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

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

Bovine Respiratory Syncytial Virus Decreased Pasteurella multocida Adherence by Downregulating the Expression of Intercellular Adhesion Molecule-1 on the Surface of Upper Respiratory Epithelial Cells

The synergistic infection of bovine respiratory syncytial virus (BRSV) and Pasteurella multocida (PM) may predispose cattle to develop severe pneumonia. Previously, we reported that BRSV infection significantly decreased PM adherence to the upper respiratory epithelial cells. It may allow bacteria to invade into the lower respiratory tract and lead to severe pneumonia. To investigate whether BRSV infection regulates the cell surface adherence receptor on bovine trachea epithelial cells (bTECs), we performed proteomic and functional analyses. BRSV infection decreased the expression of intercellular adhesion molecule-1 (ICAM1) on bTECs. Inhibition and knockdown experiments using anti-ICAM1 antibody and siRNAs targeting ICAM1 indicated that PM adherence to bTECs was dependent on ICAM1 expression. These data suggest that under normal conditions bTECs may capture PM in the upper respiratory tract, while BRSV infection reverses this mechanism. The proposed gateway function of bTECs is disrupted by BRSV infection that may facilitate bacterial invasion into the lower respiratory tract and lead to secondary or more severe respiratory infection.

Comparative analysis reveals the Genomic Islands in Pasteurella multocida population genetics: on Symbiosis and adaptability

BACKGROUND

Pasteurella multocida (P. multocida) is a widespread opportunistic pathogen that infects human and various animals. Genomic Islands (GIs) are one of the most important mobile components that quickly help bacteria acquire large fragments of foreign genes. However, the effects of GIs on P. multocida are unknown in the evolution of bacterial populations.

RESULTS

Ten avian-sourced P. multocida obtained through high-throughput sequencing together with 104 publicly available P. multocida genomes were used to analyse their population genetics, thus constructed a pan-genome containing 3948 protein-coding genes. Through the pan-genome, the open evolutionary pattern of P. multocida was revealed, and the functional components of 944 core genes, 2439 accessory genes and 565 unique genes were analysed. In addition, a total of 280 GIs were predicted in all strains. Combined with the pan-genome of P. multocida, the GIs accounted for 5.8% of the core genes in the pan-genome, mainly related to functional metabolic activities; the accessory genes accounted for 42.3%, mainly for the enrichment of adaptive genes; and the unique genes accounted for 35.4%, containing some defence mechanism-related genes.

CONCLUSIONS

The effects of GIs on the population genetics of P. multocida evolution and adaptation to the environment are reflected by the proportion and function of the pan-genome acquired from GIs, and the large quantities of GI data will aid in additional population genetics studies.

Bovine respiratory syncytial virus infection enhances Pasteurella multocida adherence on respiratory epithelial cells

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BRSV is the causative agent of bovine respiratory disease complex (BRDC).

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The interaction between BRSV and Pasteurella multocida (PM) during BRDC is unclear.

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BRSV infection increased adherence of PM to respiratory epithelial cells.

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These interactions might account for the serious symptoms of BRDC.

Primary infection with bovine respiratory syncytial virus (BRSV) predisposes cattle to secondary infection with bacteria that cause bovine respiratory disease complex (BRDC). However, the interaction between BRSV and bacteria is unclear. This in vitro study examined the adherence of Pasteurella multocida (PM) to BRSV-infected cells was assessed in colony forming unit assays, by flow cytometry analysis, and by indirect immunofluorescence analysis (IFA) of epithelial cells (A549, HEp-2, and MDBK). An in vitro model based on infection of BRSV-infected epithelial cells revealed that PM adherence to BRSV-infected cells was 2- to 8-fold higher than uninfected cells. This was confirmed by flow cytometry analysis and IFA. Epithelial cell expression of mRNA encoding cytokines and chemokines increased after exposure to PM, but increased further after co-infection with BRSV and PM. BRSV-mediated adherence of PM to epithelial cells may underlie the serious symptoms of BRDC.

Mutual antagonism between Mannheimia haemolytica and Pasteurella multocida when forming a biofilm on bovine bronchial epithelial cells in vitro

Mannheimia haemolytica and Pasteurella multocida are two bacterial species implicated in the bovine respiratory disease complex (BRDC) that is costly to the beef and dairy cattle industries. Both bacterial species are thought to occupy a similar niche as commensals in the upper respiratory tract. Many bacteria are thought to exist as biofilms in their hosts, perhaps in close proximity with other bacterial species. We previously showed that M. haemolytica forms biofilm on bovine respiratory epithelial cells in vitro. We are interested in the possibility that M. haemolytica and P. multocida co-exist as biofilms in the upper respiratory tract of cattle. In this study, we begin to explore this possibility by assessing the ability of M. haemolytica and P. multocida to form a biofilm on bovine respiratory epithelial cells in vitro. We found that M. haemolytica and P. multocida are separately able to form biofilms on bovine respiratory epithelial cells, but mutually inhibit one another when incubated together as a biofilm. Both the biofilm matrix (crystal violet stain) and bacterial numbers (CFU and PCR) were reduced when M. haemolytica and P. multocida were incubated together on fixed epithelial cells. This inhibition does not appear to result from a soluble factor, as neither conditioned medium nor separation of the two species by a transwell filter membrane reproduced the effect. We infer that when located in close proximity on the epithelial surface, M. haemolytica and P. multocida mutually regulate one another.

Biofilm inhibitors targeting the outer membrane protein A of Pasteurella multocida in swine

Pasteurella multocida (Pm) is the causative agent of atrophic rhinitis in swine. This study aimed to discover biofilm inhibitors against swine Pm to counteract antibiotic resistance and decrease virulence. The virulence factor outer membrane protein A (OmpA) was targeted. A library of drugs approved by the Food and Drug Administration (FDA) was used to perform virtual screening against PmOmpA. The top-scoring compounds had no effect on the growth of Pm serotype A or D. Mycophenolate mofetil showed the highest efficacy in inhibiting biofilm formation by Pm serotype A, with an IC₅₀ of 7.3 nM. For Pm serotype D, indocyanine green showed the highest effect at an IC₅₀ of 11.7 nM. Nevertheless, these compounds had no effect on an established biofilm of Pm. This study offers an alternative way to prevent biofilm formation by Pm that could also be applied to other pathogens.

Feed exposure to FB1 can aggravate pneumonic damages in pigs provoked by P. multocida

The possible interaction between Pasteurella multocida and the mycotoxin fumonisin B1 (FB1), recognised as one of the most often food/feed contaminant, was studied with the aim to evaluate whether and how FB1 can influence and/or complicate the development and severity of various pathological damages provoked by Pasteurella multocida in some internal organs of pigs. Heavier lung pathology was seen in pigs experimentally infected with Pasteurella multocida, when the same were exposed to 20ppm dietary levels of fumonisin B1 (FB1) as was assessed by gross pathology, pathomorphological examinations, clinical biochemistry and some immunological investigations. The most typical damages in FB1 treated pigs were the strong oedema in the lung and the slight oedema in the other internal organs and mild degenerative changes in the kidneys, whereas the typical pathomorphological findings in pigs infected with Pasteurella multocida was broncho-interstitial pneumonia. FB1 was found to aggravate pneumonic changes provoked by P. multocida in the cranial lobes of the lung and to complicate pneumonic damages with interstitial oedema in the lung. No macroscopic damages were observed in the pigs infected only with Pasteurella multocida. It can be concluded that the feed intake of FB1 in pigs may complicate or exacerbate the course of P. multocida serotype A infection.

Pasteurella multocida: from zoonosis to cellular microbiology

In a world where most emerging and reemerging infectious diseases are zoonotic in nature and our contacts with both domestic and wild animals abound, there is growing awareness of the potential for human acquisition of animal diseases. Like other Pasteurellaceae, Pasteurella species are highly prevalent among animal populations, where they are often found as part of the normal microbiota of the oral, nasopharyngeal, and upper respiratory tracts. Many Pasteurella species are opportunistic pathogens that can cause endemic disease and are associated increasingly with epizootic outbreaks. Zoonotic transmission to humans usually occurs through animal bites or contact with nasal secretions, with P. multocida being the most prevalent isolate observed in human infections. Here we review recent comparative genomics and molecular pathogenesis studies that have advanced our understanding of the multiple virulence mechanisms employed by Pasteurella species to establish acute and chronic infections. We also summarize efforts being explored to enhance our ability to rapidly and accurately identify and distinguish among clinical isolates and to control pasteurellosis by improved development of new vaccines and treatment regimens.

[Construction and characterization of ompH gene knockout mutant of avian Pasteurella multocida C48-3]

OBJECTIVE

To study the role of the outer membrane protein H (OmpH) in pathogenicity of avian Pasteurella multocida.

METHODS

The ompH knock-out mutant of avian P. multocida C48-3 was constructed by homologous recombination. The DNA replacement was confirmed by PCR, RT-PCR and Western blot. We compared the differences of biological characteristics such as growth rate, capsular structure, adhesion ability and virulence between the ompH knockout mutant of C48-3 Delta ompH and parent strain C48-3, as well as the complemented strain C48-3C.

RESULTS

C48-3 Delta ompH was successfully constructed. Electron microscopy examination of C48-3 Delta ompH shows the absence of capsular material compared to the parent strain C48-3 and complemented strain C48-3C. The adhesion assay shows that the number of C48-3 Delta ompH adhered to CEF cells was significantly lower than that of C48-3 and C48-3C. C48-3 Delta ompH was relatively attenuated in mice by intraperitoneal injection.

CONCLUSION

The construction of C48-3 Delta ompH would facilitate further study on pathogenesis of avian Pasteurella multocida.

A case of a late and atypical knee prosthetic infection by no-biofilm producer Pasteurella multocida strain identified by pyrosequencing

Prosthetic joint infections due to Pasteurella multocida are rarely but increasingly reported but no data on production of biofilm are available. We report the case of a woman with a late, haematogenous peri-prosthetic infection of cemented total knee arthroplasty caused by a strain of P. multocida identified by pyrosequencing and unable to produce biofilm. Comparison of clinical and laboratory findings with those reported in other patients evidenced differences mainly in the period of symptoms' onset and in the behaviour of some inflammatory markers.

Cellular and molecular action of the mitogenic protein-deamidating toxin from Pasteurella multocida

The mitogenic toxin from Pasteurella multocida (PMT) is a member of the dermonecrotic toxin family, which includes toxins from Bordetella, Escherichia coli and Yersinia. Members of the dermonecrotic toxin family modulate G-protein targets in host cells through selective deamidation and/or transglutamination of a critical active site Gln residue in the G-protein target, which results in the activation of intrinsic GTPase activity. Structural and biochemical data point to the uniqueness of PMT among these toxins in its structure and action. Whereas the other dermonecrotic toxins act on small Rho GTPases, PMT acts on the α subunits of heterotrimeric G(q) -, G(i) - and G(12/13) -protein families. To date, experimental evidence supports a model in which PMT potently stimulates various mitogenic and survival pathways through the activation of G(q) and G(12/13) signaling, ultimately leading to cellular proliferation, whilst strongly inhibiting pathways involved in cellular differentiation through the activation of G(i) signaling. The resulting cellular outcomes account for the global physiological effects observed during infection with toxinogenic P. multocida, and hint at potential long-term sequelae that may result from PMT exposure.

Capsular serotyping of Pasteurella multocida from various animal hosts - a comparison of phenotypic and genotypic methods

One hundred and fourteen strains of Pasteurella multocida were isolated from different domestic animals species (cattle, buffalo, sheep, goat, pig, rabbit, dog, cat), avian species (chicken, duck, turkey) and wild animals (deer, tiger, orang utan, marmoset). The serogroups of P. multocida were determined by both conventional capsular serotyping and a multiplex PCR assay targeting specific capsular genes. Based on the conventional serotyping method, the 114 strains of P. multocida were subtyped into 55 species-specific (untypeable strains) P. multocida, 15 serogroup A, 23 serogroup B and 21 serogroup D. Based on the multiplex PCR assay on the specific capsular genes associated with each serogroup, the 114 strains were further divided to 22 species-specific P. multocida (KMT1 - 460 bp), 53 serogroup A (A - 1,044 bp), 33 serogroup B (B - 760 bp) and 6 serogroup D (D - 657 bp). No serogroup E (511 bp) or F (851 bp) was detected among the Malaysian P. multocida. PCR-based typing was more discriminative and could further subtype the previously untypeable strains. Overall, there was a significant and positive correlation between both methods in serogrouping P. multocida (r = 0.7935; p<0.4893). Various serogroups of P. multocida were present among the livestock with 75% of the strains belonging to serogroups A or B. PCR serotyping was therefore a highly species-specific, sensitive and robust method for detection and differentiation of P. multocida serogroups compared to conventional serotyping. To the best of our knowledge, this is the first report from Malaysia of the application of a PCR to rapidly define the species-specific P. multocida and its serogroups as an important zoonotic pathogen in Malaysia.

Expression of the dermonecrotic toxin by Bordetella bronchiseptica is not necessary for predisposing to infection with toxigenic Pasteurella multocida

This experiment was designed to determine whether a Bordetella bronchiseptica mutant that does not produce dermonecrotic toxin (DNT) is still capable of predisposing pigs to infection with toxigenic Pasteurella multocida. Three groups of pigs were initially inoculated intranasally with a wild type B. bronchiseptica that produces DNT, an isogenic mutant of B. bronchiseptica that does not produce DNT, or PBS. All pigs were then challenged intranasally with a toxigenic strain of P. multocida 4 days later. P. multocida was recovered infrequently and in low numbers from pigs initially inoculated with PBS, and no turbinate atrophy was present in these pigs. P. multocida was isolated in similar numbers from the pigs initially inoculated with either the wild type or the DNT mutant of B. bronchiseptica, and turbinate atrophy of a similar magnitude was also seen in pigs from both of these groups. Thus, although the DNT has been shown to be responsible for much of the pathology seen during infection with B. bronchiseptica by itself, infection with non-DNT-producing strains can still predispose to secondary respiratory infections with P. multocida.

Pasteurella multocida toxin (PMT) activates RhoGTPases, induces actin polymerization and inhibits migration of human dendritic cells, but does not influence macropinocytosis

Dendritic cells (DCs) are considered as one of the principal initiators of immune responses. In their immature state, they migrate into peripheral tissue in order to uptake antigen and to patrol for danger signals. Upon maturation, they acquire the ability to migrate to the lymph nodes and present the captured antigens to T cells in order to direct the development of specific immune responses. There is evidence that microbial compounds interfere with proper functions of DCs in order to block innate and specific immunity. Here we characterized the influence of Pasteurella multocida toxin (PMT) on monocyte-derived DCs. Using pull-down assays with recombinant rhotekin or p21-activated kinase, we demonstrated the activation of RhoGTPases by PMT in DCs. Moreover, PMT induced changes in DC morphology and actin polymerization, impaired chemotaxin-induced actin re-organization and inhibited their migration response. However, macropinocytosis was not influenced by PMT. In summary, these data indicate that PMT inhibits proper function of the motility machinery in DCs, which might limit the development of adaptive immune surveillance during infection with Pasteurella multocida.

How does Pasteurella multocida respond to the host environment?

Pasteurella multocida is a Gram-negative bacterial pathogen, which causes diseases of economic importance in a wide range of animal species. The response of P. multocida to the host environment has been analysed at the transcription level, using DNA microarrays, and at the protein-expression level, using proteomics techniques. Furthermore, a growing number of P. multocida-directed mutants have been assessed for their ability to cause disease. Although technical impediments mean that it is currently difficult to analyse bacterial responses at the earliest stages of infection, it is clear that during later stages of infection the bacteria encounter host niches that require them to modify the expression of genes involved in central energy metabolism and in the uptake of various nutrients such as iron and amino acids. Furthermore, in vitro experiments have defined the varying bacterial responses to low iron and to different iron sources, including haemoglobin and transferrin. To date, most P. multocida genes shown to be upregulated during infection are involved in nutrient acquisition and metabolic processes, indicating that true virulence genes might be constitutively expressed, upregulated only during initial stages of infection or upregulated at levels below current detection limits.

Adherence of to fibronectin

For many pathogens, adherence and/or invasion involve association with host extracellular matrix molecules, such as fibronectin (Fn). Pasteurella multocida was found to bind significantly to Fn and collagen type IX but not to laminin and collagen types IV and X. The binding of P. multocida to Fn was dose-dependent and was inhibited by heparin (Hep). Removal of polysaccharide capsule enhanced the binding capacity of the bacterium to Fn and inhibition by Hep. Protease treatment of bacteria decreased binding, implicating surface protein(s) as adhesive components. Investigation of the binding domain(s) of P. multocida on the Fn molecule revealed preferential binding to the N-terminal Hep-binding domain of Fn but not to the carboxyl-terminal Hep-binding domain. Furthermore, Fn, and anti-Fn antibodies inhibited P. multocida adherence to Madin-Darby bovine kidney cells, suggesting the involvement of Fn in the bacterium adherence to host cells. Ligand blotting, batch affinity purification and MALDI-TOF mass spectrometry implicated several proteins as putative adhesins of P. multocida in the Fn-mediated adherence. Taken together, the data suggest that P. multocida-Fn interaction may play a role in the bacterium adherence to host cells, and this may be mediated by bacterial surface proteins with preferential affinity for the Hep-1 binding domain of Fn.

An experimental mouse model of progressive atrophic rhinitis of swine

Pasteurella multocida is responsible for a variety of diseases of veterinary importance, including the pig disease progressive atrophic rhinitis (PAR). The feasibility of using the mouse as an experimental model of PAR was evaluated. We experimentally infected the upper respiratory tract of immature mice with a pig isolate of P. multocida that produces the toxin responsible for causing the nasal lesions characteristic of PAR. We tracked the health status and weight gain of these mice for one month following infection, after which the mice were killed and the integrity of the nasal turbinates was examined. Mice infected with P. multocida appeared healthy throughout the study, although the growth rate of these mice was reduced significantly compared with non-infected control animals. Infected animals also demonstrated marked nasal atrophy analogous to that seen in naturally occurring PAR of swine, with shortening and thinning of the turbinate scrolls and inflammatory cell involvement. The mouse therefore provides a convenient model for the further investigation of PAR of swine.

Invasion of chicken embryo fibroblast cells by avian Pasteurella multocida

Invasion of chicken embryo fibroblast (CEF) cells by the virulent encapsulated Pasteurella multocida strains P-1059 (serovar A:3) and X-73 (serovar A:1) and an avirulent noncapsulated derivative P-1059B (serovar -:3) was investigated. The number of intracellular bacteria increased for all the strains after 2, 4 and 6 h post-inoculation to CEF cells. By 6 h post-inoculation, the number of invaded bacteria of encapsulated strains was significantly higher than noncapsulated strain and reached 150- and 112-fold for strains P-1059 and X-73, respectively, while it was 9-fold for strain P-1059B as compared to the number of invaded bacteria recovered after 2 h post-inoculation. Electron microscopy of invasion by encapsulated strains showed that the bacteria were adhering to CEF cells membrane after 1 h of inoculation. By 4-h, one or two bacteria were detected within membrane-bound vacuoles of the intracellular space. The number of intracellular bacteria markedly increased at 14 h post-inoculation. Invasion of all strains was inhibited significantly when the monolayers were treated with periodic acid (P<0.001) or trypsin (P<0.05). The treatment of bacteria with hyaluronidase did not affect invasion. The present results indicate that avian P. multocida capsular type A strains are invasive and that the receptor on CEF cell surface might be glycoprotein.

A 39kDa protein mediates adhesion of avian Pasteurella multocida to chicken embryo fibroblast cells

To clarify the role of avian Pasteurella multocida capsule in pathogenesis, adhesion of capsulated strains P-1059, X-73 and Pm-18, and noncapsulated strains P-1059B, Pm-1 and Pm-3 to chicken embryo fibroblast (CEF) cells was compared. Number of adherent organisms of the capsulated strains to CEF cells were approximately three times as much as noncapsulated strains indicating that adhesive properties were enhanced by the presence of bacterial capsule. Pretreatments of the bacterial cells with heat, trypsin, or with antiserum caused a marked decrease in adhesion of capsulated strain P-1059 and its noncapsulated variant P-1059B. However, depolymerization of capsular hyaluronic acid with high dose of hyaluronidase enhanced adhesion of these strains. Combined treatments of the bacterial cells with both hyaluronidase and trypsin significantly (P < 0.05) inhibited the adherence of strain P-1059 as compared to the treatment only with trypsin, but strain P-1059B was not affected. SDS-PAGE profiles of crude capsular extract (CCE) prepared from capsulated strain P-1059 and its noncapsulated variant P-1059B grown on dextrose starch agar (DSA) plates by heating at 56 degrees C in a 2.5% NaCl solution demonstrated eight protein bands of 28, 34, 36, 39, 52, 56, 63 and 93 kDa. The 28, 34 and 36 kDa proteins were commonly major for both strains, and the 39 kDa protein was major only for strain P-1059 but poor in strain P-1059B. Outer membrane protein (OMP) profiles were identical with a major protein at 34 kDa and four minor proteins between the two strains. The adhesion of strain P-1059 and strain P-1059B to CEF cells was inhibited significantly (P < 0.01) by treatment with rabbit antisera against P-1059, P-1059B, CCE or 39 kDa protein of strain P-1059 as compared to the treatment with either PBS or with normal rabbit serum. These results indicated that an antigenic 39 kDa protein in the capsule may be responsible for adhesion of avian P. multocida type A strains to CEF cells as a virulence factor.

Influences of naturally occurring and experimentally induced porcine pneumonia on blood parameters

It had been the objective of the studies described to establish local and systemic changes by naturally occurring pneumonia or pneumonia experimentally induced by Pasteurella multocida and Haemophilus parasuis in swine. Acute and chronic pneumonia was found to alter the cytokine level of lung lavage fluid and affect the composition and function of blood cells, especially with regard to phagocytosis, radical formation and cell surface receptors. Interleukin-6 levels in blood plasma rose 24h after experimental intrabronchial infection. The influences of the changes on growth and meat quality are discussed.

Coinfection with BHV-1 modulates cell adhesion and invasion by P. multocida and Mannheimia (Pasteurella) haemolytica

Viruses are thought to facilitate bacterial infections of the respiratory tract. The present study shows the effect of BHV-1 on Pasteurella multocida and Mannheimia haemolytica adherence and invasion of MDBK cells. The virus-infected MDBK cells become more susceptible to the adherence of both species of Pasteurella. The observed adherence increase depends on the length of virus pre-incubation time and on virus concentration. When MDBK cells are not infected with virus, they are only invaded by P. multocida, while M. haemolytica is not able to penetrate. The viral infection favours also the invasion by M. haemolytica.

Experimental induction of pneumonic pasteurellosis in calves by intratracheal infection with Pasteurella multocida biotype A:3

The study aimed to establish an experimental model to investigate the pathogenesis of lung infection by Pasteurella multocida, an important cause of bovine respiratory disease. An experimental model is required to assist the development of an effective vaccine. Sixteen 8-week-old calves were challenged intratracheally with 10(9) or 10(10) colony forming units of P. multocida in either 60 or 300 ml saline in a 2 x 2 factorial experiment. All animals became dull within 2-6h post-infection (p.i.) and two calves were killed humanely because of suspected endotoxic shock. Remaining animals showed increased respiratory rates by 15-20 h p.i. and, at 23 h p.i., calves given the high dose, high volume challenge showed higher (P < 0.05) rectal temperatures. From 24 to 36 h p.i., clinical signs decreased in a majority of animals. Plasma haptoglobin concentrations increased (P < 0.05) in calves given the high volume challenge irrespective of the number of bacteria. At post-mortem examination (4d p.i.), lung lesions, mainly in the apical lobes, were found in all calves. Histopathological examination showed areas of purulent pneumonia with a tendency to abscessation and inflamed interlobular septa characterised by accumulation of neutrophils and oedema. The clinical and pathological responses described were typical of bovine pneumonic pasteurellosis.

Serum resistance of Pasteurella multocida in avian and porcine sera, and comparative virulence investigations of selected serum-sensitive and resistant strains in chickens

Growth in serum of Pasteurella multocida and related species in chicken, turkey, duck and pig sera were compared, and selected serum-resistant and serum-sensitive strains were inoculated into 18-week-old layers. Eighty-seven field strains of Pasteurella spp. and nine reference strains representing different clones defined by restriction endonuclease analysis (REA) profiles were used in the study. Serum activity was measured by changes in the optical density (OD) of the serum after inoculation and incubation at 41 degrees C for chicken, turkey and duck serum and 39 degrees C for pig serum. Serum activity was measured by comparison with previously determined serum-resistant (P-1059) and serum-sensitive (CU vaccine) strains, and classified into highly serum-resistant, moderately serum-resistant and serum-sensitive. Strains of the same REA type were found to have identical growth curves and the same maximum OD values when tested in serum from the same host species. Turkey serum was shown to be less inhibitory to a wide range of P. multocida strains than chicken, duck and pig sera. Serum-resistant strains were demonstrated among avian as well as mammalian strains. Among the avian strains, the proportion of serum-resistant strains was higher in outbreak strains than in strains from apparently healthy carriers. Removal of the capsule from selected strains by hyaluronidase treatment failed to change the serum activity. The most severe lesions in experimentally infected chickens were produced by a serum-resistant strain; however, lesions were also found in chickens infected by serum-sensitive strains, indicating the involvement of multiple factors in the virulence of P. multocida. Further investigations on serum resistance are indicated in order to relate other host and bacterial factors responsible for the development of fowl cholera.

Interactions between bovine endothelial cells and Pasteurella multocida: association and invasion

We investigated the association and the invasion of a bovine aortic endothelial cell (BAEC) line by Pasteurella multocida to study the potential role of internalized bacteria and possible intracellular survival during Pasteurella infections. Our data indicate that P. multocida is able to adhere to and to invade BAECs. The density of the bacterial population plays a defined role for an optimal mechanism of interaction between bacteria and cells, as does the incubation period of association and invasion. The optimal bacteria/cells ratio was found to be 100/1, while the optimal infection time was approximately 4 h of incubation. Bacterial internalization was dependent on microfilament and microtubule stability. The invasion ability of P. multocida in the presence of cytochalasin D was reduced by 60%; in the presence of colchicine it was reduced by 97% and in the presence of nocodazole it was reduced by 95%. Our data show that internalized P. multocida did not induce mortality of invaded endothelial cells. Some Pasteurella cells were able to survive and undergo exocytosis.

In vitro study of Pasteurella multocida adhesion to trachea, lung and aorta of rabbits

In vitro experiments were undertaken to study the adhesion and colonization to tracheal mucosa, lung and aorta explants from freshly killed rabbits of two different strains of Pasteurella multocida. Serotype A:3 (capsulated, fimbriae +, haemagglutination -, dermonecrotic toxin -) isolated from a rabbit with rhinitis, and serotype D:1 (non-capsulated, fimbriae +, haemagglutination +, dermonecrotic toxin +) isolated from a dead rabbit with septicaemia, were used. When the explants were observed under the scanning electron microscope, the type D strain was highly adherent to trachea and aorta explants compared to the type A strain. Adhesion to lung explants was best achieved by the type A strain after 45 min incubation, but after 2 h incubation no significant difference was observed between the strains. Our data indicate that the presence of fimbriae and the absence of capsule seem to enhance the adherence of P. multocida type D strain to tracheal tissue. The capsular material of P. multocida type A strain and the toxin of the type D strain seem to influence the adherence to lung tissue in rabbit. Adhesion of strain D to aorta may indicate the expression of receptors on the endothelium to that strain and may also explain the ability of certain strains to cause septicaemia.

Role of Pasteurella multocida, Pasteurella haemolytica and Salmonella typhimurium porins on inducible nitric oxide release by murine macrophages

The aim of this study was to verify whether Pasteurella haemolytica, P. multocida and Salmonella typhimurium porins could affect the inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) release by murine resident peritoneal macrophages in vitro. We also compared their effect with that elicited by P. haemolytica, P. multocida and S. typhimurium lipopolysaccharide (LPS) whose biological activity is well known. Variations in NO release and iNOS mRNA expression due to variable concentrations of porins were recorded and compared. We also investigated the synergism between bacterial products and interferon gamma (IFN-gamma). With this aim cells were incubated with porins together with murine rIFN-gamma prior to assessing the presence of NO in the supernatant and mRNA analysis. Porins in themselves were not able to induce NO release by resident peritoneal macrophages. Incubation of macrophages with IFN-gamma in the presence of porins increased NO release, whereas incubation in the presence of the arginine analog N(G)-monomethyl-L-arginine (NMA) inhibited NO release. The greatest NO release was obtained using porins at a concentration of 5 microg/mL. Porins, together with IFN-gamma, were also able to upregulate the mRNA expression of iNOS. Our findings suggest that gram-negative porins are able to modulate inflammatory and immunological responses by affecting the release of NO and the expression of iNOS gene in activated macrophages.

Intranasally inoculated Mycoplasma hyorhinis causes eustachitis in pigs

Specific-pathogen-free pigs were experimentally inoculated with Mycoplasma hyorhinis, Pasteurella multocida, or both bacterial isolates to evaluate the role of these bacteria in the pathogenesis of otitis media. Six pigs were inoculated intranasally with 4.4 X 10(8) colony-forming units (CFU) of M. hyorhinis. Twenty-one days later, three of these six pigs were inoculated intranasally with 5.0 X 10(8) CFU of P. multocida. Three additional pigs were also inoculated intranasally at the time with P. multocida alone. Two pigs served as uninoculated controls. Seven days later, all pigs were euthanatized. Histologically, subacute inflammation was found in 10 auditory tubes of six pigs and two tympanic cavities of two pigs inoculated with M. hyorhinis. Immunohistochemically, M. hyorhinis antigens were detected on the luminal surface of eight of 10 inflamed auditory tubes, and ultrastructural examination confirmed mycoplasmal organisms in two pigs. M. hyorhinis was isolated from the inflamed tympanic cavities of two pigs. None of the pigs inoculated only with P. multocida had otitis, and P. multocida was not isolated from the tympanic cavity. These findings indicate that M. hyorhinis can cause eustachitis but rarely otitis media in specific-pathogen-free pigs.

Enhanced adhesion of Pasteurella multocida to cultured turkey peripheral blood monocytes

Capsular hyaluronic acid (HA) mediates adhesion of serogroup A strains of Pasteurella multocida to elicited turkey air sac macrophages (TASM). In contrast, freshly isolated turkey peripheral blood monocytes (TPBM) do not bind serogroup A strains. Following culture of TPBM for 6 days in chamber slides, adhesion of the bacteria to TPBM increased gradually. Incubation in chamber slides coated with entactin-collagen IV-laminin (ECL) attachment matrix or exposure to phorbol myristate acetate (PMA) further enhanced the adhesion of P. multocida to TPBM. Addition of HA, but not Arg-Gly-Asp peptide, to TPBM culture inhibited bacterial adherence similarly to the inhibition previously reported for TASM. Exposure of TPBM to monoclonal antibody directed against HA-binding cell surface proteoglycan (CD44) decreased binding of P. multocida. Collectively, these findings indicate that P. multocida adhesion to TPBM is mediated by capsular HA and can be increased by culture on ECL attachment matrix or PMA exposure. Additionally, the findings suggest that the capsular mucopolysaccharide of serogroup A strains of P. multocida recognizes an isoform of CD44 expressed on cultured TPBM.

Adaptive acquisition of novobiocin resistance in Pasteurella multocida strains of avian origin

Naturally occurring strains of Pasteurella multocida are atypically susceptible to hydrophobic antibiotics such as novobiocin, despite their Gram-negative cell envelope ultrastructure. Four strains adaptively resistant to 1000 micrograms/ml of novobiocin were obtained by sequentially subculturing cell surface hydrophobic variants of avian origin in the presence of increasing antibiotic concentrations. Adaptive novobiocin resistance was accompanied in all cases by the concomitant acquisition of resistance to coumermycin, a hydrophobic antibiotic possessing the same mechanism of action, but not to the functionally disparate hydrophobic antibiotic rifamycin. The acquisition of resistance was not accompanied by alterations in the lipid composition of the cell envelope. Subsequent growth of adaptively resistant strains in the absence of novobiocin did not result in the restoration of susceptibility to either novobiocin or coumermycin. Acquisition of adaptive resistance in encapsulated parental strains resulted in an inability to synthesize capsular material and enhanced cell surface hydrophobicity; however, parental encapsulation and decreased cell surface hydrophobicity were restored upon removal of novobiocin. These data suggest that acquisition of adaptive resistance to novobiocin conferred in this manner is the result of a stable genetic event affecting the mechanistic target of both novobiocin and coumermycin rather than a physiological adaptation involving outer membrane impermeability.

[Experimental affecting of pulmonary clearance of Pasteurella multocida induced pneumonia in swine]

The pulmonary clearance of Pasteurella multocida in weaner pigs was not affected by Carrageenan and Silica, two substances which block the function of monocytes/macrophages. Neutropenia, caused by the application of hydroxyurea, however, inhibit the pulmonary clearance markedly and reduced the severity of simultaneously induced pneumonias considerably. This indicates the importance of polymorphonuclear neutrophils for early clearance mechanisms and their inflammation inducing and maintaining effects.

Pasteurella multocida enters polarized epithelial cells by interacting with host F-actin

We investigated the interaction of an avian strain of Pasteurella multocida with the cytoskeleton of MDCK cells, which formed a polarized epithelium when grown on type I collagen coated filters. Bacteria were incubated with MDCK cells for 30 min. 2, 4 and 6 hours and their location and association with the cell cytoskeleton determined by double-label immunofluorescence confocal microscopy. Cells were stained with a polyclonal antiserum to the outer-membrane proteins of P. multocida and with rhodamine phalloidin which specifically binds filamentous (F) actin. Confocal microscopy revealed that bacteria entered the cells by 30 min, and that by 6 hours there was a marked alteration in the actin cytoskeleton in which long filaments were reorganized to discrete foci of short actin filaments, within which were one or more bacteria. Electron microscopy demonstrated that by 2 hours, each bacterium was associated with many short 5-6 nm filaments. Treatment of MDCK cells with cytochalasin D for either 30 minutes or 24 hours prior to infection disrupted the actin cytoskeleton and inhibited entry of P. multocida.

Capsular hyaluronic acid-mediated adhesion of Pasteurella multocida to turkey air sac macrophages

Serogroup A strains of Pasteurella multocida, the major cause of fowl cholera, are resistant to phagocytosis in nonimmunized birds. Adherence studies with a capsulated strain of P. multocida (serotype A:3) and turkey air sac macrophages in culture showed that the bacteria were capable of adhering in large numbers to the macrophages but were not internalized. A noncapsulated variant of the bacteria (serotype -:3) showed little or no adherence and was not internalized. These data indicated that the adhesive properties were caused by the presence of a capsule on the bacteria. The role of capsular hyaluronic acid in adherence to macrophages was investigated. Depolymerization of the bacterial capsule with hyaluronidase increased phagocytosis by macrophage cultures, and addition of hyaluronic acid to the macrophages inhibited bacterial adherence. Additionally, exposure of macrophages to chondroitin sulfate B, an anionic polysaccharide similar to hyaluronic acid, did not affect the adhesive properties and resistance to phagocytosis of capsulated organisms. Treatment of macrophages with sodium metaperiodate or trypsin suppressed bacterial binding. Collectively, these data indicate that P. multocida adhesion to air sac macrophages, but not internalization, is mediated by capsular hyaluronic acid and suggest that recognition of this bacterial polysaccharide is a result of a specific glycoprotein receptor.

The goat as a model for studies of pneumonic pasteurellosis caused by Pasteurella multocida

A model of pneumonic pasteurellosis has been established in goats using Pasteurella multocida harvested from pneumonic lungs of goats (types A and D), rabbits (type A) and sheep (type D). The resultant infections were acute, subacute or chronic. The gross and histological lesions of the subacute and chronic infections were typical of pneumonic pasteurellosis. P. multocida type D produced significantly (P < 0.01) more severe lesions when compared with other isolates. There were strong correlations between the clinical signs and the severity of lesions.

Serum haptoglobin concentration in growing swine after intranasal challenge with Bordetella bronchiseptica and toxigenic Pasteurella multocida type D

The acute phase reaction, in association with progressive atrophic rhinitis (AR), was monitored for 3 wk using serum haptoglobin (HPT) quantification in thirty-six, 15 kg swine after intranasal challenge with varying doses of Pasteurella multocida type D (toxigenic strain) and Bordetella bronchiseptica. The challenge doses were administered alone or in combination with pigs divided into 9 isolated treatment groups. Increasing doses of B. bronchiseptica were associated with lower serum HPT (P < 0.05), whereas increasing doses of P. multocida tended to increase serum HPT (0.05 < P < 0.10). Significant and positive correlation of mean HPT and AR score was found in these pigs; increased AR scores were associated with elevated mean HPT concentration (r = 0.41, P < 0.01). A significant interaction between P. multocida and B. bronchiseptica dose indicated that increasing the dose of B. bronchiseptica, for a fixed P. multocida dose, was associated with less AR (P < 0.05). The AR scores were greater in pigs given P. multocida, than B. bronchiseptica alone. These results indicate that a complex interaction between Pasteurella multocida and Bordetella bronchiseptica causes progressive atrophic rhinitis and alters serum HPT concentration in swine.

Influence of chondroitinase on indirect hemagglutination titers and phagocytosis of Pasteurella multocida serogroups A, D and F

Capsules of Pasteurella multocida serogroups A, D and F contain mucopolysaccharides which block antigenic determinants and prevent phagocytosis. In this study, capsules of serogroup A, D and F strains of P. multocida were depolymerized by enzyme treatment. Capsule depolymerization of serogroup D and F strains with chondroitinase increased indirect hemagglutination (IHA) test titers and enhanced phagocytosis by swine neutrophils. Capsule depolymerization of serogroup A strains with hyaluronidase increased IHA titers, but depolymerization with chondroitinase did not. When serogroup A strains were treated with a combination of chondroitinase and hyaluronidase, IHA test titers were lower than titers of the same strains treated with hyaluronidase alone. Combined enzyme treatment of serogroup D strains resulted in IHA test titers similar to those of chondroitinase treatment alone.

Effects of atrophic rhinitis induced by Pasteurella multocida toxin on heat production and activity of pigs kept under different climatic conditions

Effects of moderate, artificially induced atrophic rhinitis symptoms on level and changes in heat production and activity were determined in pigs kept under different climatic conditions. Eight groups of 30 pigs each, housed in one of two climatically controlled respiration chambers, were exposed to a 2 x 2 factorial arrangement of treatments: challenged with 0 or 13 micrograms of Pasteurella multocida toxin (Pm-T)/mL, and two climatic environments (good: 25 degrees C, or adverse: 15 degrees C with draught periods). The Pm-T challenge reduced (P < .05) day averages of total (HP) and activity-related heat production (Har). The response to Pm-T treatment was similar in both climatic environments. Differences in the heat production and activity caused by the climatic treatment declined (P < .001) with time and acclimation to the environment. Analyses of HP, Har, and activity-free heat production in 12 2-h periods showed a biphasic activity rhythm. Both treatments affected (P < .05) level of HP and Har in several of the 2-h periods, but the biphasic rhythm was not altered. Day averages of Har showed a disposition to be differently affected (P < .068) by Pm-T challenge in the climatic treatments dependent on duration of exposure. This interaction effect (P < .001) seemed to originate from the periods between 1500 and 2100. Therefore, it might be wise to distinguish between overall effects (day means) on total, activity-related, and activity-free heat production and effects within a day (e.g., 2-h means). Treatment with Pm-T seemed to suppress the general well-being of pigs, reducing pigs' activity and food intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterisation of Pasteurella multocida isolated from fowl cholera outbreaks on turkey farms

Biochemical profiles, restriction endonuclease analysis (REA) and ribotyping were used to investigate Pasteurella multocida isolates from outbreaks of fowl cholera on 7 turkey farms in New South Wales. While only a single isolate was available from 5 of the farms, multiple isolates, 4 and 12 respectively, were available from the other 2 farms. The available field evidence suggested that 8 outbreaks had occurred with one farm suffering 2 outbreaks. The isolates obtained were all confirmed as Pasteurella multocida. Biochemical profiles allocated the isolates to 4 groups, 3 being variants of P multocida subsp multocida and the fourth being P multocida subsp septica. REA performed with HpaII established 7 groups. Ribotyping using the HpaII digests probed with the 16S rRNA operon of Haemophilus paragallinarum recognised the same 7 groups as REA. Unlike the biochemical profiles, both REA and ribotyping provided a fine subdivision that identified outbreaks as either related or unrelated. The REA and ribotyping patterns as well as biochemical profiles were stable for all isolates from the outbreaks in which multiple isolates were obtained from either the same bird or from different birds. REA and ribotyping were found to be superior to biotyping methods for the investigation of fowl cholera outbreaks.

[Evaluation of phagocytosis, bactericidal effect, and cytotoxicity of Pasteurella haemolytica and Pasteurella multocida in bovine alveolar macrophages]

Evaluation of phagocytosis and bactericidal effect of Pasteurella haemolytica and P. multocida was conducted on bovine alveolar macrophages freshly obtained through bronchioalveolar washings from live animals. Cytotoxic activity of these bacteria on the alveolar macrophages was evaluated through the simple visual assay in microplates, using bovine blood leukocytes as a comparative target cell. In order to evaluate phagocytosis the following variables were considered P. haemolytica and P. multocida (independently) in contact with alveolar macrophages, P. haemolytica and P. multocida in suspension as a positive control of bacterial growth, and RPMI-1640 medium alone, as a negative control of bacterial growth. To measure bactericidal capacity, bacteria were incubated with plastic adhered alveolar macrophages at 30 minutes and 3 hours intervals. Samples incubated 30 minutes were taken as phagocytosis-base readings and at the 3 h interval to evaluate bactericidal capacity of the alveolar macrophages on phagocytized bacteria. Reading of the samples of each evaluation was conducted in a spectrophotometer a 380 nm. Phagocytosis results indicated that bacterial proliferation was higher when bacteria were alone as compared when they were with alveolar macrophages (p < 0.05). Bactericidal capacity of the macrophages was efficient because bacterial numbers were higher in the first evaluation as compared to the second (p < 0.05). It was demonstrated that the cytotoxic effect of P. haemolytica was more severe on blood leukocytes as compared to alveolar macrophages (p < 0.05). There was no evidence of P. multocida cytotoxicity on the evaluated cells. With the development of this technique for the obtention of alveolar macrophages and using spectrophotometry for the phagocytosis and bactericidal effect evaluations, numerous variables and samples can be tested, such as opsonized bacteria or to measure the behaviour of alveolar macrophages infected with different agents involved in the bovine pneumonic complex.

Invasion of epithelial cell monolayers by turkey strains of Pasteurella multocida

Two serotype 3,4:A strains of Pasteurella multocida that differ in virulence in turkeys were examined for their ability to invade epithelial cell monolayers grown in tissue culture. Both organisms were comparably adherent to cells of turkey kidney origin. However, the virulent strain (86-1913) penetrated primary turkey kidney epithelial cell monolayers at 10 times the level of the low-virulence vaccine strain. The virulent strain was also able to invade porcine epithelial cells (PK15) and feline epithelial cells (CRFK) in cell culture. Neither organism invaded rabbit epithelial cells (RK13). Invasion of turkey cells was prevented by inhibition of bacterial protein or RNA synthesis but not by pretreatment of the monolayers with periodate, trypsin, or neuraminidase. Invasion might be a mechanism of pathogenicity for this organism, contributing to colonization or virulence.

Adherence of Pasteurella multocida to rabbit respiratory epithelial cells in vitro

Adult clinically healthy New Zealand rabbits were sampled bacteriologically to detect carriers and non-carriers of Pasteurella multocida. Both groups of rabbits were killed separately to obtain samples of nasal, buccal, pharyngeal and tracheal epithelial cells. The cells were tested for adherence in vitro to 18 isolates of P. multocida from healthy and sick rabbits, from ovine, bovine, cat and swine. The number of bacteria adhered per cell up to 25 cells per preparation were registered. Analysis of variance was used to interpret the significance of results. Adherence of P. multocida was significantly higher to carrier rabbit cells than to non-carrier rabbit cells. Bacterial isolates from rabbits were more adherent to rabbit cells than to isolates from other species. The frequency was higher to buccal and pharyngeal cells than to nasal and tracheal cells. Isolates from healthy animals adhered better to rabbit cells than isolates from sick animals, except the isolates from sick animals which adhered better to nasal cells of non carriers than did isolates from healthy rabbits.

Nasal epithelial changes induced in piglets by acetic acid and by Bordetella bronchiseptica

Research on atrophic rhinitis of pigs has shown that both Bordetella bronchiseptica infection and experimental treatment with acetic acid predispose the nasal mucosa to colonization with Pasteurella multocida. Gnotobiotic piglets aged 3 days were dosed intranasally with either B. bronchiseptica (n = 6) or acetic acid 1 per cent (n = 10) and killed at intervals up to the 4th day after treatment. Samples of the ventral turbinates were examined by light microscopy and scanning and transmission electron microscopy. Within 12 h acetic acid induced loss of cilia, oedema, focal cell exfoliations, mitochondrial swelling and inflammatory cell infiltration. Bordetella bronchiseptica induced only a limited oedema and loss of cilia. Colonization of cilia by the bacteria was observed 96 h after infection. We conclude that, although acetic acid and B. bronchiseptica do not induce the same modifications of the nasal respiratory epithelium, their action causes stagnation of nasal mucus, which results in a nasal environment favourable to colonization by Pasteurella multocida.

Effects of Pasteurella multocida toxin on the osteoclast population of the rat

Pasteurella multocida type D toxin is a peptide shown to induce severe atrophic rhinitis in the pig as the result of an increased osteoclastic resorption of the ventral nasal turbinates. In the present study, the effects of the toxin on the histological, cytochemical and ultrastructural features of the osteoclast population of the rat were examined. Pasteurella multocida toxin induced atrophy of the ventral and dorsal nasal turbinates and thinning of the nasal bones. The number and size of the long bone metaphyseal osteoclasts were significantly increased, but not the number of nuclei per cell. Osteoclasts of toxin-treated rats had more developed clear zones and ruffled borders than those of the controls and their cytoplasmic vacuoles were more abundant and larger. We concluded that P. multocida toxin stimulates bone resorption by osteoclasts in the rat by increasing resorption activity and by increasing their number. Its action is not limited to the nasal turbinates but occurs also in the other bones, such as the long bones.

Interaction between Bordetella bronchiseptica and toxigenic Pasteurella multocida on the nasal mucosa of SPF piglets

The interaction between Bordetella bronchiseptica and type D toxigenic Pasteurella multocida was studied in five groups of 4 specific-pathogen-free (SPF) piglets each. At 28 days of age, piglets of groups 3 and 4 were inoculated into both nostrils with 10(8) colony-forming-units (CFU) of a non-dermonecrotic toxin (DNT)-producing, phase I strain of B. bronchiseptica. Piglets of groups 1 and 3 were treated intranasally with a sonic extract of the non-toxic strain of B. bronchiseptica and those of groups 2 and 4 with B. bronchiseptica DNT into the left nostril. Sonic extract and DNT treatment was started at 33 days of age and lasted for 5 days. Piglets of group 5 served as controls. At the age of 37 days, piglets of all groups except group 5 were inoculated into both nostrils with 5 x 10(7) CFU of toxigenic P. multocida. At slaughter at 50 days of age, P. multocida was recovered from the left nasal cavity of 3 piglets of group 2 and all piglets of group 4. In piglets inoculated with B. bronchiseptica DNT the mucosal epithelial cells of the left nasal cavity showed loss of cilia, regressive lesions such as vacuolation, karyopycnosis and necrosis, hypertrophy of the epithelium, infiltration of the epithelium and submucosa by inflammatory cells, could also be seen. The results suggest that action of the B. bronchiseptica DNT on the nasal mucosa is a precondition of the growth of P. multocida in the nasal cavity.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental atrophic rhinitis in 2 and 4 month old pigs infected sequentially with Bordetella bronchiseptica and toxigenic type D Pasteurella multocida

Experimental infections with Bordetella bronchiseptica and/or toxigenic type D Pasteurella multocida were studied in 2- and 4-month-old primary specific-pathogen-free pigs. None of the 2-month-old pigs inoculated with B. bronchiseptica or P. multocida alone developed turbinate atrophy. All the pigs inoculated with B. bronchiseptica (10(7) CFU/head) and P. multocida (10(9) CFU/head for 5 consecutive days) together, however, developed clinical and post-mortem signs of atrophic rhinitis (AR) similar to the naturally occurring disease. Slight to severe turbinate atrophy was observed in the 4-month-old pigs inoculated with B. bronchiseptica and P. multocida (at the same concentration as above) at necropsy.

A quantitative measurement of the effect of avian influenza virus on the ability of turkeys to eliminate Pasteurella multocida from the respiratory tract

The effect of avian influenza virus (AIV) infection on the ability of turkeys to eliminate Pasteurella multocida from the respiratory tract was evaluated. Four-week-old turkeys were experimentally infected with an apathogenic AIV subtype (H5N2) by the oculonasal route and subsequently superinfected with P multocida (Urbach strain) by the intranasal route three days after infection with AIV. Quantitative clearance of P multocida from the trachea and lung was determined using a pour plate technique on samples collected at intervals after infection. Samples from turkeys which had been infected with AIV were found to yield more P multocida than those from turkeys which had not been infected with AIV. The numbers of P multocida increased in infected birds to a greater extent than in birds which had not been infected with the virus. The present study suggests that AIV infection may contribute to the increased numbers and a decreased clearance of P multocida in turkeys.

The fate of Pasteurella multocida after intratracheal inoculation into turkeys

Young adult turkeys were intratracheally inoculated with the P-1059 strain of Pasteurella multocida, and the fate of the organism was studied by quantifying the organism in various respiratory and systemic tissues at various times after the inoculation. The results showed that, in the first 2 h, on the order of 10(8) to 10(9) organisms deposited at the upper trachea multiplied in situ to gradually spread downwards to the lower respiratory tract. In the majority of turkeys, by 6 h postinoculation the organism invaded the circulatory system and multiplied vigorously in the liver and spleen. In some birds, however, the organism appeared to have reached the liver from the trachea instantaneously by an unidentified mechanism. Vaccination with inactivated vaccines protected turkeys from intratracheal challenge exposure, as well as from intramuscular inoculation.