Genotypic prevalence of apx1V in Actinobacillus pleuropneumoniae field isolates

Global Gene Networks in 3D4/31 Porcine Alveolar Macrophages Treated with Antigenic Epitopes of Actinobacillus pleuropneumoniae ApxIA, IIA, and IVA

Actinobacillus pleuropneumoniae (App) is the causative agent of porcine pleuropneumonia. Although App produces several virulence factors, Apx toxins, the primary App virulence factors, have been the focus of numerous studies. However, the host response against the Apx toxins has not been elucidated at the transcriptomic level. Therefore, in this study, we examined the response of an immortalized porcine alveolar macrophage cell line (IPAM 3D4/31) to four antigenic epitopes of the App exotoxins, ApxIA, IIA and IVA. The antigenic epitopes of the Apx toxins (ApxIA Ct, ApxIIA Nt, ApxIVA C1 and ApxIV C2) were determined by an in-silico antigenicity prediction analysis. Gene expression in IPAMs was analyzed by RNA-Seq after treatment with the four proteins for 24 h. A total of 15,269 DEGs were observed to be associated with cellular and metabolic processes in the GO category Biological Process and nuclear receptors and apoptosis signaling in IPA analyses. These DEGs were also related to M2 macrophage polarization and apoptosis in IPAMs. These host transcriptional analyses present novel global gene networks of the host response to treatment with Apx toxins.

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 an Actinobacillus pleuropneumoniae serotype 2 mutant lacking the Apx toxin secretion protein genes apxIIIB and apxIIID

Apx toxins have been identified as important virulence factors of Actinobacillus pleuropneumoniae, the etiologic agent of porcine pleuropneumonia. In some A. pleuropneumoniae serotypes, Apx toxins are secreted by the cell membrane proteins encoded by apxIIIB and apxIIID genes. In an effort to develop a live vaccine strain against A. pleuropneumoniae, we inactivated the apxIIIB and apxIIID genes in A. pleuropneumoniae 1536, a serotype 2 strain, resulting in the DeltaapxIIIB/DapxIIID mutant strain (1536DeltaBDeltaD). Immunization of pigs with live 1536DeltaBDeltaD A. pleuropneumoniae conferred protection against homologous challenge with wild-type A. pleuropneumoniae 1536. Thus, impaired Apx toxin secretion may decrease the virulence of A. pleuropneumoniae and may be an effective strategy for the development of a live-attenuated A. pleuropneumoniae vaccine.

Microarray-based comparative genomic profiling of reference strains and selected Canadian field isolates of Actinobacillus pleuropneumoniae

Background

Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumonia, is a highly contagious respiratory pathogen that causes severe losses to the swine industry worldwide. Current commercially-available vaccines are of limited value because they do not induce cross-serovar immunity and do not prevent development of the carrier state. Microarray-based comparative genomic hybridizations (M-CGH) were used to estimate whole genomic diversity of representative Actinobacillus pleuropneumoniae strains. Our goal was to identify conserved genes, especially those predicted to encode outer membrane proteins and lipoproteins because of their potential for the development of more effective vaccines.

Results

Using hierarchical clustering, our M-CGH results showed that the majority of the genes in the genome of the serovar 5 A. pleuropneumoniae L20 strain were conserved in the reference strains of all 15 serovars and in representative field isolates. Fifty-eight conserved genes predicted to encode for outer membrane proteins or lipoproteins were identified. As well, there were several clusters of diverged or absent genes including those associated with capsule biosynthesis, toxin production as well as genes typically associated with mobile elements.

Conclusion

Although A. pleuropneumoniae strains are essentially clonal, M-CGH analysis of the reference strains of the fifteen serovars and representative field isolates revealed several classes of genes that were divergent or absent. Not surprisingly, these included genes associated with capsule biosynthesis as the capsule is associated with sero-specificity. Several of the conserved genes were identified as candidates for vaccine development, and we conclude that M-CGH is a valuable tool for reverse vaccinology.

Association of porcine circovirus 2 with porcine respiratory disease complex

A retrospective study was performed on natural cases of porcine respiratory disease complex (PRDC) to determine the association and prevalence of PRDC with porcine circovirus 2 (PCV2) and other co-existing pathogens in Korea. Histologically, alveolar septa were markedly thickened by infiltrates of mononuclear cells. Moderate to marked multifocal peribronchial and peribronchiolar fibrosis were present and often extended into the airway lamina propria. Among the 105 pigs with PRDC, 85 were positive for PCV2, 66 were positive for porcine reproductive and respiratory syndrome virus (PRRSV), 60 were positive for porcine parvovirus (PPV), and 14 were positive for swine influenza virus (SIV). There were 80 co-infections and 25 single infections. A co-infection of PCV2 with another additional bacterial pathogen is frequently diagnosed in PRDC. The combination of PCV2 and Pasteurella multocida (38 cases) was most prevalent followed by PCV2 and Mycoplasma hyopneumoniae (33 cases). The consistent presence of PCV2, but lower prevalence of other viral and bacterial pathogens in all pigs examined with PRDC, has led us to speculate that PCV2 plays an important role in PRDC.

PCR detection of Actinobacillus pleuropneumoniaeapxIV gene in formalin-fixed, paraffin-embedded lung tissues and comparison with in situ hybridization

AIMS

Formalin-fixed, paraffin-embedded lung tissues from pigs experimentally infected with 12 Actinobacillus pleuropneumoniae serotypes were used to develop nested PCR for the detection of apxIV gene.

METHODS AND RESULTS

The PCR results from formalin-fixed, paraffin-embedded tissues were compared with in situ hybridization. The apxIV gene was detected in formalin-fixed, paraffin-embedded lung tissues from all 39 pigs experimentally infected with 12 A. pleuropneumoniae serotypes by nested PCR. In situ hybridization produced a distinct positive signal in all 39 pigs experimentally infected with 12 A. pleuropneumoniae serotypes. Agreement rates between nested PCR and in situ hybridization were 100% for the detection of apxIV gene in formalin-fixed paraffin-embedded lung tissues. Acceptable PCR signals were detected from lung tissues fixed for periods up to 180 days.

CONCLUSIONS

The apxIV gene is species-specific rather than serotype-specific and is therefore an important diagnostic marker. The nested PCR assay would be a useful method for the detection of apxIV gene to diagnose A. pleuropneumoniae infection when formalin-fixed tissues are submitted.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study confirmed the possibility of using formalin-fixed, paraffin-embedded tissues for the diagnosis of A. pleuropneumoniae infection in pigs.

Expression of the apxIV gene in pigs naturally infected with Actinobacillus pleuropneumoniae

The apxIV gene was detected, by in-situ hybridization with a non-radioactive digoxigenin-labelled probe, in formalin-fixed, paraffin wax-embedded samples of lung tissue from 10 pigs naturally infected with Actinobacillus pleuropneumoniae. A 442 base pair DNA probe of the apxIV gene from A. pleuropneumoniae serotype 2 was generated by the polymerase chain reaction. All 10 pigs infected with A. pleuropneumoniae serotypes 2, 5, 6, or an untypable strain showed a distinct, positive signal in the degenerate alveolar leucocytes in alveolar spaces, and in the dense zone of degenerated cells in granulation tissue surrounding the necrotic areas. Thus, the study demonstrated the presence of the apxIV gene in pleuropneumonic lesions caused by A. pleuropneumoniae.