Pasteurella multocidaand its role in porcine pneumonia

Development and application of a WebGIS-based prediction system for multi-criteria decision analysis of porcine pasteurellosis

Porcine pasteurellosis is an infectious disease caused by Pasteurella multocida (P. multocida), which seriously endangers the healthy development of pig breeding industry. Early detection of disease transmission in animals is a crucial early warning for humans. Therefore, predicting risk areas for disease is essential for public health authorities to adopt preventive measures and control strategies against diseases. In this study, we developed a predictive model based on multi-criteria decision analysis (MCDA) and assessed risk areas for porcine pasteurellosis in the Chinese mainland. By using principal component analysis, the weights of seven spatial risk factors were determined. Fuzzy membership function was used to standardize all risk factors, and weight linear combination was used to create a risk map. The sensitivity of the risk map was analyzed by calculating the mean of absolute change rates of risk factors, as well as calculating an uncertainty map. The results showed that risk areas for porcine pasteurellosis were predicted to be locate in the south-central of the Chinese mainland, including Sichuan, Chongqing, Guangdong, and Guangxi. The maximum standard deviation of the uncertain map was less than 0.01and the ROC results showed that the prediction model has moderate predictive performance with the area under the curve (AUC) value of 0.80 (95% CI 0.75-0.84). Based on the above process, MCDA was combined with WebGIS technology to construct a system for predicting risk areas of porcine pasteurellosis. Risk factor data was directly linked to the developed model, providing decision support for disease prevention and control through monthly updates.

Gut microbiome perturbation and its correlation with tylosin pharmacokinetics in healthy and infected pigs

Tylosin, an antibiotic with a long history in treating respiratory bacterial infections, has unknown effects on the gut microbiota of healthy and infected pigs. The study aimed to investigate the effect of a therapeutic dose of tylosin on swine gut microbiota and explored the relationship between this effect and tylosin pharmacokinetics (PK). We also assessed whether changes in gut microbiota after tylosin administration differ between healthy animals (n = 7) and animals intranasally co-infected (n = 7) with Actinobacillus pleuropneumoniae and Pasteurella multocida. Both groups were intramuscularly administered with tylosin (20 mg/kg). The 16S rRNA gene analyses revealed a significantly lower species richness and diversity, after tylosin treatment, in the infected than the healthy pigs, with infected pigs having lower levels of Bacteroidetes and Firmicutes and higher levels of Proteobacteria. Greater tylosin exposure (greater area under curve (AUC) and maximum plasma concentration (Cmax), and slower elimination (longer terminal half-life, T1/2) were observed in healthy than infected pigs. Relative abundance of Lactobacillus, Oscillibacter, Prevotella, and Sporobacter was positively and significantly correlated with AUC and Cmax, whereas the abundance of Acinetobacter, Alishewanella, and Pseudomonas was positively and significantly correlated with T1/2 and mean residence time (MRT) of tylosin. Our findings, for the first time, demonstrated significant changes in swine gut microbiota after a single therapeutic dose of tylosin was administered, whereas the effect of these changes on tylosin PK was not evident.

A comparative study of the bacterial diversity and composition of nursery piglets' oral fluid, feces, and housing environment

The oral cavity is the portal of entry for many microorganisms that affect swine, and the swine oral fluid has been used as a specimen for the diagnosis of several infectious diseases. The oral microbiota has been shown to play important roles in humans, such as protection against non-indigenous bacteria. In swine, studies that have investigated the microbial composition of the oral cavity of pigs are scarce. This study aimed to characterize the oral fluid microbiota of weaned pigs from five commercial farms in Brazil and compare it to their respective fecal and environmental microbiotas. Bacterial compositions were determined by 16S rRNA gene sequencing and analyzed in R Studio. Oral fluid samples were significantly less diverse (alpha diversity) than pen floor and fecal samples (P < 0.01). Alpha diversity changed among farms in oral fluid and pen floor samples, but no differences were observed in fecal samples. Permutational ANOVA revealed that beta diversity was significantly different among sample types (P = 0.001) and farms (P = 0.001), with separation of sample types (feces, pen floor, and oral fluid) on the principal coordinates analysis. Most counts obtained from oral fluid samples were classified as Firmicutes (80.4%) and Proteobacteria (7.7%). The genera Streptococcus, members of the Pasteurellaceae family, and Veillonella were differentially abundant in oral fluid samples when compared to fecal samples, in which Streptococcus was identified as a core genus that was strongly correlated (SparCC) with other taxa. Firmicutes and Bacteroidota were the most relatively abundant phyla identified in fecal and pen floor samples, and Prevotella_9 was the most classified genus. No differentially abundant taxa were identified when comparing fecal samples and pen floor samples. We concluded that under the conditions of our study, the oral fluid microbiota of weaned piglets is different (beta diversity) and less diverse (alpha diversity) than the fecal and environmental microbiotas. Several differentially abundant taxa were identified in the oral fluid samples, and some have been described as important colonizers of the oral cavity in human microbiome studies. Further understanding of the relationship between the oral fluid microbiota and swine is necessary and would create opportunities for the development of innovative solutions that target the microbiota to improve swine health and production.

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.

Community engagement strengthens pig disease knowledge and passive surveillance in Timor-Leste

Smallholder pig production in Timor-Leste is culturally and economically important for most households. However, regular and ongoing disease surveillance and pig husbandry training for farmers are limited. This article describes collaborative social and diagnostic research followed by a pilot community engagement program to improve farmer and technician knowledge, skills, and working relationships. There were three phases: (1) A qualitative study in 2020 to explore the experiences and knowledge of 133 pig farmers, 6 village leaders, and 16 district veterinary technicians on pig diseases and reporting, treatment methods, and access to information or assistance. (2) A pilot community engagement program in 3 villages in 2021 with the diagnostic investigation with samples analyzed from 27 dead pigs, and (3) Evaluation of community engagement and training outcomes. Results of the qualitative study revealed limited reporting of sick or dead pigs by farmers to veterinary technicians due to a lack of trust in the veterinary diagnostic system. Most technicians lacked experience with sampling or post-mortems so diagnostic training was undertaken for the pilot disease investigation. Evaluation results showed improved knowledge, motivation, and confidence of government staff and farmers. The credibility of veterinary technicians improved and gave them more confidence to work with communities. Farmers felt supported because all aspects of pig husbandry were addressed, and they were more willing to report dead or sick pigs. The project indicates that improved passive disease surveillance can be achieved by engaging communities in smallholder pig farming in Timor-Leste. Further research and testing of the approach in other districts and countries is recommended.

Effect of conditioned media from Aeromonas caviae on the transcriptomic changes of the porcine isolates of Pasteurella multocida

Background

Pasteurella multocida is an opportunistic pathogen causing porcine respiratory diseases by co-infections with other bacterial and viral pathogens. Various bacterial genera isolated from porcine respiratory tracts were shown to inhibit the growth of the porcine isolates of P. multocida. However, molecular mechanisms during the interaction between P. multocida and these commensal bacteria had not been examined. 

Methods

This study aimed to investigate the interaction between two porcine isolates of P. multocida (PM2 for type D and PM7 for type A) with Aeromonas caviae selected from the previously published work by co-culturing P. multocida in the conditioned media prepared from A. caviae growth and examining transcriptomic changes using RNA sequencing and bioinformatics analysis. 

Results

In total, 629 differentially expressed genes were observed in the isolate with capsular type D, while 110 genes were significantly shown in type A. High expression of genes required for energy metabolisms, nutrient uptakes, and quorum sensing were keys to the growth and adaptation to the conditioned media, together with the decreased expression of those in the unurgent pathways, including translation and antibacterial resistance.

Conclusion

This transcriptomic analysis also displayed the distinct capability of the two isolates of P. multocida and the preference of the capsular type A isolate in response to the tough environment of the A. caviae conditioned media. Therefore, controlling the environmental sensing and nutrient acquisition mechanisms of P. multocida would possibly prevent the overpopulation of these bacteria and reduce the chance of becoming opportunistic pathogens.

Genomic diversity and molecular epidemiology of Pasteurella multocida

Pasteurella multocida is a bacterial pathogen with the ability to infect a multitude of hosts including humans, companion animals, livestock, and wildlife. This study used bioinformatic approaches to explore the genomic diversity of 656 P. multocida isolates and epidemiological associations between host factors and specific genotypes. Isolates included in this study originated from a variety of hosts, including poultry, cattle, swine, rabbits, rodents, and humans, from five different continents. Multi-locus sequence typing identified 69 different sequence types. In-silico methodology for determining capsular serogroup was developed, validated, and applied to all genome sequences, whereby capsular serogroups A, B, D, and F were found. Whole genome phylogeny was constructed from 237,670 core single nucleotide variants (SNVs) and demonstrated an overall lack of host or capsular serogroup specificity, with the exception of isolates from bovine sources. Specific SNVs within the srlB gene were identified in P. multocida subsp. septica genomes, representing specific mutations that may be useful for differentiating one of the three known subspecies. Significant associations were identified between capsular serogroup and virulence factors, including capsular serogroup A and OmpH1, OmpH3, PlpE, and PfhB1; capsular serogroup B and HgbA and PtfA; and capsular serogroup F and PtfA and PlpP. Various mobile genetic elements were identified including those similar to ICEPmu1, ICEhin1056, and IncQ1 plasmids, all of which harbored multiple antimicrobial resistance-encoding genes. Additional analyses were performed on a subset of 99 isolates obtained from turkeys during fowl cholera outbreaks from a single company which revealed that multiple strains of P. multocida were circulating during the outbreak, instead of a single, highly virulent clone. This study further demonstrates the extensive genomic diversity of P. multocida, provides epidemiological context to the various genotyping schemes that have traditionally been used for differentiating isolates, and introduces additional tools for P. multocida molecular typing.

Research Relevant Background Lesions and Conditions: Ferrets, Dogs, Swine, Sheep, and Goats

Animal models provide a valuable tool and resource for biomedical researchers as they investigate biological processes, disease pathogenesis, novel therapies, and toxicologic studies. Interpretation of animal model data requires knowledge not only of the processes/diseases being studied but also awareness of spontaneous conditions and background lesions in the model that can influence or even confound the study results. Species, breed/stock, sex, age, anatomy, physiology, diseases (noninfectious and infectious), and neoplastic processes are model features that can impact the results as well as study interpretation. Here, we review these features in several common laboratory animal species, including ferret, dog (beagle), pig, sheep, and goats.

Variability in in vitro biofilm production and antimicrobial sensitivity pattern among Pasteurella multocida strains

Biofilm production, hitherto an uncharacterized feature among circulating Pasteurella multocida strains, was studied along with the antibiotic susceptibility pattern. On the basis of biofilm formation ability, all the strains were categorized into four groups under six different culture conditions: strong biofilm-forming (22%), moderate (19%), weak (51%), and non-adherent (7%). Strains from serogroups A and B formed significant biofilms in at least one culture condition whereas strains from serogroup D were unable to form biofilms. All strains were found to be susceptible to tetracycline. In addition, the correlation between diverse factors (host, capsule type, clinical condition and the tadD gene) as well as antimicrobial susceptibility in biofilm production were analyzed by Joint distribution models, and showed that enrofloxacin and azithromycin resistant strains were positively correlated with strong biofilm production.

Pathogenic variability among Pasteurella multocida type A isolates from Brazilian pig farms

Background

Pasteurella multocida type A (PmA) is considered a secondary agent of pneumonia in pigs. The role of PmA as a primary pathogen was investigated by challenging pigs with eight field strains isolated from pneumonia and serositis in six Brazilian states. Eight groups of eight pigs each were intranasally inoculated with different strains of PmA (1.5 mL/nostril of 10e7 CFU/mL). The control group (n = 12) received sterile PBS. The pigs were euthanized by electrocution and necropsied by 5 dpi. Macroscopic lesions were recorded, and swabs and fragments of thoracic and abdominal organs were analyzed by bacteriological and pathological assays. The PmA strains were analyzed for four virulence genes (toxA: toxin; pfhA: adhesion; tbpA and hgbB: iron acquisition) by PCR and sequencing and submitted to multilocus sequence typing (MLST).

Results

The eight PmA strains were classified as follows: five as highly pathogenic (HP) for causing necrotic bronchopneumonia and diffuse fibrinous pleuritis and pericarditis; one as low pathogenic for causing only focal bronchopneumonia; and two as nonpathogenic because they did not cause injury to any pig. PCR for the gene pfhA was positive for all five HP isolates. Sequencing demonstrated that the pfhA region of the HP strains comprised four genes: tpsB1, pfhA1, tpsB2 and pfhA2. The low and nonpathogenic strains did not contain the genes tpsB2 and pfhA2. A deletion of four bases was observed in the pfhA gene in the low pathogenic strain, and an insertion of 37 kb of phage DNA was observed in the nonpathogenic strains. MLST clustered the HP isolates in one group and the low and nonpathogenic isolates in another. Only the nonpathogenic isolates matched sequence type 10; the other isolates did not match any type available in the MLST database.

Conclusions

The hypothesis that some PmA strains are primary pathogens and cause disease in pigs without any co-factor was confirmed. The pfhA region, comprising the genes tpsB1, tpsB2, pfhA1 and pfhA2, is related to the pathogenicity of PmA. The HP strains can cause necrotic bronchopneumonia, fibrinous pleuritis and pericarditis in pigs and can be identified by PCR amplification of the gene pfhA2.

Ex vivo penetration of fosfomycin into healthy and Lawsonia intracellularis-colonized swine intestinal mucosa

Fosfomycin (FOS) is an antibiotic used, mostly in Latin America, for the treatment of lung and enteric infections of pigs. Intracellular fluids of enterocytes can act as biophase for Lawsonia intracellularis, the causative agent of porcine proliferative enteropathy (PPE). The aim of this study was to determine whether the presence of L. intracellularis in the enterocytes modifies FOS penetration. Eight healthy pigs in growth-finishing stage were used to produce healthy (group A) and L. intracellularis-colonized (group B) intestinal explants. For both groups, treatment consisted of a 580 μg/ml concentration of calcium FOS, which was added to each explant (0.5-6 hr). For group B, the Enterisol Ileitis^® vaccine was used as source of the micro-organism. Previously to the assay, the time necessary for L. intracellularis to colonize the enterocytes was defined. Also, a PCR protocol was optimized to determine the presence of the pathogen in the explants. There were nonstatistical differences for the penetration of the antibiotic into healthy and L. intracellularis-colonized enterocytes. MIC₉₀ of FOS for L. intracellularis is unknown; nevertheless, MIC₉₀ of various antibiotics ranges between 0.125 and 128 μg/ml. FOS reaches inside the enterocyte concentrations which surpass the MICs₉₀ of other antibiotics that also act by the inhibition of cell wall synthesis; however, further studies should be carried out to determine fosfomycin MIC₉₀ for L. intracellularis to discern the usefulness of this antibiotic in the treatment of PPE.

Capsular Polysaccharide Interferes with Biofilm Formation by Pasteurella multocida Serogroup A

Pasteurella multocida is an important multihost animal and zoonotic pathogen that is capable of causing respiratory and multisystemic diseases, bacteremia, and bite wound infections. The glycosaminoglycan capsule of P. multocida is an essential virulence factor that protects the bacterium from host defenses. However, chronic infections (such as swine atrophic rhinitis and the carrier state in birds and other animals) may be associated with biofilm formation, which has not been characterized in P. multocida. Biofilm formation by clinical isolates was inversely related to capsule production and was confirmed with capsule-deficient mutants of highly encapsulated strains. Capsule-deficient mutants formed biofilms with a larger biomass that was thicker and smoother than the biofilm of encapsulated strains. Passage of a highly encapsulated, poor-biofilm-forming strain under conditions that favored biofilm formation resulted in the production of less capsular polysaccharide and a more robust biofilm, as did addition of hyaluronidase to the growth medium of all of the strains tested. The matrix material of the biofilm was composed predominately of a glycogen exopolysaccharide (EPS), as determined by gas chromatography-mass spectrometry, nuclear magnetic resonance, and enzymatic digestion. However, a putative glycogen synthesis locus was not differentially regulated when the bacteria were grown as a biofilm or planktonically, as determined by quantitative reverse transcriptase PCR. Therefore, the negatively charged capsule may interfere with biofilm formation by blocking adherence to a surface or by preventing the EPS matrix from encasing large numbers of bacterial cells. This is the first detailed description of biofilm formation and a glycogen EPS by P. multocida.

Pasteurella multocida is an important pathogen responsible for severe infections in food animals, domestic and wild birds, pet animals, and humans. P. multocida was first isolated by Louis Pasteur in 1880 and has been studied for over 130 years. However, aspects of its lifecycle have remained unknown. Although formation of a biofilm by P. multocida has been proposed, this report is the first to characterize biofilm formation by P. multocida. Of particular interest is that the biofilm matrix material contained a newly reported amylose-like glycogen as the exopolysaccharide component and that production of capsular polysaccharide (CPS) was inversely related to biofilm formation. However, even highly mucoid, poor-biofilm-forming strains could form abundant biofilms by loss of CPS or following in vitro passage under biofilm growth conditions. Therefore, the carrier state or subclinical chronic infections with P. multocida may result from CPS downregulation with concomitant enhanced biofilm formation.

Evaluation of the biofilm formation capacity of Pasteurella multocida strains isolated from cases of fowl cholera and swine lungs and its relationship with pathogenicity

ABSTRACT: Pasteurella multocida is a Gram-negative bacillus that causes economic losses due to the development of respiratory diseases in several animal species. Among the mechanisms of virulence, the formation of biofilms is an important factor for bacterial survival in hostile environments. Studies of biofilm formation by P. multocida are needed because P. multocida is an important pathogen involved in respiratory infections. However, in contrast to other microorganisms, few studies of biofilm formation have examined P. multocida. Studies comparing the pathogenicity of microbial strains as a function of their biofilm production capacity are also rare. Consequently, the aim of this study was to evaluate the biofilm formation capacity of 94 P. multocida strains isolated from cases of fowl cholera and from swine lungs on polystyrene plates. The associations of the biofilm formation capacity with the pathogenicity index (PI) in vivo and with the presence of four genes (screened by PCR) of the tad locus (tadB, tadD, tadE and tadG), described as adhesion markers, were also determined. Strains from both animal origins were able to form biofilms. However, most of the specimens (52.13%) were classified as weak producers, and more than 40% of the strains of P. multocida (40.42%) did not produce biofilms. There was no significant difference (p>0.05) in the degree of biofilm production between the two sources of isolation. Of the analyzed strains, 56.52% contained all four genes (tadB, tadD, tadE and tadG). The PI arithmetic mean of the strains classified as non-biofilm producers was significantly different (p<0.05) from the PI of moderate-producer strains. The PI of specimens classified as weak biofilm producers also differed significantly (p<0.05) from that of the moderate-producer strains. The results indicate that even though the P. multocida strains isolated from cases of fowl cholera and swine lungs formed biofilms on polystyrene surfaces, adhesion was usually weak. The genes tadB, tadD, tadE and tadG were not significantly associated (p>0.05) with the production of biofilms and with the origin of a given strain. Finally, low virulence strains may suggest a higher biofilm formation capacity on polystyrene plates.

Experimental pathogenicity and complete genome characterization of a pig origin Pasteurella multocida serogroup F isolate HN07

Pasteurella multocida serotype F isolates are predominately prevalent in avian hosts, but rarely seen in pigs. However, we isolated several strains of P. multocida serotype F from clinical samples of pigs in China. To understand the pathogenicity of these strains, one of the serotype F isolates designated HN07, was used to challenge experimental chickens, as P. multocida of this serotype is predominately prevalent in avian hosts. However, strain HN07 could not resulted in significant clinical signs in experimental chickens even at an infective dose of ∼10⁹ CFU, suggesting the isolate was avirulent to chickens and therefore raising the possibility that the porcine serotype F isolate is not transmitted by chickens. We then used HN07 to challenge experimental pigs, as this strain was isolated from pigs. As expected, the strain led to the clinical signs and the pathological lesions in experimental pigs that are similar to the pasteurellosis disease. We then determined the complete genome sequence of the pig origin serogroup F isolate HN07 for the first time. Genome comparison between HN07 and the avian serotype F P. multocida Pm70 identified a novel integrative conjugative element (ICE) ICEpmcn07 which was likely to harbor a series of genes responsible for a putative type IV secretion system (T4SS) in HN07. This is the first time that we determined an ICE carrying a T4SS in P. multocida. Besides, comparative analysis also defined a number of virulence-associated genes in HN07 but absent in Pm70 which may have a contribution to the pathogenicity of the strain. This is the first report of the pathogenicity and genome characterization of a pig origin Pasteurella multocida serogroup F isolate. The pathogenic and genomic definition of the pig origin P. multocida serogroup F in our study would have significance on the pathogenesis and genetic diversity and virulence variability of P. multocida.

Histopathological and immunohistochemical approaches for the diagnosis of Pasteurellosis in swine population of Punjab

Aim:

Infectious porcine bronchopneumonia, caused by Pasteurella multocida, is a widespread disease of major economic significance. Thus, the aim of the present study was to diagnose swine Pasteurellosis using gross, histopathological, and immunopathological approaches in the swine population of Punjab and to compare the efficacy of immunohistochemical (IHC) techniques with conventional diagnostic techniques.

Materials and Methods:

A total of 71 adult swine lung samples showing gross pneumonic changes were collected along with the associated lymph nodes to carry out the study. The collected samples were then processed for histopathological and IHC studies.

Results:

Out of the total 71 lung samples, 26 samples were found to be suspected for Pasteurellosis as per the microscopic changes observed, and out of these 26 samples, 16 cases were confirmed to be positive for Pasteurellosis by IHC. Varied macroscopic changes noted in lungs were pneumonic patches with consolidation of many lobes, congestion, and focal hemorrhages. Main lesions associated with lymph nodes were its enlargement and hemorrhages. Histologically, the lung showed fibrinous and suppurative bronchopneumonia, multifocal suppuration, thickening of septa with fibrin combined with cellular infiltration and edema. The higher IHC expression of P. multocida was seen in the bronchial epithelium besides in alveolar and bronchial exudate. Moreover, on comparing the histopathological and IHC scores which were calculated on the basis of characteristic microscopic lesions and number of antigen positive cells, respectively, a significant positive correlation (r=0.4234) was found.

Conclusion:

It was concluded that swine population of Punjab is having P. multocida infection. The gross and histopathological lesions can be helpful in the preliminary diagnosis of Pasteurellosis but needs to be supplemented by other immunodiagnostic tests. Moreover, IHC technique proved to be a specific, reliable, precise, and rapid technique to supplement these conventional methods of diagnosis for Pasteurellosis.

Pasteurella multocida type A as the primary agent of pneumonia and septicaemia in pigs

Abstract: In order to understand better the pathological aspects and spread of Pasteurella multocida type A as the primary cause of pneumonia in pigs, was made an experiment with intranasal inoculation of different concentrations of inocula [Group (G1): 108 Colony Forming Units (CFU)/ml; G2: 107 CFU/ml; G3: 106 CFU/ml and G4: 105 CFU/ml], using two pigs per group. The pigs were obtained from a high health status herd. Pigs were monitored clinically for 4 days and subsequently necropsied. All pigs had clinical signs and lesions associated with respiratory disease. Dyspnoea and hyperthermia were the main clinical signs observed. Suppurative cranioventral bronchopneumonia, in some cases associated with necrosuppurative pleuropneumonia, fibrinous pericarditis and pleuritic, were the most frequent types of lesion found. The disease evolved with septicaemia, characterized by septic infarctions in the liver and spleen, with the detection of P. multocida type A. In this study, P. multocida type A strain #11246 was the primary agent of fibrinous pleuritis and suppurative cranioventral bronchopneumonia, pericarditis and septicaemia in the pigs. All concentrations of inoculum used (105-108 CFU/ml) were able to produce clinical and pathological changes of pneumonia, pleuritis, pericarditis and septicemia in challenged animals.

Pasteurella multocida: diseases and pathogenesis

Pasteurella multocida is an enigmatic pathogen. It is remarkable both for the number and range of specific disease syndromes with which it is associated, and the wide range of host species affected. The pathogenic mechanisms involved in causing the different syndromes are, for the most part, poorly understood or completely unknown. The biochemical and serological properties of some organisms responsible for quite different syndromes appear to be similar. Thus, the molecular basis for host predilection remains unknown. The recent development of genetic manipulation systems together with the availability of multiple genome sequences should help to explain the association of particular pathological conditions with particular hosts as well as helping to elucidate pathogenic mechanisms.

Biofilm formation in bacterial pathogens of veterinary importance

Bacterial biofilms are structured communities of bacterial cells enclosed in a self-produced polymer matrix that is attached to a surface. Biofilms protect and allow bacteria to survive and thrive in hostile environments. Bacteria within biofilms can withstand host immune responses, and are much less susceptible to antibiotics and disinfectants when compared with their planktonic counterparts. The ability to form biofilms is now considered a universal attribute of micro-organisms. Diseases associated with biofilms require novel methods for their prevention, diagnosis and treatment; this is largely due to the properties of biofilms. Surprisingly, biofilm formation by bacterial pathogens of veterinary importance has received relatively little attention. Here, we review the current knowledge of bacterial biofilms as well as studies performed on animal pathogens.

Disease patterns and immune responses in the offspring to sows with high or low antibody levels to Actinobacillus pleuropneumoniae serotype 2

The serum antibody responses to Actinobacillus pleuropneumoniae and the secondary invader Pasteurella multocida were monitored from birth until slaughter in the offspring to sows with high or low levels of serum antibodies to A. pleuropneumoniae. Serum antibody concentrations to A. pleuropneumoniae were higher from birth to the age of 9 weeks in piglets delivered by high responding sows. In contrast, antibody levels to P. multocida were similar in both groups during this period. From the age of 20 and 15 weeks, antibody levels to A. pleuropneumoniae and P. multocida, respectively, were higher in the offspring to high responding sows. This implies that the offspring to sows with high levels of antibodies may be better protected during the first period of life because of a higher level of passively derived immunity. These piglets will also mount a higher antibody response when later infected, indicating a heritability of the humoral immune response.

An investigation of the pathology and pathogens associated with porcine respiratory disease complex in Denmark

Respiratory infections are among the most important diseases of growing pigs. In order to elucidate the multifactorial aetiology of porcine respiratory disease complex (PRDC) in Denmark, lungs from 148 finishing pigs with cranioventral bronchopneumonia (case group) and 60 pigs without lung lesions (control group) were collected from abattoirs. The pathogens involved in PRDC and their interactions were identified and linked to the histopathological diagnosis. The lung samples were cultured for bacteria and tested by multiplex polymerase chain reaction for presence of swine influenza virus (type A), porcine reproductive and respiratory syndrome virus (both European and US type), porcine circovirus type 2 (PCV2), porcine respiratory coronavirus, porcine cytomegalovirus, Mycoplasma hyopneumoniae and Mycoplasma hyorhinis. All cases had cranioventral lobular bronchopneumonia consistent with PRDC. There was a broad range of microscopical lesions and the cases were characterized as acute (n = 10), subacute (n = 24) or chronic (n = 114) bronchopneumonia. Five bacterial species, five viruses and two Mycoplasma spp. were detected in different combinations. PCV2, M. hyopneumoniae, M. hyorhinis and Pasteurella multocida were detected most frequently among the PRDC affected swine and the diversity and number of pathogens were higher in these animals compared with controls. No clear-cut associations were detected between pathogens and histological lesions or histopathological diagnoses. PRDC occurs more frequently than enzootic pneumonia among Danish finishing pigs and has complex and varied histopathology.