Diversity analysis of genes encoding Mfa1 fimbrial components in Porphyromonas gingivalis strains.

Porphyromonas gingivalis, a gram-negative anaerobic bacterium, is associated with the development of periodontal disease. The genetic diversity in virulence factors, such as adhesive fimbriae, among its strains affects the bacterial pathogenicity. P. gingivalis generally expresses two distinct types of fimbriae, FimA and Mfa1. Although the genetic diversity of fimA, encoding the major FimA fimbrilin protein, has been characterized, the genes encoding the Mfa1 fimbrial components, including the Mfa1 to Mfa5 proteins, have not been fully studied. We, therefore, analyzed their genotypes in 12 uncharacterized and 62 known strains of P. gingivalis (74 strains in total). The mfa1 genotype was primarily classified into two genotypes, 53 and 70. Additionally, we found that genotype 70 could be further divided into two subtypes (70A and 70B). The diversity of mfa2 to mfa4 was consistent with the mfa1 genotype, although no subtype in genotype 70 was observed. Protein structure modeling showed high homology between the genotypes in Mfa1 to Mfa4. The mfa5 gene was classified into five genotypes (A to E) independent of other genotypes. Moreover, genotype A was further divided into two subtypes (A1 and A2). Surprisingly, some strains had two mfa5 genes, and the 2nd mfa5 exclusively occurred in genotype E. The Mfa5 protein in all genotypes showed a homologous C-terminal half, including the conserved C-terminal domain recognized by the type IX secretion system. Furthermore, the von Willebrand factor domain at the N-terminal was detected only in genotypes A to C. The mfa1 genotypes partially correlated with the ragA and ragB genotypes (located immediately downstream of the mfa gene cluster) but not with the fimA genotypes.

Development of a multiplex PCR assay based on the pilA gene sequences to detect different types of Acidovorax citrulli.

Bacterial fruit blotch (BFB) of cucurbits, caused by Acidovorax citrulli, is a major threat to commercial watermelon and melon production worldwide. At present, there are at least two genetically distinct sub-populations (group I and II) of A. citrulli that differ in host preference among cucurbit species and copper sensitivity. In this study, we analyzed the pilA gene sequences of 103 A. citrulli strains from China and other countries. Based on these data, we classified all tested A. citrulli strains into three types. The pilA-based type 1 strains in this study coincided with the previously established group I strains; while the type 2 strains coincided with group II strains. Ten strains that did not cluster with group I or II strains were classified into a new type, designated type 3. Based on differences in pilA sequences, we designed a multiplex PCR assay to distinguish the three A. citrulli pilus types. This multiplex PCR assay has proven to be viable for strain typing of 139 A. citrulli strains and for the detection of this pathogen in artificially inoculated seeds and leaves and naturally infected leaves and fruits. This assay proved to be rapid, accurate, reliable and applicable for early distinction of A. citrulli types associated with BFB epidemics. It may also inform the judicious and environmentally sound use of bactericides, especially copper-based compounds.

[VNTR-genotyping of Vibrio cholerae strains isolated from objects in the territory of Russian Federation in 2012].

AIM: VNTR-typing of Vibrio cholerae strains isolated in the territory of Russian Federation in 2012. MATERIALS AND METHODS: 71 Vibrio cholerae O3 and 3 V cholerae O1/O139 strains were used in the study. Genotyping was performed by using PCR for 5 VNTR-loci. RESULTS: Multilocus VNTR-typing allowed to group the strains into 31 VNTR-genotypes. Genotypes were divided among 10 discrete clusters by results of a cluster analysis. The presence of tcpA gene is clearly linked with the presence of VcB locus. Each geographic region was characterized by their own VNTR-genotypes. CONCLUSION: In the course of the carried out VNTR-genotyping of V. cholerae isolated in 2012, 2 types of vibrio population formation were detected. A geographic attachment to specific regions was characteristic for most of the genotypes.

[Proteome mass-spectrometric analysis and typing of Vibrio cholerae strains isolated in the territory of Russian Federation in 2010 - 2012].

AIM: Conduction of a comparative proteomic mass-spectrometric (MS) analysis using a personal database of V. cholerae protein mass-spectra and genetic VNTR-typing of cholera causative agent strains. MATERIALS AND METHODS: V. cholerae O1 El Tor strains - 7, V. cholerae non O1/non O139 - 2. Protein profiling and VNTR-genotyping of strains was carried out on MALDI TOF-MS Autoflex (Bruker Daltonics) mass-spectrometer and SIS Cholera-strains-VNTR. RESULTS: The established community of a proteomic profile of epidemic cholera vibrio strains isolated in 2010 - 2012 in Moscow allowed to determine Indian origin of a toxigenic strain isolated in Taganrog in 2011. M/z proteins distinguishing V. cholerae O1 and non O1/non O139 strains were identified. Proteomic analysis confirms the results of VNTR-genotyping. CONCLUSION: Study and typing of V. cholerae members with determination of their origin and phylogenetic relationship is possible using a collection of V. cholerae mass-spectra.

Genetic analysis of Porphyromonas gingivalis (fimA), Aggregatibacter actinomycetemcomitans, and red complex in coronary plaque.

AIM: The objective of the present study was to detect the presence of Porphyromonas gingivalis (fimA), Aggregatibacter actinomycetemcomitans, and red complex in the coronary plaque of patients with coronary artery disease. METHODS: The study population consisted of 51 patients with chronic periodontitis undergoing coronary artery bypass grafting. DNA was extracted from subgingival and coronary atherosclerotic plaque samples. Polymerase chain reaction was used to amplify the part of 16S rRNA gene to detect the presence of Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis (fimA), Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola. RESULTS: Aggregatibacter actinomycetemcomitans, Tannerella forsythia, Porphyromonas gingivalis, Porphyromonas gingivalis (fimA), and Treponema denticola were detected in 0%, 31.4%, 45.1%, 39.2%, and 51% of the atherosclerotic plaque samples, respectively. In both subgingival and coronary atherosclerotic plaque samples, Tannerella forsythia was detected in 19.6%, Porphyromonas gingivalis in 39.2%, Porphyromonas gingivalis (fimA) in 33.3%, and Treponema denticola in 35.3% of the samples. CONCLUSION: The study confirmed the detection of red complex bacteria in coronary plaque samples. However Aggregatibacter actinomycetemcomitans could not be detected in these samples.

Genetic and antigenic analyses of Porphyromonas gingivalis FimA fimbriae.

The periodontal pathogen Porphyromonas gingivalis generally expresses two distinct fimbriae, FimA and Mfa1, which play a role in biofilm formation. The fimA gene that encodes FimA fimbrilin is polymorphic, and polymerase chain reaction analysis has identified six genotypes called types I-V and Ib. We found recently that fimbriae exhibit antigenic heterogeneity among the genotypes. In the present study, we analysed the fimA DNA sequences of 84 strains of P. gingivalis and characterized the antigenicity of FimA fimbriae. Strains analysed here comprised 10, 16, 29, 13, 10 and 6 strains of types I, Ib, II, III, IV and V, respectively. DNA sequencing revealed that type Ib does not represent a single cluster and that type II sequences are remarkably diverse. In contrast, the fimA sequences of the other types were relatively homogeneous. Antigenicity was investigated using antisera elicited by pure FimA fimbriae of types I-V. Antigenicity correlated generally with the respective genotype. Type Ib strains were recognized by type I antisera. However, some strains showed cross-reactivity, especially, many type II strains reacted with type III antisera. The levels of fimbrial expression were highly variable, and expression was positively correlated with ability of biofilm formation on a saliva-coated plate. Further, two strains without FimA and Mfa1 fimbriae expressed fimbrial structures, suggesting that the strains produce other types of fimbriae.

Clonal composition and community clustering of drug-susceptible and -resistant Escherichia coli isolates from bloodstream infections.

Multidrug-resistant Escherichia coli strains belonging to a single lineage frequently account for a large proportion of extraintestinal E. coli infections in many parts of the world. However, limited information exists on the community prevalence and clonal composition of drug-susceptible E. coli strains. Between July 2007 and September 2010, we analyzed all consecutively collected Gram-negative bacterial isolates from patients with bloodstream infection (BSI) admitted to a public hospital in San Francisco for drug susceptibility and associated drug resistance genes. The E. coli isolates were genotyped for fimH single nucleotide polymorphisms (SNPs) and multilocus sequence types (MLSTs). Among 539 isolates, E. coli accounted for 249 (46%); 74 (30%) of them were susceptible to all tested drugs, and 129 (52%) were multidrug resistant (MDR). Only five MLST genotypes accounted for two-thirds of the E. coli isolates; the most common were ST131 (23%) and ST95 (18%). Forty-seven (92%) of 51 ST131 isolates, as opposed to only 8 (20%) of 40 ST95 isolates, were MDR (P < 0.0001). The Simpson's diversity index for drug-susceptible ST genotypes was 87%, while the index for MDR ST genotypes was 81%. ST95 strains were comprised of four fimH types, and one of these (f-6) accounted for 67% of the 21 susceptible isolates (P < 0.003). A large proportion (>70%) of both MDR and susceptible E. coli BSI isolates represented community-onset infections. These observations show that factors other than the selective pressures of antimicrobial agents used in hospitals contribute to community-onset extraintestinal infections caused by clonal groups of E. coli regardless of their drug resistance.

Structure of the CFA/III major pilin subunit CofA from human enterotoxigenic Escherichia coli determined at 0.90 Å resolution by sulfur-SAD phasing.

CofA, a major pilin subunit of colonization factor antigen III (CFA/III), forms pili that mediate small-intestinal colonization by enterotoxigenic Escherichia coli (ETEC). In this study, the crystal structure of an N-terminally truncated version of CofA was determined by single-wavelength anomalous diffraction (SAD) phasing using five sulfurs in the protein. Given the counterbalance between anomalous signal strength and the undesired X-ray absorption of the solvent, diffraction data were collected at 1.5 Å resolution using synchrotron radiation. These data were sufficient to elucidate the sulfur substructure at 1.38 Å resolution. The low solvent content (29%) of the crystal necessitated that density modification be performed with an additional 0.9 Å resolution data set to reduce the phase error caused by the small sulfur anomalous signal. The CofA structure showed the αß-fold typical of type IVb pilins and showed high structural homology to that of TcpA for toxin-coregulated pili of Vibrio cholerae, including spatial distribution of key residues critical for pilin self-assembly. A pilus-filament model of CofA was built by computational docking and molecular-dynamics simulation using the previously reported filament model of TcpA as a structural template. This model revealed that the CofA filament surface was highly negatively charged and that a 23-residue-long loop between the α1 and α2 helices filled the gap between the pilin subunits. These characteristics could provide a unique binding epitope for the CFA/III pili of ETEC compared with other type IVb pili.

Prevalence of Porphyromonas gingivalis fimA genotypes in Japanese children.

Porphyromonas gingivalis FimA fimbriae have been classified into 6 genotypes (types I-V and Ib) based on the diversity of the fimA genes encoding the fimbrial subunits. We investigated the prevalence of fimA genotype in Japanese children. Dental plaque specimens were obtained from 400 subjects (age; 2 to 15 years), including 134 with healthy gingiva, 239 with gingivitis and 27 with periodontitis, and then analyzed by polymerase chain reaction. P. gingivalis was detected in 1.5%, 10.0% and 29.6% of these subjects, respectively. Significant differences were observed with regard to P. gingivalis infection among the groups [chi-squared analysis: gingivitis vs. healthy, P < 0.01, odds ratio (OR) = 7.4; periodontitis vs. healthy, P < 0.001, OR = 27.8]. In P. gingivalis-positive subjects with periodontitis, the most prevalent fimA types were type Ib/type II combination (37.5%) and type IV (37.5%), followed by type II (25.0%), while type IV (33.3%) and type II (29.2%) were most often detected in those with gingivitis. Our results suggest that the presence of P. gingivalis is associated with periodontal diseases, and that the type II, IV and Ib/II combination are the most common among fimA genotypes.

Diversity of fimbrillin among Porphyromonas gulae clinical isolates from Japanese dogs.

Porphyromonas gulae, a gram-negative black-pigmented anaerobe, is a pathogen for periodontitis in dogs. An approximately 41-kDa fimbrial subunit protein (FimA) encoded by fimA is regarded as associated with periodontitis. In the present study, the fimA genes of 17 P. gulae strains were sequenced, and classified into two major types. The generation of phylogenetic trees based on the deduced amino acid sequence of FimA of P. gulae strains along with sequences from several strains of Porphyromonas gingivalis, a major cause of human periodontitis, revealed that the two types of FimA (types A and B) of P. gulae were similar to type I FimA and types II and III FimA of P. gingivalis, respectively. A PCR system for classification was established based on differences in the nucleotide sequences of the fimA genes. Analysis of 115 P. gulae-positive oral swab specimens from dogs revealed that 42.6%, 22.6%, and 26.1% of them contained type A, type B, and both type A and B fimA genes, respectively. Experiments with a mouse abscess model demonstrated that the strains with type B fimA caused significantly greater systemic inflammation than those with type A. These results suggest that the FimA proteins of P. gulae are diverse with two major types and that strains with type B fimA could be more virulent.

Structural characterization of CFA/III and Longus type IVb pili from enterotoxigenic Escherichia coli.

The type IV pili are helical filaments found on many Gram-negative pathogenic bacteria, with multiple diverse roles in pathogenesis, including microcolony formation, adhesion, and twitching motility. Many pathogenic enterotoxigenic Escherichia coli (ETEC) isolates express one of two type IV pili belonging to the type IVb subclass: CFA/III or Longus. Here we show a direct correlation between CFA/III expression and ETEC aggregation, suggesting that these pili, like the Vibrio cholerae toxin-coregulated pili (TCP), mediate microcolony formation. We report a 1.26-Å resolution crystal structure of CofA, the major pilin subunit from CFA/III. CofA is very similar in structure to V. cholerae TcpA but possesses a 10-amino-acid insertion that replaces part of the α2-helix with an irregular loop containing a 3(10)-helix. Homology modeling suggests a very similar structure for the Longus LngA pilin. A model for the CFA/III pilus filament was generated using the TCP electron microscopy reconstruction as a template. The unique 3(10)-helix insert fits perfectly within the gap between CofA globular domains. This insert, together with differences in surface-exposed residues, produces a filament that is smoother and more negatively charged than TCP. To explore the specificity of the type IV pilus assembly apparatus, CofA was expressed heterologously in V. cholerae by replacing the tcpA gene with that of cofA within the tcp operon. Although CofA was synthesized and processed by V. cholerae, no CFA/III filaments were detected, suggesting that the components of the type IVb pilus assembly system are highly specific to their pilin substrates.

Distribution of Porphyromonas gingivalis fimA genotypes in chronic apical periodontitis associated with symptoms.

INTRODUCTION: Porphyromonas gingivalis (P. gingivalis) is an anaerobic bacterium involved in root canal infections whose fimbriae are classified into six genotypes (types I-V and Ib) based on nucleotide sequence. Accumulated evidence suggests there is significant association between P. gingivalis and some clinical symptoms of periodontal diseases. The present study aims to determine the prevalence of P. gingivalis fimA genotypes in apical periodontitis and to investigate the correlation between P. gingivalis fimA genotypes and clinical symptoms. METHODS: Samples were obtained from 158 infected root canals with apical periodontitis. DNA was extracted and analyzed with a polymerase chain reaction-based identification assay. Odds ratios, 95% confidence intervals, and contingency coefficient were calculated for associating the fimA-specific genes with clinical symptoms. RESULTS: P. gingivalis was detected in 39.9% of the inflected root canal samples and was found in 44.5% of P. gingivalis-positive specimens with symptoms. Types II (69.4%) were the most frequent in the symptomatic cases followed by type IV (32.7%). The occurrence of type I (64.3%) was significantly higher than any other genotypes in the asymptomatic apical periodontitis, whereas type II and type Ib were not identified. Statistical analysis revealed that the occurrences of types II, IV, and Ib fimA were associated with greater risk of clinical signs (swelling, sinus tract, or intracanal exudates) than type I. CONCLUSIONS: Results from this study reinforce the association between P. gingivalis-specific fimA genotypic clones and apical periodontitis, indicating that fimA genotypes (types II, IV, and Ib) were related to the etiology of symptomatic periradicular diseases.

Molecular analysis of type 3 fimbrial genes from Escherichia coli, Klebsiella and Citrobacter species.

BACKGROUND: Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection in the United States and is caused by a range of uropathogens. Biofilm formation by uropathogens that cause CAUTI is often mediated by cell surface structures such as fimbriae. In this study, we characterised the genes encoding type 3 fimbriae from CAUTI strains of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Citrobacter koseri and Citrobacter freundii. RESULTS: Phylogenetic analysis of the type 3 fimbrial genes (mrkABCD) from 39 strains revealed they clustered into five distinct clades (A-E) ranging from one to twenty-three members. The majority of sequences grouped in clade A, which was represented by the mrk gene cluster from the genome sequenced K. pneumoniae MGH78578. The E. coli and K. pneumoniae mrkABCD gene sequences clustered together in two distinct clades, supporting previous evidence for the occurrence of inter-genera lateral gene transfer. All of the strains examined caused type 3 fimbriae mediated agglutination of tannic acid treated human erythrocytes despite sequence variation in the mrkD-encoding adhesin gene. Type 3 fimbriae deletion mutants were constructed in 13 representative strains and were used to demonstrate a direct role for type 3 fimbriae in biofilm formation. CONCLUSIONS: The expression of functional type 3 fimbriae is common to many Gram-negative pathogens that cause CAUTI and is strongly associated with biofilm growth. Our data provides additional evidence for the spread of type 3 fimbrial genes by lateral gene transfer. Further work is now required to substantiate the clade structure reported here by examining more strains as well as other bacterial genera that make type 3 fimbriae and cause CAUTI.

Sequence conservation of pilus subunits in Neisseria meningitidis.

The rapid onset and dramatic consequences of Neisseria meningitidis infections make the design of a broadly protective vaccine a priority for public health. There is an ongoing quest for meningococcal components that are surface exposed, widely conserved and can induce protective antibodies. Type IV pili (Tfp) are filamentous structures with a key role in pathogenesis that extend beyond the surface of the bacteria and have demonstrated vaccine potential. However, extensive antigenic variation of PilE, the major subunit of Tfp, means that they are currently considered to be unsuitable vaccine components. Recently it has been shown that Tfp also contain low abundance pilins ComP, PilV and PilX in addition to PilE. This prompted us to examine the prevalence and sequence diversity of these proteins in a panel of N. meningitidis disease isolates. We found that all minor pilins are highly conserved and the major pilin genes are also highly conserved within the ST-8 and ST-11 clonal complexes. These data have important implications for the re-consideration of pilus subunits as vaccine antigens.

Structural characterization of novel Pseudomonas aeruginosa type IV pilins.

Pseudomonas aeruginosa type IV pili, composed of PilA subunits, are used for attachment and twitching motility on surfaces. P. aeruginosa strains express one of five phylogenetically distinct PilA proteins, four of which are associated with accessory proteins that are involved either in pilin posttranslational modification or in modulation of pilus retraction dynamics. Full understanding of pilin diversity is crucial for the development of a broadly protective pilus-based vaccine. Here, we report the 1.6-A X-ray crystal structure of an N-terminally truncated form of the novel PilA from strain Pa110594 (group V), which represents the first non-group II pilin structure solved. Although it maintains the typical T4a pilin fold, with a long N-terminal alpha-helix and four-stranded antiparallel beta-sheet connected to the C-terminus by a disulfide-bonded loop, the presence of an extra helix in the alphabeta-loop and a disulfide-bonded loop with helical character gives the structure T4b pilin characteristics. Despite the presence of T4b features, the structure of PilA from strain Pa110594 is most similar to the Neisseria gonorrhoeae pilin and is also predicted to assemble into a fiber similar to the GC pilus, based on our comparative pilus modeling. Interactions between surface-exposed areas of the pilin are suggested to contribute to pilus fiber stability. The non-synonymous sequence changes between group III and V pilins are clustered in the same surface-exposed areas, possibly having an effect on accessory protein interactions. However, based on our high-confidence model of group III PilA(PA14), compensatory changes allow for maintenance of a similar shape.

fimA genotypes and PFGE profile patterns in Porphyromonas gingivalis isolates from subjects with periodontitis.

BACKGROUND AND OBJECTIVES: Porphyromonas gingivalis is frequently identified to type by evaluation of fimA polymorphisms and less often by pulsed-field gel electrophoresis (PFGE) because of the technical intricacies of PFGE. To compare these techniques, we genotyped P. gingivalis clinical isolates as to (i) their fimA type and (ii) their whole genome restriction profile (PFGE analysis). MATERIAL AND METHODS: Thirty-two P. gingivalis strains were isolated from 16 unrelated periodontitis patients. Two strains were isolated from each patient. Strains were subjected to a fimA-typing polymerase chain reaction (PCR) assay. Strains that could not be typed by PCR were submitted to sequencing of the entire fimA gene. The PFGE profiles of clinical strains were compared using bioinformatic analysis. RESULTS: Seven of the 32 isolates were not typeable by PCR and so their entire fimA gene was sequenced. The sequencing identified each strain as belonging to a single fimA type. In one case, sequencing of the fimA gene did not agree with the result obtained using fimA PCR typing. With the exception of one patient, each patient presented isolates bearing the same fimA type. However, in three patients, isolates with the same fimA type presented different PFGE pulsotypes. CONCLUSION: The P. gingivalis typing using fimA PCR has limitations in typeability and discriminatory power. A typing technique for P. gingivalis that is easy to perform but that presents adequate typeability and discriminatory power is needed if we want to better understand the epidemiology of periodontal disease.

Diversity of archaeal type IV pilin-like structures.

Bacterial type IV pili perform important functions in such disparate biological processes as surface adhesion, cell-cell interactions, autoaggregation, conjugation, and twitching motility. Unlike bacteria, archaea use a type IV pilus related structure to drive swimming motility. While this unique flagellum is the best-studied example of an archaeal IV pilus-like structure, recent in silico, in vivo and structural analyses have revealed a highly diverse set of archaeal non-flagellar type IV pilus-like structures. Accumulating evidence suggests that these structures play important diverse roles in archaea.

Surface components of Porphyromonas gingivalis.

BACKGROUND AND OBJECTIVE: Research on Porphyromonas gingivalis, a periodontopathogen, has provided a tremendous amount of information over the last 20 years, which may exceed in part than that on other closely related members in terms of phylogenetic as well as proteomic criteria, including Bacteroides fragilis and B. thetaiotaomicron as major anaerobic, opportunistic pathogens in the medical field. In this minireview, we focused on recent research findings concerning surface components such as outer membrane proteins and fimbriae, of P. gingivalis. MATERIAL AND METHODS: Elucidation of the surface components in P. gingivalis was especially difficult because outer membrane proteins are tightly bound to lipopolysaccharide and they are resistant to dissociation and separation from each other, even during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, unless samples are appropriately heated. In addition, P. gingivalis is asaccharolytic and therefore a potent proteolytic bacterium, another factor causing difficulty in research. The study of the surface components was carefully carried out considering these unique features in P. gingivalis when compared with other gram-negative bacteria, including Escherichia coli and Pseudomonas aeruginosa. RESULTS: Separation of outer membrane proteins, and characterization of OmpA-like proteins and RagAB as major proteins, is described herein. Our recent findings on FimA and Mfa1 fimbriae, two unique appendages in this organism, and on their regulation of expression are also described briefly. CONCLUSION: Surface components of P. gingivalis somehow have contact with host tissues and cells because of the outermost cell elements. Therefore, such bacterial components are potentially important in the occurrence of periodontal diseases.

Prevalence of fimA genotypes of Porphyromonas gingivalis and periodontal health status in Chinese adults.

BACKGROUND AND OBJECTIVE: Porphyromonas gingivalis fimbriae play a key role in colonization of the oral cavity. The fimA gene, which encodes fimbrillin (FimA), can be classified into six types (I-V and Ib) according to nucleotide sequence. In the present study, we investigated the relationship between the prevalence of P. gingivalis-specific fimA genotypes and periodontal health status in Chinese adults. MATERIAL AND METHODS: One-hundred and fifteen patients with chronic periodontitis and 136 periodontally healthy adults were selected. P. gingivalis detection, determination of fimA genotypes, and the co-existence of Actinobacillus actinomycetemcomitans and Tannerella forsythia with various fimA types, were assessed by the polymerase chain reaction. Odds ratios and 95% confidence intervals were calculated for associating the fimA-specific genes with periodontitis. RESULTS: P. gingivalis was detected in 22.1% of healthy subjects and in 81.7% of the patients. A single fimA genotype was detected in most samples. In healthy adults, the most prevalent fimA genotype was type I (66.7%). However, type II was detected most frequently (43.6%) in the patient group, followed by type IV (30.9%). The frequency of co-existing A. actinomycetemcomitans and T. forsythia was highest in type II fimA-positive sites. Statistical analysis revealed that periodontitis was associated with occurrences of type I (odds ratio 0.97), Ib (odds ratio 13.26), II (odds ratio 36.62), III (odds ratio 4.57), IV (odds ratio 22.86) and V (odds ratio 1.19). CONCLUSION: P. gingivalis type II followed by type IV were considered as disease-associated strains that account for the pathogenesis of chronic periodontitis in Chinese adults.

Sortase-catalyzed assembly of distinct heteromeric fimbriae in Actinomyces naeslundii.

Two types of adhesive fimbriae are expressed by Actinomyces; however, the architecture and the mechanism of assembly of these structures remain poorly understood. In this study we characterized two fimbrial gene clusters present in the genome of Actinomyces naeslundii strain MG-1. By using immunoelectron microscopy and biochemical analysis, we showed that the fimQ-fimP-srtC1-fimR gene cluster encodes a fimbrial structure (designated type 1) that contains a major subunit, FimP, forming the shaft and a minor subunit, FimQ, located primarily at the tip. Similarly, the fimB-fimA-srtC2 gene cluster encodes a distinct fimbrial structure (designated type 2) composed of a shaft protein, FimA, and a tip protein, FimB. By using allelic exchange, we constructed an in-frame deletion mutant that lacks the SrtC2 sortase. This mutant produces abundant type 1 fimbriae and expresses the monomeric FimA and FimB proteins, but it does not assemble type 2 fimbriae. Thus, SrtC2 is a fimbria-specific sortase that is essential for assembly of the type 2 fimbriae. Together, our experiments pave the way for several lines of molecular investigation that are necessary to elucidate the fimbrial assembly pathways in Actinomyces and their function in the pathogenesis of different biofilm-related oral diseases.