Hyper-production of porcine contagious pleuropneumonia subunit vaccine proteins in Escherichia coli by developing a bicistronic T7 expression system

The ApxII toxin and the outer membrane lipoprotein (Oml) of Actinobacillus pleuropneumoniae are important vaccine antigens against porcine contagious pleuropneumonia (PCP), a prevalent infectious disease affecting the swine industry worldwide. Previous studies have reported the recombinant expression of ApxII and Oml in Escherichia coli; however, their yields were not satisfactory. Here, we aimed to enhance the production of ApxII and Oml by constructing a bicistronic expression system based on the widely used T7 promoter. To create efficient T7 bicistronic expression cassettes, 16 different fore-cistron sequences were introduced downstream of the T7 promoter. The expression of three vaccine antigens Oml1, Oml7, and ApxII in the four strongest bicistronic vectors were enhanced compared to the monocistronic control. Further optimization of the fermentation conditions in micro-well plates (MWP) led to improved production. Finally, the production yields reached unprecedented levels of 2.43 g L-1 of Oml1, 2.59 g L-1 of Oml7, and 1.21 g L-1 of ApxII, in a 5 L bioreactor. These three antigens also demonstrated well-protective immunity against A. pleuropneumoniae infection. In conclusion, this study establishes an efficient bicistronic T7 expression system that can be used to express recombinant proteins in E. coli and achieves the hyper-production of PCP vaccine proteins.

N-terminus of flagellin enhances vaccine efficacy against Actinobacillus pleuropneumoniae

BACKGROUND

Flagellin elicits potent immune response and may serve as a vaccine adjuvant. We previously reported that the N-terminus of flagellin (residues 1-99, nFliC) is sufficient for vaccine efficacy enhancement against Pasteurella multocida challenge in chickens. In this study, we futher tested the adjuvancy of nFliC in a subunit vaccine against the pig pathogen Actinobacillus pleuropneumoniae in a mice model. For vaccine formulation, the antigen ApxIIPF (the pore-forming region of the exotoxin ApxII) was combined with nFliC, either through genetic fusion or simple admixture.

RESULTS

Immune analysis showed that nFliC, introduced through genetic fusion or admixture, enhanced both humoral (antibody levels) and cellular (T cell response and cytokine production) immunity. In a challenge test, nFliC increased vaccine protective efficacy to 60-80%, vs. 20% for the antigen-only group. Further analysis showed that, even without a supplemental adjuvant such as mineral salt or oil emulsion, genetically linked nFliC still provided significant immune enhancement.

CONCLUSIONS

We conclude that nFliC is a versatile and potent adjuvant for vaccine formulation.

Actinobacillus pleuropneumoniae: The molecular determinants of virulence and pathogenesis

Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia, is responsible for high economic losses in swine herds across the globe. Pleuropneumonia is characterized by severe respiratory distress and high mortality. The knowledge about the interaction between bacterium and host within the porcine respiratory tract has improved significantly in recent years. A. pleuropneumoniae expresses multiple virulence factors, which are required for colonization, immune clearance, and tissue damage. Although vaccines are used to protect swine herds against A. pleuropneumoniae infection, they do not offer complete coverage, and often only protect against the serovar, or serovars, used to prepare the vaccine. This review will summarize the role of individual A. pleuropneumoniae virulence factors that are required during key stages of pathogenesis and disease progression, and highlight progress made toward developing effective and broadly protective vaccines against an organism of great importance to global agriculture and food production.

Effects of different antimicrobial treatments on serum acute phase responses and leucocyte counts in pigs after a primary and a secondary challenge infection with Actinobacillus pleuropneumoniae

The susceptibility to an initial challenge and a re-challenge inoculation with Actinobacillus pleuropneumoniae was analysed in pigs that were treated with antimicrobials of different efficacies following the first exposure to A pleuropneumoniae. In brief, 30 nine-week-old specific pathogen-free pigs were allocated to five groups of six. After acclimatisation, four groups were inoculated with A pleuropneumoniae serotype 2. At the onset of clinical signs, three of the groups of pigs were treated with enrofloxacin, tetracycline or penicillin. A fourth group served as the inoculated control and the fifth group as a control group that had not been inoculated. On day 28, all five groups were re-challenged with the same strain of A pleuropneumoniae serotype 2 as had been used in the first inoculation. No treatments were carried out at this time. The acute phase responses and differential leucocyte counts were monitored in detail after both inoculations. Leucocytosis and acute phase responses in the forms of serum amyloid A, pig-major acute phase protein and haptoglobin were recorded in all of the inoculated groups after the onset of clinical signs following the first inoculation. A porcine mannan-binding lectin-A response was less evident in the pigs. Acute phase responses resembling those of the first inoculation were observed in the pigs that had not previously been inoculated and in the pigs treated with enrofloxacin. Acute phase responses were not recorded in the other three groups, where the pigs had seroconverted to A pleuropneumoniae serotype 2 following the first inoculation.

Cloning, expression, and characterization of TonB2 from Actinobacillus pleuropneumoniae and potential use as an antigenic vaccine candidate and diagnostic marker

In this study the tonB2 gene was cloned from Actinobacillus pleuropneumoniae JL01 (serovar 1) and expressed as a glutathione-S-transferase (GST) fusion protein in Escherichia coli BL21(DE3). The GST fusion protein was recognized by antibodies in serum positive for A. pleuropneumoniae by Western blot analysis. Purified soluble GST-TonB2 was assessed for its ability to protect BALB/c mice against A. pleuropneumoniae infection. Mice were vaccinated with GST-TonB2 subcutaneously and challenged intraperitoneally with either ~4.0 × 10(5) colony-forming units (CFU) or ~1.0 × 10(6) CFU of A. pleuropneumoniae 4074. They were examined daily for 7 d after challenge. The survival rate of the TonB2-vaccinated mice was significant higher than that of the mice given recombinant GST or adjuvant alone. These results demonstrate that A. pleuropneumoniae TonB2 is immunogenic in mice and should be further assessed as a potential candidate for a vaccine against A. pleuropneumoniae infection. In addition, an indirect enzyme-linked immunosorbent assay (ELISA) based on the GST-TonB2 recombinant protein was developed. Compared with the ApxIVA ELISA, the TonB2 ELISA provided earlier detection of antibodies in pigs at various times after vaccination with A. pleuropneumoniae live attenuated vaccine. When compared with an indirect hemagglutination test, the sensitivity and specificity of the TonB2 ELISA were 95% and 88%, respectively. The TonB2 ELISA provides an alternative method for rapid serologic diagnosis of A. pleuropneumoniae infection through antibody screening, which would be especially useful when the infection status or serovar is unknown.

Population-based analysis of Actinobacillus pleuropneumoniae ApxIVA for use as a DIVA antigen

APXIVA is an RTX toxin of Actinobacillus pleuropneumoniae that is a candidate antigen to differentiate infected from vaccinated animals (DIVA). Insertion of ISApl1 into the apxIVA gene is known to compromise an APXIVA-based DIVA approach, as is potentially a TGG to TGA mutation in the apxIVA gene. ISApl1 was found in 63/349 (18.1%) A. pleuropneumoniae isolates from England and Wales including serovars 2, 3, 6-8 and 12. No ISApl1 insertions into apxIVA were found. Only two serovar 3 isolates contained the TGG to TGA mutation. We conclude that an ApxIVA-based DIVA approach would potentially be viable in England and Wales.

[Construction and characterization of Actinobacillus pleuropneumoniae serovar 7 live attenuated vaccine strain co-expressing ApxIA]

Actinobacillus pleuropneumoniae (A. pleuropneumoniae), the causative agent of porcine contagious pleuropneumonia (PCP), is a significant pathogen of the world pig industry, vaccination is potentially an effective tool for the prevention of PCP. The purpose of present study was to enhance the immunogenicity of A. pleuropneumoniae live vaccine strain HB04C- (serovar 7), which was unable to express ApxIA, and to develop effective multivalent vaccines for the respiratory pathogens based on the attenuated A. pleuropneumoniae. We introduced a shuttle vector containing intact apxIA gene into HB04C-, generating HB04C2, an A. pleuropneumoniae serovar 7 live attenuated vaccine strain co-expressing ApxIA. Then we investigated the biological characteristics of HB04C2. We found that the shuttle vector expressing ApxIA was stable in HB04C2, and the growth ability of HB04C2 was not affected by the shuttle vector. We observed that HB04C2 elicited detectable antibodies against ApxIA and ApxIIA when it was administrated intratracheally as a live vaccine in pigs, and all immunized pigs were protected from heterologous virulent A. pleuropneumoniae (serovar 1) challenge. In conclusion, we demonstrated that A. pleuropneumoniae live vaccine could be used as a vector for expression of heterologous antigens.

[Construction and characterization of an attenuate strain apxIC-/P36+ of Actinobacillus pleuropneumoniae serovar 10]

OBJECTIVE

To construct an attenuate Actinobacillus pleuropneumoniae serovar 10 strain apxIC-/P36+ for new vaccine development.

METHODS

The mutant was constructed by transconjugation and counter-selection and then verified by PCR, western blot and sequence analysis. A transconjugation plasmid pEICALDH was constructed and transformed into donor strain Escherichia coli X7213. After mixing the donor cells with A. pleuropneumoniae acceptor cells, we cultivated the mixture for 6 hours and plated on solid medium containing chloromycetin. Then the Cm(R) positive clones were picked and inoculated into liquid medium without any antibiotic. Cultures were pelleted, plated on sucrose plates and incubated overnight. Finally, Sucrose-resistant colonies (SucB(R)) were selected and considered as mutant.

RESULTS

Compared with parental strain, the mutant have the same growth rate in vitro and reduced virulence in mice; additionally, the animal experiment indicated that the mutant strain can successfully induce as good immune response as the parental strain, despite of deletion of apxIC gene.

CONCLUSION

In conclusion, we successfully constructed the attenuate strain apxIC-/P36+ of Actinobacillus pleuropneumoniae serovar 10, and this mutation system will facilitate development of live attenuated vaccines.

[Study of the virulence of Actinobacillus pleuropneumoniae in finishing pigs as a basis for vaccination development]

For vaccine licensing data about efficiency and duration of protection are essential. Within the scope of the developement of a new subunit vaccine against Actinobacillus pleuropneumoniae (A.pp.) the protective efficiency over the whole length of the fattening period must be proven. This required infection experiments in finishing pigs. Eight pigs in the age of six months were infected experimentally into the trachea with an A.pp. serotyp 2 strain. To our knowledge data about the susceptibility of pigs of this age do not exist, so that the infectious dose for pigs of this age and this route of infection had to be determined. Two pigs each were infected with different doses of 10(10), 6 x 10(5), 8 x 10(3) and 2 x 10(3) CFU (colony forming units). The aim of the study was to produce a typical pleuropneumonia with fever and severe respiratory symptoms as well as characteristic pathomorphological lung alterations without loss of animals during the acute stage of infection. The pathogen should be cultivated from lung tissue. The recommended dose for testing the efficiency of vaccines turned out to be approximately 10(3) CFU A.pp. serotyp 2.

[Cloning and expression of hemolytic-toxin from Actinobacillus pleuropneumoniae and the immunoprotection in mice]

The ApxIIA, ApxIIIA, ApxIVA genes from Actinobacillus pleuropneumoniae serotype 3 and the ApxIA gene from Actinobacillus pleuropneumoniae serotype 5 were respectively cloned into the prokaryotic expression vector pGEX-5X-3. Then the recombinant expression plasmids were respectively transformed into E. coli BL 21 and fusion protein expression were induced by IPTG. The expression products were purified by precipitation with ammonium sulfate and chromatography on Sephadex G-200. SDS-PAGE indicated that the productsexpressed at a high level when the recombinant E. coli BL21 was induced 2h, joining IPTG to final concentration 1 mmol/L. Western blot analysis showed that the expression products had immunogenicity and specificity. Subunit vaccines were made by different purified expression products and Freund's adjuvant. Mice were immunized at 30 days and 45 days with the subunit vaccines. Then the mice were challenged with the APP of serotype 1, 3, 5, 7 or 10 at 60 days. The result of animal immunoprotection test showed that subunit vaccines (ApxIA + ApxIVA, ApxIA + ApxIIIA + ApxIVA, ApxIA + ApxIIA + ApxIIIA + ApxIVA) could offer 58.4%, 66.6%, 91.7% protection in mice against the challenge of serotype 1, 5 and 7 APP, respectively. These results suggested that the recombinant proteins had good immunogenicity and the subunit vaccine containing four kind of recombinant proteins could induce better immunoprotection.

A successful national control programme for enzootic respiratory diseases in pigs in Switzerland

Before the start of systematic disease control, respiratory diseases in swine in Switzerland caused estimated losses of several million euros per year. In 1993, a national programme to control enzootic respiratory diseases in pigs was proposed, with the aim of reducing the incidence of clinical cases to less than 1%. Enzootic pneumonia (EP) caused by Mycoplasma hyopneumoniae and clinical cases of pleuropneumonia caused by any serotype of Actinobacillus pleuropneumoniae (APP) would be targeted, in addition to any cases with serological evidence of APP serotype 2. This control programme was initiated in 1996, region by region, and fully implemented by 2004. Clinical, epidemiological and laboratory test results were used to identify the appropriate disease control measures. Partial depopulation was used to control EP on breeding and breeding-finishing farms. Total depopulation was implemented on all farms affected with APP and finishing farms affected with EP Animal trade was strictly regulated during the programme and all suspected cases of respiratory disease in pigs were made notifiable. Continued monitoring is based on clinical suspicion of infection and/or the detection of gross pathological lesions at slaughter, followed by laboratory confirmation. In 2005, the incidence of clinical cases was less than 1%. Regulations have been introduced to control the international trade in live pigs and prevent the re-introduction of respiratory diseases into Switzerland.

Evaluation of immunogenicity and protective efficacy of Actinobacillus pleuropneumoniae HB04C− mutant lacking a drug resistance marker in the pigs

Previously, we reported the construction and characterization of a genetically defined Actinobacillus pleuropneumoniae (A. pleuropneumoniae) apxIIC gene mutant, HB04C(-), which conferred protection to mice against infection with A. pleuropneumoniae. In this study, we further evaluated HB04C(-) for safety and its ability to elicit protective immunity in pigs. It was demonstrated that a dose of 2 x 10(8) CFU HB04C(-) was safe to the pigs via intranasal or intramuscular injection. Immunization with a dose of 2 x 10(8) HB04C(-) by both intranasal and intramuscular routine could yield equal protective efficacy and elicited significant protection against experiment challenge with homologous or heterologous serotypes of a virulent A. pleuropneumonia. Taken together, HB04C(-) might serve as a promising vaccine candidate against infection with A. pleuropneumoniae.

[Construction and immunogenicity of an attenuated mutant of Actinobacillus pleuropneumoniae by insertional inactivation of apxIC]

Actinobacillus pleuropneumoniae is the aetiological agent of porcine pleuropneumonia. Apx toxin, an exotoxin secreted by A. pleuropneumoniae, is one of the most important virulence factors. To construct an avirulent mutant strain by inactivation of ApxI toxin, the apxIC gene of A. pleuropneumoniae serovar 10 was inactivated by inserting a chloramphenicol resistance gene cassette into the downstream XhoI site of the apxIC gene for constructing the transfer plasmid. The transfer plasmid was introduced into the electrocompetent A. pleuropneumoniae serovar 10 for homologous recombination by electroporation. The mutant strain was obtained and identified by PCR and Southern blotting. The mutant strain was phenotypically identical to the parent strain except that it showed no haemolytic activity. The mutant strain was also able to secret the same ApxI toxin as the parent strain. In the intra-peritoneal mouse model, the virulence of the mutant strain decreased at least 100 fold compared with the parent strain. The mutant was evaluated as a potential vaccine using a vaccination-challenge trial in which pigs were given two intra-nasal doses of the mutant with 14 days' interval and then challenged 14 days after the last vaccination with A. pleuropneumoniae serovar 1 and serovar 10 reference strains respectively. The death number and lung lesion score in the vaccinated pigs given the serovar 1 challenge were obviously lower than those in the unvaccinated pigs. And the lower lung lesion score was also observed in the vaccinated pigs challenged with serovar 10. And the positive numbers of A. pleuropneumoniae re-isolation and PCR detection showed the same consistency. The vaccination-challenge trial suggested that the mutant strain could offer partial cross-protection as a live attenuated vaccine against A . pleuropneumoniae infection.

Construction and immunogencity of a DeltaapxIC/DeltaapxIIC double mutant of Actinobacillus pleuropneumoniae serovar 1

The apxIC and apxIIC genes of the Actinobacillus pleuropneumoniae serovar 1 strain SLW01, encoding the ApxI- and ApxII-activating proteins, respectively, were deleted successively by a method involving sucrose counterselection. The resulting strain, SLW03, contained no foreign DNA and could secrete unactivated ApxIA and ApxIIA RTX toxins with complete antigenicity. Strain SLW03 was attenuated at least 1000-fold in Balb/C mice and caused no adverse effects in pigs at doses of up to 1 x 10(9) CFU mL(-1). SLW03 was able to induce a significant immune response and provide complete protection from clinical signs upon homologous (serovar 1) and heterologous (serovar 9) challenge of A. pleuropneumoniae. Pigs vaccinated via the intranasal (i.n.) route had significantly higher serum titers and fewer pulmonary lesions than pigs vaccinated via the intramuscular route postchallenge. These results suggest that the mutant strain SLW03 could be used as a candidate live vaccine that can induce reliable cross-serovar protection following i.n. immunization.

Induction of protective immune responses against the challenge of Actinobacillus pleuropneumoniae by the oral administration of transgenic tobacco plant expressing ApxIIA toxin from the bacteria

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia. Among the virulence factors, ApxIIA, a bacterial exotoxin, is reportedly expressed in many serotypes and is considered as a candidate for the development of a vaccine against the bacterial infection. Previously, we isolated a field strain of A. pleuropneumoniae serotype 2 in Korea and characterized its exotoxins to develop an oral vaccine. In this study, we initially confirmed the immunogenicity of ApxIIA expressed in Escherichia coli. We then developed transgenic tobacco expressing ApxIIA and tested its efficacy to induce a protective immune response against A. pleuropneumoniae infection after oral administration of the plant powder. We observed that protective immune responses were induced in mice after oral administration of the plant powder once a week for 4 weeks. Immunoassays revealed that the levels of antigen-specific immunoglobulin G against ApxIIA increased in mice that were fed a powder made from the transgenic plant, but not in mice fed a powder made from wild-type tobacco. Additionally, mice fed the transgenic plant powder were protected from an injection of a lethal dose of A. pleuropneumoniae. These results support that the transgenic plant may be a suitable candidate for an oral vaccine that could be used effectively against A. pleuropneumoniae infection.

Characterization and immunogenicity of an apxIA mutant of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is the aetiological agent of porcine pleuropneumonia, a highly contagious and often fatal disease. A candidate live vaccine strain, potentially capable of cross-serovar protection, was constructed by deleting the section of the apxIA gene coding for the C-terminal segment of ApxI toxin of the A. pleuropneumoniae serovar 10 reference strain (D13039) and inserting a chloramphenicol resistance gene cassette. The mutant strain (termed D13039A(-)Chl(r)) produced an approximately 48kDa protein corresponding to the N-terminus of the ApxI toxin, and exhibited no haemolytic activity and lower virulence in mice compared with the parental strain. The mutant was evaluated in a vaccination-challenge trial in which pigs were given two intra-nasal doses of the mutant at 14 days intervals and then challenged 14 days after the last vaccination with either A. pleuropneumoniae serovar 1 (4074) or serovar 2 (S1536) or serovar 10 (D13039) reference strains. The haemolysin neutralisation titres of the pre-challenge sera were significantly higher in the vaccinated pigs than in the unvaccinated pigs. The mortalities, clinical signs and lung lesion scores in the vaccinated pigs were significantly lower than those in the unvaccinated pigs for the serovar 1 challenge. A significantly lower lung lesion score was also observed in the vaccinated pigs, compared with unvaccinated pigs, for serovar 2 challenge. Our work suggests that the mutant strain offers potential as a live attenuated pleuropneumonia vaccine that can provide cross-serovar protection.

Development of a DIVA subunit vaccine against Actinobacillus pleuropneumoniae infection

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia which leads to high economic losses in the swine industry worldwide. Vaccination against this pathogen is hampered by the occurrence of 15 serotypes, and commonly used whole cell bacterin vaccines are not sufficiently cross-serotype protective. In addition, for generating and maintaining specified pathogen-free herds it is desirable to use DIVA (differentiating infected from vaccinated animals) vaccines. Based on a detergent wash extraction of outer membrane associated proteins and secreted proteins we developed a DIVA vaccine using the immunogenic ApxII toxin which is present in 13 of the 15 A. pleuropneumoniae serotypes as the DIVA antigen. The apxIIA gene was deleted in one strain each of serotypes 1, 2, and 5 using a single-step transconjugation system, and equal parts of detergent washes from these strains served as the vaccine antigen. After intramuscular immunisation all pigs developed a strong humoral immune response to the vaccine antigen and showed no reactivity in an ApxIIA ELISA. Upon challenge all pigs were completely protected from clinical symptoms in trials with a homologous (serotype 2) as well as with a heterologous strain (serotype 9); in addition, colonisation of the challenge strain was clearly reduced but not abolished completely. As a result of the highly efficient protection, however, immunised pigs did not develop antibodies to the DIVA-antigen at levels detectable by ELISA but only by a more sensitive Western blotting approach, thereby demonstrating the challenge in developing appropriate marker vaccines for the livestock industry.

Use of an Actinobacillus pleuropneumoniae multiple mutant as a vaccine that allows differentiation of vaccinated and infected animals

Vaccination against Actinobacillus pleuropneumoniae is hampered by the lack of vaccines inducing reliable cross-serotype protection. In contrast, pigs surviving natural infection are at least partially protected from clinical symptoms upon reinfection with any serotype. Thus, we set out to construct an attenuated A. pleuropneumoniae live vaccine allowing the differentiation of vaccinated from infected animals (the DIVA concept) by successively deleting virulence-associated genes. Based on an A. pleuropneumoniae serotype 2 prototype live negative marker vaccine (W. Tonpitak, N. Baltes, I. Hennig-Pauka, and G.-F. Gerlach, Infect. Immun. 70:7120-7125, 2002), genes encoding three enzymes involved in anaerobic respiration and the ferric uptake regulator Fur were deleted, resulting in a highly attenuated sixfold mutant; this mutant was still able to colonize the lower respiratory tract and induced a detectable immune response. Upon a single aerosol application, this mutant provided significant protection from clinical symptoms upon heterologous infection with an antigenically distinct A. pleuropneumoniae serotype 9 challenge strain and allowed the serological discrimination between infected and vaccinated groups.

The structural basis for the serospecificity ofActinobacillus suisserogroup O:2

Actinobacillus suis is an important bacterial pathogen of healthly pigs. An O-antigen (lipopolysaccharide; LPS) serotyping system is being developed to study the prevalence and distribution of representative isolates from both healthy and diseased pigs. In a previous study, we reported that A. suis serogroup O:1 strains express LPS with a (1→6)-β-D-glucan O-antigen chain polysaccharide that is similar in structure to a key cell-wall component in yeasts, such as Saccharomyces cerevisiae and Candida albicans. This study describes the O-antigen polysaccharide chemical structure of an O:2 serogroup strain, A. suis H91-0380, which possesses a tetrasaccharide repeating block with the structure: →3)-β-D-Galp-(1→4)-[α-D-Galp-(1→6)]-β-D-Glcp-(1→6)-β-D-GlcpNAc-(1→. Studies have shown that A. suis serogroup O:2 strains are associated with severely diseased animals; therefore, work on the synthesis of a glycoconjugate vaccine employing O:2 O-antigen polysaccharide to vaccinate pigs against A. suis serogroup O:2 strains is currently underway.Key words: Actinobacillus suis, lipopolysaccharide, serogroup O:2, vaccine.

Generation of monoclonal antibodies and epitope mapping of ApxIVA of Actinobacillus pleuropneumoniae

To study functions of ApxIV, a species-specific and in vivo inducible RTX toxin identified in Actinobacillus pleuropneumoniae recently, and to develop a diagnostic trial distinguishing the pigs infected naturally and vaccinated with inactivated and/or subunit vaccines, we attempted to prepare monoclonal antibodies against ApxIV. BALB/c mice were immunized with ApxIVAN and ApxIVAC which are N- and C-terminal halvies (814 and 997 amino acids, respectively) of ApxIVA produced in E. coli BL21 (DE3), respectively. Eight monoclonal antibodies were selected, four (designated as 1A8, 1G5, 3E7 and 4H9) against ApxIVAN and another four (named as 1B12, 2E5, 4D8 and 4G2) against ApxIVAC. Western blot and ELISA additivity assays suggested that all monoclonal antibodies except 1A8 are specific to the corresponding immunogen, 1A8 reacts with both immunogens which have a overlapping region of 156 residues. ELISA additivity tests revealed that at least five epitopes in ApxIV are defined by eight monoclonal antibodies, two between 1 and 866 amino acids, one between 867 and 1022 amino acids and two between 1023 and 1863 amino acids. In conclusion, we have succeeded in producing eight monoclonal antibodies, which react with five different epitopes of ApxIV.

Porphyromonas gingivalis heat shock protein vaccine reduces the alveolar bone loss induced by multiple periodontopathogenic bacteria

OBJECTIVES

Heat shock protein (HSP) can be utilized as a vaccine to cross-protect against multiple pathogenic species. The present study was performed to evaluate Porphyromonas gingivalis heat shock protein 60 (HSP60) as a vaccine candidate to inhibit multiple bacteria-induced alveolar bone loss.

MATERIAL AND METHODS

Recombinant P. gingivalis HSP60 was produced and purified from P. gingivalis GroEL gene. Rats were immunized with P. gingivalis HSP60, and experimental alveolar bone loss was induced by infection with multiple periodontopathogenic bacteria.

RESULTS

There was a very strong inverse relationship between postimmune anti-P. gingivalis HSP immunoglobulin G (IgG) levels and the amount of alveolar bone loss induced by either P. gingivalis or multiple bacterial infection (p=0.007). Polymerase chain reaction data indicated that the vaccine successfully eradicated the multiple pathogenic species.

CONCLUSIONS

We concluded that P. gingivalis HSP60 could potentially be developed as a vaccine to inhibit periodontal disease induced by multiple pathogenic bacteria.

Study on the Immunogenicity of N-terminal Polypeptide of RTX Toxin I of Actinobacillus pleuropneumoniae

ApxI is one of the most important virulence factors of Actinobacillus pleuropneumoniae (APP). To study the immunogenicity of the ApxI, the complete coding sequence (3146bp) and its 5'-terminal 1140 bp fragment of the apxIA gene were separately cloned into the prokaryotic expression vector pET-28a, and expressed in the E. coli BL21 (DE3) with induction by IPTG. The expression products, rApxIA and rApxIAN, were present in a form of inclusion bodies and showed the same immunological reactivity as natural ApxI (nApxI) in Western-blot analysis. BALB/c mice were intraperitoneally immunized with the rApxIA, rApxIAN and nApxI respectively. The serum antibody levels of the rApxIAN immunized mice were significantly lower than those immunized with rApxIA or nApxI in an ApxI-specific ELISA, but serum neutralization test demonstrated that immunized mice with rApxIAN, rApxIA and nApxI could generate similar levels of antibodies neutralizing the hemolytic activity of the natural ApxI. The rApxIAN was able to elicite 80% protection rate against APP serovar 1 and 100% against serovar 2 when challenged at a dose of one LD50 after 2 weeks of boost immunization.

[Acute toxicity and immunoprotection of recombinant apxI toxin of Actinobacillus pleuropneumoniae in mice]

Acute toxicity and immunoprotection of Actinobacillus pleuropneumoniae (APP) ApxI toxin recombinant proteins (include crude inclusion bodies and refolded recombinant protein) were evaluated in mice, and compared with the natural ApxI extracted from culture supernatant of APP serotype 10. In the acute toxicity experiment, the three proteins were intraperitoneally injected into Kunming mice in a dose of 200microg per mouse. The body and organ weight, heamatological and biochemical indexes were examined at 24h, 7 days and 14 days post administration. There was no death after the intraperitoneal administration of the three proteins, and no significant change was found in the body weight, organ indexes, heamatological and biochemical indexes. To study their immunoprotection, the three proteins were emulsified with Freund's adjuvant respectively and vaccinated the mice twice with a 2-week of interval. Two weeks after the second vaccination, the mice were challenged intraperitoneally with a lethal dose of APP serotype 10 (1.09 x 10(8) cfu), and serums were examined by an ApxI-specific ELISA. The results revealed that the recombinant protein had a good immunogenicity and could induce protection immune reaction.

An evaluation of the role of antibodies to Actinobacillus pleuropneumoniae serovar 1 and 15 in the protection provided by sub-unit and live streptomycin-dependent pleuropneumonia vaccines

OBJECTIVE

To evaluate the serological response of pigs receiving either the Porcilis APP vaccine or a modified live vaccine based on a streptomycin-dependent (SD) strain of Actinobacillus pleuropneumoniae, and then challenged with an Australian isolate of A. pleuropneumoniae of either serovar 1 or 15 as a means of understanding the protection provided by both vaccines against serovar 1 but not against serovar 15.

DESIGN

The serological tests evaluated were serovar-specific polysaccharide ELISA tests (for serovar 1 and 15), ELISA tests for antibodies to three A. pleuropneumoniae toxins (ApxI, ApxII and ApxIII) as well as to a 42 kDa outer membrane protein (OMP), a haemolysin neutralisation (HN) assay and immunoblotting. The tests were used to detect antibodies in vaccinated pigs that had been shown to be protected against serovar 1 but not serovar 15.

RESULTS

In the polysaccharide antigen ELISA assays, both vaccines resulted in a significant rise in the titre in the serovar 1 ELISA but not the serovar 15 ELISA. The Porcilis APP vaccinated pigs showed a significant response in the ApxI, ApxIII and 42 kDa OMP ELISA. In the ApxII ELISA, all pigs tested (the Porcilis APP vaccinates and the controls) were positive on entry to the trial. In the HN assay, the Porcilis APP vaccinated pigs showed a significant response after one dose while the SD vaccinated pigs required two doses of vaccine before a marked rise in titre was induced. Immunoblotting revealed that neither vaccine generated antibodies that recognised the ApxIII produced by serovar 15.

CONCLUSIONS

The failure of these vaccines to provide protection against serovar 15 may be due to novel virulence factors possessed by serovar 15, significant differences between the ApxIII toxin of serovar 15 and those present in the Porcilis APP vaccine or failure by both vaccines to induce antibodies to the serovar 15 specific polysaccharide.

Assessment of the efficacy of tilmicosin phosphate to eliminate Actinobacillus pleuropneumoniae from carrier pigs

The aim of this study was to evaluate the efficacy of in-feed medication with tilmicosin phosphate in order to eliminate or reduce the carriage of Actinobacillus pleuropneumoniae in the tonsils of carrier pigs. Two groups of 6 carrier animals received either a non-medicated feed (control group) or feed medicated with 400 ppm of tilmicosin phosphate (treated group) for 30 d. Three sentinel pigs were then introduced in each group and left for 29 d. The presence of A. pleuropneumoniae in tonsils was monitored using several techniques, including polymerase chain reaction (PCR). At the end of the treatment all of the control animals, but only 1 treated pig, were positive by PCR from tonsillar surface material. However, at necropsy, all control and most treated animals, as well as 1 sentinel animal, in both groups were positive by PCR from whole tonsils. In conclusion, under the experimental conditions, in-feed treatment with 400 ppm of tilmicosin phosphate significantly reduced the presence of A. pleuropneumoniae on the surface of tonsils but was unable to completely eliminate the organism from deeper tonsillar tissues and to prevent bacterial shedding by carrier animals.

Induction of antigen-specific immune responses by oral vaccination withSaccharomyces cerevisiaeexpressingActinobacillus pleuropneumoniaeApxIIA

An effective way of inducing both mucosal and systemic immune responses to protect against Actinobacillus pleuropneumoniae serotype 2 Korean isolate was examined in mice by oral immunization using Saccharomyces cerevisiae expressing the ApxIIA protein. The immunogenicity of the yeast-derived ApxIIA antigen was confirmed by the challenge test and ApxIIA-specific IgG antibody response assay. The group subcutaneously immunized with the protein extracted from the yeast expressing ApxIIA showed a higher survival rate after challenging with A. pleuropneumoniae serotype 2 isolate and IgG antibody level in serum than the group injected with that prepared from the yeast harboring vector only. Feeding the yeast expressing ApxIIA to mice induced both systemic and mucosal immune responses against the antigen. ApxIIA-specific IgA antibody titers and the number of IgA-secreting cells of mice vaccinated with S. cerevisiae expressing ApxIIA dose-dependently increased from the third immunization in both intestine and lung (P<0.01). A similar tendency of ApxIIA-specific IgG antibody responses was observed in the sera. The protective efficacy of the oral immunization was then evaluated by a challenge with a minimal lethal dose (MLD, 4.5 x 10(7) CFU/ml) of the A. pleuropneumoniae serotype 2 isolate. Fifty percent of the 30 mg administered group and 30% of the 15 mg administered group survived while none of the mice in the control groups survived after 36 h. These results suggest that feeding animals the yeast expressing the antigen can be an effective strategy to induce protective immune responses against A. pleuropneumoniae infection.

Construction and characterization of a live, attenuated apxIICA inactivation mutant ofActinobacillus pleuropneumoniaelacking a drug resistance marker

The apxIIC gene of Actinobacillus pleuropneumoniae serotype 7 was inactivated by homologous recombination using a sucrose counter-selectable marker system, resulting in a mutant strain that had no antibiotic resistance marker and expressed an inactivated ApxII toxin. The safety and immunogenicity of the mutant were evaluated in mice. The mutant strain caused no adverse effects in mice at doses up to 2 x 10(9) CFU via the intraperitoneal route while the parental strain induced total mortality at a dose of 2 x 10(7) CFU. Mice vaccinated intraperitoneally with the mutant strain had 100% and 70% protection against homologous (serotype 7) or heterologous (serotype 1, 3) challenge with A. pleuropneumoniae, respectively. The A. pleuropneumoniae mutant strain HB04C- and the counterselection method used in the study show promise in developing effective live vaccines for porcine pleuropneumonia and for other infections diseases of the respiratory system.

Comparison of the efficacy of a subunit and a live streptomycin-dependent porcine pleuropneumonia vaccine

OBJECTIVE

To evaluate the efficacy of two new-generation porcine pleuropneumonia vaccines when challenged with Australian isolates of Actinobacillus pleuropneumoniae of serovars 1 and 15.

DESIGN

The Porcilis APP vaccine and an experimental streptomycin-dependent strain of A pleuropneumoniae were evaluated in a standardised pen trial. Each vaccine/challenge group consisted of 10 pigs.

RESULTS

With the serovar 1 challenge, the Porcilis APP vaccine and the live vaccine, compared with the control group, gave significant protection in terms of clinical signs, lung lesions, re-isolation scores and average daily gain (ADG) postchallenge. Only the Porcilis APP vaccine provided significant protection against mortality. In the serovar 15 challenged pigs, the only significant difference detected was that the Porcilis APP vaccinated pigs had a better postchallenge ADG than the controls. None of the Porcilis APP vaccinated pigs showed signs of depression postvaccination and none were euthanased after challenge with either serovar 1 or 15. The pigs vaccinated with the live vaccine showed obvious depression after each vaccination and a total of 3 pigs were euthanased after challenge (one with serovar 1 and two with serovar 15).

CONCLUSIONS

Both of the vaccines provided significant protection against a severe challenge with serovar 1 A pleuropneumoniae. Neither vaccine was effective against a serovar 15 A pleuropneumoniae challenge. There was evidence that the Porcilis APP vaccine did provide some protection against the serovar 15 challenge because the ADG, after challenge of pigs given this vaccine, was greater than the control pigs.

Antibody response in sows and piglets following vaccination against Mycoplasma hyopneumoniae, toxigenic Pasteurella multocida, and Actinobacillus pleuropneumoniae

The aim of the experimental study was to compare the humoral immune response and occurrence of adverse effects following single or multiple simultaneous vaccination of sows against Mycoplasma hyopneumonia, toxigenic Pasteurella multocida, and Actinobacillus pleuropneumoniae. In addition, passively transferred antibodies to piglets were studied until weaning at 3 weeks of age. Fever was seen in a few sows within the first 12 hours after the 1st and 2nd vaccination. No difference in the occurrence of other adverse effects was observed between groups. Antibody levels were significantly higher in vaccinated sows and their offspring compared with the control group. This was found to be independent of single or simultaneous vaccinations with the 3 vaccines. In conclusion, applying multiple vaccines simultaneously to sows appeared not to influence the occurrence of adverse effects or the sow's serum levels of antibodies at the time of farrowing, nor the offspring's serum levels up to 3 weeks of age.

Effect of endobronchial challenge with Actinobacillus pleuropneumoniae serotype 10 of pigs vaccinated with bacterins consisting of A. pleuropneumoniae serotype 10 grown under NAD-rich and NAD-restricted conditions

The efficacy of two bacterins containing an Actinobacillus pleuropneumoniae serotype 10 strain was evaluated. The bacterial cells constituting bacterin 1 and 2 were grown under nicotinamide adenine dinucleotide (NAD)-rich (low-adherence capacity to alveolar epithelial cell cultures) and NAD-restricted (high-adherence capacity to alveolar epithelial cell cultures) conditions, respectively. Ten pigs were vaccinated twice with the bacterin 1 and nine pigs with the bacterin 2. Ten control animals were injected twice with a saline solution. Three weeks after the second vaccination, all pigs were endobronchially inoculated with 106.5 colony-forming units (CFU) of an A. pleuropneumoniae serotype 10 strain. In the bacterin 1 and 2 group, three and two pigs died after inoculation, respectively. Only two pigs of the control group survived challenge. Surviving pigs were killed at 7 days after challenge. The percentage of pigs with severe lung lesions (> 10% of the lung affected) was 100% in the control group, 70% in the bacterin 1 group and 22% in the bacterin 2 group. Actinobacillus pleuropneumoniae was isolated from the lungs of all animals. The mean bacterial titres of the caudal lung lobes were 7.0 x 10(6) CFU/g in the control group, 6.3 x 10(5) CFU/g in the bacterin 1 group and 1.3 x 10(6) CFU/g in the bacterin 2 group. It was concluded that both bacterins induced partial protection against severe challenge. Furthermore, there are indications that the bacterin 2, containing A. pleuropneumoniae bacteria grown under conditions resulting in high in vitro adhesin, induced better protection than the bacterin 1.

Interference of outer membrane protein PalA with protective immunity against Actinobacillus pleuropneumoniae infections in vaccinated pigs

The role of antibodies to the outer membrane protein PalA of Actinobacillus pleuropneumoniae in protective immunity was studied in pigs vaccinated with purified PalA alone and PalA in combination with toxoids of the RTX toxins ApxI and ApxII using an established challenge model with the virulent serotype 1 of A. pleuropneumoniae. Pigs that developed antibody titers against PalA after immunization were more significantly affected by challenge with A. pleuropneumoniae serotype 1. Following challenge, pigs that were immunized with PalA showed more severe respiratory symptoms, had a higher mortality rate and died faster. They also displayed much more severe lung lesions after necropsy than animals not immunized with PalA. Pigs that were immunized with toxoids of the two cytotoxins ApxI and ApxII were protected against challenge with A. pleuropneumoniae. In contrast, the protective efficacy of the ApxI and ApxII vaccine was completely lost when it was supplemented with PalA. Hence, antibodies induced against the outer membrane protein PalA of A. pleuropneumoniae aggravated the consequences of infection and counteracted the protective effect of anti-ApxI and anti-ApxII antibodies. Due to the high similarity between protein analogues of PalA from various bacteria of the Pasteurellaceae family such as P6 of Haemophilus influenzae or 16kDa Omp of Pasteurella multocida, this deleterious effect of PalA in vaccination should be taken into consideration in the development of vaccines against infections with other Pasteurellaceae.

Oral immunization using formalin-inactivated Actinobacillus pleuropneumoniae antigens entrapped in microspheres with aqueous dispersion polymers prepared using a co-spray drying process

Oral-vaccine microspheres based on formalin-inactivated Actinobacillus pleuropneumoniae serotype 1 (AP-1) antigens and enteric-coated polymers were prepared using a co-spray drying process. We evaluated using this for a peroral vaccine. We measured specific-antibody titers and protection from challenge in mouse and pig models. In mice (24 per group), a subcutaneous aluminum-adjuvant vaccine or oral vaccination with three doses of AQ6-AP microspheres provided similar protection against intranasal challenge with 5 x 10(8) colony-formation units (cfu) of AP-1 bacterial culture broth. Two weeks after four oral vaccinations with 600 mg of AQ6-AP microsphere acetate solution (containing formalin-inactivated AP-1 antigens of 1.0 x 10(10) cfu bacterial broth), pigs (9 per group) were challenged intranasally with 1 ml of AP-1 bacterial culture broth (5 x 10(9) cfu). The clinical signs, percentage of pig survival ratio, lung lesion areas, and microscopic examinations indicated that the oral AQ6-AP vaccine provided more protection than vaccinating pigs intramuscularly with AP-1 aluminum vaccine.

Design and analysis of an Actinobacillus pleuropneumoniae transmission experiment

This paper describes a methodology to quantify the transmission of Actinobacillus (A.) pleuropneumoniae from subclinically infected carrier pigs to susceptible contact pigs, and to test the effect of possible interventions on the transmission. The methodology includes the design of a transmission experiment, and a method with which A. pleuropneumoniae transmission can be quantified and with which the effect of an intervention on the transmission can be tested. The experimental design consists of two parts. First, subclinically infected carrier pigs are created by contact exposure of specific-pathogen-free pigs to endobronchially inoculated pigs. Second, transmission is observed from the group of carrier pigs to a second group of susceptible contact pigs after replacing the inoculated pigs by new contact pigs. The presented analytical method is a generalised linear model (GLM) with which the effect of an intervention on the susceptibility and infectivity can be tested separately, if the transmission is observed in heterogeneous populations. The concept of the experimental transmission model is illustrated by describing an A. pleuropneumoniae transmission experiment in which the effect of vaccination on the susceptibility is quantified. Although it could not be demonstrated that vaccination has an effect on the susceptibility of pigs, it was demonstrated that nasal excretion of A. pleuropneumoniae is related to the infectivity of pigs.

Construction of an Actinobacillus pleuropneumoniae serotype 2 prototype live negative-marker vaccine

Deletions were introduced into the ureC and apxIIA genes of an Actinobacillus pleuropneumoniae serotype 2 strain by homologous recombination and counterselection. The double-mutant contains no foreign DNA, is highly attenuated, protects pigs from homologous challenge upon a single aerosol application, and facilitates the serological discrimination of immunized and infected herds.

Blood lymphocyte subsets in pigs vaccinated and challenged with Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae bacterins do not induce protection in pigs while infection with low doses of the CM5 strain of A. pleuropneumoniae given by aerosol induces complete protection. To evaluate possible correlates of protection in blood lymphocyte subset phenotypes, pigs were treated with a commercial bacterin given intramuscularly, low dose (10(5)cfu/ml) aerosol infection with CM5 or control treatments of the bacterin adjuvant or phosphate buffered saline. All pigs were challenged with a high dose (10(7)cfu/ml) of A. pleuropneumoniae. Lymphocytes and sera were collected prior to and following primary and secondary immunizations and challenge, for evaluation of B- and T-cell markers and antibody to four A. pleuropneumoniae antigens. IgM(micro)+ B-cells were increased following primary exposure to antigen in the bacterin-vaccinated group only. An increase in CD4+ cells in the LD aerosol-infected group was apparent following secondary exposure to antigen. These early changes suggest little difference in lymphocyte populations between treatment groups, however, greater differences were observed following high-dose challenge; CD4+ lymphocytes were increased significantly in both bacterin and LD-challenged groups (p<0.05) while CD8+ cells decreased in the LD-group at this time period. Consequently, there were significant differences (p<0.05) in the CD4:CD8 ratio after high-dose challenge compared to earlier time points and control groups. Variation in cellular expression of SLA-DR and DQ was observed but trends correlating to treatment group were not evident. Complete protection or lack of protection associated with LD challenge or immunisation resulted in significant differences in B-cell frequencies and CD4:CD8 ratio phenotypes in pigs, but only changes in CD4:CD8 ratios appeared relevant to protection.

Overcoming immune tolerance during oral vaccination against Actinobacillus pleuropneumoniae

In the preliminary study mice were vaccinated orally with Actinobacillus pleuropneumoniae microsphere oral vaccine. The lung and eye mucous membranes of these mice did not contain increased immunoglobulin A (IgA) following the initial oral vaccination, possibly through antibody persistence and the phenomenon of immune exclusion. A similar tendency was found for serum IgG. However, after the second vaccination, IgA still did not increase significantly, which could be attributed to immune suppression due to the possibility of the intestine inducing immune tolerance. Only the third vaccination overcame this effect and increased the level of IgA. In order to achieve a high systemic and local immune response this study attempted to overcome the initial tolerance to oral vaccination by using temporary immunosuppression, increasing antigen dose, and prolonging vaccine influence. Triamcinolone, used in the later productive phase of the immune response after the first and second vaccinations, but restricted in the inductive phase of the second and third vaccinations, could disable immune tolerance. Suppression of antibody production before the next induction of the immune response by an oral vaccine combined with suppression of cell-suppressor activity led to the creation of systemic immunity with the possibility of high levels of A. pleuropneumoniae growth inhibition. Increased antigen doses or durable consumption of antigen could overcome immune exclusion of antigen by primary antibodies. Even very low doses of vaccine (4.5 mg) could induce a primary immune response, and a dose increased by 10-fold for the second vaccination could overcome tolerance and maintain high systemic immunity. Chronic consumption of oral vaccine led to benefits in the quantity of local (not systemic) antibodies. The outcomes of the study can be adapted for practical oral immunization of pigs.

Attenuation of Actinobacillus pleuropneumoniae by inactivation of aroQ

Actinobacillus pleuropneumoniae is the aetiological agent of porcine pleuropneumonia, a disease resulting in morbidity and mortality of pigs and accordingly economic losses within the swine industry. In order to construct a potential vaccine strain of A. pleuropneumoniae for control of this disease, the aroQ gene, required for the aromatic biosynthetic pathway, was targeted for inactivation. The resulting strain was tested for virulence within pigs. The aroQ gene and an adjacent gene, dapD, were cloned. A recombination cassette, for inactivation of aroQ, was constructed from these cloned genes by inserting an ampicillin resistance gene and this was transformed into A. pleuropneumoniae. Integration of this construct into the chromosomal location of aroQ and disruption of the aroQ/dapD gene arrangement was confirmed through PCR and Southern analysis. The resulting HS25 aroQ mutants were unable to grow in a chemically defined medium and following intratracheal delivery to pigs were only able to induce lung lesions when given at a level 10,000 times greater than that of the parent strain. Complementation with an in trans, functional, aroQ gene restored the ability of the mutant strain to grow in a chemically defined medium and virulence, when tested in pigs, confirming attenuation results from inactivation of aroQ. In conclusion, this work has constructed a defined mutant of A. pleuropneumoniae that is attenuated and may be safely delivered live to pigs.

Cloning and characterization of the gene coding for NADPH-sulfite reductase hemoprotein from Actinobacillus pleuropneumoniae and use of the protein product as a vaccine

An expression library was constructed from an Actinobacillus pleuropneumoniae serotype 1 clinical isolate and screened with serum produced in pigs that had been vaccinated with the anionic fraction of a sodium chloride extract. One E. coli transformant was isolated that produced a large amount of a protein with an electrophoretic mobility of about 67,000 molecular mass. The A. pleuropneumoniae-derived DNA encoding the protein was localized and characterized by restriction enzyme digestion and nucleotide sequence analysis which showed strong homology with the cysI gene of E. coli. One open reading frame of 1764 bases in length was detected which encoded a cysI protein from serotype 1, with a calculated molecular mass of 66,678. The DNA encoding the protein was labeled with radio-isotope and the homologous gene was isolated from an A. pleuropneumoniae serotype 5a library. The serotype 5a gene was the same length, but the cysI protein from serotype 5a was slightly larger (66,849) due to 8 substitutions in the amino acid sequence. Expression plasmids containing cysI from either serotype of A. pleuropneumoniae complemented an E. coli cysI mutant. Pigs vaccinated with the recombinant cysI were protected from challenge with A. pleuropneumoniae of the homologous serotype.

Release characteristics of microspheres prepared by co-spray drying Actinobacillus pleuropneumoniae antigens and aqueous ethyl-cellulose dispersion

Using formalin inactivated Actinobacillus pleuropneumoniae antigens and aqueous ethylcellulose dispersions, microspheres of oral vaccines were developed by a co-spray drying process. The present study attempted to determine whether the dosage formulations of microspheres could form enteric matrices. To assess the enteric characteristics, an in vitro dissolution test was performed with the AQ6-AP microspheres; 95% of the A. pleuropneumoniae protein was released within 3 h at pH 7, but there was no release at pH 1.5. The scanning microscopy revealed that the surface structure of AQ6-AP microspheres became porous at neutral pH. The SDS-PAGE analysis showed that the release rate of proteins from the microspheres was pH dependent not only for the AQ6-AP formulation but also when antigens of A. pleuropneumoniae were replaced with porcine serum. The results suggest that the A. pleuropneumoniae antigens were entrapped in the AQ6 microspheres under the acidic conditions. In a mouse model, oral immunization with AQ6-AP microspheres containing A. pleuropneumoniae evoked systemic IgG and mucosal IgA responses against A. pleuropneumoniae antigens. Thus, the present method may further provide an opportunity to develop oral vaccines and mucosal immunity.

No overall relationship between average daily weight gain and the serological response to Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae in eight chronically infected Danish swine herds

The association between the average daily weight gain (from approximately 4 to 20 weeks of age) and the serological responses to respiratory infections was examined in a longitudinal study including 825 pigs from eight chronically infected herds. Pigs were bled every 4th week (starting from approximately 4 weeks of age), and sera were analyzed for antibodies to Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae serotypes 2, 5-7 and 12.Mixed analysis of covariance analyzed the relationship between the average daily weight gain and a categorical variable defining seroconversion as none, early or late as compared to the median time (estimated across herds) of seroconversion for the particular pathogen. The variables "gender", "weight at an approximate age of 4 weeks" and "time" (defining the exact length of the follow-up period), were included as explanatory variables, and "litter" and "herd" were included as explanatory random variables. The individual pig was the unit of concern. The variable defining time at seroconversion was not significantly associated with the average daily weight gain, when evaluating models across all eight herds. The apparent lack of effect could be because most pigs included in the study were subclinically infected, or because a temporary negative influence of the infections is hidden due to an increased growth in the period following infection. In conclusion, at least in these eight herds, seroresponses to M. hyopneumoniae and A. pleuropneumoniae could not be used to predict the effect of the pathogens on the daily weight gain.

Effect of endobronchial challenge with Actinobacillus pleuropneumoniae serotype 9 of pigs vaccinated with a vaccine containing Apx toxins and transferrin-binding proteins

The efficacy of a subunit vaccine containing the Apx toxins of Actinobacillus pleuropneumoniae and transferrin-binding proteins was determined. Ten pigs were vaccinated twice with the vaccine. Eight control animals were injected twice with a saline solution. Three weeks after the second vaccination, all pigs were endobronchially inoculated with 10(6.5) colony-forming units (CFU) of an A. pleuropneumoniae serotype 9 strain. In the vaccine group, none of the pigs died after inoculation. Only one pig of the control group survived challenge. Surviving pigs were killed at 7 days after challenge. The mean percentage of affected lung tissue was 64% in the control group and 17% in the vaccine group. Actinobacillus pleuropneumoniae was isolated from the lungs of all animals. The mean bacterial titres of the caudal lung lobes were 5.0 x 10(8) CFU/g in the control group and 3.0 x 10(6) CFU/g in the vaccine group. It was concluded that the vaccine induced partial protection against severe challenge.

[The importance of different pig diseases in the Netherlands]

As part of the project 'Clean pigs', IPG Institute for Pig Genetics BV made an inventory of the impact of different diseases on the Dutch pig industry. An expert panel assessed the importance of the different diseases with regard to public health, farm economy, the pig sector and export sales. The possibilities for the diagnosis of the different pathogens were listed and the goal for the next years, was set. Diseases were classified into three categories, according to their importance for the Dutch pig industry (Table 2). The diseases that can be eradicated are Salmonella (only specific strains), Pasteurella multocida DNT + PAR), Actinobacillus pleuropneumoniae, Haematopinus suis (lice) and Sarcoptes scabei (var. suis) (mange). National introduction of list A en most list B diseases of the OIE classification must be prevented.

Actinobacillus pleuropneumoniae surface polysaccharides: their role in diagnosis and immunogenicity

Actinobacillus pleuropneumoniae is an important pig pathogen that is responsible for swine pleuropneumonia, a highly contagious respiratory infection. Knowledge of the importance, composition and structural determination of the major antigens involved in virulence provides crucial information that could lead to the development of a rationale for the production of specific serodiagnostic tools as well as vaccine development. Thus, efforts have been devoted to study mainly A. pleuropneumoniae virulence determinants with special emphasis on the Apx toxins (for A. pleuropneumoniae RTX toxins). In comparison, little attention has been given to the surface polysaccharides, which include capsular polysaccharides (CPS) and cell-wall lipopolysaccharides (LPS). Here, we review current knowledge on CPS and LPS of A. pleuropneumoniae used as diagnostic tools to monitor the infection and as immunogens for inclusion in vaccine preparations for animal protection.

A novel strategy for protective Actinobacillus pleuropneumoniae subunit vaccines: detergent extraction of cultures induced by iron restriction

We have characterized antigens from Actinobacillus (A.) pleuropneumoniae grown under iron restriction with respect to their immunogenic and protective potential. Antigens were the cell-free culture supernatants (CFS) obtained after treatment of A. pleuropneumoniae broth cultures with sodium deoxycholate. Using the iron-repressible transferrin-binding lipoprotein TbpB and the constitutively expressed outer membrane lipoprotein OmlA as markers, we have shown that the detergent extraction enriched the CFS with lipoproteins from the outer membrane (OM). Extractions with 0.05% of sodium deoxycholate increased the lipoprotein contents in the CFS, but did not affect the integrity of the OM. This was demonstrated by the absence of the iron-repressible integral OM transferrin-binding protein TbpA. Furthermore, the absence of periplasmic and cytoplasmic proteins in CFS after extraction was determined in immunoblot analyses with anti-bacterial alkaline phosphatase and anti-Hsp60 antisera, demonstrating that there was no rupture of the OMs or the plasma membranes due to the extraction procedure. Antigen preparations from A. pleuropneumoniae serotype 2 and 9 grown under iron restrictive conditions were combined, emulsified, and tested for their ability to confer protection in pigs. Pigs immunized with CFS from sodium deoxycholate extracted cultures developed a strong antibody response and, upon challenge with A. pleuropneumoniae serotype 2, the immunized pigs showed no or only mild clinical signs of disease and had a significantly lower degree of lung damage than the control pigs.

Effectiveness of doxycycline in the prevention of an experimental infection with Actinobacillus pleuropneumoniae in pigs

The effectiveness of medication with doxycycline in feed in the control of pleuropneumonia in pigs was tested using an Actinobacillus pleuropneumoniae serotype 1 aerosol challenge model. Two groups of 10 animals were used for the challenge, a 'medicated group' and an 'unmedicated group'. A third group of four animals was used as a 'control group'. Pigs from the medicated group were provided with feed containing 250 p.p.m. doxycycline (HIPRAMIX/DOXI) for 8 consecutive days and were challenged on the fifth day of treatment. No clinical signs were observed in pigs from the 'control group'. Four animals from the 'unmedicated group' died within the first 48 h after challenge with clinical and lesional evidence of an acute form of pleuropneumonia. Clinical signs of animals surviving the first 48 h were progressively less severe and showed lesions similar to those described for subacute-chronic forms of the disease. However, only one animal from the 'medicated group' showed clinical signs of a chronic form of pleuropneumonia. Reisolation of A. pleuropneumoniae was more evident from lung tissues of animals fed the doxycycline-free feed (70%), coinciding with the presence of both acute and subacute lesions. However, the micro-organism could be reisolated from only one animal which belonged to the 'medicated group'. It is concluded that the treatment of pigs with 250 p.p.m. doxycycline (HIPRAMIX/DOXI) prevents disease caused by A. pleuropneumoniae.

Prevention of pleuropneumonia in pigs by in-feed medication with sulphadimethoxine and sulphamethoxazole in combination with trimethoprim

The prophylactic effect of in-feed medication of conventional pigs with sulphadimethoxine (SDM), sulphamethoxazole (SMX), and trimethoprim (TMP) was tested by using an Actinobacillus pleuropneumoniae infection model. In each of five experiments, six pigs were given medicated feed twice daily and three pigs received antibiotic-free feed and served as positive (unmedicated, infected) controls. The following drugs or drug combinations were tested (in mg per kg feed): 500 SDM + 100 TMP, 500 SMX + 100 TMP, 125 SMX + 25 TMP, 125 SMX (alone) and 25 TMP (alone). After six days of feed medication, all animals were endobronchially inoculated with A. pleuropneumoniae in a dose of 1-3.10(4) colony-forming units (CFU). The response to the challenge in all control pigs was characterized by fever, lethargy, anorexia, reduced water consumption, and laboured breathing. At autopsy all controls manifested a fibrinous haemorrhagic pleuropneumonia. In-feed medication with 500 SDM + 100 TMP, 500 SMX + 100 TMP as well as 125 SMX + 25 TMP resulted in an effective protection against the challenge in all treated animals. After consumption of feed medicated with 125 mg per kg SMX or 25 mg per kg TMP, pleuropneumonia was evident in all challenged pigs. The results of this study indicate an in vivo potentiation of SMX and TMP in pigs against this respiratory tract pathogen.

Identification of Actinobacillus pleuropneumoniae virulence genes using signature-tagged mutagenesis in a swine infection model

Actinobacillus pleuropneumoniae is a significant respiratory pathogen of swine causing a severe and often fatal fibrinous hemorrhagic bronchopneumonia with significant economic losses resulting from chronic as well as acute infections. This study describes the application of a signature-tagged mutagenesis (STM) system to identify in vivo critical genes of A. pleuropneumoniae. Twenty pools representing over 800 A. pleuropneumoniae mutants were screened in a natural-host porcine infection model and presumptive attenuated mutants were selected. The identity of the disrupted gene in each mutant was determined using an inverse PCR approach to amplify DNA sequences adjacent to the transposon insertion, followed by sequencing of the PCR product and comparison to bacterial databases. In vitro and in vivo competitive indices were determined for each unique mutant, and a total of 20 unique, attenuating gene disruptions were identified including insertions into homologues of genes involved in biosynthesis, virulence determinants, regulation, translation and unknown functions. Three of the genes required for virulence of A. pleuropneumoniae in this study were also identified in a previous STM study of Pasteurella multocida. Seven of the STM-derived mutants were also evaluated for their potential as live vaccine strains and provided good protection against homologous challenge.

Intramuscular immunization with genetically inactivated (ghosts) Actinobacillus pleuropneumoniae serotype 9 protects pigs against homologous aerosol challenge and prevents carrier state

Bacterial ghosts are empty cell envelopes achieved by the expression of a cloned bacteriophage lysis gene and, unlike classical bacterins, suffer no denaturing steps during their production. These properties may lead to a superior presentation of surface antigens to the immune system. Currently available porcine Actinobacillus pleuropneumoniae vaccines afford only minimal protection by decreasing mortality but not morbidity. Pigs which survive infection can still be carriers of the pathogen, so a herd once infected remains infected. Carrier pigs harbour A. pleuropneumoniae in their nasal cavities, in their tonsils, or within lung lesions. A dose-defined nose-only aerosol infection model for pigs was used to study the immunogenic and protective potential of systemic immunization with ghosts made from A. pleuropneumoniae serotype 9 reference strain CVI 13261 against an homologous aerogenous challenge. Pigs were vaccinated twice intramuscularly with a dose of 5x10(9) CFU ghosts (GVPs) or formalin-inactivated A. pleuropneumoniae bacterins (BVPs). After 2 weeks vaccinated pigs and non-vaccinated placebo controls (PCs) were challenged with a dose of 10(9) CFU by aerosol. The protective efficacy of immunization was evaluated by clinical, bacteriological, serological and post-mortem examinations. Bronchoalveolar lavage in pigs was performed during the experiment to obtain lavage samples (BALF) for assessment of local antibodies. Isotype-specific antibody responses in serum and BALF were determined by ELISAs based on whole-cell antigen. Immunization with ghosts did not cause clinical side-effects. After aerosol challenge PCs developed fever and pleuropneumonia. GVPs or BVPs were found to be fully protected against clinical disease or lung lesions in both vaccination groups, whereas colonization of the respiratory tract with A. pleuropneumoniae was only prevented in GVPs. Specific immunoglobins against A. pleuropneumoniae were not detectable in BALF after immunization. A significant systemic increase of IgM, IgA, IgG(Fc'), or IgG(H+L) antibodies reactive with A. pleuropneumoniae was measured in GVPs and BVPs when compared to the non-exposed controls. BVPs reached higher titers of IgG(Fc') and IgG(H+L) than GVPs. However, prevention of carrier state in GVPs coincided with a significant increase of serum IgA when compared to BVPs. These results suggest that immunization with ghosts, that bias antibody populations specific to non-denaturated surface antigens, may be more efficacious in protecting pigs against colonization and infection than bacterins.

Actinobacillus actinomycetemcomitans in destructive periodontal disease. Three-year follow-up results

BACKGROUND

Convincing data exist that A. actinomycetemcomitans is an etiologic agent of periodontal disease. The purpose of this longitudinal study was to evaluate A. actinomycetemcomitans as a diagnostic indicator for periodontal disease in treated and periodontally maintained patients.

METHODS

Following comprehensive mechanical/surgical and supportive amoxicillin plus metronidazole therapy in 13 subjects with A. actinomycetemcomitans-associated destructive periodontal disease, we monitored subgingival A. actinomycetemcomitans at 4 individual sites in each patient up to 3 years post-therapy. The periodontal status was determined, and A. actinomycetemcomitans levels were quantitatively enumerated on TSBV agar in CFU/ml. Six patients with a persistence of subgingival A. actinomycetemcomitans at each reexamination within 3 years post-therapy were selected to be at risk for minor periodontal treatment outcomes and further recurrence of periodontal disease (test group). Seven subjects with a complete suppression of A. actinomycetemcomitans at each post-therapy visit served as controls.

RESULTS

The periodontal parameters decreased from overall values of 6.39 mm (probing depth, PD) and 7.64 mm (clinical attachment level, CAL) at the outset to 3.81 mm (PD) and 5.62 mm (CAL) 2 years post-therapy (Friedman, P< or =0.05). At the 3-year reexamination, the PD/CAL scores increased to 4.03/5.78 mm. Among the 6 individuals (46%) with persistence of subgingival A. actinomycetemcomitans at the final 3-year visit (test group), periodontal status yielded increased levels of 4.45 mm (PD) and 6.60 mm (CAL). The control subjects (n = 7) revealed lower values of 3.67 mm (PD) and 5.09 mm (CAL). However, on a patient level, during the 3-year observational trial, the periodontal status of the 13 individuals was not statistically affected by subgingival infection with A. actinomycetemcomitans.

CONCLUSIONS

Although in advanced periodontal disease, comprehensive mechanical and antimicrobial treatment is an appropriate regimen for sustained improvement of periodontal health, long-term control of subgingival infection with A. actinomycetemcomitans could not be achieved. In the maintenance care of destructive periodontitis, the persistence of A. actinomycetemcomitans is not a diagnostic parameter for periodontal disease.