Concurrence between the gene expression pattern of Actinobacillus actinomycetemcomitans in localized aggressive periodontitis and in human epithelial cells

Human Cytomegalovirus Enhances A. actinomycetemcomitans Adherence to Cells

Adherence of Actinobacillus actinomycetemcomitans to epithelial cells is an important step in periodontal disease pathogenesis. Recent publications describe the subgingival presence of a wide array of viruses [ e.g., human cytomegalo-virus (hCMV)]. Since viruses can increase cellular susceptibility for bacterial adherence, we investigated whether hCMV renders epithelial cells more prone to adherence by Actinobacillus actinomycetemcomitans. Cultivated HeLa and primary epithelial cells were shown to be semi-permissive for hCMV infection, which resulted in increased bacterial adherence. This increase correlated with viral concentrations, was evident in all Actinobacillus actinomycetemcomitans strains examined, and increased during the first 24 hrs, followed by a slight decrease. Immediate early antigen expression was not correlated with the increased adherence of Actinobacillus actinomycetemcomitans. The results confirmed our hypothesis that the adherence of Actinobacillus actinomycetemcomitans is influenced by hCMV in vitro.

Validation of Reference Genes for Real-Time Quantitative PCR (qPCR) Analysis of Avibacterium paragallinarum

Real-time quantitative reverse transcription PCR (qRT-PCR) offers a robust method for measurement of gene expression levels. Selection of reliable reference gene(s) for gene expression study is conducive to reduce variations derived from different amounts of RNA and cDNA, the efficiency of the reverse transcriptase or polymerase enzymes. Until now reference genes identified for other members of the family Pasteurellaceae have not been validated for Avibacterium paragallinarum. The aim of this study was to validate nine reference genes of serovars A, B, and C strains of A. paragallinarum in different growth phase by qRT-PCR. Three of the most widely used statistical algorithms, geNorm, NormFinder and ΔCT method were used to evaluate the expression stability of reference genes. Data analyzed by overall rankings showed that in exponential and stationary phase of serovar A, the most stable reference genes were gyrA and atpD respectively; in exponential and stationary phase of serovar B, the most stable reference genes were atpD and recN respectively; in exponential and stationary phase of serovar C, the most stable reference genes were rpoB and recN respectively. This study provides recommendations for stable endogenous control genes for use in further studies involving measurement of gene expression levels.

Bacteria Interfere with A. actinomycetemcomitans Colonization

It is known that beneficial bacteria can suppress the emergence of pathogenic bacteria, particularly in the gastrointestinal tract. This study examined the potential for a similar suppression of Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans colonization of epithelial cells, due to its potential relevance in periodontal diseases. Seven presumed beneficial bacteria were examined for their ability to interfere, exclude, or displace A. actinomycetemcomitans from epithelial cells in vitro. Streptococcus sanguinis, Streptococcus mitis, and Streptococcus salivarius showed prominent inhibitory effects on either A. actinomycetemcomitans recovery or colonization. These results confirmed the hypothesis that bacterial interactions interfere with A. actinomycetemcomitans colonization of epithelial cells in vitro, and demonstrated the potential beneficial effects of S. mitis, S. salivarius, and S. sanguinis.

Validation of reference genes for quantitative real-time PCR (qPCR) analysis of Actinobacillus suis

Background

Quantitative real-time PCR is a valuable tool for evaluating bacterial gene expression. However, in order to make best use of this method, endogenous reference genes for expression data normalisation must first be identified by carefully validating the stability of expression under experimental conditions. Therefore, the objective of this study was to validate eight reference genes of the opportunistic swine pathogen, Actinobacillus suis, grown in aerobic cultures with (Epinephrine) or without (Aerobic) epinephrine in the growth medium and in anoxic static cultures (Anoxic), and sampled during exponential and stationary phases.

Results

Using the RefFinder tool, expression data were analysed to determine whether comprehensive stability rankings of selected reference genes varied with experimental design. When comparing Aerobic and Epinephrine cultures by growth phase, pyk and rpoB were both among the most stably expressed genes, but when analysing both growth phases together, only pyk remained in the top three rankings. When comparing Aerobic and Anoxic samples, proS ranked among the most stable genes in exponential and stationary phase data sets as well as in combined rankings. When analysing the Aerobic, Epinephrine, and Anoxic samples together, only gyrA ranked consistently among the top three most stably expressed genes during exponential and stationary growth as well as in combined rankings; the rho gene ranked as least stably expressed gene in this data set.

Conclusions

Reference gene stability should be carefully assessed with the design of the experiment in mind. In this study, even the commonly used reference gene 16S rRNA demonstrated large variability in stability depending on the conditions studied and how the data were analysed. As previously suggested, the best approach may be to use a geometric mean of multiple genes to normalise qPCR results. As researchers continue to validate reference genes for various organisms in multiple growth conditions and sampling time points, it may be possible to make informed predictions as to which genes may be most suitable to validate for a given experimental design, but in the meantime, the reference genes used to normalise qPCR data should be selected with caution.

Differential transcription of virulence genes in Aggregatibacter actinomycetemcomitans serotypes

Background

Aggregatibacter actinomycetemcomitans serotypes are clearly associated with periodontitis or health, which suggests distinct strategies for survival within the host.

Objective

We investigated the transcription profile of virulence-associated genes in A. actinomycetemcomitans serotype b (JP2 and SUNY 465) strains associated with disease and serotype a (ATCC 29523) strain associated with health.

Design

Bacteria were co-cultured with immortalized gingival epithelial cells (OBA-9). The adhesion efficiency after 2 hours and the relative transcription of 13 genes were evaluated after 2 and 24 hours of interaction.

Results

All strains were able to adhere to OBA-9, and this contact induced transcription of pgA for polysaccharide biosynthesis in all tested strains. Genes encoding virulence factors as Omp29, Omp100, leukotoxin, and CagE (apoptotic protein) were more transcribed by serotype b strains than by serotype a. ltxA and omp29, encoding the leukotoxin and the highly antigenic Omp29, were induced in serotype b by interaction with epithelial cells. Factors related to colonization (aae, flp, apaH, and pgA) and cdtB were upregulated in serotype a strain after prolonged interaction with OBA-9.

Conclusion

Genes relevant for surface colonization and interaction with the immune system are regulated differently among the strains, which may help explaining their differences in association with disease.

Identification of Toxoplasma gondii in-vivo induced antigens by cDNA library immunoscreening with chronic toxoplasmosis sera

Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii. Chronically-infected individuals with a compromised immune system are at risk for reactivation of the disease. In-vivo induced antigen technology (IVIAT) is a promising method for the identification of antigens expressed in-vivo. The aim of the present study was to apply IVIAT to identify antigens which are expressed in-vivo during T. gondii infection using sera from individuals with chronic toxoplasmosis. Forty serum samples were pooled, pre-adsorped against three different preparations of antigens, from each in-vitro grown T. gondii and Escherichia coli XLBlue MRF', and then used to screen a T. gondii cDNA expression library. Sequencing of DNA inserts from positive clones showed eight open reading frames with high homology to T. gondii genes. Expression analysis using quantitative real-time PCR showed that SAG1-related sequence 3 (SRS3) and two hypothetical genes were up-regulated in-vivo relative to their expression levels in-vitro. These three proteins also showed high sensitivity and specificity when tested with individual serum samples. Five other proteins namely M16 domain peptidase, microneme protein, elongation factor 1-alpha, pre-mRNA-splicing factor and small nuclear ribonucleoprotein F had lower RNA expression in-vivo as compared to in-vitro. SRS3 and the two hypothetical proteins warrant further investigation into their roles in the pathogenesis of toxoplasmosis.

In vivo gene expression in Mannheimia haemolytica A1 during a time-course trial in the bovine host

The objective of this study is to examine the expression of Mannheimia haemolytica genes over time during the early stage of infection. In addition, gene expression at different sites of infection in the bovine host was examined. A time-course experiment was designed to collect pharyngeal swabs and lung washings from the same animals over two time points. Six calves were experimentally challenged with M. haemolytica A1; pharyngeal swabs were collected from all animals 5h post infection. Three calves were euthanized at 6h; pharyngeal swabs were collected from the remaining 3 calves at 12h and the calves were euthanized. Lung washings were recovered from all animals at necropsy. Total RNA was prepared from the pharyngeal swabs and lung washings and primers for eight well characterized virulence-associated genes were used in qRT-PCR to examine mRNA levels. The expression of key virulence genes such as lktA, gcp and tbpB was higher in vivo compared to in vitro with the highest changes observed from 6 to 12h. The expression of lktA and gapA increased while expression of fbpA, gs60, nmaA and tbpB was found to decreased over time in the 6h period. Gene expression profiles in the lungs versus the pharynx also differed, with most genes (fbpA, tbpB, nmaA, gs60, lktA and narP) showing higher expressing in lung washings. This is the first study to follow gene expression by M. haemolytica in the same animal over time during an infection.

Use of in vivo-induced antigen technology (IVIAT) to identify virulence factors of Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium associated with the initiation and progression of adult periodontal disease. The pathogenicity of P. gingivalis is multifaceted and the infection process is influenced by both microbial and host factors. It is generally accepted that genes of a pathogen that are specifically expressed during infection are likely to be important for pathogenicity. Numerous technologies have been developed to identify these genes. A novel strategy known as in vivo-induced antigen technology (IVIAT) avoids the use of animal models and utilizes serum from patients who have experienced disease caused by the pathogen of interest. While a number of putative virulence factors have been described for P. gingivalis, the identity, relevance, and mechanisms of action of virulence factors that actually provide a selective advantage to the organism in the oral cavity of diseased patients is still unclear. Here we describe the IVIAT protocol for identification of in vivo-induced genes of P. gingivalis, which can be adapted with few modifications to any microbial pathogen.

Identification and characterization of antigenic proteins potentially expressed during the infectious process of Paracoccidioides brasiliensis

Paracoccidioides brasiliensis causes paracoccidioidomycosis (PCM), a systemic mycosis presenting clinical manifestations ranging from mild to severe forms. A P. brasiliensis cDNA expression library was produced and screened with pooled sera from PCM patients adsorbed against antigens derived from in vitro-grown P. brasiliensis yeast cells. Sequencing DNA inserts from clones reactive with PCM patients sera indicated 35 open reading frames presenting homology to genes involved in metabolic pathways, transport, among other predicted functions. The complete cDNAs encoding aromatic-l-amino-acid decarboxylase (Pbddc), lumazine synthase (Pbls) and a homologue of the high affinity copper transporter (Pbctr3) were obtained. Recombinant proteins PbDDC and PbLS were obtained; a peptide was synthesized for PbCTR3. The proteins and the synthetic peptide were recognized by sera of patients with confirmed PCM and not by sera of healthy patients. Using the in vivo-induced antigen technology (IVIAT), we identified immunogenic proteins expressed at high levels during infection. Quantitative real time RT-PCR demonstrated high transcript levels of Pbddc, Pbls and Pbctr3 in yeast cells infecting macrophages. Transcripts in yeast cells derived from spleen and liver of infected mice were also measured by qRT-PCR. Our results suggest a putative role for the immunogenic proteins in the infectious process of P. brasiliensis.

Oral bacteria modulate invasion and induction of apoptosis in HEp-2 cells by Pseudomonas aeruginosa

Pseudomonas aeruginosa is an important opportunistic bacterial pathogen, causing infections of the respiratory and other organ systems in susceptible hosts. P. aeruginosa infection is initiated by adhesion to and invasion of mucosal epithelial cells. The failure of host defenses to eliminate P. aeruginosa from mucosal surfaces results in P. aeruginosa proliferation, sometimes followed by overt infection and tissue destruction. There is growing evidence that associates poor oral health and respiratory infection. An in vitro model system for bacterial invasion of respiratory epithelial cells was used to investigate the influence of oral bacteria on P. aeruginosa epithelial cell invasion. Oral pathogens including Porphyromonas gingivalis, Fusobacterium nucleatum and Aggregatibacter (Actinobacillus) actinomycetemcomitans increased invasion of P. aeruginosa into HEp-2 cells from one- to threefold. In contrast, non-pathogenic oral bacteria such as Actinomyces naeslundii and Streptococcus gordonii showed no significant influence on P. aeruginosa invasion. P. aeruginosa together with oral bacteria stimulated greater cytokine production from HEp-2 cells than did P. aeruginosa alone. P. aeruginosa in combination with periodontal pathogens also increased apoptosis of HEp-2 cells and induced elevated caspase-3 activity. These results suggest that oral bacteria, especially periodontal pathogens, may foster P. aeruginosa invasion into respiratory epithelial cells to enhance host cell cytokine release and apoptosis.

Effects of prolonged exposure to alkaline pH on Enterococcus faecalis survival and specific gene transcripts

INTRODUCTION

The persistence of Enterococcus faecalis in treated root canals has been attributed to its resistance to the high pH of antimicrobial agents used during treatment, but the specific mechanisms are not clear. We investigated the survival and gene expression of E. faecalis maintained in alkaline media.

METHODS

E. faecalis JH2-2 was maintained in media at pH 7, 10, 11 and 12 at either 25 degrees C or 37 degrees C for 1 week (168 h). At 24, 48, 72, 120 and 168 h, cell viability was determined in parallel with real-time quantitative polymerase chain reaction analyses of stress response genes (dnaK, fba, ftsZ, GroEL, napA, pbp5, tsf and tuf).

RESULTS

After 1 week the E. faecalis showed survival levels of 100% in pH 7, 1% in pH 10, 0.001% in pH 11 and 0.00001% in pH 12 media. At 37 degrees C increased levels of gene transcripts occurred between 72 and 120 h in pH 7 media for ftsZ and dnaK, and in pH 10 media for ftsZ, pbp5, dnaK, napA, tsf, fba and GroEL. No increase in transcripts was observed at 37 degrees C in media at pH 11 or pH 12, nor at 25 degrees C in any media.

CONCLUSION

Transcripts of ftsZ, a gene involved in cell division, increased by 37-fold after 120 h at pH 10 at 37 degrees C. Overall, the greatest increase in levels of gene transcripts occurred in cultures maintained in pH 10 media at 37 degrees C. These data may assist in understanding the survival strategies of E. faecalis following prolonged exposure to alkaline pH levels.

Regulation of Aggregatibacter (Actinobacillus) actinomycetemcomitans leukotoxin secretion by iron

The gram-negative oral and systemic pathogen Aggregatibacter (Actinobacillus) actinomycetemcomitans produces a leukotoxin (LtxA) that is a member of the RTX (repeats in toxin) family of secreted bacterial toxins. We have recently shown that LtxA has the ability to lyse erythrocytes, which results in a beta-hemolytic phenotype on Columbia blood agar. To determine if LtxA is regulated by iron, we examined beta-hemolysis under iron-rich and iron-limiting conditions. Beta-hemolysis was suppressed in the presence of FeCl3. In contrast, strong beta-hemolysis occurred in the presence of the iron chelator deferoxamine. We found that secretion of LtxA was completely inhibited by free iron, but expression of ltxA was not regulated by iron. Free chromium, cobalt, and magnesium did not affect LtxA secretion. Other LtxA-associated genes were not regulated by iron. Thus, iron appears to play an important role in the regulation of LtxA secretion in A. actinomycetemcomitans in a manner independent of gene regulation.

Distinctive characteristics of transcriptional profiles from two epithelial cell lines upon interaction with Actinobacillus actinomycetemcomitans

Transcriptional profiling and gene ontology analyses were performed to investigate the unique responses of two different epithelial cell lines to an Actinobacillus actinomycetemcomitans challenge. A total of 2867 genes were differentially regulated among all experimental conditions. The analysis of these 2867 genes revealed that the predominant specific response to infection in HeLa cells was associated with the regulation of enzyme activity, RNA metabolism, nucleoside and nucleic acid transport and protein modification. The predominant specific response in immortalized human gingival keratinocytes (IHGK) was associated with the regulation of angiogenesis, chemotaxis, transmembrane receptor protein tyrosine kinase signaling, cell differentiation, apoptosis and response to stress. Of particular interest, stress response genes were significantly - yet differently - affected in both cell lines. In HeLa cells, only three regulated genes impacted the response to stress, and the response to unfolded protein was the only term that passed the ontology filters. This strikingly contrasted with the profiles obtained for IHGK, in which 61 regulated genes impacted the response to stress and constituted an extensive network of cell responses to A. actinomycetemcomitans interaction (response to pathogens, oxidative stress, unfolded proteins, DNA damage, starvation and wounding). Hence, while extensive similarities were found in the transcriptional profiles of these two epithelial cell lines, significant differences were highlighted. These differences were predominantly found in pathways that are associated with host-pathogen interactions.

Fusobacterium nucleatum transports noninvasive Streptococcus cristatus into human epithelial cells

Analysis of human buccal epithelial cells frequently reveals an intracellular polymicrobial consortium of bacteria. Although several oral bacteria have been demonstrated to invade cultured epithelial cells, several others appear unable to internalize. We hypothesized that normally noninvasive bacteria may gain entry into epithelial cells via adhesion to invasive bacteria. Fusobacterium nucleatum is capable of binding to and invading oral epithelial cells. By contrast, Streptococcus cristatus binds weakly to host cells and is not internalized. F. nucleatum and S. cristatus coaggregate strongly via an arginine-sensitive interaction. Coincubation of KB or TERT-2 epithelial cells with equal numbers of F. nucleatum and S. cristatus bacteria led to significantly increased numbers of adherent and internalized streptococci. F. nucleatum also promoted invasion of KB cells by other oral streptococci and Actinomyces naeslundii. Dissection of fusobacterial or streptococcal adhesive interactions by using sugars, amino acids, or antibodies demonstrated that this phenomenon is due to direct attachment of S. cristatus to adherent and invading F. nucleatum. Inhibition of F. nucleatum host cell attachment and invasion with galactose, or fusobacterial-streptococcal coaggregation by the arginine homologue l-canavanine, abrogated the increased S. cristatus adhesion to, and invasion of, host cells. In addition, polyclonal antibodies to F. nucleatum, which inhibited fusobacterial attachment to both KB cells and S. cristatus, significantly decreased invasion by both species. Similar decreases were obtained when epithelial cells were pretreated with cytochalasin D, staurosporine, or cycloheximide. These studies indicate that F. nucleatum may facilitate the colonization of epithelial cells by bacteria unable to adhere or invade directly.

Distinct transcriptional profiles characterize oral epithelium-microbiota interactions

Transcriptional profiling, bioinformatics, statistical and ontology tools were used to uncover and dissect genes and pathways of human gingival epithelial cells that are modulated upon interaction with the periodontal pathogens Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. Consistent with their biological and clinical differences, the common core transcriptional response of epithelial cells to both organisms was very limited, and organism-specific responses predominated. A large number of differentially regulated genes linked to the P53 apoptotic network were found with both organisms, which was consistent with the pro-apoptotic phenotype observed with A. actinomycetemcomitans and anti-apoptotic phenotype of P. gingivalis. Furthermore, with A. actinomycetemcomitans, the induction of apoptosis did not appear to be Fas- or TNF(alpha)-mediated. Linkage of specific bacterial components to host pathways and networks provided additional insight into the pathogenic process. Comparison of the transcriptional responses of epithelial cells challenged with parental P. gingivalis or with a mutant of P. gingivalis deficient in production of major fimbriae, which are required for optimal invasion, showed major expression differences that reverberated throughout the host cell transcriptome. In contrast, gene ORF859 in A. actinomycetemcomitans, which may play a role in intracellular homeostasis, had a more subtle effect on the transcriptome. These studies help unravel the complex and dynamic interactions between host epithelial cells and endogenous bacteria that can cause opportunistic infections.