Genomic diversity and molecular epidemiology of Pasteurella multocida

Exploring the Impact of Land Cover on the Occurrence of Ornithobacteriosis and Fowl Cholera: A Case-Case Study

Ornithobacterium rhinotrachealis (ORT) and Pasteurella multocida (PM) are two major bacterial pathogens affecting the United States (US) commercial turkey industry. This retrospective observational case-case study aimed to investigate the association between land cover and confirmed disease occurrences attributed to PM or ORT in commercial turkey sites located in the Midwestern US A total of 65 farms from one poultry production company were included, where 28 had PM disease occurrences and 37 had ORT disease occurrences between 2014 and 2021. Risk factors of interest included land cover types (wetlands, forest, urban, pasture, herbaceous, barren, shrub), poultry-farm density in the area, and season and year of confirmed outbreak(s). A multivariable logistic regression model revealed that for every 1 m increase in distance from a farm to the nearest wetland, the odds of a confirmed disease occurrence related to PM decreased by approximately 0.24% compared to an ORT-related disease occurrence (p = 0.004). Meanwhile, PM occurrence during 2014-2017 was 98.5% higher than 2018-2019 and 93.2% higher than in 2020-2021. Broadly, the findings contribute to the dearth of research on land cover and turkey respiratory diseases and demonstrate that land cover is an important consideration for farm management and future study.

Characterization and Potential Application of Phage vB_PmuM_CFP3 for Phage Therapy Against Avian Pasteurella multocida

The rise of antibiotic-resistant bacterial infections necessitates alternative therapeutic strategies, such as phage therapy. This study investigates the potential of phage vB_PmuM_CFP3 (CFP3) as a therapeutic agent against avian cholera caused by Pasteurella multocida (P. multocida). Phage CFP3 was isolated from the feces and wastewater of a laying hen farm and underwent comprehensive biological characterization, including host range, lytic activity, and environmental stability. Transmission electron microscopy revealed CFP3's typical myovirus morphology, with a head diameter of approximately 60 nm and a tail length of about 120 nm. CFP3 demonstrated high stability across a pH range of 4-10 and temperatures of 30-40 °C, making it suitable for oral administration in poultry. The phage exhibited a latent period of about 90 min and an optimal multiplicity of infection (MOI) of 1. Despite its narrow host range, with a lysis rate of 28.2% against avian-derived type A P. multocida, CFP3's specificity minimizes impact on non-target bacteria. Whole-genome sequencing revealed a 32,696 bp linear double-stranded DNA genome with 46 predicted open reading frames (ORFs) and no tRNA or antibiotic resistance genes, enhancing its safety profile. Phylogenetic analysis indicated a close evolutionary relationship with Haemophilus phages HP1, HP2, and Pasteurella phage F108. While CFP3 shows promise as a precision therapeutic tool, further in vivo studies are required to evaluate its efficacy and safety. Future research should focus on expanding the phage library, optimizing phage mixtures, and exploring synergistic effects with other antimicrobial strategies. This study provides foundational data supporting the development of CFP3 as a viable alternative to antibiotics for controlling avian cholera.

Clinical features of pasteurellosis without an animal bite or scratch in comparison with bite/scratch pasteurellosis

Pasteurellosis is a common zoonotic infection that occurs after an animal bite or scratch (B/S). We compared the clinical features of six patients with non-B/S pasteurellosis with those of 14 patients with B/S infections. Pasteurella multocida was identified with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in all six non-B/S infections, whereas 13 of the 14 B/S infections were identified with diagnostic kits. The non-B/S infections were pneumonia (n = 3), skin and soft tissue infections (n = 2), and bacteremia (n = 1). Pneumonia occurred in two patients with underlying pulmonary disease, whereas ventilator-associated pneumonia developed in one patient with cerebral infarction. Pasteurella multocida was isolated from a blood specimen and nasal swab from a patient with liver cirrhosis (Child-Pugh class C) and diabetes. Cellulitis developed in one patient with diabetes and normal-pressure hydrocephalus, who had an open wound following a fall, and in one patient with diabetes and a foot ulcer. Three patients with non-B/S infections had no pet and no episode of recent animal contact. The rate of moderate-to-severe comorbidities was significantly higher in patients with non-B/S infections than in those with B/S infections (100% and 14.3%, respectively, p < 0.001). In conclusion, non-B/S infections can develop in patients with chronic pulmonary disease, invasive mechanical ventilation, or open wounds, or who are immunocompromised, irrespective of obvious animal exposure. In contrast to B/S infections, non-B/S pasteurellosis should be considered opportunistic.

Antimicrobial Susceptibility Profiles of Pasteurella multocida Isolates from Clinical Cases of Waterfowl in Hungary between 2022 and 2023

The waterfowl industry represents a narrow, yet economically significant, sector within the poultry industry. Although less prominent, the waterfowl sector is nonetheless of equal importance to any other livestock sector in terms of antimicrobial resistance and animal health issues. This study assesses the antimicrobial resistance profile of Pasteurella multocida bacterial strains isolated from clinical cases in Hungary's duck and goose populations, determining the minimal inhibitory concentration (MIC) of 27 samples collected from 15 different locations. The results indicate that the isolated strains were susceptible to most antibiotics, except for notable resistance to enrofloxacin. These findings support that Pasteurella multocida largely retained its susceptibility. However, the observed resistance to enrofloxacin suggests overuse of fluoroquinolones, which indicates the potential need for stricter regulation of their use in the poultry industry.

Pathogenomic analysis and characterization of Pasteurella multocida strains recovered from human infections

Pasteurella multocida is an upper respiratory tract commensal in several mammal and bird species but can also cause severe disease in humans and in production animals such as poultry, cattle, and pigs. In this study, we performed whole-genome sequencing of P. multocida isolates recovered from a range of human infections, from the mouths of cats, and from wounds on dogs. Together with publicly available P. multocida genome sequences, we performed phylogenetic and comparative genomic analyses. While isolates from cats and dogs were spread across the phylogenetic tree, human infections were caused almost exclusively by subsp. septica strains. Most of the human isolates were capsule type A and LPS type L1 and L3; however, some strains lacked a capsule biosynthesis locus, and some strains contained a novel LPS outer-core locus, distinct from the eight LPS loci that can currently be identified using an LPS multiplex PCR. In addition, the P. multocida strains isolated from human infections contained novel mobile genetic elements. We compiled a curated database of known P. multocida virulence factor and antibiotic resistance genes (PastyVRDB) allowing for detailed characterization of isolates. The majority of human P. multocida isolates encoded a reduced range of iron receptors and contained only one filamentous hemagglutinin gene. Finally, gene-trait analysis identified a putative L-fucose uptake and utilization pathway that was over-represented in subsp. septica strains and may represent a novel host predilection mechanism in this subspecies. Together, these analyses have identified pathogenic mechanisms likely important for P. multocida zoonotic infections.IMPORTANCEPasteurella multocida can cause serious infections in humans, including skin and wound infections, pneumonia, peritonitis, meningitis, and bacteraemia. Cats and dogs are known vectors of human pasteurellosis, transmitting P. multocida via bite wounds or contact with animal saliva. The mechanisms that underpin P. multocida human predilection and pathogenesis are poorly understood. With increasing identification of antibiotic-resistant P. multocida strains, understanding these mechanisms is vital for developing novel treatments and control strategies to combat P. multocida human infection. Here, we show that a narrow range of P. multocida strains cause disease in humans, while cats and dogs, common vectors for zoonotic infections, can harbor a wide range of P. multocida strains. We also present a curated P. multocida-specific database, allowing quick and detailed characterization of newly sequenced P. multocida isolates.

Pasteurella multocida ST20 is widespread in Australian poultry farms and may infect wild waterbirds

The bacterial agent that causes fowl cholera, Pasteurella multocida, was isolated from two deceased wild waterbirds in Victoria, Australia, in 2013. Whole genome sequence analysis placed the isolates into ST20, a subtype described in farmed chickens from Queensland, Australia and more recently in feedlot cattle and in pigs across a broader area of the continent. This study also found ST20 between 2009 and 2022 on three chicken farms and two turkey farms located in four Australian states. The sequences of 25 of these ST20 isolates were compared to 280 P. multocida genomes from 23 countries and to 94 ST20 Illumina datasets from Queensland that have been deposited in public databases. The ST20 isolates formed a single phylogenetic clade and were clustered into four sub-groups with highly similar genomes, possessing either LPS type 1 or type 3 loci. Various repertoires of mobile genetic elements were present in isolates from farmed, but not wild birds, suggesting complex histories of spill-over between avian populations and gene acquisition within farm environments. No major antimicrobial resistance was predicted in any of the ST20 isolates by the genomic analysis. The closest relative of these isolates was a ST394 bovine respiratory tract isolate from Queensland, which differed from ST20 by only one allele and carried beta-lactam and tetracycline resistance genes. These findings underline the importance of understanding the role of wild and commercial birds in the maintenance of fowl cholera, and of implementing regular epidemiological surveillance and biosecurity management programmes in wildlife, as well as free-range poultry farms.

Properties of Pasteurella multocida isolated from animals during the seasonal migration of saigas

The paper describes data from the study of cultural, morphological, and biochemical properties and the pathogenicity and virulence of epizootic isolates of Pasteurella multocida obtained from cattle and saigas. The study aimed to investigate the properties of P. multocida isolated from saigas and cattle during their seasonal migration, with a focus on its role in the epizootic process and potential transmission to farm animals. The research was conducted in a laboratory setting at the West Kazakhstan Agrarian-Technical University. White mice, saigas, and cattle were examined, and pathological and bacteriological analyses were performed on tissues and secretions. Pathogenicity, virulence, and toxigenicity of the isolated Pasteurella cultures were determined through biological tests on white mice. The morphological, cultural, and biochemical properties of the isolates were studied using standard microbiological methods. The study found that P. multocida isolates from both saigas and cattle exhibited high pathogenicity and virulence when tested on white mice. The isolates from sick and dead animals displayed 65.3 and 83.3% pathogenicity, respectively. The isolates were toxic to white mice, with filtrate dilutions showing 100% toxigenicity. Comparative analysis showed morphological and cultural similarities between Pasteurella isolates from saigas and cattle, confirming their identity. This research demonstrates that P. multocida, isolated from both saigas and cattle, contributes to the epizootic process and poses a threat to farm animals. Saigas, in particular, play a role in disease transmission during seasonal migrations. Understanding the ecological interactions between wild and farm animals is crucial for implementing preventive measures to control the spread of infectious diseases, emphasizing the need for comprehensive monitoring and intervention strategies.

A Comprehensive Review of the Common Bacterial Infections in Dairy Calves and Advanced Strategies for Health Management

Dairy farming faces a significant challenge of bacterial infections in dairy calves, which can have detrimental effects on their health and productivity. This review offers a comprehensive overview of the most prevalent bacterial infections in dairy calves, including Escherichia coli, Salmonella typhimurium, Salmonella dublin, Salmonella enterica, Clostridium perfringens, Pasteurella multocida, Listeria monocytogenes, Mycoplasma bovis, and Haemophilus somnus. These pathogens can cause various clinical signs and symptoms, leading to diarrhea, respiratory distress, septicemia, and even mortality. Factors such as management practices, environmental conditions, and herd health influence the incidence and severity of the infections. Efficient management and prevention strategies include good colostrum and nutrient feeding, early detection, appropriate treatment, hygiene practices, and supportive care. Regular health monitoring and diagnostic tests facilitate early detection and intervention. The use of antibiotics should be judicious to prevent antimicrobial resistance and supportive care such as fluid therapy and nutritional support promotes recovery. Diagnostic methods, including immunological tests, culture, polymerase chain reaction (PCR), and serology, aid in the identification of specific pathogens. This review also explores recent advancements in the diagnosis, treatment, and prevention of bacterial infections in dairy calves, providing valuable insights for dairy farmers, veterinarians, and researchers. By synthesizing pertinent scientific literature, this review contributes to the development of effective strategies aimed at mitigating the impact of bacterial infections on the health, welfare, and productivity of young calves. Moreover, more research is required to enhance the understanding of the epidemiology and characterization of bacterial infections in dairy calves.

Genomic analysis reveals the population structure and antimicrobial resistance of avian Pasteurella multocida in China

OBJECTIVES

To investigate the population structure and antimicrobial resistance (AMR) of avian Pasteurella multocida in China.

METHODS

Utilizing WGS analysis, we explored the phylogeny using a dataset of 546 genomes, comprising avian P. multocida isolates from China (n = 121), the USA (n = 165), Australia(n = 153), Bangladesh (n = 3) and isolates of other hosts from China (n = 104). We examined the integrative and conjugative element (ICE) structures and the distribution of their components carrying resistance genes, and reconstructed the evolutionary history of A:L1:ST129 (n = 110).

RESULTS

The population structure of avian P. multocida in China was dominated by the A:L1:ST129 clone with limited genetic diversity. A:L1:ST129 isolates possessed a broader spectrum of resistance genes at comparatively higher frequencies than those from other hosts and countries. The novel putative ICEs harboured complex resistant clusters that were prevalent in A:L1:ST129. Bayesian analysis predicted that the A:L1:ST129 clone emerged around 1923, and evolved slowly.

CONCLUSIONS

A:L1:ST129 appears to possess a host predilection towards avian species in China, posing a potential health threat to other animals. The complex AMR determinants coupled with high frequencies may strengthen the population dominance of A:L1:ST129. The extensive antimicrobial utilization in poultry farming and the mixed rearing practices could have accelerated AMR accumulation in A:L1:ST129. ICEs, together with their resistant clusters, significantly contribute to resistance gene transfer and facilitate the adaptation of A:L1:ST129 to ecological niches. Despite the genetic stability and slow evolution rate, A:L1:ST129 deserves continued monitoring due to its propensity to retain resistance genes, warranting global attention to preclude substantial economic losses.

Comparative genome analysis of Pasteurella multocida strains of porcine origin

Pasteurella multocida causes acute/chronic pasteurellosis in porcine, resulting in considerable economic losses globally. The draft genomes of two Indian strains NIVEDIPm17 (serogroup D) and NIVEDIPm36 (serogroup A) were sequenced. A total of 2182-2284 coding sequences (CDSs) were predicted along with 5-6 rRNA and 45-46 tRNA genes in the genomes. Multilocus sequence analysis and LPS genotyping showed the presence of ST50: genotype 07 and ST74: genotype 06 in NIVEDIPm17 and NIVEDIPm36, respectively. Pangenome analysis of 61 strains showed the presence of 1653 core genes, 167 soft core genes, 750 shell genes, and 1820 cloud genes. Analysis of virulence-associated genes in 61 genomes indicated the presence of nanB, exbB, exbD, ptfA, ompA, ompH, fur, plpB, fimA, sodA, sodC, tonB, and omp87 in all strains. The 61 genomes contained genes encoding tetracycline (54%), streptomycin (48%), sulphonamide (28%), tigecycline (25%), chloramphenicol (21%), amikacin (7%), cephalosporin (5%), and trimethoprim (5%) resistance. Multilocus sequence type revealed that ST50 was the most common (34%), followed by ST74 (26%), ST13 (24%), ST287 (5%), ST09 (5%), ST122 (3%), and ST07 (2%). Single-nucleotide polymorphism and core genome-based phylogenetic analysis clustered the strains into three major clusters. In conclusion, we described the various virulence factors, mobile genetic elements, and antimicrobial resistance genes in the pangenome of P. multocida of porcine origin, besides the rare presence of LPS genotype 7 in serogroup D.

Identification of Aztreonam as a potential antibacterial agent against Pasteurella multocida sialic acid binding protein: A combined in silico and in-vitro analysis

Pasteurella multocida, a Gram-negative zoonotic bacterial pathogen, interacts with the host environment, immune response, and infection through outer membrane proteins, adhesins, and sialic acid binding proteins. Sialic acids provide nutrition and mask bacterial identity, hindering the complement system, facilitates tissue access and biofilm formation. Sialic acid binding protein (SAB) enable adhesion to host cells, immune evasion, and nutrient acquisition, making them potential targets for preventing Pasteurella multocida infections. In this study, in silico molecular docking assessed 11 antibiotics targeting SAB (4MMP) comparing their docking scores to Amoxicillin. As SAB (4MMP) exhibits a highly conserved sequence in various Pasteurella multocida strains, including the specific strain PMR212 studied in this article, with a 96.09% similarity score. Aztreonam and Gentamicin displayed the highest docking scores (-6.025 and -5.718), followed by a 100ns molecular dynamics simulation. Aztreonam exhibited stable simulation with protein RMSD fluctuations of 1.8-2.2 Å. The ligand initially had an RMSD of 1.6 Å, stabilizing at 4.8 Å. Antibiotic sensitivity testing confirmed Aztreonam's efficacy with the largest inhibition zone of 42 mm, while Amoxicillin and Gentamicin had inhibition zones of 32 mm and 25 mm, respectively. According to CLSI guidelines, all three antibiotics were effective against Pasteurella multocida. Aztreonam's superior efficacy positions it as a promising candidate for further investigation in targeting Pasteurella multocida.

Pathology, virulence-associated gene profiling, antimicrobial susceptibility, and pathogenicity of untypeable capsular serotypes of Pasteurella multocida isolated from slaughtered pigs of India

Pasteurella multocida is widely distributed in all pig-rearing countries, affecting the economic viability and profitability of pig production. The present research highlights the molecular characterization and pathology of untypeable capsular serotypes of P. multocida in slaughtered pigs from prominent pig-rearing states of India. The prevalence of Pasteurellosis was 27.17% by Pasteurella multocida specific Pasteurella multocida specific PCR (PM-PCR). assay, while isolation rate was 7.62%. The microscopic lesions of bronchopneumonia, tonsillitis, and the presence of bacterial antigens in immunohistochemistry confirmed P. multocida with pathologies. In capsular typing, the majority of the isolates were untypeable with prevalence of 52.15% and 43.58% in molecular and microbiological methods, respectively. All the isolates showed the uniform distribution of virulence genes such as exbB, nanB, sodC, plpB, and oma87 (100%), while the variations were observed in ptfA, hasR, ptfA, pfhA, hsf-1, and plpE genes. The untypeable isolates showed higher prevalence of hsf-1 gene as compared to others. The untypeable serotypes showed a higher degree of resistance to ampicillin, amoxicillin, and penicillin antibiotics. The mouse pathogenicity testing of untypeable capsular isolates confirmed its pathogenic potential. The higher frequency of pathogenic untypeable isolates with antibiotic resistance profile might pose a serious threat to the pigs, and therefore, preventive measures should be adopted for effective control.

Bloodstream infection, peritonitis, and pneumonia caused by Pasteurella multocida in a patient with liver cirrhosis despite no animal contact: case report and literature review

Pasteurella multocida is an opportunistic pathogen. Previously reported infections associated with P. multocida have often been linked to contact with cats, dogs, and other animals. Cases of systemic multiple-site infections following P. multocida infection are rare. This case study presents a 49-year-old middle-aged man with post-hepatitis B cirrhosis and no history of animal contact. The patient was admitted with symptoms of fever accompanied by diarrhea, abdominal distension, and cough. Blood tests showed elevated levels of CRP, PCT, and IL-6, and blood culture revealed the growth of P. multocida. CT scans revealed a large amount of abdominal effusion, a small amount of pleural effusion, and pulmonary infection foci. The patient's condition improved after successive administration of ceftriaxone and levofloxacin to fight the infection, and abdominal puncture and drainage. Multiple-site infections caused by P. multocida are rarely encountered in patients with liver cirrhosis but without animal contact, which could be regarded as serious conditions warranting careful attention in terms of clinical diagnosis and treatment.

Genomic characterization and comparative genomic analysis of HS-associated Pasteurella multocida serotype B:2 strains from Pakistan

BACKGROUND

Haemorrhagic septicaemia (HS) is a highly fatal and predominant disease in livestock, particularly cattle and buffalo in the tropical regions of the world. Pasteurella multocida (P. multocida), serotypes B:2 and E:2, are reported to be the main causes of HS wherein serotype B:2 is more common in Asian countries including Pakistan and costs heavy financial losses every year. As yet, very little molecular and genomic information related to the HS-associated serotypes of P. multocida isolated from Pakistan is available. Therefore, this study aimed to explore the characteristics of novel bovine isolates of P. multocida serotype B:2 at the genomic level and perform comparative genomic analysis of various P. multocida strains from Pakistan to better understand the genetic basis of pathogenesis and virulence.

RESULTS

To understand the genomic variability and pathogenomics, we characterized three HS-associated P. multocida serotype B:2 strains isolated from the Faisalabad (PM1), Peshawar (PM2) and Okara (PM3) districts of Punjab, Pakistan. Together with the other nine publicly available Pakistani-origin P. multocida strains and a reference strain Pm70, a comparative genomic analysis was performed. The sequenced strains were characterized as serotype B and belong to ST-122. The strains contain no plasmids; however, each strain contains at least two complete prophages. The pan-genome analysis revealed a higher number of core genes indicating a close resemblance to the studied genomes and very few genes (1%) of the core genome serve as a part of virulence, disease, and defense mechanisms. We further identified that studied P. multocida B:2 strains harbor common antibiotic resistance genes, specifically PBP3 and EF-Tu. Remarkably, the distribution of virulence factors revealed that OmpH and plpE were not present in any P. multocida B:2 strains while the presence of these antigens was reported uniformly in all serotypes of P. multocida.

CONCLUSION

This study's findings indicate the absence of OmpH and PlpE in the analyzed P. multocida B:2 strains, which are known surface antigens and provide protective immunity against P. multocida infection. The availability of additional genomic data on P. multocida B:2 strains from Pakistan will facilitate the development of localized therapeutic agents and rapid diagnostic tools specifically targeting HS-associated P. multocida B:2 strains.

Pharmacokinetic/pharmacodynamic integration of tilmicosin against Pasteurella multocida in a piglet tissue cage model

Tilmicosin is a semi-synthetic macrolide for veterinary use with strong antibacterial effect on respiratory bacteria. In this study, the pharmacokinetic/pharmacodynamic (PK/PD) integration of tilmicosin against Pasteurella multocida (P. multocida) was evaluated by establishing a piglet tissue cage infection model. Concentration of tilmicosin and bacterial numbers of P. multocida in the tissue-cage fluid were monitered. After the population of P. multocida was equal to or greater than 107 CFU/mL in a tissue cage, piglets received an oral administration of tilmicosin at a dose of 30, 40, 50, and 60 mg/kg b.w., once daily for 3 days, respectively. Bacteria were counted every 24 h after drug administration and at 48 and 72 h after the last administration. A sigmoidal Emax model was used to fit the relationship between PK/PD parameters and the antibacterial effect. AUC24h/MIC was the best PK/PD index that correlated with effectiveness of tilmicosin against P. multocida. The magnitude of AUC24h/MIC required for continuous 1/3-log, 1/2-log, and 3/4-log reductions were 19.65 h, 23.86 h, and 35.77 h, respectively, during each 24 h treatment period. In this study, when the dosage was >50 mg/kg, the AUC24h/MIC was still >35.77 h in the period of 24-48 h after the last administration due to the slow elimination, that is, tilmicosin exhibited a potent antibacterial effect against P. multocida after three successive daily administrations. The data provide meaningful guidance to optimize regimens of tilmicosin to treat respiratory tract infections caused by P. multocida.

Genotypic Comparison of Pasteurella multocida from Healthy Animals at Entry to the Feedlots with That and from Bovine Respiratory Disease-Affected Animals during the Fattening Period

The aim of this study was to investigate the possible genotypic differences between commensal Pasteurella multocida isolates from apparently healthy animals (AHA) at the time of entry to feedlots and those from BRD-affected animals (BRD-AA). A total of 20 batches of beef calves in seven feedlots were followed-up during the fattening period. P. multocida was isolated from 28.1% of AHA and 22.9% of BRD-AA. All isolates belonged to the A: L3 genotype. Most isolates from clinical cases (81.0%) grouped into a PFGE cluster were significantly associated with BRD cases (OR, 24.9; 95% CI, 6.4-96.2). The whole genomes of 14 isolates representative of the pulsotypes most frequently detected in BRD-AA and AHA were sequenced and compared with 53 bovine genomes belonging to the identified ST13, ST79, and ST80 genotypes for a global comparison. No differences were found in the virulence-associated gene content between sequence types (STs) globally or between BRD-AA and AHA isolates in this study. Significantly, ST79 isolates harbored ARGs, conferring resistance to different antimicrobials, including macrolides and tetracyclines, which are commonly used for the treatment of BRD. Two Spanish ST79 isolates carried an ICE highly similar to ICE Tn7407, which was recently detected in Germany, suggesting that ST79 P. multocida isolates in Europe and North America may be associated with different ICEs.

Space-Time Patterns of Poultry Pathogens in the USA: A Case Study of Ornithobacterium rhinotracheale and Pasteurella multocida in Turkey Populations

Respiratory infections caused by Ornithobacterium rhinotrachealis (ORT) and Pasteurella multocida (PM) bacteria are significant threats to the poultry industry by causing economic losses and welfare issues. Due to characterization difficulties and underutilization of epidemiological tools, description of the spatio-temporal spread of these diseases in the field is limited. The objectives of this retrospective observational cross-sectional study were to (a) investigate the existence of space-time clusters (hotspots); and (b) investigate the association between genetic similarity and spatial proximity for both pathogens using molecular typing and a recently developed Core-Genome Multilocus Sequencing Typing (cgMLST) scheme. ORT (n = 103) and PM (n = 69) isolates from confirmed disease outbreaks from one commercial company between 2013 and 2021 were obtained from a veterinary diagnostic laboratory, characterized using a cgMLST scheme and visualized using a minimum spanning tree. Spatio-temporal cluster analysis using SaTScanTM and a Spearman's rank correlation were performed to investigate clustering and any association between allelic diversity and geospatial distance. The cgMLST sequencing revealed three allelic clusters for ORT and thirteen clusters for PM. The spatio-temporal analysis revealed two significant clusters for PM, one with a 259.3 km cluster containing six cases between May and July 2018 and a 9 km cluster containing five cases between February 2019 and February 2021. No spatio-temporal clusters were found for ORT. A weak negative correlation between allelic diversity and geospatial distance was observed for ORT (r = -0.04, p < 0.01) and a weak positive correlation was observed for PM (r = 0.11, p < 0.01). This study revealed regional spatio-temporal clusters for PM in commercial turkey sites between 2018 and 2021 and provided additional insight into bacterial strain subgroups and the geographical spread of ORT and PM over time.

Antibacterial activity mechanism of coptisine against Pasteurella multocida

Objective

Pasteurella multocida is a widespread zoonotic pathogen that causes severe damage to the poultry industry. This study focused on the antibacterial effects and mechanism of action of coptisine against P. multocida.

Methods

The minimum inhibitory concentration and half maximal inhibitory concentration of coptisine against P. multocida was measured. Additionally, the effect of coptisine on growth, cell wall, activity of respiratory enzymes, soluble protein content and DNA synthesis were also analyzed. Finally, the effect of coptisine on gene transcription was determined using RNA sequencing.

Results

We demonstrated that coptisine has a strong antibacterial effect against P. multocida, with a minimum inhibitory concentration of 0.125 mg/mL. Moreover, the measurement of the half maximal inhibitory concentration confirmed that coptisine was safe for the pathogen. The growth curve showed that coptisine inhibited bacterial growth. Measurement of alkaline phosphatase activity in the culture solution showed that coptisine affected cell wall permeability. Transmission electron microscopy revealed that coptisine chloride destroyed the cell structure. In addition, coptisine blocked the respiratory system, as measured by the levels of critical enzymes of the tricarboxylic acid cycle and glycolysis, succinate dehydrogenase and lactate dehydrogenase, respectively. Similarly, coptisine inhibited the synthesis of soluble proteins and genomic DNA. The KEGG pathway analysis of the differentially expressed genes showed that they were associated with cellular, respiratory, and amino acid metabolism, which were downregulated after coptisine treatment. Additionally, genes related to RNA degradation and the aminoacyl-tRNA pathway were upregulated.

Conclusion

In this study, we demonstrated that coptisine exerts an antibacterial effect on P. multocida. These findings suggest that coptisine has a multifaceted impact on various pathways, resulting in the inhibition of P. multocida. Thus, coptisine is a potential alternative to antibiotics for the treatment of P. multocida infections in a clinical setting.

18β-Glycyrrhetinic Acid Alleviates P. multocida-Induced Vascular Endothelial Inflammation by PARP1-Mediated NF-κB and HMGB1 Signalling Suppression in PIEC Cells

Background

At present, the treatment and prevention of Pasteurella multocida infections in pigs mainly rely on antibiotics and vaccines, but inflammatory injury cannot be eliminated. The compound 18β-glycyrrhetinic acid (GA), a pentacyclic triterpenoid extracted from Glycyrrhiza glabra L. root (liquorice) and with a chemical structure similar to that of steroidal hormones, has become a research focus because of its anti-inflammatory, antiulcer, antimicrobial, antioxidant, immunomodulatory, hepatoprotective and neuroprotective effects, but its potential for the treatment of vascular endothelial inflammatory injury by P. multocida infections has not been evaluated. This study aimed to investigate the effects and mechanisms of GA intervention in the treatment of vascular endothelial inflammatory injury by P. multocida infections.

Materials and Methods

Putative targets of GA intervention in the treatment of vascular endothelial inflammatory injury by P. multocida infections were identified using network pharmacological screening and molecular docking simulation. The cell viability of PIEC cells was investigated via the CCK-8 assay. The mechanism of GA intervention in the treatment of vascular endothelial inflammatory injury by P. multocida infections were investigated using cell transfection and western blot.

Results

Through network pharmacological screening and molecular docking simulation, this study found that PARP1 may be a core target for GA to exert anti-inflammatory effects. Mechanistically, GA alleviates P. multocida-induced vascular endothelial inflammation by PARP1-mediated NF-κB and HMGB1 signalling suppression.

Conclusion

These findings, for the first time, demonstrate the potential therapeutic relationship among GA, PARP1 and inflammatory injury, providing a candidate drug, therapeutic targets and explanation for treating vascular endothelial inflammatory injury caused by P. multocida infection.

Construction of a one-step multiplex real-time PCR assay for the detection of serogroups A, B, and E of Pasteurella multocida associated with bovine pasteurellosis

Bovine pasteurellosis, caused by serogroups A, B, and E of Pasteurella multocida (Pm), is mainly manifested as bovine respiratory disease (BRD) and hemorrhagic septicemia (HS). The disease has caused a great economic loss for the cattle industry globally. Therefore, identifying the Pm serogroups is critical for optimal diagnosis and subsequent clinical treatment and even epidemiological studies. In this study, a one-step multiplex real-time PCR assay was established. Three pairs of specific primers were prepared to detect the highly conserved genomic regions of serogroups A (HyaD), B (bcbD), and E (ecbJ) of Pm, respectively. The results depicted that the method had no cross-reaction with other bovine pathogens (Mannheimia hemolytica, Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, Salmonella Dublin, Mycobacterium paratuberculosis, infectious bovine rhinotracheitis virus, and Mycoplasma bovis). The linear range (10⁷ to 10² copies/μL) showed the R² values for serogroups A, B, and E of Pm as 0.9975, 0.9964, and 0.996, respectively. The multiplex real-time PCR efficiency was 90.30%, 90.72%, and 90.57% for CartA, CartB, and CartE, respectively. The sensitivity result showed that the serogroups A, B, and E of Pm could be detected to be as low as 10 copies/μL. The repeatability result clarified that an intra-assay and an inter-assay coefficient of variation of serogroups A, B, and E of Pm was < 2%. For the clinical samples, the detection rate was higher than the OIE-recommended ordinary PCR. Overall, the established one-step multiplex real-time PCR assay may be a valuable tool for the rapid and early detection of the serogroups A, B, and E of Pm with high specificity and sensitivity.

Genomic profiling of Pasteurella multocida isolated from feedlot cases of bovine respiratory disease

Pasteurella multocida causes a range of diseases in many host species throughout the world, including bovine respiratory disease (BRD) which is predominantly seen in feedlot cattle. This study assessed genetic diversity among 139 P. multocida isolates obtained from post-mortem lung swabs of BRD-affected feedlot cattle in four Australian states: New South Wales, Queensland, South Australia, and Victoria during 2014-2019. Whole-genome sequencing (WGS) was used to determine capsular serogroup, lipopolysaccharide genotypes, multi-locus sequence types and phylogenetic relationships. Two capsular types (A and D), with most isolates (132/139; 95%) belonging to type A; and three lipopolysaccharide (LPS) genotypes were identified (L1 [6/139; 4.3%], L3 [124/139; 89.2%] and L6 [9/139; 6.4%)]). Multi-locus sequence types (STs) ST9, ST13, ST17, ST20, ST36, ST50, ST58, ST79, ST124, ST125, ST132, ST167, ST185, ST327, ST394, and three novel STs [ST396, ST397, and ST398] were identified, with ST394 (59/139; 42.4%) and ST79 (44/139; 32%) the most prevalent in all four states. Isolates displaying phenotypic resistance to single, dual or multiple antibiotics (macrolide, tetracycline and aminopenicillins) were predominantly ST394 (23/139; 17%). Laterally mobile elements identified in the resistant ST394 isolates included small plasmids, encoding macrolide and/or tetracycline resistance, distributed in all states; and chromosomally located integrative conjugative elements (ICEs) (4 ST394 and 1 ST125) from the same Queensland feedlot. This study highlights the genomic diversity, epidemiological relationships and AMR associations in bovine P. multocida isolates from Australia and provides insight into the unique ST prevalence compared to other major beef-producing countries.

Naked-eye on-site detection platform for Pasteurella multocida based on the CRISPR-Cas12a system coupled with recombinase polymerase amplification

Pasteurella multocida (P. multocida) is an important pathogenic bacterium that poses a serious threat to the development of the livestock economy and human health. Currently, the existing methods for P. multocida detection are time-consuming and require complex professional operations, limiting the application of field detection. In the study, we presented a single-pot naked-eye CRISPR-Cas12a platform (Cas12a-NEye) for the detection of P. multocida. The round tube cover allowed more Cas12a detection solution to be temporarily stored than the flat cap, enabling single-pot assays and avoiding aerosol contamination. The positive samples generated obvious red using naked eye using no excitation light and the negative samples generated blue. The limit of detection (LOD) was a single copy, without cross-reactivity with other closely related bacteria. Furthermore, we validated this platform using 16 P. multocida clinical lung samples and obtained consistent results with the real-time quantitative polymerase chain reaction (qPCR) method. The entire experimental process included rapid DNA extraction (<1 h) and Cas12a-NEye assay (25 min), which was accomplished within 1.5 h. Thus, this "sample-to-answer" platform has significant potential for P. multocida detection.

Immunogenicity and efficacy of serogroup A and D bacterins against Pasteurella multocida in mice

Introduction

Pasteurella multocida is a widespread respiratory pathogen in pigs, causing swine pneumonia and atrophic rhinitis, and the capsular serogroups A and D are the main epidemic serogroups in infected animals. This study investigated the protective effects of serogroup A and D bacterins against current circulating P. multocida strains, to better understand the immunity generated by bacterins.

Method

13 serogroup A (seven A: L3 and six A: L6 strains) and 13 serogroup D (all D: L6 strains) P. multocida strains were isolated, and used as inactivated whole cell antigen to prepare P. multocida bacterins. Mice were immunized with these bacterins at 21-day interval and intraperitoneally challenged with the homologous and heterologous P. multocida strains, respectively. The antibody titer levels and immunization protective efficacy of vaccines were evaluated.

Results

All of the bacterins tested induced high titer levels of immunoglobulin G antibodies against the parental bacterial antigen in mice. Vaccination with the six A: L6 bacterins provided no protection against the parent strain, but some strains did provide heterologous protection against A: L3 strains. Vaccination with the seven A: L3 bacterins provided 50%-100% protection against the parent strain, but none gave heterologous protection against the A:L6 strains. Immunization with the thirteen D: L6 bacterins offered 60%-100% protection against the parent strain, and almost all D: L6 strains gave cross-protection.

Discussion

This study found that the cross-protectivity of serogroup A strains was poor, while serogroup D strains was effective, which provided some insights for P. multocida vaccine development.

Development of ELISA-based diagnostic methods for the detection of haemorrhagic septicaemia in animals

Haemorrhagic septicaemia (HS) is an acute infection of cattle and buffaloes caused by the B:2 serotype of Pasteurella multocida. This disease is highly endemic in South Asia. In some peracute cases, there is 100% mortality in infected animals within a few hours of infection. Therefore, timely diagnosis of infection may contribute to its treatment and control to minimize economic losses. The current work reported the development of ELISA-based assays for the detection of anti-P. multocida antibodies and pathogen i.e. P. multocida. Owing to high immunogenicity, membrane proteins (MPs) extracted from local isolates of P. multocida serotype B:2 (PM1, PM2, and PM3) were employed as a potential diagnostic antigen for the development of indirect ELISA (i-ELISA) to detect HS antibodies in animals. MPs extracted from PM1, PM2 and PM3 isolates showed very low heterogeneity; hence MPs from the PM3 isolate were selected for the development of i-ELISA. The concentration of MPs (as coating antigen) of 3.13 μg/well and test sera dilution 1:100 was found to be optimal to perform i-ELISA. The developed method was validated through the detection of anti-P. multocida antibodies in sera of mice, immunized with MPs and formalin killed cells from the three local isolates (PM1, PM2 and PM3) of P. multocida. The significantly higher antibody titer in immunized mice was determined compared to unimmunized mice with the cut off value of 0.139. To detect P. multocida directly from the blood of infected animals, whole cell-based ELISA (cb-ELISA) assay was developed. A better detection signal was observed in the assay where bacterial cells were directly adsorbed on plate wells as compared to poly L-lysine (PLL) assisted attachment at a cell concentration of 10⁶ CFU and 10⁷ CFU respectively. The developed assays can be scaled up and potentially be used for the rapid detection of HS antibodies to gauge the immune status of the animal as well as vaccination efficacy and pathogen detection.

Molecular Epidemiology of Pasteurella multocida Associated with Bovine Respiratory Disease Outbreaks

Studies that characterize bovine respiratory disease (BRD)-associated Pasteurella multocida isolates are scarce compared with research on isolates from other hosts and clinical backgrounds. In the present study, 170 P. multocida isolates from 125 BRD outbreaks were characterized by capsular and LPS typing as well as by virulotyping. Three capsular types (A, B, F) and three LPS genotypes (L2, L3, L6) were identified. Capsular and LPS typing revealed a very low genetic diversity (GD = 0.02) among P. multocida, with most isolates belonging to genotype A:L3 (97.6%). Virulotyping identified seven virulence-associated gene profiles, with two profiles including 95.9% of the isolates. A subset of isolates was further characterized by MLST and PFGE. The sequence types ST79 and ST13 were the most frequently identified and were grouped into the same clonal complex (CC13), a result that supports the clonal population structure of BRD-associated P. multocida isolates. PFGE typing also revealed a low genetic diversity (GD = 0.18), detecting a single pattern in 62.5% of the outbreaks in which multiple isolates were analyzed. Overall, 85.2% of the isolates belonged to pulsotypes with at least 80% genetic similarity, consistent with a clonal population structure observed by MLST analysis and corroborating the genetic relatedness of most P. multocida isolates associated with BRD in cattle.

Pathogenicity, colonization, and innate immune response to Pasteurella multocida in rabbits

BACKGROUND

Pasteurella multocida (P. multocida) infection can cause a series of diseases in different animals and cause huge economic losses to the breeding industry. P. multocida is considered to be one of the most significant pathogens in rabbits. In order to elucidate the pathogenic mechanism and innate immune response of P. multocida, an infection experiment was carried out in this study.

RESULTS

Our results showed that the clinical symptoms of rabbits were severe dyspnoea and serous nasal fluid. During the course of the disease, the deaths peaked at 2 days post infection (dpi) and mortality rate was 60%. The pathological changes of the lung, trachea, and thymus were observed. In particular, consolidation and abscesses appeared in lung. Histopathologic changes in rabbits showed edema, hemorrhage, and neutrophil infiltration in the lung. P. multocida can rapidly replicate in a variety of tissues, and the colonization in most of the tested tissues reached the maximum at 2 dpi and then decreased at 3 dpi. The number of P. multocida in lung and thymus remained high level at 3 dpi. Toll-like receptors 2 and 4 signaling pathways were activated after P. multocida infection. The expression of Il1β, Il6, Il8, and Tnf-α was significantly increased. The expression of most proinflammatory cytokines peaked at 2 dpi and decreased at 3 dpi, and the expression trend of cytokines was consistent with the colonization of P. multocida in rabbit tissues.

CONCLUSIONS

The P. multocida can rapidly replicate in various tissues of rabbit and cause bacteremia after infection. TLRs signaling pathways were activated after P. multocida infection, significantly inducing the expression of proinflammatory cytokines, which is might the main cause of respiratory inflammation and septicemia.

Detection of Porcine Circovirus Type 2a and Pasteurella multocida Capsular Serotype D in Growing Pigs Suffering from Respiratory Disease

In order to diagnose a respiratory disease in a pig farm, the lungs, spleen, and lymph nodes of three dead pigs were collected for pathogen detection by PCR and isolation on the basis of preliminary clinical diagnosis. The virus isolate was identified by gene sequence analysis and Immunoperoxidase monolayer assay (IPMA). The bacterial isolate was identified by biochemical tests, 16S rDNA sequence analysis, and species- and serotype-specific PCR, and the pathogenicity was analyzed. Porcine circovirus type 2a (PCV2a) genotype from the lungs, spleen, and lymph nodes and Pasteurella (P.) multocida capsular serotypes D from the lungs were found. The PCV2a isolates could specifically bound the anti-PCV2-Cap polyclonal antibody. The 16S rDNA sequence of P. multocida isolates had 99.9% identity with that of the strain from cattle, and the isolate was highly pathogenic to mice. The results showed that the co-infection of PCV2a and P. Multocida capsular serotypes D should be responsible for the disease. The uncommon PCV2a is still prevalent in some pig farms besides the dominant PCV2d genotype. This study could provide important etiological information for effective control and treatment of the disease in pig farms.

Spreading of Pasteurella multocida Infection in a Pet Rabbit Breeding and Possible Implications on Healed Bunnies

The number of pets such as dogs, cats, rabbits, and parrots has increased in European families. Social benefits to owners such as decreasing feelings of loneliness and anxiety are provided by pets which are also used in Animal-assisted Therapy (AAT). Nevertheless, human-animal interactions are also associated with health problems including allergies, asthma, and zoonosis. Rabbits may carry potential pathogens for humans. One of the most common bacteria that colonizes the oro-pharynx and the upper respiratory tract of rabbits is Pasteurella (P.) multocida. Transmission of the infection to humans results from scratches, licks, and bites but it also can occur from the inhalation of air particles containing the microorganism. Immunocompromised people or persons with pulmonary disorders are particularly susceptible to the infection. Infected rabbits may carry P. multocida with or without clinical signs. In this paper, the sensitivity to antibiotics and the invasiveness ability of P. multocida identified in a farm of pet rabbits affected by severe pasteurellosis were investigated. The strain was P. multocida belonging to capsular type A which is the type most often detected in humans. The identified strain was susceptible to the tested antibiotics, but it appeared equipped with several virulence genes which are responsible for fimbriae production, adhesion processes to host cells, enzyme production, and are involved in iron acquisition processes. These findings are of particular interest because rabbits recovered from pasteurellosis very often become carriers of the bacteria. Therefore, we suggest considering P. multocida screening in the routine medical checks of rabbits, especially if they are meant to be companion animals for children and elder people, given that the transmission of the pathogen cannot be excluded.

Prediction of Pasteurella multocida serotypes based on whole genomic sequences

The serotypes of Pasteurella multocida were predicted based on whole genomic sequences (WGS) with specific genes of the capsular and liposaccharide (LPS) outer core polysaccharide regions as targets. A total of 56 strains were whole genomic sequenced and in addition all assembled genomes from NCBI were included for comparison. BIGSdb (Bacterial Isolate Genome Sequence Database) was installed on a Linux server and targets for capsular types A, B, D, E and F were defined as gene sequences of hyaD, bcbD, dcbF, ecbJ and fcbD, respectively and targets for LPS groups 1, 2, 3, 4, 5, 6, 7 and 8 were defined as gene sequences of pcgB, nctA, gatF, latB, rmlA, nctB, ppgB and natG, respectively. The serotypes of P. multocida were predicted from WGS by designating the capsular type and LPS group as well as subtype alleles to isolates. Comparisons between WGS predictions of capsular types and classical phenotypic typing showed correspondence in 87 % of cases whereas comparisons of WGS predictions of LPS groups to phenotypic typing corresponded for 82 % of the strains. In total 93 % and 94 % of the strains available with WGS could be capsular and LPS group typed, respectively. The server is free to access from https://ivsmlst.sund.ku.dk.

Development of a multiplex PCR assay for the detection of key genes associated with Pasteurella multocida subspecies

The ability to distinguish among the subspecies of Pasteurella multocida isolates is important epidemiologically; however, classification at the subspecies level based on the results of conventional biochemical tests (fermentation of sorbitol and dulcitol) is reportedly not accurate in all cases. Therefore, we developed a rapid, multiplex PCR assay to differentiate among the 3 subspecies of P. multocida. The PCR assay includes the P. multocida species-specific primers KMT1SP6 and KMT1T7 as an internal amplification control, with a newly designed gatD (galactitol-1-phosphate-5-dehydrogenase)-specific primer pair (unique for subsp. gallicida), and primers targeting a 16S rRNA gene region specific for subsp. septica. The subspecies specificity of the PCR was demonstrated by applying the test to a collection of 70 P. multocida isolates, including the Heddleston serovar reference strains; all isolates and strains were assigned correctly. The PCR assay is a sensitive, specific, and highly effective method for the identification of P. multocida subspecies, and an alternative to biochemical test-based differentiation. A possible relationship was noticed between P. multocida subspecies and lipopolysaccharide (LPS) genotype; all but one of the subsp. gallicida strains were isolated only from avian hosts and represented L1 LPS genotype. Subsp. multocida and subsp. septica isolates were classified into 5 and 4 different LPS genotypes, respectively, of which L3 was the only LPS genotype shared between these 2 subspecies.

Virulence genes and enterobacterial repetitive intergenic consensus region (ERIC) profiling reveals highly diverse genetic population among avian strains of Pasteurella multocida

Pasteurella multocida is a multispecies pathogen with certain host specific capsular types but interspecies transmission cannot be overlooked. Knowing the diversity of P. multocida in a geographical location is essential to formulate a vaccination programme. Diversity among the P. multocida isolates from different avian species recovered in the state of Tamil Nadu, India was studied using enterobacterial repetitive intergenic consensus region (ERIC)-PCR and virulence gene profiling (VP). Capsular typing revealed that 44 (97.78%) strains belonged to capsular type A while only one (2.22%) strain belonged to capsular type B. ERIC-PCR analysis showed eight different clusters and four individual strains. The index of discrimination (D value) was found to be 0.8899. Virulence profiling showed that genes fimA, pfhA, hsf-2 and pmHAS were found in 100% of the strains while ompH, omp87, ompA, plpB, sodA, sodC, ptfA, hsf-1, exbB, fur, hgbA and hgbB were found in ≥90% of the strains. Dermonecrotoxin gene toxA was present only in 4.44% of the strains, while nanH in 68.89% and nanB in 88.89% of the strains. One strain each from turkey and Guinea fowl had toxA gene. Correlation analysis revealed a positive correlation between ptfA and hgbA gene, exbB and fur gene, ptfA and sodC gene, exbB and hsf-1 gene, ompA and ompH gene. Majority of duck strains clustered together both in ERIC and virulence gene profiles. Turkey strains were highly diverse with different VPs and ERIC-PCR patterns.

Pasteurella multocida capsular: lipopolysaccharide types D:L6 and A:L3 remain to be the main epidemic genotypes of pigs in China

Pasteurella multocida is a leading cause of respiratory disorders in pigs. This study was designed to understand the genotypical and antimicrobial resistant characteristics of P. multocida from pigs in China. To achieve this, we briefly investigated 158 P. multocida isolates from pigs with respiratory disorders in China between 2019 and 2020. Genotyping through multiplex PCR assays assigned these 158 isolates into capsular genotypes A (60.13%, 95/158), D (35.44%, 56/158), F (4.43%, 7/158), and/or lipopolysaccharide (LPS) genotypes L3 (28.48%, 45/158) and L6 (66.46%, 105/158). In addition, eight isolates (5.06%, 8/158) were found to be nontypable using the LPS genotyping method. When combining the capsular genotypes and the LPS genotypes, D: L6 (34.81%, 55/158) and A: L6 (31.65%, 50/158) were the predominant genotypes, followed by A: L3 (24.05%, 38/158). PCR detection of virulence factor-encoding genes showed that over 80% of the isolates were positive for exbB, tonB, exbD, ompH, ptfA, fimA, sodA, sodC, fur, ompA, oma87, plpB, hsf-2, nanH and hgbB, suggesting the presence of these genes were broad characteristics of P. multocida. We also found approximately 63.92% (101/158), 51.27% (81/158), 8.86% (14/158), 7.59% (12/158), 3.16% (5/158), 0.63% (1/158), and 0.63% (1/158) of the isolates grew well in media with the presence of colistin (4 μg/mL), tetracycline (16 μg/mL), tigecycline (1 μg/mL), ampicillin (32 μg/mL), chloramphenicol (32 μg/mL), cefepime (16 μg/mL), and ciprofloxacin (1 μg/mL), respectively. This study contributes to the understanding of genotypes and antimicrobial resistance profile of P. multocida currently circulation in pigs of China.

Characterization of Pasteurella multocida isolated from ducks in China from 2017 to 2019

Pasteurella multocida, an important gram-negative pathogen that mainly inhibits the upper respiratory tracts of domestic and wild animals such as chicken, duck, cattle and pig, which can cause cholera fowl, haemorrhagic septicaemia and infectious pneumonia. Currently, the prevalence and infection of P.multocida is still one of the most serious threats to the poultry industry in China, but studies on its characteristics are still insufficient. Here, this study was conducted to isolate and identify P.multocida in infected ducks and determined the leading serotypes and epidemiology of the diseases this pathogen causes. Results indicated that all the isolates were positive for KMT1 gene and the PCR amplified products were approximately 460 bp, demonstrating that these strains were all P.multocida. Moreover, all the isolated strains were identified as capsular type A and lipopolysaccharide type L1. Virulence factor identification results revealed that all strains possessed genes related to pili, adhesin, iron metabolism and uptake. In contrast, toxin coding gene (toxA) and sialidase encodes genes (nan B and nan H) were not detected in any isolates. The drug susceptibility results indicated that all the isolates were resistant to Lincomycin, Chloramphenicol, Clindamycin and Oxacillin but were sensitive to Ceftriaxone and Cefalotin. The animal experiments were also performed to further determine the pathogenicity of these isolated strains. Animal experiment revealed that the liver, kidney, and heart of infected ducks were swollen and had bleeding spots. We also observed hepatocyte hypertrophy, hepatic sinus congestion and single-cell infiltration in infected ducks through H&E staining. In summary, this study demonstrated that all the isolated strains belong to capsular A and lipopolysaccharide type L1 P.multocida, but their virulence factors, drug resistance and pathogenicity were different.