Biofilm formation and avian immune response following experimental acute and chronic avian cholera due to Pasteurella multocida

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.

Development of fluorinated nicotinonitriles and fused candidates as antimicrobial, antibiofilm, and enzyme inhibitors

The antimicrobial assessments of two new series of nicotinonitriles and pyrido[2,3-d]pyrimidines were performed using amoxicillin and nystatin as reference standards. Outstanding antifungal activities were achieved by some target compounds; for instance, compounds 7 and 9 displayed a minimal inhibitory concentration (MIC) value of 1.95 µg/ml toward Candida albicans, compound 11 showed a potent anti-Rhizopus effect (MIC 1.95 µg/ml) and compound 14 elicited remarkable antifungal effects against both Aspergillis niger and C. albicans (MIC 1.95 µg/ml). However, pyrido[2,3-d]pyrimidines 12, 14, and 16 showed moderate antibacterial activities against some gram-negative bacteria. The antibiofilm results of these compounds against resistant strains of Proteus mirabilis were better than those of Pseudomonas aeruginosa. Docking studies of these hits at the DNA gyrase active site revealed affinity and docking scores comparable to that of the reference standards. Gyrase-inhibitory activities revealed that 14 (IC₅₀  = 0.31 µM) is the most potent hit as DNA gyrase A inhibitor; it exhibited 1.66-fold the activity of ciprofloxacin (IC₅₀  = 0.50 µM) and it was a 44.3 times more potent gyrase B inhibitor (IC₅₀  = 0.04 µM) than novobiocin (IC₅₀  = 1.77 µM). Regarding its antifungal activity, it displayed 0.78% of the fluconazole activity as a 14α-demethylase inhibitor. The cytotoxicity of 12, 14, and 16 on human diploid lung fibroblasts (WI38 cells) ensured their safety. Moreover, they are orally bioavailable with no permeation of the blood-brain barrier.

Characterization of Bacterial Microbiota Composition in Healthy and Diarrheal Early-Weaned Tibetan Piglets

The occurrence of diarrhea in Tibetan piglets is highly notable, but the microorganisms responsible are yet unclear. Its high incidence results in serious economic losses for the Tibetan pig industry. Moreover, the dynamic balance of intestinal microflora plays a crucial role in maintaining host health, as it is a prime cause of diarrhea. Therefore, the present study was performed to analyze the characteristics of bacterial microbiota structure in healthy, diarrheal and treated weaned piglets in Tibet autonomous region for providing a theoretical basis to prevent and control diarrhea. The study was based on the V3–V4 region of the 16S rRNA gene and gut microbiota functions following the metagenome analysis of fresh fecal samples (n = 5) from different groups. The Shannon and Simpson indices differed substantially between diarrheal and treated groups (p < 0.05). According to our findings, the beta diversities, especially between healthy and diarrheal groups, were found different. Firmicutes, Bacteroidetes and Proteobacteria were the dominant phyla in three groups. Furthermore, the abundance of Fusobacteria in the diarrheal group was higher than the other groups. The dominant genera in the diarrheal group were Fusobacterium, Butyricimonas, Sutterella, Peptostreptococcus, and Pasteurella. Moreover, Lactobacillus, Megasphaera and Clavibacter were distinctly less abundant in this group. It is noteworthy that the specific decrease in the abundance of pathogenic bacteria after antibiotic treatment in piglets was noticed, while the level of Lactobacillus was evidently increased. In conclusion, fecal microbial composition and structure variations were discovered across the three groups. Also, the ecological balance of the intestinal microflora was disrupted in diarrheal piglets. It might be caused by a reduction in the relative number of beneficial bacteria and an increase in the abundance of pathogenic bacteria. In the context of advocating for non-resistant feeding, we suspect that the addition of probiotics to feed may prevent early-weaning diarrhea in piglets. Moreover, our findings might help for preventing diarrhea in weaned Tibetan piglets with a better understanding of microbial population dynamics.

Novel multi-strain probiotics reduces Pasteurella multocida induced fowl cholera mortality in broilers

Pasteurella multocida causes fowl cholera, a highly contagious poultry disease of global concern, causing significant ecological and economic challenges to the poultry industry each year. This study evaluated the effects of novel multi-strain probiotics consisting of Lactobacillus plantarum, L. fermentum, Pediococcus acidilactici, Enterococcus faecium and Saccharomyces cerevisiae on growth performance, intestinal microbiota, haemato-biochemical parameters and anti-inflammatory properties on broilers experimentally challenged with P. multocida. A total of 120 birds were fed with a basal diet supplemented with probiotics (10⁸ CFU/kg) and then orally challenged with 10⁸ CFU/mL of P. multocida. Probiotics supplementation significantly (P < 0.05) improved growth performance and feed efficiency as well as reducing (P < 0.05) the population of intestinal P. multocida, enterobacteria, and mortality. Haemato-biochemical parameters including total cholesterol, white blood cells (WBC), proteins, glucose, packed cell volume (PCV) and lymphocytes improved (P < 0.05) among probiotic fed birds when compared with the controls. Transcriptional profiles of anti-inflammatory genes including hypoxia inducible factor 1 alpha (HIF1A), tumor necrosis factor- (TNF) stimulated gene-6 (TSG-6) and prostaglandin E receptor 2 (PTGER2) in the intestinal mucosa were upregulated (P < 0.05) in probiotics fed birds. The dietary inclusion of the novel multi-strain probiotics improves growth performance, feed efficiency and intestinal health while attenuating inflammatory reaction, clinical signs and mortality associated with P. multocida infection in broilers.

Macrophage Activation Assays to Evaluate the Immunostimulatory Capacity of Avibacterium paragallinarum in A Multivalent Poultry Vaccine

High-quality vaccines are crucial to prevent infectious disease outbreaks in the poultry industry. In vivo vaccination tests are routinely used to test poultry vaccines for their potency, i.e., their capacity to induce protection against the targeted diseases. A better understanding of how poultry vaccines activate immune cells will facilitate the replacement of in vivo potency tests for in vitro assays. Using the chicken macrophage-like HD11 cell line as a model to evaluate innate immune responses, the current explorative study addresses the immunostimulatory capacity of an inactivated multivalent vaccine for infectious bronchitis, Newcastle disease, egg-drop syndrome, and infectious coryza. The vaccine stimulated HD11 cells to produce nitric oxide and to express pro-inflammatory cytokines IL-1β, TNF, and IL-12p40, chemokines CXCLi1 and CXCLi2, and the anti-inflammatory cytokine IL-10, but only when inactivated Avibacterium paragallinarum, the causative agent of infectious coryza, was present. Lipopolysaccharides from Avibacterium paragallinarum were crucial for the production of nitric oxide and expression of IL-1β and CXCLi1. The described immune parameters demonstrate the capacity of this multivalent vaccine to activate innate immune cells and may in the future, combined with antigen quantification methods, contribute to vaccine quality testing in vitro, hence the replacement of current in vivo vaccination tests.

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.

Antibacterial and antibiofilm activity of acetone leaf extracts of nine under-investigated south African Eugenia and Syzygium (Myrtaceae) species and their selectivity indices

BACKGROUND

Antimicrobial resistance (AMR) remains an important global health issue but the gap between AMR and development of new antimicrobials is increasing. Plant extracts may have good activity per se or may be sources of effective antimicrobial compounds which can act against planktonic and/or biofilms of pathogens. We determined the antimicrobial efficacy and cytotoxicity of some under-investigated plants from the Myrtaceae family endemic to South Africa. The ability of the plant extracts to inhibit or destroy pre-formed bacterial biofilms was also determined.

METHODS

Based on previous preliminary in vitro screening and on chemotaxonomy, nine species from the Myrtaceae family were selected. The antimicrobial activity of the crude acetone leaf extracts was determined against six common nosocomial pathogens, namely: Gram-positive bacteria (Bacillus cereus, Enterococcus faecalis, Staphylococcus aureus), Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Salmonella Typhimurium) using a two-fold serial microdilution assay with p-iodonitrotetrazolium violet as growth indicator. The number of antimicrobial compounds present in extracts was determined by bioautography. Cytotoxicity of extracts was determined against Vero kidney cells using a colorimetric tetrazolium-based assay. The total antibacterial activity (TAA) in ml/g and selectivity index (LC₅₀/MIC) of the plant extracts were calculated. A modified crystal violet assay was used to determine the antibiofilm activity of the extracts.

RESULTS

Syzygium legatii, Syzygium masukuense, and Syzygium species A had the best activities against Gram-negative and Gram-positive bacteria (MIC) values ranging from 0.04-0.08 mg/ml. Eugenia erythrophylla had the best MIC (0.02 mg/ml) against Bacillus cereus. Many extracts had relatively low cytotoxicity (LC₅₀ > 20 μg/ml) leading to reasonable selectivity indices. Three leaf extracts (Syzygium masukuense, Syzygium species A, and Eugenia natalitia) were moderately cytotoxic (20 μg/ml < LC₅₀ < 100 μg/ml). The plant extracts had a good capacity to reduce biofilm formation and good to poor potential to destroy pre-formed biofilms.

CONCLUSIONS

The plant species examined in this study had varying degrees of antibacterial activity against bacterial planktonic and biofilm forms with some having good activity against both forms. Several of these selected species may be potential candidates for further investigation to isolate antimicrobial compounds and to determine the mechanism of activity.