Two novel cross‑protective antigens for bovine Pasteurella multocida

Developing a PmSLP3-based vaccine formulation that provides robust long-lasting protection against hemorrhagic septicemia-causing serogroup B and E strains of Pasteurella multocida in cattle

Background

Pasteurella multocida is a bacterial pathogen that causes a variety of infections across diverse animal species, with one of the most devastating associated diseases being hemorrhagic septicemia. Outbreaks of hemorrhagic septicemia in cattle and buffaloes are marked by rapid progression and high mortality. These infections have particularly harmful socio-economic impacts on small holder farmers in Africa and Asia who are heavily reliant on a small number of animals kept as a means of subsistence for milk and draft power purposes. A novel vaccine target, PmSLP-3, has been identified on the surface of hemorrhagic septicemia-associated strains of P. multocida and was previously shown to elicit robust protection in cattle against lethal challenge with a serogroup B strain.

Methods

Here, we further investigate the protective efficacy of this surface lipoprotein, including evaluating the immunogenicity and protection upon formulation with a variety of adjuvants in both mice and cattle.

Results

PmSLP-3 formulated with Montanide ISA 61 elicited the highest level of serum and mucosal IgG, elicited long-lasting serum antibodies, and was fully protective against serogroup B challenge. Studies were then performed to identify the minimum number of doses required and the needed protein quantity to maintain protection. Duration studies were performed in cattle, demonstrating sustained serum IgG titres for 3 years after two doses of vaccine and full protection against lethal serogroup B challenge at 7 months after a single vaccine dose. Finally, a serogroup E challenge study was performed, demonstrating that PmSLP-3 vaccine can provide protection against challenge by the two serogroups responsible for hemorrhagic septicemia.

Conclusion

Together, these data indicate that PmSLP-3 formulated with Montanide ISA 61 is an immunogenic and protective vaccine against hemorrhagic septicemia-causing P. multocida strains in cattle.

Pharmacokinetic/pharmacodynamic evaluation of gamithromycin against rabbit pasteurellosis

BACKGROUND

Gamithromycin is an effective therapy for bovine and swine respiratory diseases but not utilized for rabbits. Given its potent activity against respiratory pathogens, we sought to determine the pharmacokinetic profiles, antimicrobial activity and target pharmacokinetic/pharmacodynamic (PK/PD) exposures associated with therapeutic effect of gamithromycin against Pasteurella multocida in rabbits.

RESULTS

Gamithromycin showed favorable PK properties in rabbits, including high subcutaneous bioavailability (86.7 ± 10.7%) and low plasma protein binding (18.5-31.9%). PK analysis identified a mean plasma peak concentration (Cmax) of 1.64 ± 0.86 mg/L and terminal half-life (T1/2) of 31.5 ± 5.74 h after subcutaneous injection. For P. multocida, short post-antibiotic effects (PAE) (1.1-5.3 h) and post-antibiotic sub-inhibitory concentration effects (PA-SME) (6.6-9.1 h) were observed after exposure to gamithromycin at 1 to 4× minimal inhibitory concentration (MIC). Gamithromycin demonstrated concentration-dependent bactericidal activity and the PK/PD index area under the concentration-time curve over 24 h (AUC24h)/MIC correlated well with efficacy (R2 > 0.99). The plasma AUC24h/MIC ratios of gamithromycin associated with the bacteriostatic, bactericidal and bacterial eradication against P. multocida were 15.4, 24.9 and 27.8 h in rabbits, respectively.

CONCLUSIONS

Subcutaneous administration of 6 mg/kg gamithromycin reached therapeutic concentrations in rabbit plasma against P. multocida. The PK/PD ratios determined herein in combination with ex vivo activity and favorable rabbit PK indicate that gamithromycin may be used for the treatment of rabbit pasteurellosis.

Attenuated vaccine PmCQ2Δ4555-4580 effectively protects mice against Pasteurella multocida infection

Pasteurella multocida type A (PmA) mainly causes respiratory diseases such as pneumonia in bovines, leading to great economic losses to the breeding industry. At present, there is still no effective commercial vaccine against PmA infection. In this study, a mutant strain (PmCQ2Δ4555-4580) with brand-new phenotypes was obtained after serially passaging at 42 °C. Whole genome resequencing and PCR analysis showed that PmCQ2Δ4555-4580 missed six genes, including PmCQ2_004555, PmCQ2_004560, PmCQ2_004565, PmCQ2_004570, PmCQ2_004575, and PmCQ2_004580. Importantly, the virulence of PmCQ2Δ4555-4580 was reduced by approximately 2.8 × 109 times in mice. Notably, live PmCQ2Δ4555-4580 could provide 100%, 100% and 40% protection against PmA, PmB and PmF, respectively; and inactivated PmCQ2Δ4555-4580 could provide 100% and 87.5% protection against PmA and PmB. Interestingly, immune protection-related proteins were significantly upregulated in PmCQ2Δ4555-4580 based on RNA-seq and bioinformatics analysis. Meaningfully, by in vitro expression, purification and in vivo immunization, 12 proteins had different degrees of immune protective effects. Among them, PmCQ2_008205, PmCQ2_010435, PmCQ2_008190, and PmCQ2_004170 had the best protective effect, the protection rates against PmA were 50%, 40%, 30%, and 30%, respectively, and the protective rates against PmB were 62.5%, 42.9%, 37.5%, and 28.6%, respectively. Collectively, PmCQ2Δ4555-4580 is a potential vaccine candidate for the prevention of Pasteurellosis involving in high expression of immune protective related proteins.

Slc6a13 Deficiency Attenuates Pasteurella multocida Infection-Induced Inflammation via Glycine-Inflammasome Signaling

We have previously demonstrated that Slc6a13-deficient (Slc6a13-/-; KO) mice are resistant to P. multocida infection, which might be in connection with macrophage-mediated inflammation; however, the specific metabolic mechanism is still enigmatic. Here we reproduce the less sensitive to P. multocida infection in overall survival assays as well as reduced bacterial loads, tissue lesions, and inflammation of lungs in KO mice. The transcriptome sequencing analysis of wild-type (WT) and KO mice shows a large number of differentially expressed genes that are enriched in amino acid metabolism by functional analysis. Of note, glycine levels are substantially increased in the lungs of KO mice with or without P. multocida infection in comparison to the WT controls. Interestingly, exogenous glycine supplementation alleviates P. multocida infection-induced inflammation. Mechanistically, glycine reduces the production of inflammatory cytokines in macrophages by blocking the activation of inflammasome (NALP1, NLRP3, NLRC4, AIM2, and Caspase-1). Together, Slc6a13 deficiency attenuates P. multocida infection through lessening the excessive inflammatory responses of macrophages involving glycine-inflammasome signaling.

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.

A single point mutation in the hyaC gene affects Pasteurella multocida serovar A capsule production and virulence

Pasteurella multocida (P. multocida) is a Gram-negative bacterium which causes diseases in poultry, livestock, and humans, resulting in huge economic losses. P. multocida serovar A CQ6 (PmCQ6) is a naturally occurring attenuated strain with a thin capsule. Thus, we aimed to explore why this strain is less virulent and produces less capsule compared with P. multocida serovar A strain CQ2 (PmCQ2). Analysis of capsular polysaccharide synthesis genes in PmCQ6 revealed that, compared with PmCQ2, there was only a single point mutation in the initiation codon sequence of the hyaC gene. To test whether this point mutation caused capsular deficiency and reduced virulence, we rescued this hyaC mutation and observed a restoration of capsule production and higher virulence. Transcriptome analysis showed that the hyaC point mutation led to a downregulation of capsule synthesis and/or iron utilization related-genes. Taken together, the results indicate that the start codon mutation of hyaC is an important factor affecting the capsule synthesis and virulence of PmCQ6.

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.