High and low-virulent bovine Pasteurella multocida capsular type A isolates exhibit different virulence gene expression patterns in vitro and in vivo

Characterisation of Pasteurella multocida Strains from Different Lesions in Rabbits

Pasteurellosis, a disease caused by Pasteurella multocida, is responsible for economic losses in rabbit industrial farms due to rhinitis, conjunctivitis, pneumonia, metritis, mastitis, orchitis, subcutaneous abscesses, otitis, encephalitis, and septicaemic forms. Although the occurrence of the disease is conditioned by predisposing factors that affect the rabbit immune response, the strains of P. multocida involved in the infection may have a different pathogenic ability. Therefore, typing of strains spread among the rabbits is important to assess their pathogenic potential. The aim of this study is to investigate the P. multocida strains responsible for disease in rabbit industrial farms. A total of 114 strains identified from different lesions were serotyped. Additionally, the presence of virulence-associated genes was investigated using three PCR (polymerase chain reaction) protocols. Capsular type A was prevalently found in strains from respiratory lesions while types D and F in those from metritis, mastitis, and other lesions. Different associations between some virulence-associated genes and both capsular type and lesions found in rabbits were detected. The presence of 8 virulence-associated genes seems to increase the occurrence of metritis. In addition, strains belonging to capsular type A and responsible for respiratory disorders especially, were found equipped with 10 and 11 virulence-associated genes. Nevertheless, the presence of strains responsible only for rhinitis was also detected among the latter, suggesting that the pathogenic ability of the bacteria depends on the expression rather than the presence of a gene.

Deleting qseC downregulates virulence and promotes cross-protection in Pasteurella multocida

QseC, a histidine sensor kinase of the QseBC two-component system, acts as a global regulator of bacterial stress resistance, biofilm formation, and virulence. The function of QseC in some bacteria is well understood, but not in Pasteurella multocida. We found that deleting qseC in P. multocida serotype A:L3 significantly down-regulated bacterial virulence. The mutant had significantly reduced capsule production but increased resistance to oxidative stress and osmotic pressure. Deleting qseC led to a significant increase in qseB expression. Transcriptome sequencing analysis showed that 1245 genes were regulated by qseC, primarily those genes involved in capsule and LPS biosynthesis and export, biofilm formation, and iron uptake/utilization, as well as several immuno-protection related genes including ompA, ptfA, plpB, vacJ, and sodA. In addition to presenting strong immune protection against P. multocida serotypes A:L1 and A:L3 infection, live ΔqseC also exhibited protection against P. multocida serotype B:L2 and serotype F:L3 infection in a mouse model. The results indicate that QseC regulates capsular production and virulence in P. multocida. Furthermore, the qseC mutant can be used as an attenuated vaccine against P. multocida strains of multiple serotypes.

Transcriptomic Analysis of High- and Low-Virulence Bovine Pasteurella multocida in vitro and in vivo

Pasteurella multocida is a gram-negative opportunistic pathogen that causes various diseases in poultry, livestock, and humans, resulting in huge economic losses. Pasteurella multocida serotype A CQ6 (PmCQ6) is a naturally occurring attenuated strain, while P. multocida serotype A strain CQ2 (PmCQ2) is a highly virulent strain isolated from calves. Compared with PmCQ2, it was found that bacterial loads and tissue lesions of lung tissue significantly decreased and survival rates significantly improved in mice infected with PmCQ6 by intranasal infection. However, comparative genome analysis showed that the similarity between the two strains is more than 99%. To further explore the virulence difference mechanism of PmCQ2 and PmCQ6, transcriptome sequencing analysis of the two strains was performed. The RNA sequencing analysis of PmCQ2 and PmCQ6 showed a large number of virulence-related differentially expressed genes (DEGs) in vivo and in vitro. Among them, 38 virulence-related DGEs were significantly up-regulated due to PmCQ6 infection, while the number of PmCQ2 infection was 46, much more than PmCQ6. In addition, 18 virulence-related DEGs (capsule, iron utilization, lipopolysaccharide, and outer membrane protein-related genes) were up-regulated in PmCQ2 infection compared to PmCQ6 infection, exhibiting a higher intensive expression level in vivo. Our findings indicate that these virulence-related DEGs (especially capsule) might be responsible for the virulence of PmCQ2 and PmCQ6, providing prospective candidates for further studies on pathogenesis.

Pasteurella multocida Pm0442 Affects Virulence Gene Expression and Targets TLR2 to Induce Inflammatory Responses

Pasteurella multocida is an important pathogenic bacterium of domestic animals. However, the mechanisms of infection are still poorly understood. Here, we found that Pm0442 was dramatically up-regulated in infected mice among 67 predicted lipoproteins of P. multocida serotype A CQ2 strain (PmCQ2). To explore the role of Pm0442 in virulence and the potential of the mutant as a vaccine, Pm0442 mutant of PmCQ2 was successfully constructed. Then, the virulence characteristics, immune/inflammatory responses, and the survival rates of challenged mice were determined. As a result, it was found that the Pm0442 deletion of PmCQ2 significantly decreased bacterial loads and inflammatory responses of lung tissue in mice, resulting in improved survival. Mechanically, Pm0442 affects PmCQ2 capsular and lipopolysaccharide (LPS) synthesis and iron utilization-related genes expression affecting adhesion and phagocytosis. Furthermore, PM0442 bound directly to Toll-like receptor 2 (TLR2) to mediate the secretion of pro-inflammatory cytokine (IL-1β, TNF-α, IL-6, and IL-12p40) in macrophages via activation of the NF-κB, ERK1/2 and p38 signaling pathways. Notably, PmCQ2Δ0442 could provide 70-80% protection to mice challenged with 3.08 × 107 CFU of PmCQ2. Our findings demonstrate that Pm0442 is a virulence-related gene of PmCQ2, which provides new guidance for the prevention and control of Pasteurellosis.

Transcriptomic Analysis of Chicken Lungs Infected With Avian and Bovine Pasteurella multocida Serotype A

Pasteurella multocida (P. multocida) is a common animal pathogen responsible for many animal diseases. Strains from different hosts exhibit disparate degrees of effect in other species. Here, we characterize an avian P. multocida serogroup A strain (PmQ) showing high lethality to chickens and a bovine P. multocida serogroup A strain (PmCQ2) with no lethality to chickens. We used RNA-seq to profile the transcriptomes of chicken lungs infected with PmQ and PmCQ2. A total of 1,649 differentially expressed genes (DEGs) due to PmQ infection (831 upregulated genes and 818 downregulated genes) and 1427 DEGs (633 upregulated genes and 794 downregulated genes) due to PmCQ2 infection were identified. Functional analysis of these DEGs demonstrated that the TNF signaling pathway, the toll-like receptor signaling pathway, complement and coagulation cascades, and cytokine–cytokine receptor interaction were both enriched in PmQ and PmCQ2 infection. STAT and apoptosis signaling pathways were uniquely enriched by PmQ infection, and the NOD-like receptor signaling pathway was enriched only by PmCQ2 infection. Cell-type enrichment analysis of the transcriptomes showed that immune cells, including macrophages and granulocytes, were enriched in both infection groups. Collectively, our study profiled the transcriptomic response of chicken lungs infected with P. multocida and provided valuable information to understand the chicken responses to P. multocida infection.

Molecular pathogenesis of the hyaluronic acid capsule of Pasteurella multocida

Pasteurella multocida possesses a viscous capsule polysaccharide on the cell surface, which is a critical structural component and virulence factor. Capsular polysaccharides are structurally similar to vertebrate glycosaminoglycans, providing an immunological mechanism for bacterial molecular mimicry, resistance to phagocytosis, and immune evasion during the infection process. Based on the capsular antigen, P. multocida is divided into A, B, D, E, and F five serogroups. Previously, we systematically reported the biosynthesis and regulation mechanisms of the P. multocida capsule. In this paper, we take serogroup A capsular polysaccharide as the representative, systematically illuminating the P. multocida capsular virulence and epidemiology, molecular camouflage, adhesion and colonization, anti-phagocytosis, anti-complement system, cell invasion and signal transduction mechanism, to provide a theoretical basis for the research of molecular pathogenic mechanism of P. multocida capsule and the development of polysaccharides vaccine.

High- and low-virulent bovine Pasteurella multocida induced differential NLRP3 inflammasome activation and subsequent IL-1β secretion

Pasteurella multocida is a gram-negative bacterial pathogen, which causes a large number of diseases in mammals, birds and human. Although the bacterium has been known for decades, the pathogenesis and the mechanisms of P. multocida induced host immunity are poorly understood. Recently, we have reported that nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome plays an important role in caspase-1 activation and IL-1β secretion in macrophages infected with P. multocida. In this study, the inflammasome activation and IL-1β secretion were further demonstrated by using high- and low-virulent bovine P. multocida isolates. The results showed that, comparing with macrophages infected with the high-virulent PmCQ2 isolates, the low-virulent PmCQ6 induced higher levels of NLRP3 transcription, caspase-1 activation and mature IL-1β secretion. Furthermore, the capsule of the high-virulent PmCQ2 was much thicker than that of low-virulent PmCQ6, which indicating that capsular thickness might influence the bacteria colonization and NLRP3 inflammasome activation. The results suggested that differences in maturation of IL-1β in macrophages upon high- and low- virulent P. multocida infection are critically dependent on the differential activation of NLRP3 inflammasome. This study provided more understanding for the host immune responses induced by P. multocida and further extended the knowledge of P. multocida virulence from the view of host innate immunity.

Differences in pathogenicity and virulence-associated gene expression among Pasteurella multocida strains with high and low virulence in a lung tissue model

Pasteurella multocida capsular type A can cause a pulmonary infection, leading to serious pecuniary losses in cattle. The heterogeneity of infection outcome of P. multocida strains showing different virulence may be related to divergent expression of virulence genes. In this study, we compared the transcriptional response of virulence-associated genes in high (PMPAN001) and low (PMPAN007) virulence P. multocida capsular type A strains in lung tissues and in vitro. These clinical isolates differ in their organ bacterial loads, mRNA abundance of the same virulence genes between lung and culture medium, and extent of lung damage. Among the eight virulence-associated genes (fimA, tbpA, exbD, fur, oma87, pmHAS, nanH, and tonB), seven genes showed higher expression in lung compared with in vitro at 16 h (P ≤ 0.05) in PMPAN001, but not in PMPAN007. FimA, exbD, fur, oma87, pmHAS, and tonB gene transcripts showed significantly higher expression in PMPAN001 than in PMPAN007 in the lung tissues at 16 h post-infection (P ≤ 0.05). Specially, the virulence gene, nanH, in both strains was associated with poor expression in vitro and lung tissue (mean relative mRNA abundance values < 0.6). Strain PMPAN001 had a higher proliferation rate in vivo than strain PMPAN007. The bacterial loads of PMPAN001 in the organs increased from 12 h post-infection, with maximum bacteria count ranging from 1 million to 20 million/mg. In addition, lungs treated with PMPAN001 produced serious and extensive lesions marked with inflammation at 20 h. Overall, our results reveal that the highly expressed virulence-associated genes, fimA, exbD, fur, oma87, pmHAS, and tonB can be used as markers for assessing the virulence of P. multocida capsular type A strains.

l-Serine Lowers the Inflammatory Responses during Pasteurella multocida Infection

Pasteurella multocida causes a variety of infectious diseases in various species of mammals and birds, resulting in enormous economic loss to the modern livestock and poultry industry. However, the mechanism of host-pathogen interaction is unclear. Here, we found that l-serine levels were significantly decreased in murine lungs infected with P. multocida.

Pasteurella multocida causes a variety of infectious diseases in various species of mammals and birds, resulting in enormous economic loss to the modern livestock and poultry industry. However, the mechanism of host-pathogen interaction is unclear. Here, we found that l-serine levels were significantly decreased in murine lungs infected with P. multocida. Exogenous l-serine supplementation significantly increased the survival rate of mice and decreased the colonization of P. multocida in the lungs of mice. Notably, l-serine decreased the macrophage- and neutrophil-mediated inflammatory responses in mice during P. multocida infection.

OmpA protein sequence-based typing and virulence-associated gene profiles of Pasteurella multocida isolates associated with bovine haemorrhagic septicaemia and porcine pneumonic pasteurellosis in Thailand

Background

Pasteurella multocida is a Gram-negative bacterium that causes economically significant infections of a broad range of animal species. Pneumonic and septicaemic pasteurellosis caused by this bacterium remain important problems in pigs, cattle, and water buffaloes in Thailand. The aim of this study was to characterise the virulence-associated gene profiles and to develop an OmpA molecular typing scheme for classifying 191 bovine and porcine isolates of P. multocida collected between 1989 and 2012 in Thailand using polymerase chain reactions (PCRs), nucleotide sequencing, and sequence and structural bioinformatics analyses.

Results

PCR screening successfully characterised the profiles of 25 virulence-associated genes in all isolates. The gene profiles separated these isolates into bovine and porcine clusters based on eight genes (hgbB, hsf1, tadD, nanH, pfhA, plpE, pmHAS, and tbpA). Phylogenetic analyses of the nucleotide and protein sequences corresponding to the ompA gene, which encodes a major outer membrane surface protein, showed two major bovine and porcine clusters. Structural prediction and analysis of the dN/dS ratio revealed four hypervariable extracellular loops of the OmpA transmembrane domains. These four loops were used to develop an OmpA typing scheme. This scheme classified 186 isolates into five major loop sequence types (LST8, LST12, LST15, LST18, and LST19), consistent with the phylogenetic results. The loop regions of the bovine isolates were predicted to be more antigenic than those of the porcine isolates. Thus, molecular evolution of the OmpA proteins could be used to classify P. multocida isolates into different capsular types, host types, and, possibly, pathogenicity levels.

Conclusions

Together with the virulence-associated gene profiles, the typing reported in this work provides a better understanding of P. multocida virulence. Effective monitoring and potential strain-specific subunit vaccines could be developed based on these loop oligopeptides.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1157-6) contains supplementary material, which is available to authorized users.

Transcriptomic Analysis on Responses of Murine Lungs to Pasteurella multocida Infection

Pasteurella multocida infection in cattle causes serious epidemic diseases and leads to great economic losses in livestock industry; however, little is known about the interaction between host and P. multocida in the lungs. To explore a fully insight into the host responses in the lungs during P. multocida infection, a mouse model of Pasteurella pneumonia was established by intraperitoneal infection, and then transcriptomic analysis of infected lungs was performed. P. multocida localized and grew in murine lungs, and induced inflammation in the lungs, as well as mice death. With transcriptomic analysis, approximately 10⁷ clean reads were acquired. 4236 differently expressed genes (DEGs) were detected during P. multocida infection, of which 1924 DEGs were up-regulated. By gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichments, 5,303 GO enrichments and 116 KEGG pathways were significantly enriched in the context of P. multocida infection. Interestingly, genes related to immune responses, such as pattern recognition receptors (PRRs), chemokines and inflammatory cytokines, were significantly up-regulated, suggesting the key roles of these genes in P. multocida infection. Transcriptomic data showed that IFN-γ/IL-17-related genes were increased, which were validated by qRT-PCR, ELISA, and immunoblotting. Our study characterized the transcriptomic profile of the lungs in mice upon Pasteurella infection, and our findings could provide valuable information with respect to better understanding the responses in mice during P. multocida infection.