Isolation and characterization of a Mannheimiahaemolytica secreted serine protease that degrades sheep and bovine fibrinogen.

Mannheimiahaemolytica is an opportunistic agent of the respiratory tract of bovines, a member of the Pasteurellaceae family, and the causal agent of fibrinous pleuropneumonia. This bacterium possesses different virulence factors, allowing it to colonize and infect its host. The present work describes the isolation and characterization of a serine protease secreted by M. haemolytica serotype 1. This protease was isolated from M. haemolytica cultured media by precipitation with 50 % methanol and ion exchange chromatography on DEAE-cellulose. It is a 70-kDa protease able to degrade sheep and bovine fibrinogen or porcine gelatin but not bovine IgG, hemoglobin, or casein. Mass spectrometric analysis indicates its identity with protease IV of M. haemolytica. The proteolytic activity was active between pH 5 and 9, with an optimal pH of 8. It was stable at 50 °C for 10 min but inactivated at 60 °C. The sera of bovines with chronic or acute pneumonia recognized this protease. Still, it showed no cross-reactivity with rabbit hyperimmune serum against the secreted metalloprotease from Actinobacilluspleuropneumoniae, another member of the Pasteurellaceae family. M. haemolytica secreted proteases could contribute to the pathogenesis of this bacterium through fibrinogen degradation, a characteristic of this fibrinous pleuropneumonia.

Plasmid-located extended-spectrum ß-lactamase gene blaROB-2 in Mannheimia haemolytica.

OBJECTIVES: To identify and analyse the first ESBL gene from Mannheimia haemolytica. METHODS: Susceptibility testing was performed according to CLSI. Plasmids were extracted via alkaline lysis and transferred by electrotransformation. The sequence was determined by WGS and confirmed by Sanger sequencing. RESULTS: The M. haemolytica strain 48 showed high cephalosporin MICs. A single plasmid, designated pKKM48, with a size of 4323 bp, was isolated. Plasmid pKKM48 harboured a novel blaROB gene, tentatively designated blaROB-2, and was transferred to Pasteurella multocida B130 and to Escherichia coli JM107. PCR assays and susceptibility testing confirmed the presence and activity of the blaROB-2 gene in the P. multocida and in the E. coli recipient carrying plasmid pKKM48. The transformants had high MICs of all ß-lactam antibiotics. An ESBL phenotype was seen in the E. coli transformant when applying the CLSI double-disc confirmatory test for E. coli. The blaROB-2 gene from plasmid pKKM48 differed in three positions from blaROB-1, resulting in two amino acid exchanges and one additional amino acid in the deduced ß-lactamase protein. In addition to blaROB-2, pKKM48 harboured mob genes and showed high similarity to other plasmids from Pasteurellaceae. CONCLUSIONS: This study described the first ESBL gene in Pasteurellaceae, which may limit the therapeutic options for veterinarians. The transferability to Enterobacteriaceae with the functional activity of the gene in the new host underlines the possibility of the spread of this gene across species or genus boundaries.

Mannheimia haemolytica A2 secretes different proteases into the culture medium and in outer membrane vesicles.

Respiratory diseases in ruminants have a significantly negative impact on the worldwide economy. The bacterium Mannheimia haemolytica is involved in pneumonic infections in bovine and ovine. In gram-negative bacteria, six secretion systems related to the colonization process and host tissue damage have been reported. In addition, in the last two decades, the production of outer membrane vesicles has been studied as a different bacterial strategy to release virulence factors, such as exotoxins, lipopolysaccharides, and proteases. However, in M. haemolytica serotype A2, protease secretion and release in vesicles have not been reported as virulence mechanisms. The aim of this work was to identify proteases released into the culture supernatant and in vesicles of M. haemolytica A2. Our results showed evident differences in the molecular mass and activity of proteases present in culture supernatants and outer membrane vesicles based on zymography assays. The biochemical characterization of M. haemolytica proteases revealed that the main types were cysteine and metalloproteases. A specific metalloprotease of 100 kDa was active in the culture supernatants, but it was not active and was found in low quantities in vesicles. Proteases could be an important virulence factor during the infectious pneumonic process led by M. haemolytica.

A novel Erm monomethyltransferase in antibiotic-resistant isolates of Mannheimia haemolytica and Pasteurella multocida.

Mannheimia haemolytica and Pasteurella multocida are aetiological agents commonly associated with respiratory tract infections in cattle. Recent isolates of these pathogens have been shown to be resistant to macrolides and other ribosome-targeting antibiotics. Direct analysis of the 23S rRNAs by mass spectrometry revealed that nucleotide A2058 is monomethylated, consistent with a Type I erm phenotype conferring macrolide-lincosamide resistance. The erm resistance determinant was identified by full genome sequencing of isolates. The sequence of this resistance determinant, now termed erm(42), has diverged greatly from all previously characterized erm genes, explaining why it has remained undetected in PCR screening surveys. The sequence of erm(42) is, however, completely conserved in six independent M. haemolytica and P. multocida isolates, suggesting relatively recent gene transfer between these species. Furthermore, the composition of neighbouring chromosomal sequences indicates that erm(42) was acquired from other members of the Pasteurellaceae. Expression of recombinant erm(42) in Escherichia coli demonstrated that the enzyme retains its properties as a monomethyltransferase without any dimethyltransferase activity. Erm(42) is a novel addition to the Erm family: it is phylogenetically distant from the other Erm family members and it is unique in being a bona fide monomethyltransferase that is disseminated between bacterial pathogens.

A three-way comparative genomic analysis of Mannheimia haemolytica isolates.

BACKGROUND: Mannhemia haemolytica is a Gram-negative bacterium and the principal etiological agent associated with bovine respiratory disease complex. They transform from a benign commensal to a deadly pathogen, during stress such as viral infection and transportation to feedlots and cause acute pleuropneumonia commonly known as shipping fever. The U.S beef industry alone loses more than one billion dollars annually due to shipping fever. Despite its enormous economic importance there are no specific and accurate genetic markers, which will aid in understanding the pathogenesis and epidemiology of M. haemolytica at molecular level and assist in devising an effective control strategy. DESCRIPTION: During our comparative genomic sequence analysis of three Mannheimia haemolytica isolates, we identified a number of genes that are unique to each strain. These genes are "high value targets" for future studies that attempt to correlate the variable gene pool with phenotype. We also identified a number of high confidence single nucleotide polymorphisms (hcSNPs) spread throughout the genome and focused on non-synonymous SNPs in known virulence genes. These SNPs will be used to design new hcSNP arrays to study variation across strains, and will potentially aid in understanding gene regulation and the mode of action of various virulence factors. CONCLUSIONS: During our analysis we identified previously unknown possible type III secretion effector proteins, clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated sequences (Cas). The presence of CRISPR regions is indicative of likely co-evolution with an associated phage. If proven functional, the presence of a type III secretion system in M. haemolytica will help us re-evaluate our approach to study host-pathogen interactions. We also identified various adhesins containing immuno-dominant domains, which may interfere with host-innate immunity and which could potentially serve as effective vaccine candidates.

Mannheimia haemolytica IgA-specific proteases.

Mannheimia haemolytica colonizes the nasopharynx of cattle and can cause severe fibrinous pleuropneumonia. IgA proteases are metalloendopeptidases released by bacteria that cleave IgA, enhancing colonization of mucosa. The objectives of these studies were to characterize M. haemolytica IgA1 and IgA2 proteases in vitro and in silico, to clone and sequence the genes for these proteases, and to demonstrate immunogenicity of components of the entire IgA protease molecule. Both IgA protease genes were cloned, expressed, and sequenced. Sequences were compared to other published sequences. Components were used to immunize mice to determine immunogenicity. Sera from healthy cattle and cattle that recovered from respiratory disease were examined for antibodies to IgA proteases. In order to assay the cleavage of bovine IgA with IgA1 protease, M. haemolytica culture supernatant was incubated with bovine IgA. Culture supernatant cleaved purified bovine IgA in the presence of ZnCl2. Both IgA proteases contain three domains, 1) IgA peptidase, 2) PL1_Passenger_AT and 3) autotransporter. IgA1 and IgA2 peptidases have molecular weights of 96.5 and 87 kDa, respectively. Convalescent bovine sera with naturally high anti-M. haemolytica antibody titers had high antibodies against all IgA1 & IgA2 protease components. Mouse immunizations indicated high antibodies to the IgA peptidases and autotransporters but not to PL1_Passenger_AT. These data indicate that M. haemolytica produces two IgA proteases that are immunogenic, can cleave bovine IgA, and are produced in vivo, as evidenced by antibodies in convalescent bovine sera. Further studies could focus on IgA protease importance in pathogenesis and immunity.

Identification and characterization of transcriptional regulation of the Mannheimia haemolytica ferric uptake regulator.

The ferric uptake regulator (Fur) is an iron-dependent transcriptional regulator that regulates genes related to iron acquisition, oxidative stress response, and various other functions. Transcription of fur is typically self-regulating and sensitive to iron and oxidative stress. Following the identification of a fur gene in the genome of the bovine pathogen Mannheimia haemolytica, an attempt was made to characterize the transcriptional control of M. haemolytica fur. Northern blotting, RT-PCR, and primer extension were done to determine that M. haemolytica fur is transcribed using three distinct promoters, two of which are located within the upstream fldA gene. The third promoter is located upstream of a conserved hypothetical protein and drives transcription of a tricistronic message. Quantitative real time PCR experiments indicated that unlike current models of Fur regulation, M. haemolytica fur transcription is unchanged by iron depletion at logarithmic phase and repressed by iron depletion at stationary phase.

Characterization of carbohydrate structures of bovine MUC15 and distribution of the mucin in bovine milk.

The present work reports the characterization of carbohydrate structures and the distribution of the newly identified mucin MUC15, a highly glycosylated protein associated with the bovine milk fat globule membrane (MFGM). Distribution of MUC15 was investigated in various fractions of bovine milk by densitometric scanning of Western blots. In raw milk, MUC15 was shown to constitute 0.08% (wt) of the protein and approximately 1.5% (wt) of the MFGM-associated proteins. Surprisingly, this study showed that in addition to the fat-containing fractions, such as MFGM and buttermilk, MUC15 was present in nonfat-containing fractions as well, such as skim milk and whey. Compositional and structural studies of the carbohydrates of bovine milk MUC15 showed that the glycans are composed of fucose, galactose, mannose, N-acetylgalactosamine, N-acetylglycosamine, and sialic acid. The carbohydrate was shown to constitute 65% of the total molecular weight, and the molar ratios of the individual sugars to protein of the O-linked glycans were determined. The glycan structures of MUC15 were further studied by enzymatic deglycosylation experiments using different endo- and exoglycosidases as well as a panel of lectins. The N-linked glycans were shown to contain mainly hybrid-type N-glycans. In addition, the N-glycans were shown to be sialylated and contain terminal poly-lactosamine structures. The O-linked glycans were found to constitute some unsubstituted Core-1 structures and a substantial number of sialylated Core-1 O-linked glycans. By comparing the results of peanut agglutinin lectin binding, enzymatic deglycosylation, and monosaccharide composition analysis, we concluded that bovine MUC15 also contains more complex O-glycans containing high amounts N-acetylglucosamine residues. Furthermore, a small subset of the O-linked glycans is decorated with lactosamine on their terminal ends.

X-ray crystallographic structure of a bacterial polysialyltransferase provides insight into the biosynthesis of capsular polysialic acid.

Polysialic acid (polySia) is a homopolymeric saccharide that is associated with some neuroinvasive pathogens and is found on selective cell types in their eukaryotic host. The presence of a polySia capsule on these bacterial pathogens helps with resistance to phagocytosis, cationic microbial peptides and bactericidal antibody production. The biosynthesis of bacterial polySia is catalysed by a single polysialyltransferase (PST) transferring sialic acid from a nucleotide-activated donor to a lipid-linked acceptor oligosaccharide. Here we present the X-ray structure of the bacterial PST from Mannheimia haemolytica serotype A2, thereby defining the architecture of this class of enzymes representing the GT38 family. The structure reveals a prominent electropositive groove between the two Rossmann-like domains forming the GT-B fold that is suitable for binding of polySia chain products. Complex structures of PST with a sugar donor analogue and an acceptor mimetic combined with kinetic studies of PST active site mutants provide insight into the principles of substrate binding and catalysis. Our results are the basis for a molecular understanding of polySia biosynthesis in bacteria and might assist the production of polysialylated therapeutic reagents and the development of novel antibiotics.

Production of a D-glycero-D-manno-heptosyltransferase mutant of Mannheimia haemolytica displaying a veterinary pathogen specific conserved LPS structure; development and functionality of antibodies to this LPS structure.

Previous structural studies of the lipopolysaccharides from the veterinary pathogens Mannheimia haemolytica (Mh), Actinobacillus pleuropneumoniae (Ap) and Pasteurella multocida (Pm) had identified a conserved inner core oligosaccharide structure that was present in all strains investigated. In order to examine the potential of this inner core structure as a vaccine, a mutagenesis strategy was adopted to interrupt a D-glycero-D-manno-heptosyltransferase gene (losB) of Mh. This gene encodes the enzyme responsible for the addition of a D-glycero-D-manno-heptose residue, the first residue beyond the conserved inner core, and its inactivation exposed the conserved inner core structure as a terminal unit on the mutant LPS molecule. Subsequent analyses confirmed the targeted structure of the mutant LPS had been obtained, and complementation with losB in trans confirmed that the losB gene encodes an alpha-1,6-D-glycero-D-manno-heptosyltransferase. Monoclonal antibodies raised in mice to this LPS structure were found to recognise LPS and whole-cells of the truncated mutant and wild-type Mh. The antibodies were bactericidal against a wild-type Mh strain and were able to passively protect mice in a model of Mh disease. This illustrates that it is possible to raise functional antibodies against the conserved inner core LPS structure.

Identification of CD34+ subsets after glycoprotease selection: engraftment of CD34+Thy-1+Lin- stem cells in fetal sheep.

Epitopes on the CD34 molecule detected by some CD34 antibodies can be cleaved by a unique glycoprotease from Pasteurella haemolytica, which cleaves only glycoproteins rich in O-linked glycans. A method to isolate CD34+ cells from adult bone marrow was developed subsequently, in which CD34+ cells were isolated in high purity and yield following immunomagnetic bead selection and detachment with the glycoprotease. Using a variety of other cell-surface markers shown here to be insensitive to glycoprotease, committed progenitors of T lymphoid, B lymphoid, monomyeloid, megakaryoblastic, or erythroid lineages could be identified. Significantly, candidate hematopoietic stem cells (HSC) that are contained within a CD34+Lin- (CD2-, CD14-, CD15-, CD16-, CD19-) (or CD34+CD38-) subset expressing the Thy-1 antigen (CDw90), c-kit receptor (CD117), and CDw109 but lacking expression of CD71 and HLA-DR antigens also were detected. Functionally distinct subsets of glycoprotease-selected CD34+ cells were identified and subfractionated using flow cytometry and fluorescence-activated cell sorting (FACS). These subsets included candidate HSCs expressing the CD34+Thy-1+Lin- phenotype, which were sorted from a CD34+ fraction of a mobilized peripheral blood (MPB) sample. In a fetal sheep model, when CD34+Thy-1+Lin- cells were injected intraperitoneally, they were capable of homing to the marrow, where they generated long-term multilineage hematopoiesis and maintained human CD34+ cells, indicating that candidate HSC subsets of CD34+ cells selected with this highly specific enzyme were capable of engraftment in vivo. The ability to identify and purify virtually any phenotypically defined subset of glycoprotease-selected CD34+ stem/progenitor cells should facilitate the study of hematopoiesis in vitro and in animal models in vivo as well as the development of novel genetic techniques for the correction of specific blood cell disorders in humans.

The restriction-modification system of Pasteurella haemolytica is a member of a new family of type I enzymes.

Genes encoding the type I restriction-modification (R-M) system of the bovine pathogen, Pasteurella haemolytica, have been identified immediately downstream of a locus that encodes a transcriptional activator of P. haemolytica leukotoxin expression. Type I enzymes are encoded by three genes called hsdM, hsdS and hsdR, and have fallen into three groups, called Ia, Ib and Ic. HsdS provides a sequence recognition function which in concert with HsdM forms an active methyltransferase (MTase). Inclusion of the HsdR subunit in the complex creates an active restriction endonuclease (ENase) capable of cleaving unmethylated target DNA. The P. haemolytica hsdMSR genes were mapped using transposon Tn10d-Cam insertions, and bacteriophage restriction and modification assays in Escherichia coli. We determined the nucleotide sequences of hsdM, hsdS and hsdR, and observed that the deduced amino acid (aa) sequences were very similar to predicted R-M subunits in the respiratory pathogen, Haemophilus influenzae. Phylogenetic comparisons of all known Hsd aa sequences placed the P. haemolytica and H. influenzae proteins into a new group which we labeled the Type Id R-M family. Expression of the P. haemolytica R-M genes in E. coli was inefficient and is likely to be a consequence of the unusual codon usage in P. haemolytica genes.

Refolding of recombinant Pasteurella haemolytica A1 glycoprotease expressed in an Escherichia coli thioredoxin gene fusion system.

Pasteurella haemolytica A1 secretes an O-sialoglycoprotein endopeptidase (EC. 3.4.24.57) (glycoprotease: Gcp) which is specific for O-linked sialoglycoproteins. When the cloned gene is expressed in Escherichia coli, the recombinant glycoprotease (rGcp) is secreted to the periplasm where it is present as a disulfide-linked aggregate which lacks enzymatic activity. In vitro refolding and activation of rGcp by mammalian protein disulfide isomerase (PDI) or by the E. coli chaperones (DnaK, DnaJ and GrpE) indicate that the redox environment of rGcp is critical in restoring biological activity. A fusion protein, rTrx-Gcp, was constructed to investigate the role of thioredoxin (E. coli TrxA) in the production of enzymatically active rGcp. This 47 kDa protein was expressed at a high level, in a soluble, monomeric form, in the cytoplasm of E. coli. Cleavage of the fusion protein by enterokinase released the rGcp fragment (35 kDa) with glycoprotease activity. A higher recombinant glycoprotease activity was recovered after anion exchange chromatography of lysates of E. coli expressing rTrx-Gcp. Thus when E. coli TrxA is combined in a recombinant fusion protein with P. haemolytica A1 Gcp, productive folding of the glycoprotease can occur as a result of the chaperone action of the protein disulfide reductase coupled with its ability to retain the fusion gene product in the E. coli cytoplasm.

The detection of the sialoglycoprotease gene and assay for sialoglycoprotease activity among isolates of Pasteurella haemolytica A1 strains, serotypes A13, A14, T15 and A16.

Polymerase chain reaction (PCR) using specific primers to the sialoglycoprotease gene (gcp) of Pasteurella haemolytica biotype A, serotype 1 amplified a 1-kb fragment from each of P. haemolytica serotypes A7, A13, A14 and A16, but not T15; which was confirmed by Southern blot hybridization analysis. Using a sialoglycoprotease (Gcp) activity assay, Gcp activity was found in serotypes A13, A14 and A16. Inclusion of these three serotypes confirms that all recognized A biotypes are positive for both gcp gene and activity, with the exception of serotype A11 (which has a different genetic organization and exhibits no Gcp activity). Furthermore, all recognized T biotypes are negative for both the gene and Gcp activity.

Comparison of the recombinant and authentic forms of the Pasteurella haemolytica A1 glycoprotease.

The O-sialoglycoprotein endopeptidase (glycoprotease, Gcp) is secreted by Pasteurella haemolytica A1, a Gram-negative pathogen associated with bovine pneumonic pasteurellosis. When the cloned gcp gene is expressed in Escherichia coli, the recombinant glycoprotease (rGcp) is exported to the periplasm but does not exhibit enzymatic activity. Polyclonal calf sera and murine monoclonal antibodies to rGcp were used for the further immunological and biochemical characterization of the authentic and recombinant Gcp. The results showed that the gcp gene product is the sole component of Gcp activity. Homologues to the P. haemolytica A1 Gcp were detected by Western immunoblot analysis in a number of Gram-negative bacteria, including E. coli. However, the secretion of Gcp with O-sialoglycoprotein endopeptidase activity appears to be restricted to P. haemolytica A serotypes.

Occurrence of [copper, zinc]-cofactored superoxide dismutase in Pasteurella haemolytica and its serotype distribution.

Fifty-two ovine strains of Pasteurella haemolytica and P. trehalosi representing serotypes 1-16 were examined for the presence of [copper, zinc]superoxide dismutase DNA sequences. This was done using a combination of polymerase chain reaction with degenerate primers based on the sequence of the [Cu,Zn]superoxide dismutase gene (sodC) in related species and Southern hybridization using a fragment of sodC from P. haemolytica A2 serotype as a probe. Both detection methods identified a fragment of the sodC gene in 9/9 strains of P. haemolytica serotype 2 examined and in 5/8 strains of serotype 7. No evidence of this gene was found in any other serotype of P. haemolytica or in any P. trehalosi serotype. Comparison of DNA sequence showed near identity between sodC from the A2 and A7 serotypes of P. haemolytica and substantial similarity (70%) to sodC previously sequenced in P. multocida, Haemophilus parainfluenzae and H. influenzae. Analysis by gel electrophoresis of the superoxide dismutase activity present in cell lysates showed that one or more superoxide dismutase is present in all serotypes. However, cyanide-inhibitable activity, corresponding to [Cu,Zn]superoxide dismutase, was detected only in those strains of serotypes A2 and A7 which showed evidence of the sodC gene fragment.

Preparation of recombinant glycoprotease of Pasteurella haemolytica A1 utilizing the Escherichia coli alpha-hemolysin secretion system.

Three murine monoclonal antibodies were prepared against the recombinant glycoprotease of Pasteurella haemolytica A1 expressed in Escherichia coli. These monoclonal antibodies were able to recognize the authentic glycoprotease from P. haemolytica A1 culture supernatant. A recombinant plasmid which contained most of the glycoprotease gene of P. haemolytica A1 fused with the secretion signal sequence from hlyA of the E. coli alpha-hemolysin determinant was constructed. This recombinant plasmid expressed a fusion protein (Gcp-F) which was secreted into the culture supernatant by E. coli cells when the alpha-hemolysin secretion functions HlyB and HlyD are supplied in trans. Gcp-F could be readily recovered from the supernatant free from other cellular materials and is suitable for use in vaccine trials and challenge experiments in animals.

Divergent activity and function of superoxide dismutases in Pasteurella haemolytica serotypes A1 and A2 and Pasteurella trehalosi serotype T10.

Representative strains of Pasteurella haemolytica serotypes A1 and A2 and Pasteurella trehalosi serotype T10 were examined for the presence of superoxide dismutase. Visualisation of superoxide dismutase enzyme activity on polyacrylamide gels, and specific inhibition with potassium cyanide verified a copper/zinc (Cu/Zn) superoxide dismutase only in serotype A2 whereas serotypes A1 and T10 showed other superoxide dismutase activity. Using a simple freeze-thaw method the cellular location of superoxide dismutase enzyme activity was determined in all three serotypes. In serotypes A1 and A2 but not T10 superoxide dismutases were located in the periplasm. The viability of serotypes A2 and T10 cells in the presence of exogenous superoxide was unchanged over a 30 min period, whereas serotype A1 cells declined in viability between 15 and 30 min. Purified immunoglobulin from sheep convalescent serum did not reduce superoxide dismutase activity in the serotypes in an in vitro assay. The presence of this enzyme within the pasteurellae suggests a supportive role in the virulence of this major pathogen of ruminants.

Responses to aggregating agents after cleavage of GPIb of human platelets by the O-sialoglycoprotein endoprotease from Pasteurella haemolytica- potential surrogates for Bernard-Soulier platelets?

Most proteolytic enzymes that cleave glycoprotein lb (GPlb) also cleave other glycoproteins or receptors on the surface of platelets. We have used an O-sialoglycoprotein endoprotease from Pasteurella haemolytica that selectively cleaves the heavily O-glycosylated GPlb, but does not cleave N-linked glycoproteins or unglycosylated proteins. Isolated, [14C]serotonin-labeled platelets in Tyrode-albumin solution were incubated with 10 microg/mL endoprotease for 60 minutes at 37 degrees C. These platelets did not release [14C]serotonin, had no detectable GPIb, and were unresponsive to ristocetin/von Willebrand factor. Compared with control platelets, aggregation and release of [14C]serotonin by the endoprotease-pretreated platelets were inhibited in response to low concentrations of thrombin, SFLLRN (the PAR-1-activating peptide), collagen, and U46619 (a thromboxane A(2) mimetic); aggregates were smaller in size. The presence of fibrinogen overcame the inhibition of responses induced by SFLLRN, collagen, and U46619. With fibrinogen, primary ADP-induced aggregation was scarcely affected by pretreatment with the endoprotease. Thus, the PAR-1 receptor for thrombin, and receptors for collagen, thromboxane A(2), fibrinogen (GPIIb/IIIa), and ADP appear to function normally on the endoprotease-pretreated platelets. Since only GPIb is cleaved by the endoprotease, these platelets seem to provide potential surrogates for Bernard-Soulier syndrome platelets for further studies of platelet functions in this condition.

Further characterization of Pasteurella haemolytica-like bacteria isolated from swine enteritis.

DNA-DNA hybridization studies were conducted on six Pasteurella haemolytica-like (PHL) organisms recovered from cases of swine enteritis. Chromosomal-enriched fractions of PHL organisms served as the source of DNA for Southern blots or as whole-chromosomal DNA probes. Under stringent hybridization conditions, chromosomal DNA probes of a prototype PHL (strain 6213A) organism distinguished other PHL organisms from Pasteurella haemolytica types A1 and T3, Pasteurella multiocida types A:1 and A:3, Escherichia coli, Pseudomonas aeruginosa, Actinobacillus pleuropneumoniae type 1, and Salmonella cholerasuis. The guanine-cytosine content of the DNA of three PHL strains was 41.2 to 42.8 mol % as calculated from the thermal denaturation midpoint temperatures. The PHL strains are Gram-negative, nonmotile, beta-hemolytic, pleomorphic, oxidase-positive, urease- and indole-negative, fermentative rods with the key characteristics of the species Pasteurella haemolytica. None of the PHL strains reacted with the type-specific antisera of P. haemolytica types 1 through 12 as tested by an agglutination procedure. These swine strains differed in their biochemical differentiation from P. haemolytica types A1 and T3 in that all produced acid from M-inositol and failed to grow on MacConkey agar. Acid production from trehalose and L-arabinose was variable with PHL strains. Leukotoxicity of PHL strains was evaluated by a colorimetric micro-titration assay. Sterile culture supernatants of three of five PHL strains were toxic to bovine neutrophils. Results of these studies suggest that the PHL organisms may belong to a new group of organisms under the genus Pasteurella.