Identification of the pangenome and its components in 14 distinct Aggregatibacter actinomycetemcomitans strains by comparative genomic analysis

Background

Aggregatibacter actinomycetemcomitans is genetically heterogeneous and comprises distinct clonal lineages that may have different virulence potentials. However, limited information of the strain-to-strain genomic variations is available.

Methodology/Principal Findings

The genome sequences of 11 A. actinomycetemcomitans strains (serotypes a-f) were generated de novo, annotated and combined with three previously sequenced genomes (serotypes a-c) for comparative genomic analysis. Two major groups were identified; serotypes a, d, e, and f, and serotypes b and c. A serotype e strain was found to be distinct from both groups. The size of the pangenome was 3,301 genes, which included 2,034 core genes and 1,267 flexible genes. The number of core genes is estimated to stabilize at 2,060, while the size of the pangenome is estimated to increase by 16 genes with every additional strain sequenced in the future. Within each strain 16.7–29.4% of the genome belonged to the flexible gene pool. Between any two strains 0.4–19.5% of the genomes were different. The genomic differences were occasionally greater for strains of the same serotypes than strains of different serotypes. Furthermore, 171 genomic islands were identified. Cumulatively, 777 strain-specific genes were found on these islands and represented 61% of the flexible gene pool.

Conclusions/Significance

Substantial genomic differences were detected among A. actinomycetemcomitans strains. Genomic islands account for more than half of the flexible genes. The phenotype and virulence of A. actinomycetemcomitans may not be defined by any single strain. Moreover, the genomic variation within each clonal lineage of A. actinomycetemcomitans (as defined by serotype grouping) may be greater than between clonal lineages. The large genomic data set in this study will be useful to further examine the molecular basis of variable virulence among A. actinomycetemcomitans strains.

Modulation of gene expression in Actinobacillus pleuropneumoniae exposed to bronchoalveolar fluid

BACKGROUND

Actinobacillus pleuropneumoniae, the causative agent of porcine contagious pleuropneumonia, is an important pathogen of swine throughout the world. It must rapidly overcome the innate pulmonary immune defenses of the pig to cause disease. To better understand this process, the objective of this study was to identify genes that are differentially expressed in a medium that mimics the lung environment early in the infection process.

METHODS AND PRINCIPAL FINDINGS

Since bronchoalveolar lavage fluid (BALF) contains innate immune and other components found in the lungs, we examined gene expression of a virulent serovar 1 strain of A. pleuropneumoniae after a 30 min exposure to BALF, using DNA microarrays and real-time PCR. The functional classes of genes found to be up-regulated most often in BALF were those encoding proteins involved in energy metabolism, especially anaerobic metabolism, and in cell envelope, DNA, and protein biosynthesis. Transcription of a number of known virulence genes including apxIVA and the gene for SapF, a protein which is involved in resistance to antimicrobial peptides, was also up-regulated in BALF. Seventy-nine percent of the genes that were up-regulated in BALF encoded a known protein product, and of these, 44% had been reported to be either expressed in vivo and/or involved in virulence.

CONCLUSIONS

The results of this study suggest that in early stages of infection, A. pleuropneumoniae may modulate expression of genes involved in anaerobic energy generation and in the synthesis of proteins involved in cell wall biogenesis, as well as established virulence factors. Given that many of these genes are thought to be expressed in vivo or involved in virulence, incubation in BALF appears, at least partially, to simulate in vivo conditions and may provide a useful medium for the discovery of novel vaccine or therapeutic targets.

Granulomatous Lymphadenitis and Pneumonia Associated with Actinobacillus porcitonsillarum in a Slaughter Pig

Multiple coalescing granulomatous foci were detected in the pulmonary hilar and mediastinal lymph nodes and lung of a slaughtered pig aged 6 months. Haemolytic, Gram-negative bacilli were isolated from the lymph nodes. The isolate (strain TO17214) strongly cross-reacted with sera against Actinobacillus pleuropneumoniae serotype 12 in slide agglutination tests. Comparative 16S rDNA gene sequencing analysis identified strain TO17214 as Actinobacillus porcitonsillarum. Histologically, extensive inflammation took the form of large granulomas consisting of epithelioid cells and multinucleated giant cells in the lymph nodes and lung, and Gram-negative bacilli were discernible in the centres of the lesions. Immunohistochemically, the organisms cross-reacted with polyclonal antibodies against A. pleuropneumoniae serotypes 12 and 2. The results indicated that A. porcitonsillarum, previously considered non-pathogenic, can induce multifocal granulomatous lymphadenitis accompanied by pneumonia in the growing-finishing pig.

Non-pathogenic Actinobacillus isolates antigenically and biochemically similar to Actinobacillus pleuropneumoniae: a novel species?

Two unusual Actinobacillus isolates were recovered from pigs with no clinical signs, no lesions and no history of swine pleuropneumonia. Two representative strains (9953L55 and 0347) analyzed in this study were initially biochemically and antigenically identified as A. pleuropneumoniae serotypes 1 and 9, respectively, by traditional identification methods. Both strains presented, however, negative results with three A. pleuropneumoniae-specific PCR tests and revealed in particular the absence of the apxIV toxin genes. However, both strains produced and secreted ApxII toxin although they only harbored the toxin genes apxIICA, which is an uncommon feature for any of the known A. pleuropneumoniae serotypes. Upon experimental inoculation of pigs, these strains proved to be totally non-pathogenic. Animals infected with one of the strains produced antibodies that cross-react with A. pleuropneumoniae serotypes 1-9-11-specific LC-LPS ELISA. Phylogenetic analysis based on 16S rRNA gene sequence analysis revealed that these strains form a separate phylogenetic group that is distinct from other Actinobacillus species and is particularly different from A. pleuropneumoniae.

Host cell specific activity of RTX toxins from haemolytic Actinobacillus equuli and Actinobacillus suis

We assessed and compared host cell specificity of the haemolytic and cytotoxic activity of the RTX toxins from Actinobacillus equuli, an equine pathogen, and Actinobacillus suis, which is pathogenic for pigs. The two bacterial species are closely related, phenotypically as well as phylogenetically, sharing the same 16S rRNA gene sequence. Both species contain specific protein toxins from the family of pore-forming RTX toxins, however, the two species differ in their RTX toxin profiles. Haemolytic A. equuli contains the operon for the Aqx toxin, whereas A. suis harbours genes for ApxI and ApxII. We tested the toxic activity of the corresponding proteins on erythrocytes as well as on lymphocytes isolated from horse and pig blood. The strength of the haemolytic activity for each of the toxins was independent of the origin of erythrocytes. When testing cytotoxic activity, the Aqx protein showed a higher toxic effect for horse lymphocytes than for porcine lymphocytes. On the other hand, ApxI and ApxII showed a strong cytotoxic effect on porcine lymphocytes and a reduced toxicity for horse lymphocytes; the toxicity of ApxII was generally much lower than ApxI. Our results indicate a host species specificity of the toxic activity of RTX toxins Aqx of A. equuli and ApxI and ApxII of A. suis.

Bacterial heat shock protein-60 increases epithelial cell proliferation through the ERK1/2 MAP kinases

Heat shock proteins (hsp) have important roles in the regulation and protection of both prokaryotic and eukaryotic cells, especially during environmental stress. Hsps are also important bacterial virulence factors. We investigated whether bacterial hsp60 can alter epithelial cell mitogen-activated protein kinase (MAPK) signaling and cell proliferation. Human skin keratinocytes (HaCaT cell line) were cultured in the presence of hsp60 purified from Actinobacillus actinomycetemcomitans, an important oral pathogen. Protein kinases in the ERK1/2 and p38 MAPK signaling pathways were probed with kinase-specific and phosphorylation-site-specific antibodies on Western blots. In quiescent cultures, hsp60 increased ERK1/2 phosphorylation in a sustained manner and p38 phosphorylation transiently. Hsp60 also increased epithelial cell proliferation by about 30%. Inhibition of the ERK1/2 pathway by PD 98059 (a MEK1 inhibitor) reversed partially ERK1/2 phosphorylation and totally cell proliferation indicating that the ERK1/2 MAPK pathway is involved in the hsp60-induced cell growth. This was supported by findings that hsp60 stimulated phosphorylation of RSK1/2 and cyclic AMP response element-binding protein and increased expression of transcription factors c-Jun and c-Fos. Recombinant human hsp60 did not alter ERK1/2 or p38 phosphorylation and had no effect on epithelial cell proliferation. Inhibition of p38 MAPK pathway by SB 203580 increased both ERK1/2 phosphorylation and cell proliferation demonstrating that the inhibitor can either directly or indirectly activate the ERK1/2 MAPK pathway. The results show that exogenous bacterial hsp60 is able to activate ERK1/2 phosphorylation and thereby cause increased epithelial proliferation. In case of mucosal infection this effect may either lead to increased wound repair or participate in the pathological mechanism of some bacterial diseases that involve increased epithelial proliferation.

Virulence properties of oral bacteria: impact of molecular biology

Dental caries and periodontitis, although generally not life threatening, are nevertheless of significant importance. An understanding of the molecular nature of these diseases could aid the development of novel methods of prevention and control, and increase our knowledge of their etiology. The identification of virulence factors in oral bacteria could lead to the development of vaccines directed against these organisms, the design of inhibitors of biofilm formation, and the development of replacement therapy strategies.

Pathogenicity of Actinobacillus minor, Actinobacillus indolicus and Actinobacillus porcinus strains for gnotobiotic piglets

The purpose of the study was to evaluate the clinical significance of Actinobacillus minor, Actinobacillus porcinus and Actinobacillus indolicus strains in gnotobiotic piglets. Twenty-two 6-h-old Caesarean-delivered and colostrum-deprived piglets were intranasally and orally inoculated with 2 x 10(6) colony-forming units of an A. minor (group 2; n = 9), A. indolicus (group 3; n = 5), or A. porcinus (group 4; n = 8) strain. Six other piglets were inoculated in the same way with phosphate-buffered saline solution and used as controls (group 1). All pigs were observed for clinical signs and rectal temperatures were taken until euthanasia 7 days after inoculation. At necropsy, conchae, tonsils, lungs, brains, liver, spleen and kidneys were macroscopically examined for lesions and samples were taken for bacteriology. None of the pigs developed fever. Mild ataxia was observed in one pig from group 3 for 2 days. Clinical signs were not observed in the other animals. In none of the animals were macroscopic lesions detected at necropsy. NAD-dependent Pasteurellaceae were not isolated from control animals (group 1). The A. minor, A. indolicus and A. porcinus strains were isolated from the tonsils of one, two and one pigs, respectively. Actinobacillus porcinus was isolated from the brains of the pig with central nervous symptoms and from the conchae of another pig. The inoculation strains were not demonstrated in the other samples. It was concluded that, using these inoculation routes and dose, the A. minor, A. indolicus and A. porcinus strains had low capacity to colonize the upper respiratory tract of gnotobiotic piglets and demonstrated low or no pathogenicity in such animals.

Comparative pathogenicity of different Actinobacillus suis O/K serotypes

The pathogenicity of Actinobacillus suis serotypes O1/K1 (strain SO4), O1/K2 (strain C84), and O2/K2 (strain H91-0380) was evaluated in specific-pathogen-free (SPF) piglets challenged by intraperitoneal inoculation with approximately 1 x 10(7) colony-forming units per mL. All 3 strains produced peritonitis, but differences were observed in the composite histopathologic scores (P = 0.001) and in their ability to spread (P = 0.008) at 7 h post challenge. The O2/K2 strain caused the most severe peritonitis and disseminated most widely to other tissues. Moderate lesions were seen with the O1/K2 strain while the O1/K1 strain caused mild lesions and remained largely localized to the peritoneum. In an attempt to explain the basis of observed differences, the serum sensitivity of 9 A. suis strains with different O and K types was assessed. Regardless of the O/K type, all of the isolates tested were serum resistant. Moreover, most A. suis isolates grew as well or better in complement-replete sera as they did in complement-depleted sera. These observations indicate that although 02 and K2 strains had a greater propensity to cause a disseminating septic inflammatory response in pigs, they were no more resistant to complement-mediated killing than O1 strains.

Actinobacillus species and their role in animal disease

Actinobacillus species are Gram-negative bacteria responsible for several quite distinct disease conditions of animals. The natural habitat of the organisms is primarily the upper respiratory tract and oral cavity. A. lignieresii is the cause of actinomycosis (wooden tongue) in cattle: a sporadic, insidiously-developing granulomatous infection. In sharp contrast is A. pleuropneumoniae which is responsible for a rapidly spreading often fatal pneumonia, common among intensively reared pigs. Detailed investigation of this organism has provided a much clearer picture of the bacterial factors involved in causing disease. A. equuli similarly causes a potent septicaemia in the neonatal foal; growing apparently unrestricted once infection occurs. Other members of the genus induce characteristic pathogenesis in their preferred host, with one, A. actinomycetemcomitans, being a cause of human periodontal disease. This article reviews recent understanding of the taxonomy and bacteriology of the organisms, and the aetiology, pathogenicity, diagnosis and control of animal disease caused by Actinobacillus species.

Effects of Actinobacillus equuli culture supernatants on equine neutrophil functions and survival

After exposure of equine granulocytes from both foals and adult horses to culture supernatants from clinical isolates of Actinobacillus equuli, phagocytic capacity and respiratory burst was examined by flow-cytometry and a chemiluminescence assay, respectively. One haemolytic isolate of an equine Actinobacillus was also included in the study. An average decrease of 22% in total number of granulocytes, in the flow cytometric assay (P < 0.01), and an average decrease of 26% in light emission, in the chemiluminescence assay (P < 0.001), was seen after exposure to bacterial culture supernatants of A. equuli, indicating that the supernatants contained leukotoxic bacterial products. Supernatants from the haemolytic isolate appeared to contain a higher amount or more potent leukotoxic metabolites when haemolysis was expressed, causing a decrease in total number of granulocytes of 44% (P < 0.01) and a decrease in light emission of 52% (P < 0.01). Evaluation of the stability of the methods used revealed that within-method variation was far less than the observed results. The leukotoxic effects of A. equuli culture supernatants were mainly reflected in the decreased survival of neutrophils and not in neutrophil functions.

Oral pathogens: from dental plaque to cardiac disease

Oral bacteria exhibit highly specific adherence mechanisms and as a result they colonize and cause disease principally in the oral cavity. Oral pathogens, however, can produce systemic disease and are known causative agents of infective endocarditis. Recent studies have revealed that periodontal disease per se is also a statistically significant risk factor for cardiovascular disease. A link between the two diseases is the secretion and systemic appearance in periodontitis of pro-inflammatory cytokines capable of eliciting effects associated with atherosclerosis and coronary heart disease.

Taxonomy and identification of periodontopathogenic bacteria and related species

The tumultuous evolution of oral and periodontal microbiology has focussed the attention of many researchers on the necessity to clarify the taxonomic position and identification criteria of putative periodontopathogens, in order to elucidate the role played by each species in the pathogenesis of periodontal disease. Many of the most important periodontopathogens recently underwent a radical reclassification process that may create some confusion and certainly deserves an accurate analysis aimed at focussing the actual situation of these bacteria. The taxonomic evolution and identification criteria of species of the genera Bacteroides, Prevotella, Porphyromonas and Actinobacillus is here analyzed in detail to clarify this recent evolutive taxonomic process, and to explain the importance of molecular studies for both taxonomic and identification purposes in this field.

Production of Apx toxins by field strains of Actinobacillus pleuropneumoniae and Actinobacillus suis

The three Apx toxins of Actinobacillus pleuropneumoniae have potential value for use in vaccines and diagnostic tests which will be species specific instead of serotype specific, provided that the Apx toxins are species specific and all field strains produce these toxins. We examined 114 A. pleuropneumoniae field strains and found that they secreted either ApxI, ApxII, ApxI and ApxII, or ApxII and ApxIII and secreted no other cytolytic activities. However, proteins similar to ApxI and ApxII were also produced by Actinobacillus suis.

Ecology and significance of Pasteurellaceae in man--an update

Within the last decade new knowledge has emerged concerning the significance of Pasteurellaceae in man; the classification has undergone some changes, and new taxa were described. Haemophilus influenzae serotype b was shown to have a clonal distribution that is related to demographic patterns of the human host. Brazilian purpuric fever is caused by a special clone of Haemophilus aegyptius. H. influenzae biotype IV seems to be a genital pathogen, and may deserve species rank. New Pasteurella species have been described, that occur in well known pathological foci in man, e.g. bite wounds. Toxigenic P. multocida may occur in man also; the significance of toxigenicity in man is not known. The real actinobacilli of man, A. ureae and A. hominis are still very rarely reported. In order to avoid wrong epidemiological conclusions, correct diagnosis is emphasized.

Ecology and significance of Pasteurellaceae in animals

The reservoir of eighty-one taxa/groups classified with the family Pasteurellaceae Pohl 1981 is reviewed based upon published data and own investigations. With the exception of certain strains of P. multocida, A. pleuropneumoniae and [H.] paragallinarum organisms belonging to this family are usually regarded as opportunistic, secondary invaders which under normal conditions coexist peacefully with the animal host on mucosal membranes of the upper respiratory- and lower genital tracts. Very little is known about factors that govern the ecological preferences that certain members of this family show for specific surfaces and hosts. Mechanisms of colonization, survival and multiplication, invasion and pathogenic action are incompletely understood. The significance of Pasteurellaceae in animals and man has recently been reviewed. Subsequent publications have underlined the significance of biovars 2 of P. canis and P. avium and ornithine negative P. multocida in pneumonia in cattle. In addition, differences in pathogenicity have been demonstrated for different serovars of [H.] parasuis. The disease potential of many taxa/groups is only incompletely known.

Actinobacillus spp. and related bacteria in infected wounds of humans bitten by horses and sheep

We describe the isolation of Actinobacillus lignieresii and an A. equuli-like bacterium from an infected horse-bite wound in a 22-year-old stable foreman and A. suis from a bite injury in a 35-year-old man who had been attacked by a horse. A. lignieresii was also isolated in pure culture from an infected sheep-bite wound in a rural worker. These species of the genus Actinobacillus are primarily associated with animals and animal diseases and are rarely isolated from humans. The purpose of this report is to raise awareness of the possible occurrence of Actinobacillus spp. in bite wounds inflicted by farm animals and to discuss the difficulties encountered in the identification of species of Actinobacillus and related bacteria.

Actinobacillus pleuropneumoniae-induced thymic lesions in mice and pigs

Actinobacillus pleuropneumoniae produces several hemolysins/cytotoxins that may be important in the pathogenesis of acute lesions. Little is known, however, about the role of these virulence factors in chronic disease or the carrier state. We investigated the effects of live bacterial infection and transthoracic injection of a sterile culture supernatant on primary lymphoid organs and lymphocyte populations. Transthoracic inoculation of mice or intranasal inoculation of pigs with virulent A. pleuropneumoniae serotypes 1 and 7 induced thymic cortical lymphoid necrosis. These lesions were reproduced in mice by transthoracic injection of a concentrated sterile culture supernatant. The cytotoxic effect of this culture supernatant was also demonstrated in vitro by using a tetrazolium dye reduction assay. Both porcine and murine thymic lymphocytes as well as splenic T lymphocytes were susceptible to the toxin. Porcine convalescent serum, but not preimmune serum, prevented thymic lesions and neutralized the in vitro cytotoxic effect of the culture supernatant on murine thymic lymphocytes. Thymic lesions also were reproduced in mice by using purified lipopolysaccharide (LPS) from Escherichia coli O111:B4; however, LPS had no in vitro cytotoxic effect on either porcine or murine thymic lymphocytes. These results suggest that secreted A. pleuropneumoniae toxin(s) is capable of affecting host T-lymphocyte populations and may affect host immune function.

Evidence for invasion of a human oral cell line by Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans, an oral bacterial species associated with periodontal disease, was found to invade human cell lines. Invasion was demonstrated by recovery of viable organisms from gentamicin-treated KB cell monolayers and by light and electron microscopy. Internalization occurred through a cytochalasin D-sensitive process. Invasion efficiencies of some A. actinomycetemcomitans strains were comparable to those of invasive members of the family Enterobacteriaceae. Differences in invasiveness were correlated with bacterial colonial morphology. Smooth variants invaded more proficiently than rough variants. A. actinomycetemcomitans can undergo a smooth-to-rough colonial morphology shift which results in the loss of invasiveness. Coordinated regulation of genes involved in the rough-to-smooth phenotypic transitions may play a role in the episodic nature of periodontal disease.

Immunological properties of Actinobacillus pleuropneumoniae hemolysin I

The 105 kDa hemolysin I protein from Actinobacillus pleuropneumoniae serotype I type strain 4074 (HlyI) was shown by immunoblot analysis to be the predominant immunogenic protein if convalescent field sera or sera from pigs experimentally infected with A. pleuropneumoniae serotype 1 were used. SDS gel- and immunoblot-analysis using total culture, washed cells or culture supernatant showed that HlyI is essentially secreted and is not found attached to the bacteria. Proteins in the 105 kDa range that react strongly with anti-HlyI antibody, are produced by all serotypes and are presumed to be their hemolysins. Sera from pigs experimentally infected with each of the 12 serotypes strongly reacted with HlyI. In addition, some sera from pigs that were confirmed to be negative for A. pleuropneumoniae, also reacted with HlyI as well as with related proteins from Actinobacillus rossii and Actinobacillus suis. These two species produce proteins in the 105 kDa range which cross-react strongly with HlyI. They could be the source of the immunological reactions of the A. pleuropneumoniae-negative sera with HlyI. However, no cross-reactions could be found between HlyI and the Pasteurella haemolytica leukotoxin, the Escherichia coli alpha-hemolysin or related proteins from various hemolytic E. coli strains isolated from pigs. The immunological cross-reactions of HlyI with related proteins from A. rossii, A. suis and possibly from other bacterial species may create uncertainty in interpretation if HlyI is used as the antigen in serodiagnosis of A. pleuropneumoniae.

Characterization of a non-hemolytic mutant of Actinobacillus pleuropneumoniae serotype 5: role of the 110 kilodalton hemolysin in virulence and immunoprotection

To determine the role of hemolysin(s) in virulence and immunoprotection, non-hemolytic mutants of Actinobacillus pleuropneumoniae serotype 5, strain J45, were isolated following chemical mutagenesis. One mutant was selected for extensive characterization. Differences in capsule content, or in lipopolysaccharide or membrane protein electrophoretic profiles of the parent and mutant were not detected. A predominant, calcium-inducible protein of 110 kDa was present in culture supernatant of the parent, but absent from the mutant. Two-dimensional (2-D) gel electrophoresis confirmed that the 110 kDa protein was absent in culture supernatant of the mutant, but few, if any, minor differences could be detected in whole-cell proteins between the parent and mutant. The mutant totally lacked extracellular hemolytic and cytotoxic activity. Lysates of whole cells of the mutant contained weak hemolytic activity, and the 110 kDa protein could be detected by immunoblotting. Neutralization titers were negative in pigs immunized with the mutant or purified, denatured hemolysin, although enzyme-immunoassay titers were detected. Four additional independently isolated non-hemolytic mutants were avirulent in pigs and mice at doses greater than 10 times the lethal dose of the parent. Neither pigs nor mice were protected against lethal infection following immunization with the non-hemolytic mutant. We conclude that the 110 kDa hemolysin plays an important role in bacterial virulence and the pathogenesis of pleuropneumonia, and that sufficiently high levels of neutralizing antibodies to the 110 kDa hemolysin may be required for protection of pigs against disease.

Regulation of leukotoxin in leukotoxic and nonleukotoxic strains of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is a gram-negative bacterium that has been implicated in the etiology of several forms of periodontitis, especially localized juvenile periodontitis. A potent leukotoxin (Lkt) is produced by most A. actinomycetemcomitans isolates from patients with periodontal disease, but some isolates are leukotoxin nonproducing (Lkt-). The molecular bases for the differences in leukotoxin expression are being explored to clarify the role of leukotoxin in pathogenesis. We have previously cloned the leukotoxin structural gene, lktA, from the leukotoxin-producing (Lkt+) strain JP2 and have shown that it is linked to three other genes, lktB, lktC, and lktD, whose gene products are thought to be required for activation and localization of the leukotoxin. These genes have now been used in Southern blot analysis to demonstrate that Lkt- strains, like Lkt+ strains, contain all four genes of the lkt gene cluster. While restriction fragment length polymorphisms were detected, they did not correlate with toxin phenotype. RNA blot analysis demonstrated that Lkt+ strains produced two transcripts, one 9.3 kb in length and the other 4.3 kb. They encode lktCABD and lktCA. respectively. Lkt- strains contained significantly lower levels of the 4.3-kb transcript with no discernible 9.3-kb message. The leukotoxic activity of the A. actinomycetemcomitans strains, measured by chromium release assays, correlated with the lkt RNA content. Therefore, a major component of leukotoxin regulation is at the level of RNA transcription or stability. Interestingly, the lkt RNAs in JP2 are regulated during growth phase, being greatly reduced in cells approaching stationary phase. Thus, the regulation of lkt RNA can be affected by both genotype and environment.

The cytotoxin of Actinobacillus pleuropneumoniae (pleurotoxin) is distinct from the haemolysin and is associated with a 120 kDa polypeptide

Mutants of Actinobacillus pleuropneumoniae strain HK 361 (serotype 2) were isolated which were deficient in type II (Ca2(+)-dependent) haemolysin activity (Hly-). Some of the Hly- mutants secreted a potent, heat-labile extracellular cytotoxic activity against porcine alveolar macrophages. Comparison of cell-free culture supernatant from the parent strain and some Hly- mutants by SDS-PAGE and immunoblotting revealed the loss of a major extracellular polypeptide of 109 kDa. Two Hly- mutants which in addition failed to secrete a 120 kDa polypeptide produced no extracellular cytotoxic activity, suggesting that the 120 kDa protein was the cytotoxin. Antiserum raised to the culture supernatant from a Hly- mutant lacking the 109 kDa polypeptide recognized the 120 kDa band, but not the 109 kDa band, in immunoblots and neutralized the cytotoxic activity, but not the haemolytic activity, of A. pleuropneumoniae. The 120 kDa polypeptide and extracellular cytotoxic activity were widespread among A. pleuropneumoniae strains, but absent from related bacterial pathogens of the pig: Actinobacillus suis, Haemophilus parasuis and Pasteurella multocida. A clear correlation was found between the presence of the 120 kDa polypeptide and cytotoxic activity in culture supernatants. The cytotoxic activity of all the strains tested was neutralized by antibody to the Hly- extracellular material and by convalescent pig serum. It is proposed that the 120 kDa polypeptide represents the cytotoxin of A. pleuropneumoniae, that it is distinct from the haemolysin, and that it be termed pleurotoxin.

Endothelial cytotoxicity of Actinobacillus pleuropneumoniae

The cytotoxicity of Actinobacillus pleuropneumoniae serotype 1 strain CM5 for porcine and bovine endothelial cells in vitro, was dose-dependent. This strain and its attenuated and avirulent substrain CM5A were equally cytotoxic. The cytotoxicity observed during five hours of exposure of endothelial cells to bacterial products was abolished if the bacteria were inactivated by heat or sonication. Exposure of the endothelial cells for five hours to 100 and 200 micrograms of purified lipopolysaccharide resulted in a partial cytotoxicity only, which was not enhanced in the presence of fresh guinea pig serum. The cytotoxicity of viable bacteria could be neutralised by a polyclonal rabbit antiserum to the purified 104kD haemolysin. A bacteria-free supernate of a culture of strain CM5 had both haemolytic and cytotoxic activity. The haemolytic activity could be neutralised completely by the anti-serum to the 104kD haemolysin, whereas the cytotoxic activity was only partially neutralisable. Hence A pleuropneumoniae is cytotoxic for endothelial cells and this cytotoxicity is possibly mediated by the 104kD haemolysin.

Immune suppression induced by Actinobacillus actinomycetemcomitans: effects on immunoglobulin production by human B cells

Actinobacillus actinomycetemcomitans produces an immunosuppressive factor (ISF) which has been shown to suppress mitogen- and antigen-induced DNA, RNA, and protein synthesis in human T lymphocytes. In this study, we examined purified A. actinomycetemcomitans ISF for its ability to alter immunoglobulin production by human B cells. The ISF caused a dose-dependent inhibition of pokeweed mitogen (PWM)-induced immunoglobulin G (IgG) and IgM production. Preexposure to ISF was not required to achieve maximal inhibition of immunoglobulin synthesis, as previously observed for its effect on T-cell activation. Nevertheless, the ISF appeared to act by irreversibly affecting the early stages of cell activation. While PWM-induced immunoglobulin production is under the influence of T-regulatory circuits, it appears that the ISF interacts directly with B cells. First, ISF failed to alter either the synthesis of interleukin-2 (IL-2) or the expression of IL-2 receptors on T cells. Second, experiments in which individual purified populations of cells were exposed to ISF, washed, and placed back into tissue culture indicated that when all cells (i.e., T cells, B cells, and monocytes) were exposed to ISF, significant suppression was observed. However, when only one cell population was treated with ISF, suppression of both IgG and IgM synthesis was observed only when the B-cell-enriched population was exposed to ISF. These results in conjunction with our earlier findings suggest that the ISF functions via the activation of a regulatory subpopulation of B lymphocytes, which in turn either directly or indirectly (via suppressor T cells) downregulate both B- and T-cell responsiveness. Furthermore, it is hypothesized that patients who harbor A. actinomycetemcomitans could suffer from local or systemic immune suppression. This suppression may enhance the pathogenicity of A. actinomycetemcomitans itself or that of some other opportunistic organism.

Humoral antibody response and protective immunity in swine following immunization with the 104-kilodalton hemolysin of Actinobacillus pleuropneumoniae

Five cesarean-derived, colostrum-deprived pigs were given three adjuvant-supplemented subcutaneous and one intravenous injection of the purified 104-kDa hemolysin from serotype 1 Actinobacillus pleuropneumoniae CM-5. Six control animals received phosphate-buffered saline only. Five of six control pigs died within 24 h after challenge. The sixth control pig was moribund and euthanized after 48 h. All six pigs had pleuropneumonia, and A. pleuropneumoniae was isolated from all six lungs. None of the vaccinated pigs died as a result of challenge. After being euthanized, two pigs in this group had no lung lesions but three had chronic pleuropneumonia involving 10, 20, and 40% of the lung tissue. A. pleuropneumoniae was isolated from lung lesions of these three animals but not from the two pigs without lesions. The prechallenge hemolysin-neutralizing antibody titers in the vaccinated pigs were 1:10,900, 1:10,600, 1:4,800, 1:3,900, and 1:3,000, in order of increasing lung involvement. None of the control pigs had neutralizing antibodies. Enzyme-linked immunosorbent assay (ELISA) antibodies to capsule, lipopolysaccharide, and hemolysin were not detected in serum samples collected from the control pigs. In the vaccinated group, prechallenge sera did not contain ELISA antibodies to capsule or lipopolysaccharide. ELISA antibodies to the hemolysin were detected only in the prechallenge and postchallenge serum samples. These results indicate that pigs immunized with the 104-kDa hemolysin of serotype 1 A. pleuropneumoniae are protected against challenge with virulent bacteria. The association between neutralizing antibodies and protection indicates indirectly that the hemolysin is an important virulence factor.

Role of lipopolysaccharides in adherence of Actinobacillus pleuropneumoniae to porcine tracheal rings

The ability of 17 Actinobacillus pleuropneumoniae isolates, representing serotypes 1, 2, 5, and 7, to adhere to tracheal rings maintained in culture was examined. Porcine tracheal rings were infected, and 8 h after inoculation, adherent bacterial cells were evaluated. A. pleuropneumoniae adhered to tracheal rings, and marked variations were observed between and even within serotypes, suggesting that adherence of this microorganism is not primarily related to the serotype of the isolate. No relationship was found between adherence to porcine tracheal rings and plasmid profiles, virulence in mice, hemagglutination, capsular material thickness, or whole-cell protein profiles. On the other hand, we observed that all isolates of serotypes 1 and 5 had a semirough-type lipopolysaccharide (LPS), whereas isolates of serotypes 2 and 7 had a smooth-type LPS (75%) or a semirough-type LPS (25%). Results showed that 83% of isolates with a smooth-type LPS adhered in large numbers to tracheal rings, whereas 80% of isolates with a semirough-type LPS adhered poorly (P less than 0.007). Our data indicated that the degree of adherence of A. pleuropneumoniae to porcine tracheal rings appeared to be related, at least in part, to LPS profiles. Furthermore, LPS seemed to be the adhesin of A. pleuropneumoniae, since purified LPS blocked adherence of this microorganism to porcine tracheal rings.

Grouping of Actinobacillus pleuropneumoniae strains of serotypes 1 through 12 on the basis of their virulence in mice

Variations in virulence among strains of different serotypes of Actinobacillus pleuropneumoniae were detected on intraperitoneal or intranasal inoculation in mice. In general, strains of serotypes 1, 5, 9, 10 and 11 were found to be highly virulent and those of serotypes 2, 3, 4, 6, 7, 8 and 12 to be less virulent. However, a few strains of serotype 5 caused low mortality in mice while some strains of serotype 3 and 7 were found to be highly virulent. Highly virulent strains of A. pleuropneumoniae were invasive and appeared in the blood within 3 to 6 h of intranasal inoculation. The type specific antigen as detected by the coagglutination test was distributed in lungs, liver, heart and spleen after intraperitoneal inoculation whereas it was mostly concentrated in the lungs after intranasal inoculation. Lowest concentration of boiled whole-cell suspension of A. pleuropneumoniae showing limulus amebocyte lysate activity was variable and independent of the serotype. Mortality caused by boiled whole cell suspension was also variable and serotype independent.

[Clinical, bacteriological, and immunological examination and treatment of two Papillon-Lefevre syndrome patients]

Papillon-Lefèvre Syndrome (PLS) is a rare disease accompanied by palmo-plantar hyperkeratosis and rapidly progressive periodontal breakdown of deciduous and permanent dentition. Two unrelated female PLS patients, four and seven years old, with severe periodontal destruction were examined. Antibody titers against seven strains by the enzyme-linked immunosorbent assay (ELISA), microbial cultures from deep periodontal pockets and mouth rinse samples and immunoblotting analysis were performed. Titers against Actinobacillus actinomycetemcomitans (A.a.) were found to be high by the ELISA test. Microbial cultures of A. a. were found in high percentage and immunoblotting results against sonicated extracts of an A. a. Y4 strain had similar patterns. All deciduous teeth were extracted from the younger patient, later permanent dentition erupted uneventfully and A. a. colonies could not be detected. However, the older patient did not exhibit improvement with conventional periodontal therapy and antibiotic (minocycline/erythromycin) treatment and A. a. colonies could be consistently cultured. After a subsequent ofloxacin medication, A. a. colony detection was suppressed. Furthermore, a reduction of gingival inflammation and pocket depth were observed. Therefore, A. a. was associated as an important pathogen in the etiology of periodontal disease in these PLS patients.

[Periodontitis juvenilis--a new view on the aetiology and treatment]

The development of views on the terminology and aetiology, and a new approach to the treatment of juvenile parodontitis are described. The verification of these views has contributed to the explanation of the role of the bacterial factor (Actinomyces actinomycetecomitans) in the development of parodontal changes. This made possible outlining of an optimal therapeutic programmes.

Effects of cations and osmotic protectants on cytolytic activity of Actinobacillus actinomycetemcomitans leukotoxin

Actinobacillus actinomycetemcomitans leukotoxin permeabilized the plasma membrane of HL-60 promyelocytic leukemia cells, resulting in colloid osmotic lysis. These events were associated with efflux of 51chromium (from prelabeled cells), influx of propidium iodide, and ultrastructural evidence of cellular damage. Target cell lysis was inhibited by procedures which may interfere with the initial interaction of the toxin with the plasma membrane. For example, washing cultures (to dilute and remove toxin) or the addition of monoclonal antibodies (to neutralize toxin) or trypsin (to inactivate toxin) limited lysis when undertaken within the first 5 min of the reaction. The extent of injury was also diminished when radiolabeled HL-60 cells were exposed to toxin in the presence of unlabeled, toxin-sensitive cells (e.g., HL-60 cells or human neutrophils) or certain toxin-resistant target cells (e.g., human K562 erythroleukemia cells). This suggests that the association of the toxin with the cell membrane may not be sufficient to cause lysis without activation of additional effector mechanisms. The addition of specific trivalent (e.g., La3+) or divalent (e.g., Ca2+ and Zn2+) cations to toxin-treated cells appeared to enhance their capacity to repair or minimize the extent of toxin-mediated membrane damage. Depending on size, certain saccharides served as osmotic protectants: maltose almost completely inhibited radiolabel release, while smaller molecules provided correspondingly less protection. The results imply that the leukotoxin has membranolytic activity, producing pores in target cells with a functional diameter approximately the size of maltose (0.96 nm).

Characterization of an attenuated strain of Actinobacillus pleuropneumoniae, serotype 1

Pleuropneumonia is an important disease of swine caused by Actinobacillus pleuropneumoniae. Putative virulence determinants include capsule, lipopolysaccharide, and cytotoxin. We studied the virulence and virulence determinants of 2 strains: CM5 and CM5A of serotype 1. Strain CM5 was isolated from a pig with pleuropneumonia and passaged once in vitro; strain CM5A was a substrain of CM5 passaged 70 times in vitro. Pigs challenge exposed to an aerosol of 1.3 x 10(7) colony-forming units of CM5/ml died within 30 hours; pigs challenge exposed to an aerosol of 1.6 x 10(8) colony-forming units of CM5A/ml survived. The average thickness of the capsular layer was 137 nm in strain CM5 and 53 nm in strain CM5A in bacteria treated with homologous antibody and examined by transmission electron microscopy. Similarly, capsular material binding polycationic ferritin was found in colonies of strain CM5, but not in strain CM5A. The ratio of hexosamine to protein in extracted capsule of CM5 was more than twice that of CM5A. The polyacrylamide gel electrophoretic profile of the lipopolysaccharide, outer membrane proteins, and whole cell proteins did not differ between the 2 strains. Also, the amount of cytotoxin or endotoxin produced by the 2 strains during the logarithmic growth phase was not different. The electrophoretic profile of restriction endonuclease digested DNA was similar, with the exception of bands in the 750- and 620-basepair regions. It was concluded that attenuation of strain CM5A during in vitro passage was a result of reduced capsule production and that encapsulation is an important virulence determinant of A pleuropneumoniae, serotype 1.

Actinobacillus pleuropneumoniae: molecular aspects of virulence and pulmonary injury

Contributions made by several laboratories in the area of Actinobacillus pleuropneumoniae virulence and its relationship to pulmonary disease will be reviewed briefly. Lung injury and subsequent disease, after infection with A. pleuropneumoniae, can be related to various bacterial toxins and host factors. Similar to other gram-negative bacteria. A. pleuropneumoniae has cell wall lipopolysaccharides which have been incriminated in a wide variety of toxic and tissue damaging processes. Virulent isolates of A. pleuropneumoniae have been shown to have a thick capsule whereas some avirulent isolates have a thin and easily removed capsule. The capsule of A. pleuropneumoniae is a linear unbranched polysaccharide composed of repeating dissaccharide subunits that bestow antiphagocytic properties to the bacterium but are also immunogenic. In addition, A. pleuropneumoniae has several chemically defined exotoxins. These toxins have generally been shown to be proteinaceous molecules that are hemolytic, cytotoxic, or edemogenic. Some of these toxins are proteolytic and others have the putative activity of being lytic for secretory IgA. Several of these molecules are capable of inducing lesions that are similar to those observed in natural infections and disease. Endogenous host factors have also been implicated in the development of lung lesions after infection by A. pleuropneumoniae Coagulation and inflammatory pathways have been demonstrated to be pivotal in the early phases of lesion development. In addition, the immune status of the animal is clearly related to the severity and ultimate outcome of A. pleuropneumoniae infection. To adequately treat and prevent this disease, we must understand the distinguishable interactions that occur between the host and the various molecular virulence attributes of A. pleuropneumoniae.

[Role of Actinobacillus actinomycetemcomitans in human infection]

Actinobacillus actinomycetemcomitans (AA), is a cocobacillus thin and small, non motile, uncapsulate and capnophilic. AA, is: one of the species encountered in the mouth's comensal flora being able to be isolated in gingival crevices culture and oral mucosa in a 20% of the healthy population. An important number of pathogenic factors make it well equipped, to protect itself from host's defense mechanisms, and to destroy the periodontal tissue. Between the most important we find lipopolisacarides and leucotoxines which promote tisular invasion and destructive qualities of this microorganism. Since 1912, there are numerous reports of infectious process associated to it, between which we find: endocarditis in native and prothesic valve, soft tissues abscess, pneumonia, brain's abscess, urethritis, vertebral osteomielitis, thyroid's abscess, pericarditis and periodontal juvenile illness, being this one in which its isolation is more frequent. In vitro, AA is very susceptible to tetracicline. This antibiotic reaches high concentrations in gingival crevices, has significant affinity to the alveolar bone and contributes to protect the collagen. These special feature make them the election drug in periodontal disease produced by this microorganism.

Receptors for transferrin in pathogenic bacteria are specific for the host's protein

Transferrin receptors detected by a solid-phase binding assay were shown to be specific for the host's transferrin in the representative bacterial pathogens Neisseria meningitidis (human), Pasteurella haemolytica (bovine), and Actinobacillus pleuropneumoniae (porcine). Consistent with the receptor specificity, iron-deficient bacteria were only capable of utilizing transferrin from the host as a source of iron for growth.

Hemolysin patterns of Actinobacillus pleuropneumoniae

The secreted hemolytic activities produced by the reference strains and field isolates of the 12 serotypes and 2 subtypes of Actinobacillus pleuropneumoniae were analyzed. Serotype 1 produced a Ca2(+)-inducible hemolysin, which was previously characterized as a 105-kilodalton protein and was named hemolysin I (HlyI). Serotypes 2, 4, 6, 7, and 8 produced a different hemolytic activity that was not inducible by Ca2+ but required this ion for its activity. The hemolytic activity produced by these serotypes was much weaker than that found in serotype 1 and was not neutralized by rabbit antibodies against HlyI. It was, however, neutralized by serum from pigs that were experimentally infected with a serotype 2 strain and was called hemolysin II (HlyII). Serotypes 5a, 5b, 9, 10, and 11 produced both HlyI and HlyII. In these strains, HlyI was the major contributor to the hemolytic activity. The remaining serotypes, 3 and 12, produced a very weak hemolytic activity, which was not further analyzed. Immunoblot analysis of the culture supernatants from all 12 serotypes with rabbit polyclonal antibodies directed against HlyI revealed reactions with a protein in the 105-kilodalton size range for all serotypes, indicating that HlyI and HlyII might be serologically related. Strains producing active HlyI seem to belong to serotypes that are generally considered to be virulent types and that are frequently isolated from pigs in severe pleuropneumonia outbreaks.

Molecular approaches to leucotoxin as a virulence component in Actinobacillus actinomycetemcomitans

A strategy has been developed to examine the hypothesis that leucotoxin is a critical virulence factor of Actinobacillus actinomycetemcomitans in a non-human primate (Macaca fascicularis). Firstly the leucotoxin gene from A. actinomycetemcomitans was cloned and sequenced. This DNA contained a functional leucotoxin gene, as protein extracts of Escherichia coli with the cloned sequences lysed appropriate human cell lines. The protein encoded by lktA shared at least 42% identity with P. haemolytica leucotoxin and with the alpha-haemolysins from E. coli and A. pleuropneumoniae. The lktA gene of A. actinomycetemcomitans was linked to another gene, lktC, which is thought to be related to the LktC proteins from these other bacteria and with which it shared at least 49% amino acid identity. Despite the overall homology to the other leucotoxins/haemolysins, the LktA from A. actinomycetemcomitans has several unique properties including a very basic pI of 9.7, as compared to pIs approx. 6.2 for lktA proteins in other bacteria. Using the cloned genes as probes produced evidence that a TOX- strain contains the leucotoxin gene but fails to transcribe it at high levels. The second avenue of investigation was to develop methods for examining the humoral immune responses in the monkey to bacterial toxins such as lktA. A. actinomycetemcomitans was detected in subgingival plaque samples from approx. 40% of the animals. A. actinomycetemcomitans comprised less than 1% to 9% of the flora. Most A. actinomycetemcomitans isolates were serotype b and each of the monkeys had serum IgG antibody to A. actinomycetemcomitans serotype b (generally considered to be lktA-producing strains). An ELISA was developed to examine the isotype/subclass distribution, level and avidity of serum antibody in the monkey following parenteral immunization with a prototype bacterial exotoxin (tetanus toxoid). IgG1 and IgG3 antibody predominated over IgG2 and IgG4 after primary immunization. Secondary immunization elicited enriched IgG1 and IgG4 responses. Primary immunization increased avidity indices of IgG to tetanus toxoid from approx. 0.9 (baseline) to a mean of 1.72 and secondary immunization significantly increased the avidity index to 2.56.

Genetic approach to the study of epidemiology and pathogenesis of Actinobacillus actinomycetemcomitans in localized juvenile periodontitis

Actinobacillus actinomycetemcomitans isolates from periodontal pockets were examined for restriction fragment-length polymorphism using a characterized 4.7-kb DNA probe. A total of 6 patterns of RFLP was found in 133 isolates originating from 12 subjects. No relatedness was found between RFLP types and serotypes. Different periodontal sites within the same subject and different individuals within the same family sometimes showed only one type of A. actinomycetemcomitans RFLP. When members among the same family showed 2 RFLP types, children were always infected with the A. actinomycetemcomitans strains found in at least one of the parents. These findings support the concept of familial spread of A. actinomycetemcomitans. A. actinomycetemcomitans RFLP type B, corresponding to reference strain JP2, seems to be particularly virulent, as indicated from the presence of RFLP type B in 3 subjects who converted from a healthy periodontal state to localized juvenile periodontitis. RFLP type B was not detected in any of the 21 A. actinomycetemcomitans-infected patients with adult periodontitis. The RFLP method seems to be useful in determining the epidemiology and possibly the potential virulence of periodontal strains of A. actinomycetemcomitans.

Molecular analysis of periodontal pathogens

Both Bacteroides gingivalis and Actinobacillus actinomycetemcomitans have been implicated in the destruction of periodontal tissues. To understand better the role putative virulence factors from the two bacterial species may play in an infection, the collagenase gene from Bact. gingivalis and the leucotoxin gene from A. actinomycetemcomitans were cloned. As it is intended to generate strains carrying defined mutations in these genes for in vitro and in vivo experiments, extensive restriction mapping and sequence analyses of these clones are being undertaken. Furthermore a conjugation system for Bact. gingivalis and A. actinomycetemcomitans will be established.

The comparative pathogenicity of four serovars of Actinobacillus (Haemophilus) pleuropneumoniae

The pathogenicity of 2 isolates of each of serovars 7, 3, 1 and 2 of Actinobacillus pleuropneumoniae was tested by intranasal inoculation into 60, 6-week-old large white pigs. Four dose rates varying from 0.27 to 560 x 10(6) organisms per pig with 10-fold serial dilutions were used. Surviving pigs were necropsied 7 days after inoculation. The proportion of pigs dying and developing gross lesions following infection was significantly greater for pigs given serotype 1 than for each of the other 3 serotypes, which did not differ significantly from each other. Twelve of 16 pigs given either of the 2 isolates of serovar 1 died after acute illness and 1 of 44 pigs given either of the 2 isolates each of serovars 7, 3 and 2 died. Pigs given serovar 1 showed high temperatures, severe respiratory distress, frothy haemorrhagic nasal discharge and weight loss. Lung lesions were produced in all 16 pigs given serovar 1, in 7 of 14 pigs given serovar 7, 7 of 14 pigs receiving serovar 3 and in 5 of 16 pigs given serovar 2. The lethal infections were characterised by a severe acute fibrinohaemorrhagic necrotising pleuropneumonia, whereas non-lethal cases had lung lesions ranging from necrotising purulent pleuropneumonia to abscessation. Significant differences between isolates in proportions of tissues culture positive for A. pleuropneumoniae for serovars 7 and 2, but not for serovars 3 and 1 suggested that isolates may vary in virulence within serovars, but more detailed studies are needed to clarify this point.

Molecular cloning and characterization of a hemolysin gene from Actinobacillus (Haemophilus) pleuropneumoniae

This article describes the molecular cloning and expression of a hemolysin gene from a serotype 1 strain of Actinobacillus pleuropneumoniae. The hemolysin was a thermolabile protein with an apparent molecular weight of 29,500 (29.5K hemolysin). Unlike expression of the recently described 105K hemolysin of A. pleuropneumoniae (J. Frey and J. Nicolet, FEMS Microbiol. Lett. 55:41-46, 1988), expression of this hemolysin was not regulated by Ca2+. Antiserum prepared against the 105K hemolysin did not neutralize the activity of the 29.5K hemolysin; conversely, antiserum prepared against the 29.5K hemolysin did not neutralize the activity of the 105K hemolysin. The hemolytic activity was not neutralized with antisera against hemolytic Escherichia coli, Streptococcus agalactiae, or purified streptolysin O, but antisera prepared against recombinants containing the 29.5K gene and convalescent pig sera abrogated hemolytic activity. Although hemolytic activity could be detected in several strains of E. coli K-12 and in minicells expressing several different constructs encoding the 29.5K hemolysin, we could not rigorously exclude the possibility that the gene which we have isolated encodes a regulator of hemolytic activity rather than a hemolysin per se.

Chemical differences in lipopolysaccharides from Actinobacillus (Haemophilus) actinomycetemcomitans and Haemophilus aphrophilus: clues to differences in periodontopathogenic potential and taxonomic distinction

While Actinobacillus actinomycetemcomitans has been associated with rapidly progressive periodontal destruction in man, the closely related Haemophilus aphrophilus has not been related to periodontal disease. This may be due to differences in composition and structure of the lipopolysaccharides (LPS) of these dental-plaque bacteria, since LPS probably exerts a series of detrimental effects on the periodontium. LPS was prepared by the phenol-water procedure from the type strains of A. actinomycetemcomitans and H. aphrophilus, purified by hexane extraction and ultracentrifugation, and analyzed with gas chromatography and gas chromatography-mass spectrometry. While the lipid content of LPS from A. actinomycetemcomitans constituted 35.4%, it was only 18.4% in H. aphrophilus: 3-hydroxytetradecanoic and tetradecanoic acids were 21.1 and 14.3% in A. actinomycetemcomitans and 10.9 and 7.5% in H. aphrophilus. There were qualitative and quantitative differences in the polysaccharide portions of their LPS. A actinomycetemcomitans contained both D-glycero-D-mannoheptose and L-glycero-D-mannoheptose (7.8 and 11.3%); H. aphrophilus contained only L-glycero-D-mannoheptose (17.4%). The rhamnose, fucose, galactose, glucose, and glucosamine/galactosamine contents in A. actinomycetemcomitans were 2.6, 5.2, 10.1, 22.4, and 5.2%, respectively; in H. aphrophilus, they were 2.1, 2.6, 19.4, 36.4, and 3.7%. Chemical differences in LPS from A. actinomycetemcomitans and H. aphrophilus may contribute to the divergence in periodontopathogenic potential of these organisms and help taxonomic differentiation.