.43%) were much higher than
those in CG (only rag-2 positive); Similar to those of periodontitis
group, in those of OG, the proportion of rag genotypes were: rag-3
44.83%, rag-4 37.93%, rag-2 20.69%; but in CG: only one case of
rag-2 (14.29%) was detected.
Correlation of rag locus genes and clinical indices
It was noticed that clinical indices were all higher in OG and
PG than CG (P,0.05). The prevalence of rag locus genes, except
rag-2, elevated directly with increases of GI values in both OG and
PG. The significant positive correlation between rag locus and GI
was showed by using Spearman Correlation Test (P,0.01) (Fig. 2).
However, there were no statistical difference between rag locus and
PD/PI/SBI, while we detected the increase of rag locus in OG and
PG with higher GI and higher PD/PI/SBI. rag-1 often appeared
from the deeper periodontal pocket with higher PD/PI/SBI values
and 10/14 of rag-1 positive cases accompanied with rag-3 and/or
rag-4. Interestingly, an exception was found that one case of rag-1
gene was from a patient of GI 0 lever in orthodontic group, so
further research would be done for the possible variation of rag-1
gene. The prevalence of four rag locus genes among three groups
showed in table 3.
P.gingivalis has been known to be a risk factor for periodontal
diseases though the exact roles of it in the initiation and
progression of the oral diseases remain unclear. Mouse model
tests have indicated difference in the virulence of P.gingivalis with
and without rag locus [28,29]. Shi et al. mutated rag locus genes in
P.gingivalis by using an allele replacement strategy and clearly
showed that inactivation of the rag locus reduced the virulence of
P.gingivalis in a mouse model of soft tissue destruction . In a
collection of 168 isolates of P.gingivalis from western European
countries, including the Netherlands, Romania, Sweden, the
United Kindom, Kenya and Germany, Hall et al. found different
prevalence and geographic differences in distribution of four rag
alleles . In this case, we detected prevalence of P.gingivalis and
rag locus genotypes in local patients of orthodontic gingivitis,
periodontitis and periodontally healthy people to evaluate the
distribution of P.gingivalis and predominant genotypes of rag locus
in different periodontal health statuses, then further deduce the
pathogenicity of P.gingivalis carrying different rag locus during
In periodontal disease, gingival crevicular fluid (GCF) is an
inflammatory exudate. GCF contains substances from supra-and
subgingival located bacteria. Analysis of microflora in GCF
becomes more and more important in diagnosis and therapy of
periodontal diseases. There are a large number of
periodontopathic bacteria including P.gingivalis in GCF . Considering the
method of filter paper strips is recommended to collect the
microflora from GCF for microbiological analysis in dental
practice . With sterile filter paper strips, we collected GCF
samples divided into orthodontic gingivitis, periodontally healthy
control and periodontitis groups from 102 patients to investigate
the prevalence of P.gingivalis in above three groups. The
occurrence of P.gingivalis was 61.40% in OG, 35% in CG, and
92% in PG, respectively. There was a statistically higher
prevalence of P.gingivalis in PG followed by OG than CG.
Furthermore, a significantly strong positive correlation was
observed between the prevalence of P.gingivalis and GI by
Spearman Correlation Test (P,0.01), which was consistent with
previous reports [3133,43]. While once wearing fixed appliance,
oral hygiene will turns bad if teeth cleaning can not be paid special
attention, as a result, dental plaque will accumulate and gingival
inflammation will happen. By then, one side, anaerobic
environment will be created due to swollen gum, deeper gingival sulcus,
and pseudo periodontal pocket; on the other side, the gum will be
susceptible to bleeding and therefore it will be more conductive for
periodontal anaerobic P.gingivalis to survive. P.gingivalis may play a
similar role in orthodontic gingivitis and periodontitis.
P.gingivalis has been reported to be related with adult
periodontitis [10,12]. In this study, we analyzed correlation of
patients age and occurrence of P.gingivalis and found the age of
both P.gingivalis positive and negative was statistically different;
implying the prevalence of P.gingivalis may increase as patientsage
In order to further explore whether the P.gingivalis rag locus was
associated with gingival inflammation under orthodontic
appliance,we detected the distribution of rag locus in three groups and
discovered 52 (80%) of positive rag locus genes from 65
P.gingivalispositive GCFs. The prevalence of rag locus was higher in those of
PG and OG than those of CG. The P.gingivalis without rag locus
was mostly detected from periodontally healthy control and GI 0
level OG patients, demonstrating that they present the avirulent or
weak virulence genotype of P.gingivalis. A clear positive correlation
was indicated between the gingival index and rag locus genes,
implying rag locus genes may play a pathogenic and similar role in
the development of gum inflammation during orthodontic in
comparison with periodontitis.
The prevalence of rag-3 (27 cases) was the most detected
followed by rag-4 (20 cases) and rag-1 (14 cases); the lowest
occurrence was rag-2 (10 cases) with lower GI and PD/PI/SBI
values, showing the rag-3 and rag-4 locus genes might be the
predominant genotypes in the patients of orthodontic gingivitis
and mild-to-moderate periodontitis in the populations of
Shandong region. Besides, we found rag-1 was detected from 14 cases,
mostly with higher GI and PD/PI/SBI, and often combined with
rag-3 and/or rag-4, suggesting the P.gingivalis carrying rag-1 is the
strong virulent genotype and can be closely associated with severe
periodontitis, which is consistent with Hanley et al.
In summary, P.gingivalis carrying rag-3, rag-4 locus is one of the
risk factors that are responsible for gingivitis during orthodontic
treatment. Thus monitoring P.gingivalis is highly recommended
following the placement of orthodontic appliances. In addition,
appropriate oral hygiene is necessary to reduce invasion of
pathogens and exerts a beneficial effect to oral tissues.
Conceived and designed the experiments: YL SX. Performed the
experiments: YZ LW YG. Analyzed the data: YZ SX. Contributed
reagents/materials/analysis tools: YZ SX. Wrote the paper: YL SX.
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