Rapid development within the field of massive parallel sequencing (MPS) is about to bring this technology within reach for diagnostic microbiology laboratories. We wanted to explore its potential for improving diagnosis and understanding of polymicrobial infections, using bacterial brain abscesses as an example. We conducted a prospective nationwide study on bacterial brain abscesses. Fifty-two surgical samples were included over a 2-year period. The samples were categorized as either spontaneous intracerebral, spontaneous subdural, or postoperative. Bacterial 16S rRNA genes were amplified directly from the specimens and sequenced using Ion Torrent technology, with an average of 500,000 reads per sample. The results were compared to those from culture- and Sanger sequencing-based diagnostics. Compared to culture, MPS allowed for triple the number of bacterial identifications. Aggregatibacter aphrophilus, Fusobacterium nucleatum, and Streptococcus intermedius or combinations of them were found in all spontaneous polymicrobial abscesses. F. nucleatum was systematically detected in samples with anaerobic flora. The increased detection rate for Actinomyces spp. and facultative Gram-negative rods further revealed several species associations. We suggest that A. aphrophilus, F. nucleatum, and S. intermedius are key pathogens for the establishment of spontaneous polymicrobial brain abscesses. In addition, F. nucleatum seems to be important for the development of anaerobic flora. MPS can accurately describe polymicrobial specimens when a sufficient number of reads is used to compensate for unequal species concentrations and principles are defined to discard contaminant bacterial DNA in the subsequent data analysis. This will contribute to our understanding of how different types of polymicrobial infections develop.
Fusobacterium nucleatum subsp. nucleatum
has been associated with a variety of oral and nonoral infections such
as periodontitis, pericarditis, bone infections, and brain abscesses.
Several studies have shown the role of plasmin, a plasma serine
protease, in increasing the invasive capacity of microorganisms. In
this study, we investigated the binding of human plasminogen to
F. nucleatum subsp. nucleatum, and its
subsequent activation into plasmin. Plasminogen-binding activity of
bacterial cells was demonstrated by a solid-phase dot blot assay using
an anti-plasminogen antibody. The binding activity was heat resistant
and involved cell-surface lysine residues since it was abolished in the
presence of the lysine analog ɛ-aminocaproic acid. Activation of
plasminogen-coated bacteria occurred following incubation with either
streptokinase, urokinase-type plasminogen activator (u-PA), or a
Porphyromonas gingivalis culture supernatant. In the case
of the P. gingivalis culture supernatant, a cysteine
protease was likely involved in the activation. The plasmin activity
generated on the cell surface of F. nucleatum subsp.
nucleatum could be inhibited by aprotinin. Activation of
plasminogen by u-PA was greatly enhanced when plasminogen was bound to
bacteria rather than in a free soluble form. u-PA-activated
plasminogen-coated F. nucleatum subsp.
nucleatum was found to degrade fibronectin, as determined
by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Tissue
inhibitor of metalloproteinase-1 was also degraded by the plasmin
activity generated on the bacterial cells. This study suggests a
possible role for plasminogen, which is present in affected periodontal
sites, in promoting tissue destruction and invasion by nonproteolytic
bacteria such as F. nucleatum subsp. nucleatum.
PCR primers that target the bacterial 16S rRNA genes (or the tuf gene for the genus Enterococcus) were used to identify 10 putative bacterial pathogens in root canals with necrotic pulp. In addition, the associations of these microorganisms with symptoms and a history of diabetes mellitus were investigated. Microbial samples from the root canals of 24 teeth with necrotic pulp were included in the study. PCR with universal bacterial primers identified bacterial DNA in 22 specimens; the remaining 2 specimens were from intact teeth that had been traumatized 6 months prior to treatment. PCR with specific primers showed that preoperative symptoms were significantly associated with the presence of Streptococcus spp. (P < 0.001 by chi-square analysis). There was also a nonsignificant trend for symptoms to be associated with Fusobacterium nucleatum and Porphyromonas gingivalis (odds ratio, >2) and for diabetes mellitus to be associated with P. gingivalis and Porphyromonas endodontalis (odds ratio, >2). Cloning and sequencing of the universal PCR product in one specimen revealed the presence of an organism related to the genus Olsenella, which has not previously been described in endodontic infections.
Intracystic fluid was aseptically collected from 11 patients with postoperative maxillary cyst (POMC), and DNA was extracted from the POMC fluid. Bacterial species were identified by sequencing after cloning of approximately 580 bp of the 16S rRNA gene. Identification of pathogenic bacteria was also performed by culture methods. The phylogenetic identity was determined by sequencing 517–596 bp in each of the 1139 16S rRNA gene clones. A total of 1114 clones were classified while the remaining 25 clones were unclassified. A total of 103 bacterial species belonging to 42 genera were identified in POMC fluid samples by 16S rRNA gene analysis. Species of Prevotella (91%), Neisseria (73%), Fusobacterium (73%), Porphyromonas (73%), and Propionibacterium (73%) were found to be highly prevalent in all patients. Streptococcus mitis (64%), Fusobacterium nucleatum (55%), Propionibacterium acnes (55%), Staphylococcus capitis (55%), and Streptococcus salivarius (55%) were detected in more than 6 of the 11 patients. The results obtained by the culture method were different from those obtained by 16S rRNA gene analysis, but both approaches may be necessary for the identification of pathogens, especially of bacteria that are difficult to detect by culture methods, and the development of rational treatments for patients with POMC.
Cytokines, including granulocyte-macrophage colony-stimulating factor (GM-CSF), are used to assist in bone marrow recovery during cancer chemotherapy. Interleukin-1β (IL-1β) and tumor necrosis factor alpha (TNF-α) play important roles in inflammatory processes, including exacerbation of periodontal diseases, one of the most common complications in patients who undergo this therapy. A human monocyte cell line (THP-1) was utilized to investigate IL-1β and TNF-α production following GM-CSF supplementation with lipopolysaccharide (LPS) from two oral microorganisms, Porphyromonas gingivalis and Fusobacterium nucleatum. LPS of P. gingivalis or F. nucleatum was prepared by a phenol-water extraction method and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and determination of total protein and endotoxin contents. Resting THP-1 cells were treated with LPS of P. gingivalis or F. nucleatum and/or GM-CSF (50 IU/ml) by using different concentrations for various time periods. Production of IL-1β and TNF-α in THP-1 cells was measured by solid-phase enzyme-linked immunosorbent assay. Reverse transcription (RT)-PCR was used to evaluate the gene expression of resting and treated THP-1 cells. IL-1β was not detected in untreated THP-1 cells. IL-1β production was, however, stimulated sharply at 4 h. GM-CSF amplified IL-1β production in THP-1 cells treated with LPS from both oral anaerobes. No IL-1β-specific mRNA transcript was detected in untreated THP-1 cells. However, IL-1β mRNA was detected by RT-PCR 2 h after stimulation of THP-1 cells with LPS from both organisms. GM-CSF did not shorten the IL-1β transcriptional activation time. GM-CSF plus F. nucleatum or P. gingivalis LPS activated THP-1 cells to produce a 1.6-fold increase in TNF-α production at 4 h over LPS stimulation alone. These investigations with the in vitro THP-1 model indicate that there may be an increase in the cellular immune response to oral endotoxin following GM-CSF therapy, as evidenced by production of the tissue-reactive cytokines IL-1β and TNF-α.
Oral Campylobacter species have been found to be associated with periodontitis progression. While the etiological significance of Campylobacter rectus is quite established, the association of C. gracilis, C. concisus, and C. curvus with health or disease remains contradictory.
This study hypothesizes that the proportion of species within the Campylobacter genus rather than the absolute abundance of a single species is a suitable indicator for periodontitis progression.
Subgingival plaque from 90 periodontitis patients and gingival sulcus fluid of 32 healthy individuals were subjected to a newly developed nested PCR approach, in which all Campylobacter spp. were amplified simultaneously. The resulting mixture of 16S-rRNA-gene-amplicons were separated by single-stranded conformation polymorphism (SSCP) gel electrophoresis, followed by sequencing and identification of excised bands and relative quantification of band intensities. In all samples, the abundance of selected periodontitis marker species was determined based on DNA hybridization on a microarray.
The highly prevalent Campylobacter community was composed of varying proportions of C. rectus, C. gracilis, C. concisus, and C. curvus. Cluster analysis based on SSCP-banding pattern resulted in distinct groups which in turn coincided with significant differences in abundance of established periodontitis marker species (Tannerella forsythia, Porphyromonas gingivalis, and Fusobacterium nucleatum) and progression.
The shift in the Campylobacter community composition seems to display the general microbial community shift during clinical progression in a simplified manner. The focus on members of the Campylobacter in this study suggests that this genus can be an indicator of ecological changes in the subgingival oral microflora.
oral Campylobacter; periodontitis progression; microbial ecology; SSCP; ParoCheck genechip
The aim of the present study was to develop a monoclonal antibody that recognizes the shared antigen of Porphyromonas endodontalis so that we could use the antibody in direct identification and detection of P. endodontalis in infectious material from apical periodontal patients. We established a hybridoma cell line producing monoclonal antibody (BEB5) specific for P. endodontalis. BEB5 antibody reacted with all of the P. endodontalis strains tested, but not with any of the other black-pigmented Porphyromonas and Bacteroides spp. The antibody reacted specifically with the lipopolysaccharide (LPS) of three P. endodontalis strains of different serotypes (O1K1, O1K2, and O1K-). Western blotting (immunoblotting) analysis confirmed the specificity of the antibody to these LPSs, because the antibody recognized the typical "repetitive ladder" pattern characteristic of LPS on sodium dodecyl sulfate-polyacrylamide electrophoretic gels. These observations demonstrate that P. endodontalis LPS is the shared antigen of this species. The antibody can specifically identify P. endodontalis on nitrocellulose membrane blots of bacterial colonies grown on agar. The antibody is also capable of directly detecting the presence of P. endodontalis in infectious material by immunoslot blot assay. These results indicate that LPS is the shared antigen of P. endodontalis and that BEB5 antibody against LPS is a useful one for direct identification and detection of the organisms in samples from apical periodontal patients.
Fusobacterium nucleatum is classified into five subspecies that inhabit the human oral cavity (F. nucleatum subsp. nucleatum, F. nucleatum subsp. polymorphum, F. nucleatum subsp. fusiforme, F. nucleatum subsp. vincentii, and F. nucleatum subsp. animalis) based on several phenotypic characteristics and DNA-DNA hybridization patterns. However, the methods for detecting or discriminating the clinical isolates of F. nucleatum at the subspecies levels are laborious, expensive, and time-consuming. Therefore, in this study, the nucleotide sequences of the RNA polymerase β-subunit gene (rpoB) and zinc protease gene were analyzed to discriminate the subspecies of F. nucleatum. The partial sequences of rpoB (approximately 2,419 bp), the zinc protease gene (878 bp), and 16S rRNA genes (approximately 1,500 bp) of the type strains of five subspecies, 28 clinical isolates of F. nucleatum, and 10 strains of F. periodonticum (as a control group) were determined and analyzed. The phylogenetic data showed that the rpoB and zinc protease gene sequences clearly delineated the subspecies of F. nucleatum and provided higher resolution than the 16S rRNA gene sequences in this respect. According to the phylogenetic analysis of rpoB and the zinc protease gene, F. nucleatum subsp. vincentii and F. nucleatum subsp. fusiforme might be classified into a single subspecies. Five clinical isolates could be delineated as a new subspecies of F. nucleatum. The results suggest that rpoB and the zinc protease gene are efficient targets for the discrimination and taxonomic analysis of the subspecies of F. nucleatum.
A new molecular biological approach for the identification of bacteria is described. This approach employs PCR of bacterial cell lysates with conserved primers located in the 16S rRNA sequence flanking a variable region, and analysis of the amplified product was based on the principle of single-strand conformation polymorphism (SSCP). The PCR product was denatured and separated on a nondenaturing polyacrylamide gel. SSCP patterns were detected by silver staining the nucleic acids. The mobility of the single-stranded DNA is sequence dependent and could be used to identify the unknown bacteria. Feasibility of the technique was demonstrated for a broad panel of gram-negative and gram-positive bacteria. We tested over 100 strains of bacteria representing 15 genera and 40 species. With the use of only two primer sets, P11P-P13P and ER10-ER11, we were capable to discriminate the tested species at the genus and species levels. Species-specific patterns were obtained for, e.g., Clostridium spp., Listeria spp., Pseudomonas spp., and Enterobacter spp. PCR-SSCP is a sensitive technique; e.g., the sensitivity obtained for Escherichia coli cells was 30 CFU. This technique is a simple and rapid method for the detection and identification of a wide spectrum of bacteria by whole-cell-based PCR amplification with the use of conserved primers and identification by nondenaturing gel electrophoresis.
Fifteen Bacteroides forsythus strains freshly isolated from patients with periodontitis were used together with three collection strains and one type strain for characterization of growth on various media; determination of enzymatic profiles, antibiotic susceptibility profiles, 16S rRNA ribotypes, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) outer membrane protein profiles, and pathogenicity; and gas chromatography analysis by using a wound chamber model in rabbits. All strains were stimulated by N-acetylmuramic acid, while one strain needed a further supplement such as yeast extract for optimal growth. All strains showed trypsin-like activity. While 10 different ribotypes were found, the SDS-PAGE profiles revealed similar patterns for all strains. All strains were sensitive to penicillin G (MICs, <0.5 microg/ml), ampicillin (MICs, <1.0 microg/ml), amoxicillin (MICs, <0.38 microg/ml), metronidazole (MICs, <0.005 microg/ml), tetracycline (MICs, <0.19 microg/ml), doxycycline (MICs, 0.05 microg/ml), erythromycin (MICs, <0.4 microg/ml), and clindamycin (MICs, <0.016 microg/ml), while they were less sensitive to ciprofloxacin (MICs, <4 microg/ml). B. forsythus did not cause abscess formation by monoinoculation. B. forsythus coinoculated with Fusobacterium nucleatum ATCC 10953 caused abscess formation in 75% of rabbits, while it caused abscess formation in 100% of rabbits when it was coinoculated with Porphyromonas gingivalis FDC 381. In the case of the latter combination, four of six rabbits died of sepsis after 6 to 7 days, and P. gingivalis and B. forsythus were recovered from the heart blood at a proportion of 10:1. B. forsythus strains were highly virulent and invasive in combination with P. gingivalis.
We evaluated the usefulness of PCR analysis of the 16S-23S rRNA gene internal transcribed spacer (ITS) and the CTX-M extended-spectrum β-lactamase (ESBL) followed by microchip gel electrophoresis (MGE) for direct identification and CTX-M detection of Gram-negative bacteria (GNB) from positive blood culture bottles. Of 251 GNB isolated from blood cultures containing a single bacterium, 225 (90%) were correctly identified at the species level directly from positive blood culture bottles by comparing the ITS-PCR patterns of the sample strain with those of the control strains. There were no cases of incorrect identification. Limitations encountered included the inability to detect mixed cultures (four bottles) as well as some species (Enterobacter species and Klebsiella oxytoca) demonstrating identical ITS-PCR patterns. A total of 109 ESBL-producing isolates from various clinical materials obtained between January 2005 and December 2008 were examined for blaCTX-M, blaSHV, and blaTEM genes by PCR and sequences of PCR products. CTX-M ESBL was detected in 105 isolates, and SHV ESBL was detected in two isolates. The remaining two isolates (K. oxytoca) were shown to harbor blaOXY. Twenty (19%) of 104 Escherichia coli isolates from blood cultures were suspected to produce ESBL by the combination disk method, and these isolates were shown to harbor CTX-M ESBL by PCR-MGE. The results were obtained within 1.5 h at a calculated cost of $6.50 per specimen. In conclusion, simultaneous detection of ITS length polymorphisms and blaCTX-M by single PCR followed by MGE is useful for rapid, cost-effective, and reliable species-level identification of CTX-M ESBL-producing GNB responsible for bloodstream infections.
The Gram negative anaerobe Fusobacterium nucleatum has been implicated in the aetiology of periodontal diseases. Although frequently isolated from healthy dental plaque, its numbers and proportion increase in plaque associated with disease. One of the significant physico-chemical changes in the diseased gingival sulcus is increased environmental pH. When grown under controlled conditions in our laboratory, F. nucleatum subspecies polymorphum formed mono-culture biofilms when cultured at pH 8.2. Biofilm formation is a survival strategy for bacteria, often associated with altered physiology and increased virulence. A proteomic approach was used to understand the phenotypic changes in F. nucleatum cells associated with alkaline induced biofilms. The proteomic based identification of significantly altered proteins was verified where possible using additional methods including quantitative real-time PCR (qRT-PCR), enzyme assay, acidic end-product analysis, intracellular polyglucose assay and Western blotting.
Of 421 proteins detected on two-dimensional electrophoresis gels, spot densities of 54 proteins varied significantly (p < 0.05) in F. nucleatum cultured at pH 8.2 compared to growth at pH 7.4. Proteins that were differentially produced in biofilm cells were associated with the functional classes; metabolic enzymes, transport, stress response and hypothetical proteins. Our results suggest that biofilm cells were more metabolically efficient than planktonic cells as changes to amino acid and glucose metabolism generated additional energy needed for survival in a sub-optimal environment. The intracellular concentration of stress response proteins including heat shock protein GroEL and recombinational protein RecA increased markedly in the alkaline environment. A significant finding was the increased abundance of an adhesin, Fusobacterial outer membrane protein A (FomA). This surface protein is known for its capacity to bind to a vast number of bacterial species and human epithelial cells and its increased abundance was associated with biofilm formation.
This investigation identified a number of proteins that were significantly altered by F. nucleatum in response to alkaline conditions similar to those reported in diseased periodontal pockets. The results provide insight into the adaptive mechanisms used by F. nucleatum biofilms in response to pH increase in the host environment.
Fusobacterium nucleatum; Biofilms; Alkaline pH; Periodontal diseases; Proteomics
Bacterial biofilms have been found to develop on root surfaces outside the apical foramen and be associated with refractory periapical periodontitis. However, it is unknown which bacterial species form extraradicular biofilms. The present study aimed to investigate the identity and localization of bacteria in human extraradicular biofilms. Twenty extraradicular biofilms, used to identify bacteria using a PCR-based 16S rRNA gene assay, and seven root-tips, used to observe immunohistochemical localization of three selected bacterial species, were taken from 27 patients with refractory periapical periodontitis. Bacterial DNA was detected from 14 of the 20 samples, and 113 bacterial species were isolated. Fusobacterium nucleatum (14 of 14), Porphyromonas gingivalis (12 of 14), and Tannellera forsythensis (8 of 14) were frequently detected. Unidentified and uncultured bacterial DNA was also detected in 11 of the 14 samples in which DNA was detected. In the biofilms, P. gingivalis was immunohistochemically detected in all parts of the extraradicular biofilms. Positive reactions to anti-F. nucleatum and anti-T. forsythensis sera were found at specific portions of the biofilm. These findings suggested that P. gingivalis, T. forsythensis, and F. nucleatum were associated with extraradicular biofilm formation and refractory periapical periodontitis.
These studies determined the characteristics of tissue destruction in a murine abscess model elicited by mixed infection with the periodontopathogens Fusobacterium nucleatum and Porphyromonas gingivalis. The interbacterial effects of this synergism, the kinetics of the relationship of the bacterial interaction, and the characteristics of the bacteria required for the tissue destruction were studied. Infection of mice with P. gingivalis and F. nucleatum strains elicited lesions of various sizes as a function of infective dose. Primary infection with F. nucleatum plus P. gingivalis at various ratios (i.e., <1:1) resulted in a significantly greater lesion size (P < 0.001) compared with that resulting from primary infection with P. gingivalis alone. At F. nucleatum/P. gingivalis ratios of > or = 1:1, spreading lesion formation and progression were significantly (P < 0.001) decreased, suggesting that bacterial interaction (i.e., coaggregation) may have inhibited the spread of the P. gingivalis infection to a site distant from the initial injection. Infection with F. nucleatum and P. gingivalis simultaneously (at different sites) or F. nucleatum administered within 4 h prior to or 1 h following P. gingivalis infection significantly enhanced the ability of P. gingivalis to form large phlegmonous lesions. Chemical inhibition of the P. gingivalis trypsin-like protease activity or the use of a trypsin-negative P. gingivalis strain abrogated tissue destruction either alone or in combination with F. nucleatum. Therefore, it was possible to examine aspects of virulence of these pathogens in a murine lesion model by either altering bacterial ratios, manipulating the time of infection, or targeting vital bacterial virulence factors.
Intra-amniotic infection and inflammation are major causes of preterm birth (PTB). However, intra-amniotic inflammation is often detected in the absence of infection. This may partly be due to the culturing methods employed in hospital laboratories, which are unable to detect the uncultivated species. In this study, intra-amniotic microbial infections associated with PTB were examined by both culture and 16S rRNA-based culture-independent methods and were corroborated by the presence of intra-amniotic inflammation. Amniotic fluid (AF) specimens from 46 pregnancies complicated by PTB and 16 asymptomatic women were analyzed. No bacterial DNA was amplified in AF collected from the asymptomatic women. Among the 46 samples associated with PTB, bacterial DNA was amplified from all (16/16) of the culture-positive samples and 17% (5/30) of the culture-negative samples. In the culture-positive group, additional species were detected in more than half (9/16) of the cases by PCR and clone analysis. Altogether, approximately two- thirds of the species detected by the culture-independent methods were not isolated by culture. They included both uncultivated and difficult-to-cultivate species, such as Fusobacterium nucleatum, Leptotrichia (Sneathia) spp., a Bergeyella sp., a Peptostreptococcus sp., Bacteroides spp., and a species of the order Clostridiales. To examine intra-amniotic inflammation, an AF proteomic fingerprint (mass-restricted score) was determined by surface-enhanced laser desorption ionization-time-of-flight mass spectrometry. Inflammation was detected in all five samples which were culture negative but PCR positive. Women who were PCR positive more often had elevated interleukin-6 levels in their AF, histological chorioamnionitis, and funisitis and delivered neonates with early-onset neonatal sepsis. Previously unrecognized, uncultivated, or difficult-to-cultivate species may play a key role in the initiation of PTB.
The purpose of this study was to determine the bacterial diversity in advanced noma lesions using culture-independent molecular methods. 16S ribosomal DNA bacterial genes from DNA isolated from advanced noma lesions of four Nigerian children were PCR amplified with universally conserved primers and spirochetal selective primers and cloned into Escherichia coli. Partial 16S rRNA sequences of approximately 500 bases from 212 cloned inserts were used initially to determine species identity or closest relatives by comparison with sequences of known species or phylotypes. Nearly complete sequences of approximately 1,500 bases were obtained for most of the potentially novel species. A total of 67 bacterial species or phylotypes were detected, 25 of which have not yet been grown in vitro. Nineteen of the species or phylotypes, including Propionibacterium acnes, Staphylococcus spp., and the opportunistic pathogens Stenotrophomonas maltophilia and Ochrobactrum anthropi were detected in more than one subject. Other known species that were detected included Achromobacter spp., Afipia spp., Brevundimonas diminuta, Capnocytophaga spp., Cardiobacterium sp., Eikenella corrodens, Fusobacterium spp., Gemella haemoylsans, and Neisseria spp. Phylotypes that were unique to noma infections included those in the genera Eubacterium, Flavobacterium, Kocuria, Microbacterium, and Porphyromonas and the related Streptococcus salivarius and genera Sphingomonas and Treponema. Since advanced noma lesions are infections open to the environment, it was not surprising to detect species not commonly associated with the oral cavity, e.g., from soil. Several species previously implicated as putative pathogens of noma, such as spirochetes and Fusobacterium spp., were detected in at least one subject. However, due to the limited number of available noma subjects, it was not possible at this time to associate specific species with the disease.
The human palatine tonsils, which belong to the central antigen handling sites of the mucosal immune system, are frequently affected by acute and recurrent infections. This study compared the microbiota of the tonsillar crypts in children and adults affected by recurrent tonsillitis with that of healthy adults and children with tonsillar hyperplasia. An in-depth 16S rRNA gene based pyrosequencing approach combined with a novel strategy that included phylogenetic analysis and detection of species-specific sequence signatures enabled identification of the major part of the microbiota to species level. A complex microbiota consisting of between 42 and 110 taxa was demonstrated in both children and adults. This included a core microbiome of 12 abundant genera found in all samples regardless of age and health status. Yet, Haemophilus influenzae, Neisseria species, and Streptococcus pneumoniae were almost exclusively detected in children. In contrast, Streptococcus pseudopneumoniae was present in all samples. Obligate anaerobes like Porphyromonas, Prevotella, and Fusobacterium were abundantly present in children, but the species diversity of Porphyromonas and Prevotella was larger in adults and included species that are considered putative pathogens in periodontal diseases, i.e. Porphyromonas gingivalis, Porphyromonas endodontalis, and Tannerella forsythia. Unifrac analysis showed that recurrent tonsillitis is associated with a shift in the microbiota of the tonsillar crypts. Fusobacterium necrophorum, Streptococcus intermedius and Prevotella melaninogenica/histicola were associated with recurrent tonsillitis in adults, whereas species traditionally associated with acute tonsillitis like pyogenic streptococci and Staphylococcus aureus were scarce. The findings suggest that recurrent tonsillitis is a polymicrobial infection in which interactions within consortia of taxa play an etiologic role. The study contributes to the human microbiome data, to the understanding of the etiology of infections affecting the tonsils, and forms a basis for further insight into the consequences of the intense microbe-host interactions that take place in the tonsils.
Bacterial DNA contamination in PCR reagents has been a long standing problem that hampers the adoption of broad-range PCR in clinical and applied microbiology, particularly in detection of low abundance bacteria. Although several DNA decontamination protocols have been reported, they all suffer from compromised PCR efficiency or detection limits. To date, no satisfactory solution has been found.
We herein describe a method that solves this long standing problem by employing a broad-range primer extension-PCR (PE-PCR) strategy that obviates the need for DNA decontamination. In this method, we first devise a fusion probe having a 3′-end complementary to the template bacterial sequence and a 5′-end non-bacterial tag sequence. We then hybridize the probes to template DNA, carry out primer extension and remove the excess probes using an optimized enzyme mix of Klenow DNA polymerase and exonuclease I. This strategy allows the templates to be distinguished from the PCR reagent contaminants and selectively amplified by PCR. To prove the concept, we spiked the PCR reagents with Staphylococcus aureus genomic DNA and applied PE-PCR to amplify template bacterial DNA. The spiking DNA neither interfered with template DNA amplification nor caused false positive of the reaction. Broad-range PE-PCR amplification of the 16S rRNA gene was also validated and minute quantities of template DNA (10–100 fg) were detectable without false positives. When adapting to real-time and high-resolution melting (HRM) analytical platforms, the unique melting profiles for the PE-PCR product can be used as the molecular fingerprints to further identify individual bacterial species.
Broad-range PE-PCR is simple, efficient, and completely obviates the need to decontaminate PCR reagents. When coupling with real-time and HRM analyses, it offers a new avenue for bacterial species identification with a limited source of bacterial DNA, making it suitable for use in clinical and applied microbiology laboratories.
The bacteria found in carious dentine were correlated with the tissue response of the dental pulps of 65 teeth extracted from patients with advanced caries and pulpitis. Standardized homogenates of carious dentine were plated onto selective and nonselective media under anaerobic and microaerophilic conditions. In addition, real-time PCR was used to quantify the recovery of anaerobic bacteria. Primers and fluorogenic probes were designed to detect the total anaerobic microbial load, the genera Prevotella and Fusobacterium, and the species Prevotella melaninogenica, Porphyromonas endodontalis, Porphyromonas gingivalis, and Micromonas (formerly Peptostreptococcus) micros. The pulpal pathology was categorized according to the cellular response and degenerative changes. Analysis of cultured bacteria showed a predominance of gram-positive microorganisms, particularly lactobacilli. Gram-negative bacteria were also present in significant numbers with Prevotella spp., the most numerous anaerobic group cultured. Real-time PCR analysis indicated a greater microbial load than that determined by colony counting. The total number of anaerobes detected was 41-fold greater by real-time PCR than by colony counting, while the numbers of Prevotella and Fusobacterium spp. detected were 82- and 2.4-fold greater by real-time PCR than by colony counting, respectively. Real-time PCR also identified M. micros, P. endodontalis, and P. gingivalis in 71, 60, and 52% of carious samples, respectively. Correlation matrices of the real-time PCR data revealed significant positive associations between M. micros and P. endodontalis detection and inflammatory degeneration of pulpal tissues. These anaerobes have been strongly implicated in endodontic infections that occur as sequelae to carious pulpitis. Accordingly, the data suggest that the presence of high levels of these bacteria in carious lesions may be indicative of irreversible pulpal pathology.
Half of all men experience symptoms of prostatitis at some time in their lives, but the etiology is unknown for more than 90% of patients. Optimal clinical and culture methods were used to select 135 men with chronic prostatitis refractory to multiple previous courses of antimicrobial therapy. The subjects had no evidence of structural or functional lower genitourinary tract abnormalities of bacteriuria or bacterial prostatitis by traditional clinical tests, or of urethritis or urethral pathogens by culture. Specific PCR assays detected Mycoplasma genitalium, Chlamydia trachomatis, or Trichomonas vaginalis in 10 patients (8%). Broad-spectrum PCR tests detected tetracycline resistance-encoding genes, tetM-tetO-tetS, in 25% of patients and 16S rRNA in 77% of subjects. The tetM-tetO-tetS-positive cases constituted a subset of the 16S rRNA-positive cases. Patients with 16S rRNA were more likely to have > or = 1,000 leukocytes per mm3 in their expressed prostatic secretion than men whose prostate biopsy specimens were negative for 16S rRNA (P < 0.001). Based on direct sequencing and repetitive cloning, multiple sources of 16S rRNA were observed in individual patients. Sequences of 29 cloned PCR products revealed 16S rRNAs distinct from those of common skin and gut flora. These findings suggest that the prostate can harbor microorganisms that are not detectable by traditional approaches. These organisms may be associated with inflammation in the expressed prostatic secretions. Molecular methods hold great promise for identifying culture-resistant microorganisms in patients with chronic prostatitis.
Bacteremia continues to result in significant morbidity and mortality, particularly in patients who are immunocompromised. Currently, patients with suspected bacteremia are empirically administered broad-spectrum antibiotics, as definitive diagnosis relies upon the use of blood cultures, which impose significant delays in and limitations to pathogen identification. To address the limitations of growth-based identification, the sequence variability of the 16S rRNA gene of bacteria was targeted for rapid identification of bacterial pathogens isolated directly from blood cultures using a fluorescence-based PCR–single-strand conformation polymorphism (SSCP) protocol. Species-specific SSCP patterns were determined for 25 of the most common bacterial species isolated from blood cultures; these isolates subsequently served as a reference collection for bacterial identification for new cases of bacteremia. A total of 272 blood-culture-positive patient specimens containing bacteria were tested. A previously determined SSCP pattern was observed for 251 (92%) specimens, with 21 (8%) specimens demonstrating SSCP patterns distinct from those in the reference collection. Time to identification from blood culture positivity ranged from 1 to 8 days with biochemical testing, whereas identification by fluorescence-based capillary electrophoresis was obtained as early as 7 h at a calculated cost of $10 (U.S. currency) per specimen when tested in batches of 10. Limitations encountered included the inability to consistently detect mixed cultures as well as some species demonstrating identical SSCP patterns. This method can be applied directly to blood cultures or whole-blood specimens, where early pathogen identification would result in a timely diagnosis with possible implications for patient management costs and the mortality and morbidity of infections.
A novel strategy for the molecular identification of fungal agents of onychomycosis (including Trichophyton rubrum) has been designed based on the use of species-specific and universal primers in conjunction with a commercial kit that allows the extraction of DNA directly from the nail specimens. The microsatellite marker T1, which is based on a (GT)n repeat, was applied for the species-specific identification of Trichophyton rubrum. To evaluate how often Scopulariopsis spp. are detected in nail specimens, a second primer pair was designed to amplify specifically a 336-bp DNA fragment of the 28S region of the nuclear rRNA gene of S. brevicaulis and closely related species. Other fungal species were identified using amplification of the internal transcribed spacer (ITS) region of the rRNA gene, followed by restriction fragment length polymorphism analysis or sequencing. In addition, polyacrylamide gel separation of the T1-PCR product allowed subtyping of T. rubrum strains. We studied 195 nail specimens (the “nail sample”) and 66 previously collected etiologic strains (the “strain sample”) from 261 onychomycosis patients from Bulgaria and Greece. Of the etiologic agents obtained from both samples, T. rubrum was the most common organism, confirmed to be present in 76% of all cases and serving as the sole or (rarely) mixed etiologic agent in 199 of 218 cases (91%) where the identity of the causal organism(s) was confirmed. Other agents seen included molds (6% of cases with identified etiologic agents; mainly S. brevicaulis) and other dermatophyte species (4%; most frequently Trichophyton interdigitale). Simultaneous infections with two fungal species were confirmed in a small percentage of cases (below 1%). The proportion of morphologically identified cultures revealed by molecular study to have been misidentified was 6%. Subtyping revealed that all but five T. rubrum isolates were of the common type B that is prevalent in Europe. In comparison to microscopy and culture, the molecular approach was superior. The PCR was more sensitive (84%) than culture (22%) in the nail sample and was more frequently correct in specifically identifying etiologic agents (100%) than microscopy plus routine culture in either the nail or the strain samples (correct culture identifications in 96% and 94% of cases, respectively). Using the molecular approach, the time for diagnosing the identity of fungi causing onychomycosis could be reduced to 48 h, whereas culture techniques generally require 2 to 4 weeks. The early detection and identification of the infecting species in nails will facilitate prompt and appropriate treatment and may be an aid for the development of new antifungal agents.
AIM: To detect the variations of mitochondrial 12S rRNA in patients with gastric carcinoma, and to study their significance and the relationship between these variations and the genesis of gastric carcinoma.
METHODS: PCR amplified mitochondrial 12S rRNA of 44 samples including 22 from gastric carcinoma tissues and 22 from adjacent normal tissues, was detected by direct DNA sequencing. Then laser capture microdissection technique (LCM) was used to separate the cancerous cells and dysplasia cells with specific mutations. Denaturing high performance liquid chromatography (DHPLC) plus allele-specific PCR (AS-PCR), nest-PCR and polyacrylamide gel electrophoresis (PAGE) were used to further evaluate this mutant property and quantitative difference of mutant type between cancerous and dysplasia cells. Finally, RNAdraw biosoft was used to analyze the RNA secondary structure of mutant-type 12S rRNA.
RESULTS: Compared with Mitomap database, some new variations were found, among which np652 G insertion and np716 T-G transversion were found only in cancerous tissues. There was a statistic difference in the frequency of 12S rRNA variation between intestinal type (12/17, 70.59%) and diffusive type (5/17, 29.41%) of gastric carcinoma (P<0.05). DHPLC analysis showed that 12S rRNA np652 G insertion and np716 T-G transversion were heteroplasmic mutations. The frequency of 12S rRNA variation in cancerous cells was higher than that in dysplasia cells (P<0.01). 12S rRNA np652 G insertion showed obviously negative effects on the stability of 12S rRNA secondary structure, while others such as T-G transversion did not.
CONCLUSION: The mutations of mitochondrial 12S rRNA may be associated with the occurrence of intestinal-type gastric carcinoma. Most variations exist both in gastric carcinomas and in normal tissues, and they might not be the characteristics of tumors. However, np652 G insertion and np716 T-G transversion may possess some molecular significance in gastric carcinogenesis. During the process from normality to dysplasia, then to carcinoma, 12S rRNA tends to convert from homoplasmy (wild type) to heteroplasmy, then to homoplasmy (mutant type, np717 T-G).
Gastric carcinomas; Mitochondrial 12S rRNA; Variation
The purpose of this study was to analyze the bacterial diversity in persistent apical lesions on root-filled teeth by using culture-independent molecular methods.
Twenty surgically removed apical lesions from therapy-resistant teeth were examined for the presence of bacterial DNA using PCR targeting the 16s ribosomal RNA gene, followed by cloning and sequencing.
Bacterial DNA was detected in 17 of the 20 samples (85%). A total of 236 clones were analyzed. Seven different bacterial phyla were represented and a total of 75 different bacterial taxa were identified; 36% of the species have not yet been cultivated. Commonly detected bacterial species included Fusobacterium spp., Prevotella spp., Tannerella forsythia, Porphyromonas endodontalis, Treponema denticola, Bacteroidetes spp., Peptostreptococcus spp., and Streptococcus spp.
A wide range of bacteria was identified in periapical lesions on therapy-resistant teeth. These bacteria may contribute in the etiology of periapical infection and impede healing of these lesions.
bacterial phyla; endodontic infection; therapy-resistant teeth; 16s ribosomal RNA; sequencing
We have developed a duplex real-time PCR for the rapid diagnosis of Streptococcus pneumoniae infection from culture-negative clinical samples with the simultaneous determination of penicillin susceptibility. The assay amplifies a lytA gene target and a penicillin binding protein 2b (pbp2b) gene target in penicillin-susceptible organisms. The assay was shown to be sensitive (detects 0.5 CFU per PCR) and specific for the detection of S. pneumoniae DNA. The assay was validated by comparing pbp2b PCR results with MIC data for 27 S. pneumoniae isolates. All 5 isolates with penicillin MICs of >1.0 mg/liter were pbp2b real-time PCR negative, as were 9 of the 10 isolates with penicillin MICs of 0.12 to 1.0 mg/liter. One isolate with a penicillin MIC of 0.12 to 1.0 mg/liter gave an equivocal pbp2b real-time PCR result. Twelve isolates were penicillin susceptible (MICs of ≤0.06 mg/liter) and pbp2b real-time PCR positive. These data were used to establish an algorithm for the interpretation of penicillin susceptibility from the duplex PCR result. pbp2b real-time PCR results were also compared to an established PCR-restriction fragment length polymorphism (RFLP) method previously applied to these 27 isolates and 46 culture-negative clinical samples (containing S. pneumoniae DNA by broad-range 16S rRNA gene PCR). Discordant results were seen for four isolates and six culture-negative clinical samples, as PCR-RFLP could not reliably detect penicillin MICs of 0.12 to 1.0 mg/liter. We report prospective application of the duplex PCR assay to the diagnosis of S. pneumoniae infection from 200 culture-negative clinical specimens sent to the laboratory for diagnostic broad-range 16S rRNA gene PCR. One hundred six were negative in the duplex PCR. Ninety-four were lytA PCR positive, and 70 of these were also pbp2b PCR positive and interpreted as penicillin susceptible. Fourteen were pbp2b PCR negative and interpreted as having reduced susceptibility to penicillin. For the remaining 10 samples, susceptibility to penicillin was not determined.