Mhp182 (P102) binds fibronectin and contributes to the recruitment of plasmin(ogen) to the Mycoplasma hyopneumoniae cell surface

Mycoplasma hyopneumoniae is a major, economically damaging respiratory pathogen. Although M. hyopneumoniae cells bind plasminogen, the identification of plasminogen-binding surface proteins and the biological ramifications of acquiring plasminogen requires further investigation. mhp182 encodes a highly expressed 102 kDa protein (P102) that undergoes proteolytic processing to generate surface-located N-terminal 60 kDa (P60) and C-terminal 42 kDa (P42) proteins of unknown function. We show that recombinant P102 (rP102) binds plasminogen at physiologically relevant concentrations (K(D) ~ 76 nM) increasing the susceptibility of plasmin(ogen) to activation by tissue-specific plasminogen activator (tPA). Recombinant proteins constructed to mimic P60 (rP60) and P42 (rP42) also bound plasminogen at physiologically significant levels. M. hyopneumoniae surface-bound plasminogen was activated by tPA and is able to degrade fibrinogen, demonstrating the biological functionality of M. hyopneumoniae-bound plasmin(ogen) upon activation. Plasmin(ogen) was readily detected in porcine ciliated airways and plasmin levels were consistently higher in bronchoalveolar lavage fluid from M. hyopneumoniae-infected animals. Additionally, rP102 and rP42 bind fibronectin with K(D) s of 26 and 33 nM respectively and recombinant P102 proteins promote adherence to porcine kidney epithelial-like cells. The multifunctional binding ability of P102 and activation of M. hyopneumoniae-sequestered plasmin(ogen) by an exogenous activator suggests P102 plays an important role in virulence.

Sequence TTKF ↓ QE defines the site of proteolytic cleavage in Mhp683 protein, a novel glycosaminoglycan and cilium adhesin of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae colonizes the ciliated respiratory epithelium of swine, disrupting mucociliary function and inducing chronic inflammation. P97 and P102 family members are major surface proteins of M. hyopneumoniae and play key roles in colonizing cilia via interactions with glycosaminoglycans and mucin. The p102 paralog, mhp683, and homologs in strains from different geographic origins encode a 135-kDa pre-protein (P135) that is cleaved into three fragments identified here as P45(683), P48(683), and P50(683). A peptide sequence (TTKF↓QE) was identified surrounding both cleavage sites in Mhp683. N-terminal sequences of P48(683) and P50(683), determined by Edman degradation and mass spectrometry, confirmed cleavage after the phenylalanine residue. A similar proteolytic cleavage site was identified by mass spectrometry in another paralog of the P97/P102 family. Trypsin digestion and surface biotinylation studies showed that P45(683), P48(683), and P50(683) reside on the M. hyopneumoniae cell surface. Binding assays of recombinant proteins F1(683)-F5(683), spanning Mhp683, showed saturable and dose-dependent binding to biotinylated heparin that was inhibited by unlabeled heparin, fucoidan, and mucin. F1(683)-F5(683) also bound porcine epithelial cilia, and antisera to F2(683) and F5(683) significantly inhibited cilium binding by M. hyopneumoniae cells. These data suggest that P45(683), P48(683), and P50(683) each display cilium- and proteoglycan-binding sites. Mhp683 is the first characterized glycosaminoglycan-binding member of the P102 family.

Simultaneous glycan-peptide characterization using hydrophilic interaction chromatography and parallel fragmentation by CID, higher energy collisional dissociation, and electron transfer dissociation MS applied to the N-linked glycoproteome of Campylobacter jejuni

Campylobacter jejuni is a gastrointestinal pathogen that is able to modify membrane and periplasmic proteins by the N-linked addition of a 7-residue glycan at the strict attachment motif (D/E)XNX(S/T). Strategies for a comprehensive analysis of the targets of glycosylation, however, are hampered by the resistance of the glycan-peptide bond to enzymatic digestion or β-elimination and have previously concentrated on soluble glycoproteins compatible with lectin affinity and gel-based approaches. We developed strategies for enriching C. jejuni HB93-13 glycopeptides using zwitterionic hydrophilic interaction chromatography and examined novel fragmentation, including collision-induced dissociation (CID) and higher energy collisional (C-trap) dissociation (HCD) as well as CID/electron transfer dissociation (ETD) mass spectrometry. CID/HCD enabled the identification of glycan structure and peptide backbone, allowing glycopeptide identification, whereas CID/ETD enabled the elucidation of glycosylation sites by maintaining the glycan-peptide linkage. A total of 130 glycopeptides, representing 75 glycosylation sites, were identified from LC-MS/MS using zwitterionic hydrophilic interaction chromatography coupled to CID/HCD and CID/ETD. CID/HCD provided the majority of the identifications (73 sites) compared with ETD (26 sites). We also examined soluble glycoproteins by soybean agglutinin affinity and two-dimensional electrophoresis and identified a further six glycosylation sites. This study more than doubles the number of confirmed N-linked glycosylation sites in C. jejuni and is the first to utilize HCD fragmentation for glycopeptide identification with intact glycan. We also show that hydrophobic integral membrane proteins are significant targets of glycosylation in this organism. Our data demonstrate that peptide-centric approaches coupled to novel mass spectrometric fragmentation techniques may be suitable for application to eukaryotic glycoproteins for simultaneous elucidation of glycan structures and peptide sequence.

Mhp107 is a member of the multifunctional adhesin family of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the causative pathogen of porcine enzootic pneumonia, an economically significant disease that disrupts the mucociliary escalator in the swine respiratory tract. Expression of Mhp107, a P97 paralog encoded by the gene mhp107, was confirmed using ESI-MS/MS. To investigate the function of Mhp107, three recombinant proteins, F1(Mhp107), F2(Mhp107), and F3(Mhp107), spanning the N-terminal, central, and C-terminal regions of Mhp107 were constructed. Colonization of swine by M. hyopneumoniae requires adherence of the bacterium to ciliated cells of the respiratory tract. Recent studies have identified a number of M. hyopneumoniae adhesins that bind heparin, fibronectin, and plasminogen. F1(Mhp107) was found to bind porcine heparin (K(D) ∼90 nM) in a dose-dependent and saturable manner, whereas F3(Mhp107) bound fibronectin (K(D) ∼180 nM) at physiologically relevant concentrations. F1(Mhp107) also bound porcine plasminogen (K(D) = 24 nM) in a dose-dependent and physiologically relevant manner. Microspheres coated with F3(Mhp107) mediate adherence to porcine kidney epithelial-like (PK15) cells, and all three recombinant proteins (F1(Mhp107)-F3(Mhp107)) bound swine respiratory cilia. Together, these findings indicate that Mhp107 is a member of the multifunctional M. hyopneumoniae adhesin family of surface proteins and contributes to both adherence to the host and pathogenesis.

Distribution of class 1 integrons with IS26-mediated deletions in their 3'-conserved segments in Escherichia coli of human and animal origin

Class 1 integrons play a role in the emergence of multi-resistant bacteria by facilitating the recruitment of gene cassettes encoding antibiotic resistance genes. 512 E. coli strains sourced from humans (n = 202), animals (n = 304) and the environment (n = 6) were screened for the presence of the intI1 gene. In 31/79 integron positive E. coli strains, the gene cassette regions could not be PCR amplified using standard primers. DNA sequence analysis of 6 serologically diverse strains revealed atypical integrons harboured the dfrA5 cassette gene and only 24 bp of the integron 3′-conserved segment (CS) remained, due to the insertion of IS26. PCR targeting intI1 and IS26 followed by restriction fragment length polymorphism (RFLP) analysis identified the integron-dfrA5-IS26 element in 27 E. coli strains of bovine origin and 4 strains of human origin. Southern hybridization and transformation studies revealed the integron-dfrA5-IS26 gene arrangement was either chromosomally located or plasmid borne. Plasmid location in 4/9 E. coli strains and PCR linkage of Tn21 transposition genes with the intI1 gene in 20/31 strains, suggests this element is readily disseminated by horizontal transfer.

A processed multidomain mycoplasma hyopneumoniae adhesin binds fibronectin, plasminogen, and swine respiratory cilia

Porcine enzootic pneumonia is a chronic respiratory disease that affects swine. The etiological agent of the disease, Mycoplasma hyopneumoniae, is a bacterium that adheres to cilia of the swine respiratory tract, resulting in loss of cilia and epithelial cell damage. A M. hyopneumoniae protein P116, encoded by mhp108, was investigated as a potential adhesin. Examination of P116 expression using proteomic analyses observed P116 as a full-length protein and also as fragments, ranging from 17 to 70 kDa in size. A variety of pathogenic bacterial species have been shown to bind the extracellular matrix component fibronectin as an adherence mechanism. M. hyopneumoniae cells were found to bind fibronectin in a dose-dependent and saturable manner. Surface plasmon resonance was used to show that a recombinant C-terminal domain of P116 bound fibronectin at physiologically relevant concentrations (K(D) 24 ± 6 nm). Plasmin(ogen)-binding proteins are also expressed by many bacterial pathogens, facilitating extracellular matrix degradation. M. hyopneumoniae cells were found to also bind plasminogen in a dose-dependent and saturable manner; the C-terminal domain of P116 binds to plasminogen (K(D) 44 ± 5 nm). Plasminogen binding was abolished when the C-terminal lysine of P116 was deleted, implicating this residue as part of the plasminogen binding site. P116 fragments adhere to the PK15 porcine kidney epithelial-like cell line and swine respiratory cilia. Collectively these data suggest that P116 is an important adhesin and virulence factor of M. hyopneumoniae.

RSF1010-like plasmids in Australian Salmonella enterica serovar Typhimurium and origin of their sul2-strA-strB antibiotic resistance gene cluster

Salmonella enterica serovar Typhimurium phage type 9 isolates resistant to streptomycin and sulfonamide have been recovered from both bovine and human sources in Australia. This study aimed to identify the resistance genes and their location. Polymerase chain reaction was used to screen for resistance genes and sul2 (sulphonamide resistance) and strA and strB (streptomycin resistance) were detected. A small streptomycin and sulfonamide resistance plasmid carrying the three resistance genes was recovered from these isolates by transformation and was shown to be essentially identical to the small IncQ plasmid RSF1010. The sequences of one plasmid, pSRC15, and RSF1010 differed at only a few positions that may be errors in the older sequence. RSF1010 has been recovered from many species and in many countries since its first isolation in the early 1970s. We conclude that this plasmid has persisted unchanged in the environment for over 30 years. The antibiotic resistance gene cluster containing strA, strB, and sul2 genes has clearly arisen from other known entities by a combination of transposition and homologous recombination using a short segment of homology. This resistance gene cluster is now widely distributed in plasmids and genomic islands in a number of contexts.

Mycoplasma leachii sp. nov. as a new species designation for Mycoplasma sp. bovine group 7 of Leach, and reclassification of Mycoplasma mycoides subsp. mycoides LC as a serovar of Mycoplasma mycoides subsp. capri

The Mycoplasma mycoides cluster consists of six pathogenic mycoplasmas causing disease in ruminants, which share many genotypic and phenotypic traits. The M. mycoides cluster comprises five recognized taxa: Mycoplasma mycoides subsp. mycoides Small Colony (MmmSC), M. mycoides subsp. mycoides Large Colony (MmmLC), M. mycoides subsp. capri (Mmc), Mycoplasma capricolum subsp. capricolum (Mcc) and M. capricolum subsp. capripneumoniae (Mccp). The group of strains known as Mycoplasma sp. bovine group 7 of Leach (MBG7) has remained unassigned, due to conflicting data obtained by different classification methods. In the present paper, all available data, including recent phylogenetic analyses, have been reviewed, resulting in a proposal for an emended taxonomy of this cluster: (i) the MBG7 strains, although related phylogenetically to M. capricolum, hold sufficient characteristic traits to be assigned as a separate species, i.e. Mycoplasma leachii sp. nov. (type strain, PG50(T) = N29(T) = NCTC 10133(T) = DSM 21131(T)); (ii) MmmLC and Mmc, which can only be distinguished by serological methods and are related more distantly to MmmSC, should be combined into a single subspecies, i.e. Mycoplasma mycoides subsp. capri, leaving M. mycoides subsp. mycoides (MmmSC) as the exclusive designation for the agent of contagious bovine pleuropneumonia. A taxonomic description of M. leachii sp. nov. and emended descriptions of M. mycoides subsp. mycoides and M. mycoides subsp. capri are presented. As a result of these emendments, the M. mycoides cluster will hereafter be composed of five taxa comprising three subclusters, which correspond to the M. mycoides subspecies, the M. capricolum subspecies and the novel species M. leachii.

Mhp493 (P216) is a proteolytically processed, cilium and heparin binding protein of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae induces respiratory disease in swine by colonizing cilia causing ciliostasis, cilial loss and epithelial cell death. Heparin binds to M. hyopneumoniae cells in a dose-dependent manner and blocks its ability to adhere to porcine cilia. We show here that Mhp493 (P216), a paralogue of the cilium adhesin P97 (Mhp183), is cleaved between amino acids 1040 and 1089 generating surface-accessible, heparin-binding proteins P120 and P85. Antiphosphoserine antibodies recognized P85 in 2-D immunoblotting studies and TiO(2) chromatography of trypsin digests of P85 isolated a single peptide with an m/z of 917.3. A phosphoserine residue in the tryptic peptide (90)VSELpSFR(96) (position 94 in P85) was identified by MALDI-MS/MS. Polyhistidine fusion proteins (F1(P216), F2(P216), F3(P216)) spanning Mhp493 bound heparin with biologically significant Kd values, and heparin, fucoidan and mucin inhibited this interaction. Latex beads coated with F1(P216), F2(P216) and F3(P216) adhered to and entered porcine kidney epithelial-like (PK15) cell monolayers. Microtitre plate-based assays showed that sequences within P120 and P85 bind to porcine cilia and are recognized by serum antibodies elicited during infection by M. hyopneumoniae. Mhp493 contributes significantly to the surface architecture of M. hyopneumoniae and is the first cilium adhesin to be described that lacks an R1 cilium-binding domain.

Role of group A Streptococcus HtrA in the maturation of SpeB protease

The serine protease high-temperature requirement A (HtrA) (DegP) of the human pathogen Streptococcus pyogenes (group A Streptococcus; GAS) is localized to the ExPortal secretory microdomain and is reportedly essential for the maturation of cysteine protease streptococcal pyrogenic exotoxin B (SpeB). Here, we utilize HSC5 (M5 serotype) and the in-frame isogenic mutant HSC5DeltahtrA to determine whether HtrA contributes to the maturation of other GAS virulence determinants. Mutanolysin cell wall extracts and secreted proteins were arrayed by 2-DE and identified by MALDI-TOF PMF analysis. HSC5DeltahtrA had elevated levels of cell wall-associated M protein, whilst the supernatant had higher concentrations of M protein fragments and a reduced amount of mature SpeB protease, compared to wild-type (WT). Western blot analysis and protease assays revealed a delay in the maturation of SpeB in the HSC5DeltahtrA supernatant. HtrA was unable to directly process SpeB zymogen (proSpeB) to the active form in vitro. We therefore conclude that HtrA plays an indirect role in the maturation of cysteine protease SpeB.

Isolation and solubilization of gram-positive bacterial cell wall-associated proteins

This chapter describes a simple, rapid and reproducible method to prepare bacterial cell wall extracts for two-dimensional gel electrophoresis (2DE). The extraction process uses mutanolysin, an N-acetylmuramidase, to gently solubilize cell wall-associated proteins from Gram-positive prokaryotes. The cells are first washed with buffer and resuspended in a solution containing mutanolysin. Following incubation at 37 degrees C, the sample is centrifuged and the supernatant containing the soluble cell wall-associated proteins is harvested. Following a brief precipitation step, the pellet is solubilized in sample buffer ready for isoelectric focusing and 2DE analysis.

The Mycoplasma gallisepticum OsmC-like protein MG1142 resides on the cell surface and binds heparin

Mycoplasma gallisepticum is an avian pathogen that causes a chronic respiratory disease of chickens and results in significant economic losses to the poultry industry worldwide. Colonization of the host and the establishment of chronic disease are initiated by the cytadherence of M. gallisepticum to the host respiratory epithelium. While several proteins involved in cytadhesion have been characterized, molecules that interact with components of the host extracellular matrix, a process that is central to pathogenesis, are only now being identified. In this study, M. gallisepticum whole cells were shown to bind heparin in a specific and saturable manner. Heparin also significantly inhibited the binding of M. gallisepticum to the human lung fibroblast cell line MRC-5, suggesting a potential role for glycosaminoglycans (GAGs) in cytadherence. M. gallisepticum protein MG1142 (encoded by mga 1142), which displays homology to the osmotically induced (OsmC) family of proteins, binds strongly to heparin, is highly expressed during in vitro culture, and is surface accessible. Recombinant MG1142 bound heparin in a dose-dependent and saturable manner with a dissociation constant (K(d)) of 10+/-1.8 nM, which is within a physiologically significant range, compared to that of other heparin-binding proteins. Binding to heparin was inhibited by the heavily sulfated polysaccharide fucoidan, but not by mucin or chondroitin sulfate A or B, suggesting that electrostatic interactions between the sulfate groups of heparin and the positively charged basic residues of the MG1142 protein are important in binding. The ability of M. gallisepticum to bind GAGs may contribute to host adherence and colonization.

Clonal complexes of Campylobacter jejuni identified by multilocus sequence typing are reliably predicted by restriction fragment length polymorphism analyses of the flaA gene

Multilocus sequence typing (MLST) has provided important new insights into the population structure of Campylobacter jejuni and is rapidly becoming the gold standard for typing this species. However, the methodology is comparatively costly and slow to perform for the routine surveillance testing of large numbers of isolates required by public health laboratories. Restriction fragment length polymorphism analysis of the flaA gene (RFLP-flaA) and sequencing of the variable region in the fla locus (SVR-fla) were compared to MLST to determine if a low cost alternative could be found that reliably predicts clonal lineage (as determined by MLST). An isolate of C. jejuni from each of 153 patients from New South Wales, Australia, collected sequentially over a period of 30 months from 1999 to 2001 and comprising 40 sequence types (ST) from 15 clonal complexes (CC) was examined. Of 15 CC, 12 were represented by more than one isolate and a predominant RFLP-flaA type was found for 10 (83%). Of these, seven (70%) correctly predicted the predominant MLST CC with a probability of >0.8. Of 40 STs detected, 19 were reported for the first time, 9 of which were represented by more than one isolate. Eight of these were represented by a single RFLP-flaA type. Only two of eight major SVR-fla types were able to predict CC with a probability of >0.8, indicating that flaA-RFLP is a more reliable predictor of CC than SVR-fla and thus offers an alternative to MLST for use in routine surveillance.

SGI1-K, a variant of the SGI1 genomic island carrying a mercury resistance region, in Salmonella enterica serovar Kentucky

A multiple-antibiotic-resistant Salmonella enterica serovar Kentucky strain was found to contain SGI1-K, a variant form of the Salmonella genomic island 1 (SGI1) with an In4-type class 1 integron that contains only one cassette array, aacCA5-aadA7, and an adjacent mercury resistance module. Part of the 3'-conserved segment (3'-CS) of the integron, together with the inverted short segment from the right-hand end of the integron transposition module normally found between the 3'-CS and IS6100 in In4 family integrons, has been removed by an IS6100-mediated deletion. IRt, the right-hand inverted repeat found at the outer end of the integron, abuts a mercury resistance region instead of the usual SGI1 backbone segment. The mer module is a hybrid of those found in Tn501 and Tn21. This mer region and a further uncharacterized segment of at least 10 kb appear to have been incorporated between IRt and the SGI1 backbone. These findings demonstrate that the multidrug resistance region in SGI1 can incorporate new DNA segments in the same way as multiple antibiotic resistance regions in plasmids.

Characterisation of Erysipelothrix rhusiopathiae isolates from pigs associated with vaccine breakdowns

Swine erysipelas vaccines are routinely used to protect pigs against peracute and acute/urticarial forms of Erysipelothrix. Between 1995 and 1998, 34 swine herds across four Australian states experienced vaccine failure. Forty-four isolates of Erysipelothrix rhusiopathiae of serovars 2, 1a, 1b and 1bx21 were recovered from 15 of these 34 vaccine breakdown herds. These isolates were characterised by restriction fragment length polymorphism (RFLP) analyses using RsaI and AluI on whole cell DNA and for the presence of plasmid DNA. Results were compared with those of 20 isolates from 16 herds unaffected by vaccine breakdown and 13 isolates representing 10 reference strains. The majority of breakdown herds possessed isolates of serovar 2 (9/15 herds), followed by serovar 1a (5 herds). No geographic predominance of a single serovar was evident. The identification of 10 RsaI profiles from whole cell DNA among the 44 isolates from 15 breakdown herds indicated that a single, new clonal lineage of E. rhusiopathiae was not responsible for vaccine failure. RsaI RFLP analyses detected a further 14 distinct profiles among 20 field strains unassociated with vaccine breakdowns, and none matched profiles of the 10 serovar reference strains for serovars 1a, 1b, 2 or 21. This technique is recommended for epidemiological studies of E. rhusiopathiae strains.

Aquariums as reservoirs for multidrug-resistant Salmonella Paratyphi B

Multidrug-resistant Salmonella enterica serovar Paratyphi B dT+ isolates from patients with gastroenteritis were identical with isolates from their home aquariums. Matched isolates had identical phage types, XbaI and IS200 profiles, and Salmonella genomic island 1 (SGI1). Ornamental fish tanks are reservoirs for SGI1-containing S. Paratyphi B dT+.

P159 is a proteolytically processed, surface adhesin of Mycoplasma hyopneumoniae: defined domains of P159 bind heparin and promote adherence to eukaryote cells

Mycoplasma hyopneumoniae, the causative agent of porcine enzootic pneumonia, colonizes the respiratory cilia of affected swine causing significant economic losses to swine production worldwide. Heparin is known to inhibit adherence of M. hyopneumoniae to porcine respiratory epithelial cilia. M. hyopneumoniae cells bind heparin but the identity of the heparin-binding proteins is limited. Proteomic analysis of M. hyopneumoniae lysates identified 27 kDa (P27), 110 kDa (P110) and 52 kDa (P52) proteins representing different regions of a 159 kDa (P159) protein derived from mhp494. These cleavage fragments were surface located and present at all growth stages. Following purification of four recombinant proteins spanning P159 (F1P159, F2P159, F3P159 and F4P159), only F3P159 and F4P159 bound heparin in a dose-dependent manner (K(d) values 142.37 +/- 22.01 nM; 75.37 +/- 7.34 nM respectively). Scanning electron microscopic studies showed M. hyopneumoniae bound intimately to porcine kidney epithelial-like cells (PK15 cells) but these processes were inhibited by excess heparin and F4P159. Similarly, latex beads coated with F2P159 and F4P159 adhered to and entered PK15 cells, but heparin, F2P159 and F4P159 was inhibitory. These findings indicate that P159 is a post-translationally cleaved, glycosaminoglycan-binding adhesin of M. hyopneumoniae.

Two domains within the Mycoplasma hyopneumoniae cilium adhesin bind heparin

Mycoplasma hyopneumoniae is the causative agent of porcine enzootic pneumonia, a chronic and economically significant respiratory disease that affects swine production worldwide. M. hyopneumoniae adheres to and adversely affects the function of ciliated epithelial cells of the respiratory tract, and the cilium adhesin (Mhp183, P97) is intricately but not exclusively involved in this process. Although binding of pathogenic bacteria to glycosaminoglycans is a recognized step in pathogenesis, knowledge of glycosaminoglycan-binding proteins in M. hyopneumoniae is lacking. However, heparin and other sulfated polysaccharides are known to block the binding of M. hyopneumoniae to purified swine respiratory cilia. In this study, four regions within the cilium adhesin were examined for the ability to bind heparin. Cilium adhesin fragments comprising 653 amino acids of the N terminus and 301 amino acids of the C terminus (containing two repeat regions, R1 and R2) were cloned and expressed. These fragments bound heparin in a dose-dependent and saturable manner with physiologically significant binding affinities of 0.27 +/- 0.02 microM and 1.89 +/- 0.33 microM, respectively. Heparin binding of both fragments was strongly inhibited by the sulfated polysaccharides fucoidan and mucin but not by chondroitin sulfate B. When the C-terminal repeat regions R1 and R2 were cloned separately and expressed, heparin-binding activity was lost, suggesting that both regions are required for heparin binding. The ability of the cilium adhesin to bind heparin indicates that this molecule plays a multifunctional role in the adherence of M. hyopneumoniae to host respiratory surfaces and therefore has important implications with respect to the pathogenesis of this organism.

Bovine feces from animals with gastrointestinal infections are a source of serologically diverse atypical enteropathogenic Escherichia coli and Shiga toxin-producing E. coli strains that commonly possess intimin

Shiga toxin-producing Escherichia coli (STEC) and enteropathogenic E. coli (EPEC) cells were isolated from 191 fecal samples from cattle with gastrointestinal infections (diagnostic samples) collected in New South Wales, Australia. By using a multiplex PCR, E. coli cells possessing combinations of stx1, stx2, eae, and ehxA were detected by a combination of direct culture and enrichment in E. coli (EC) (modified) broth followed by plating on vancomycin-cefixime-cefsulodin blood (BVCC) agar for the presence of enterohemolytic colonies and on sorbitol MacConkey agar for the presence of non-sorbitol-fermenting colonies. The high prevalence of the intimin gene eae was a feature of the STEC (35 [29.2%] of 120 isolates) and contrasted with the low prevalence (9 [0.5%] of 1,692 fecal samples possessed STEC with eae) of this gene among STEC recovered during extensive sampling of feces from healthy slaughter-age cattle in Australia (M. Hornitzky, B. A. Vanselow, K. Walker, K. A. Bettelheim, B. Corney, P. Gill, G. Bailey, and S. P. Djordjevic, Appl. Environ. Microbiol. 68:6439-6445, 2002). Forty-seven STEC serotypes were identified, including O5:H-, O8:H19, O26:H-, O26:H11, O113:H21, O157:H7, O157:H- and Ont:H- which are known to cause severe disease in humans and 23 previously unreported STEC serotypes. Serotypes Ont:H- and O113:H21 represented the two most frequently isolated STEC isolates and were cultured from nine (4.7%) and seven (3.7%) animals, respectively. Fifteen eae-positive E. coli serotypes, considered to represent atypical EPEC, were identified, with O111:H- representing the most prevalent. Using both techniques, STEC cells were cultured from 69 (36.1%) samples and EPEC cells were cultured from 30 (15.7%) samples, including 9 (4.7%) samples which yielded both STEC and EPEC. Culture on BVCC agar following enrichment in EC (modified) broth was the most successful method for the isolation of STEC (24.1% of samples), and direct culture on BVCC agar was the most successful method for the isolation of EPEC (14.1% samples). These studies show that diarrheagenic calves and cattle represent important reservoirs of eae-positive E. coli.

The genomic island SGI1, containing the multiple antibiotic resistance region of Salmonella enterica serovar Typhimurium DT104 or variants of it, is widely distributed in other S. enterica serovars

The global dissemination of the multiply-antibiotic-resistant Salmonella enterica serovar Typhimurium DT104 clone with the resistance genes located in a class 1 integron, here designated In104, within genomic island SGI1 is a significant public health issue. Here, we have shown that SGI1 and variants of it carrying different combinations of resistance genes are found in several Salmonella enterica serovars. These are serovars Cerro, Derby, Dusseldorf, Infantis, Kiambu, and Paratyphi B dT(+) isolated from human infections and serovar Emek from sewage effluent. Two new variants, SGI1-I and SGI1-J, both of which include the dfrA1-orfC cassette array, were identified.

Isolation of Escherichia coli O5 :H-, possessing genes for Shiga toxin 1, intimin-beta and enterohaemolysin, from an intestinal biopsy from an adult case of bloody diarrhoea: evidence for two distinct O5 :H- pathotypes

Two typical coliforms from an intestinal biopsy from an adult case of bloody diarrhoea carried genes encoding intimin-beta, stx(1) and ehxA, and produced verocytotoxin 1 and enterohaemolysin in culture. Both were biochemically typical Escherichia coli O5 :H(-), apart from producing urease. Such O5 isolates represent a human pathogenic E. coli lineage.

Surface analyses and immune reactivities of major cell wall-associated proteins of group a streptococcus

A proteomic analysis was undertaken to identify cell wall-associated proteins of Streptococcus pyogenes. Seventy-four distinct cell wall-associated proteins were identified, 66 of which were novel. Thirty-three proteins were immunoreactive with pooled S. pyogenes-reactive human antisera. Biotinylation of the GAS cell surface identified 23 cell wall-associated proteins that are surface exposed.

New integron-associated gene cassette encoding a 3-N-aminoglycoside acetyltransferase

A fifth gene cassette containing an aacC gene, aacCA5, was found in an aacCA5-aadA7 cassette array in a class 1 integron isolated from a multiply drug resistant Salmonella enterica serovar Kentucky strain. The AacC-A5 or AAC(3)-Ie acetyltransferase encoded by aacCA5 is related to other AAC(3)-I enzymes and confers resistance to gentamicin.

Serotypes and virulence gene profiles of shiga toxin-producing Escherichia coli strains isolated from feces of pasture-fed and lot-fed sheep

Shiga toxin-producing Escherichia coli (STEC) strains possessing genes for enterohemolysin (ehxA) and/or intimin (eae), referred to here as complex STEC (cSTEC), are more commonly recovered from the feces of humans with hemolytic uremic syndrome and hemorrhagic colitis than STEC strains that do not possess these accessory virulence genes. Ruminants, particularly cattle and sheep, are recognized reservoirs of STEC populations that may contaminate foods destined for human consumption. We isolated cSTEC strains from the feces of longitudinally sampled pasture-fed sheep, lot-fed sheep maintained on diets comprising various combinations of silage and grain, and sheep simultaneously grazing pastures with cattle to explore the diversity of cSTEC serotypes capable of colonizing healthy sheep. A total of 67 cSTEC serotypes were isolated, of which 21 (31.3%), mainly isolated from lambs, have not been reported. Of the total isolations, 58 (86.6%) were different from cSTEC serotypes isolated from a recent study of longitudinally sampled healthy Australian cattle (M. Hornitzky, B. A. Vanselow, K. Walker, K. A. Bettelheim, B. Corney, P. Gill, G. Bailey, and S. P. Djordjevic, Appl. Environ. Microbiol. 68:6439-6445, 2002). Our data suggest that cSTEC serotypes O5:H(-), O75:H8, O91:H(-), O123:H(-), and O128:H2 are well adapted to colonizing the ovine gastrointestinal tract, since they were the most prevalent serotypes isolated from both pasture-fed and lot-fed sheep. Collectively, our data show that Australian sheep are colonized by diverse cSTEC serotypes that are rarely isolated from healthy Australian cattle.

Proteolytic processing of the Mycoplasma hyopneumoniae cilium adhesin

Mycoplasma hyopneumoniae is an economically significant swine pathogen that colonizes the respiratory ciliated epithelial cells. Cilium adherence is mediated by P97, a surface protein containing a repeating element (R1) that is responsible for binding. Here, we show that the cilium adhesin is proteolytically processed on the surface. Proteomic analysis of strain J proteins identified cleavage products of 22, 28, 66, and 94 kDa. N-terminal sequencing showed that the 66- and 94-kDa proteins possessed identical N termini and that the 66-kDa variant was generated by cleavage of the 28-kDa product from the C terminus. The 22-kDa product represented the N-terminal 195 amino acids of the cilium adhesin preprotein, confirming that the hydrophobic leader signal sequence is not cleaved during translocation across the membrane. Comparative studies of M. hyopneumoniae strain 232 showed that the major cleavage products of the cilium adhesin are similar, although P22 and P28 appear to be processed further in strain 232. Immunoblotting studies using antisera raised against peptide sequences within P22 and P66/P94 indicate that processing is complex, with cleavage occurring at different frequencies within multiple sites, and is strain specific. Immunogold electron microscopy showed that fragments containing the cilium-binding site remained associated with the cell surface whereas cleavage products not containing the R1 element were located elsewhere. Not all secreted proteins undergo multiple cleavage, however, as evidenced by the analysis of the P102 gene product. The ability of M. hyopneumoniae to selectively cleave its secreted proteins provides this pathogen with a remarkable capacity to alter its surface architecture.

Distribution of intimin subtypes among Escherichia coli isolates from ruminant and human sources

The intimin gene eae, located within the locus of enterocyte effacement pathogenicity island, distinguishes enteropathogenic Escherichia coli (EPEC) and some Shiga toxin-producing E. coli (STEC) strains from all other pathotypes of diarrheagenic E. coli. EPEC is a leading cause of infantile diarrhea in developing countries, and intimin-positive STEC isolates are typically associated with life-threatening diseases such as hemolytic-uremic syndrome and hemorrhagic colitis. Here we describe the development of a PCR-restriction fragment length polymorphism (RFLP) assay that reliably differentiates all 11 known intimin types (alpha1, alpha2, beta, gamma, kappa, epsilon, eta, iota, lambda, theta, and zeta) and three new intimin genes that show less than 95% nucleotide sequence identity with existing intimin types. We designated these new intimin genes Int- micro, Int-nu, and Int-xi. The PCR-RFLP assay was used to screen 213 eae-positive E. coli isolates derived from ovine, bovine, and human sources comprising 60 serotypes. Of these, 82 were STEC isolates, 89 were stx-negative (stx(-)) and ehxA-positive (ehxA(+)) isolates, and 42 were stx(-) and ehxA-negative isolates. Int-beta, the most commonly identified eae subtype (82 of 213 [38.5%] isolates), was associated with 21 serotypes, followed by Int-zeta (39 of 213 [18.3%] isolates; 11 serotypes), Int-theta (25 of 213 [11.7%] isolates; 15 serotypes), Int-gamma (19 of 213 [8.9%] isolates; 9 serotypes), and Int-epsilon (21 of 213 [9.9%] isolates; 5 serotypes). Intimin subtypes alpha1, alpha2, kappa, lambda, xi, micro, nu, and iota were infrequently identified; and Int-eta was not detected. Phylogenetic analyses with the Phylip package of programs clustered the intimin subtypes into nine distinct families (alpha, beta-xi, gamma, kappa, epsilon-eta-nu, iota- micro, lambda, theta, and zeta). Our data confirm that ruminants are an important source of serologically and genetically diverse intimin-containing E. coli strains.

Cell surface antigens of Mycoplasma species bovine group 7 bind to and activate plasminogen

Mycoplasma species bovine group 7 bound plasminogen at the cell surface in a lysine-dependent manner. Cell-bound plasminogen was rapidly activated to plasmin by exogenous urokinase, and this activity was associated with plasminogen binding capacity. Binding assays using plasminogen modified with a trifunctional cross-linking agent revealed several binding proteins.

Bovine non-O157 Shiga toxin 2-containing Escherichia coli isolates commonly possess stx2-EDL933 and/or stx2vhb subtypes

stx(2) genes from 138 Shiga toxin-producing Escherichia coli (STEC) isolates, of which 127 were of bovine origin (58 serotypes) and 11 of human origin (one serotype; O113:H21), were subtyped. The bovine STEC isolates from Australian cattle carried ehxA and/or eaeA and predominantly possessed stx(2-EDL933) (103 of 127; 81.1%) either in combination with stx(2vhb) (32 of 127; 25.2%) or on its own (52 of 127; 40.4%). Of 22 (90.9%) bovine isolates of serotype O113:H21, a serotype increasingly recovered from patients with hemolytic uremic syndrome (HUS) or hemorrhagic colitis, 20 contained both stx(2-EDL933) and stx(2vhb); 2 isolates contained stx(2vhb) only. Although 7 of 11 (63.6%) human O113:H21 isolates associated with diarrhea possessed stx(2-EDL933), the remaining 4 isolates possessed a combination of stx(2-EDL933) and stx(2vhb). Three of the four were from separate sporadic cases of HUS, and one was from an unknown source.

An aromatic amino acid auxotrophic mutant of Bordetella bronchiseptica is attenuated and immunogenic in a mouse model of infection

We have constructed an aromatic amino acid auxotrophic mutant of Bordetella bronchiseptica, harbouring mutations in aroA and trpE to investigate the use of such a strain as a live-attenuated vaccine. B. bronchiseptica aroA trpE was unable to grow in minimal medium without aromatic supplementation. Compared to the parental wild-type strain, the mutant displayed significantly reduced abilities to invade and survive within the mouse macrophage-like cell line J774A.1 in vitro and in the murine respiratory tract following experimental intranasal infection. Mice vaccinated with B. bronchiseptica aroA trpE displayed significant dose-dependent increases in B. bronchiseptica-specific antibody responses, and exhibited increases in the number of B. bronchiseptica-reactive spleen cells in lymphoproliferation assays. Immunised animals were protected against lung colonisation after challenge with the wild-type parental strain. With such a broad host range displayed by B. bronchiseptica, the attenuated strain constructed in this study may not only be used for the prevention of B. bronchiseptica-associated disease, but also for the potential delivery of heterologous antigen.

stx1c Is the most common Shiga toxin 1 subtype among Shiga toxin-producing Escherichia coli isolates from sheep but not among isolates from cattle

Unlike Shiga toxin 2 (stx(2)) genes, most nucleotide sequences of Shiga toxin 1 (stx(1)) genes from Shiga toxin-producing Escherichia coli (STEC), Shigella dysenteriae, and several bacteriophages (H19B, 933J, and H30) are highly conserved. Consequently, there has been little incentive to investigate variants of stx(1) among STEC isolates derived from human or animal sources. However stx(1OX3), originally identified in an OX3:H8 isolate from a healthy sheep in Germany, differs from other stx(1) subtypes by 43 nucleotides, resulting in changes to 12 amino acid residues, and has been renamed stx(1c). In this study we describe the development of a PCR-restriction fragment length polymorphism (RFLP) assay that distinguishes stx(1c) from other stx(1) subtypes. The PCR-RFLP assay was used to study 378 stx(1)-containing STEC isolates. Of these, 207 were isolated from sheep, 104 from cattle, 45 from humans, 11 from meat, 5 from swine, 5 from unknown sources, and 1 from a cattle water trough. Three hundred fifty-five of the 378 isolates (93.9%) also possessed at least one other associated virulence gene (ehxA, eaeA, and/or stx(2)); the combination stx(1), stx(2), and ehxA was the most common (175 of 355 [49.3%]), and 90 of 355 (25.4%) isolates possessed eaeA. One hundred thirty-six of 207 (65.7%) ovine isolates possessed stx(1c) alone and belonged to 41 serotypes. Seventy-one of 136 (52.2%) comprised the common ovine serotypes O5:H(-), O128:H2, and O123:H(-). Fifty-two of 207 isolates (25.1%) possessed an stx(1) subtype; 27 (51.9%) of these belonged to serotype O91:H(-). Nineteen of 207 isolates (9.2%) contained both stx(1c) and stx(1) subtypes, and 14 belonged to serotype O75:H8. In marked contrast, 97 of 104 (93.3%) bovine isolates comprising 44 serotypes possessed an stx(1) subtype, 6 isolates possessed stx(1c), and the remaining isolate possessed both stx(1c) and stx(1) subtypes. Ten of 11 (91%) isolates cultured from meat in New Zealand possessed stx(1c) (serotypes O5:H(-), O75:H8/H40, O81:H26, O88:H25, O104:H(-)/H7, O123:H(-)/H10, and O128:H2); most of these serotypes are commonly recovered from the feces of healthy sheep. Serotypes containing stx(1) recovered from cattle rarely were the same as those isolated from sheep. Although an stx(1c) subtype was never associated with the typical enterohemorrhagic E. coli serogroups O26, O103, O111, O113, and O157, 13 human isolates possessed stx(1c). Of these, six isolates with serotype O128:H2 (from patients with diarrhea), four O5:H(-) isolates (from patients with hemolytic-uremic syndrome), and three isolates with serotypes O123:H(-) (diarrhea), OX3:H8 (hemolytic-uremic syndrome), and O81:H6 (unknown health status) represent serotypes that are commonly isolated from sheep.

Antibiotic resistance among verocytotoxigenic Escherichia coli (VTEC) and non-VTEC isolated from domestic animals and humans

Two hundred verocytotoxigenic and 216 non-verocytotoxigenic Escherichia coli (VTEC and non-VTEC), isolated from a variety of sources were tested for their resistances to 11 antimicrobial agents. The strains included isolates from domestic food animals and both symptomatic and asymptomatic infections in man. A much higher level of resistance was found among the non-VTEC than among the VTEC, regardless of source. The resistant VTEC isolated from animals were predominantly from specimens associated with sick animals. Antibiotic resistance was detected in only four of the 59 (6.8 %) VTEC of human origin, whereas more of the human non-VTEC possessed antibiotic resistance determinants. It was particularly noteworthy that 24/87 (28 %) strains isolated from healthy babies, who had neither contact with antibiotics nor had gastrointestinal symptoms for at least 2 weeks prior to the specimen being taken, were resistant to one or more of the antibiotics tested.

Characterization of a chromosomal region of Mycoplasma sp. bovine group 7 strain PG50 encoding a glycerol transport locus (gtsABC)

Mycoplasma species bovine group 7, represented by the type strain PG50, is one of six members of the Mycoplasma mycoides cluster and has been implicated in sporadic and outbreak cases of polyarthritis and mastitis in Australian dairy cattle. This study describes cloning and sequencing a 7.9 kb region of the PG50 chromosome and identification of genes involved in glycerol transport (gtsA, gtsB and gtsC) that are followed by a putative lipoprotein gene lppB and a genomic locus containing two ORFs encoding putative membrane proteins. Long range PCR using primers spanning gtsABC and downstream flanking genes, and Southern hybridization analyses using a suite of probes derived from M. mycoides subsp. mycoides small colony type (SC) strain Afadé for gtsA, gtsB and gtsC, lppB and the two downstream genes confirmed that these genes were conserved among Mycoplasma sp. bovine group 7 isolates and mycoplasmas belonging to the M. mycoides subcluster [M. mycoides subsp. mycoides SC, M. mycoides subsp. mycoides large colony type (LC) and M. mycoides subsp. capri] but were absent in mycoplasmas belonging to the Mycoplasma capricolum subcluster (M. capricolum subsp. capricolum and M. capricolum subsp. capripneumoniae). M. capricolum subsp. capricolum type strain California kid did not hybridize with the probe for gtsA and gave only weak or no hybridization signals with probes derived from the loci downstream of gtsABC, suggesting that this region has diverged in mycoplasmas belonging to subspecies of M. capricolum. It is shown that PG50, after the addition of a physiological concentration of glycerol to the growth medium, generates H(2)O(2) at levels comparable with strain Afadé, implying that the glycerol transport system is functional in Mycoplasma sp. bovine group 7. This suggests that in PG50, as in M. mycoides subsp. mycoides SC, glycerol uptake is followed by phosphorylation to glycerol 3-phosphate and then conversion to dihydroxyacetone phosphate, catalysed by L-alpha-glycerophosphate oxidase, resulting in the production of H(2)O(2). The ability of Mycoplasma sp. bovine group 7 to generate significant amounts of hydrogen peroxide may be important in pathogenesis.

Virulence properties and serotypes of Shiga toxin-producing Escherichia coli from healthy Australian cattle

The virulence properties and serotypes of complex Shiga toxin-producing Escherichia coli (cSTEC) were determined in two studies of healthy cattle in eastern Australia. In the first, a snapshot study, 84 cSTEC isolates were recovered from 37 of 1,692 (2.2%) fecal samples collected from slaughter-age cattle from 72 commercial properties. The second, a longitudinal study of three feedlots and five pasture beef properties, resulted in the recovery of 118 cSTEC isolates from 104 animals. Of the 70 serotypes identified, 38 had not previously been reported.

Speciating Campylobacter jejuni and Campylobacter coli isolates from poultry and humans using six PCR-based assays

Six previously published polymerase chain reaction (PCR) assays each targeting different genes were used to speciate 116 isolates previously identified as Campylobacter jejuni using routine microbiological techniques. Of the 116 isolates, 84 were of poultry origin and 32 of human origin. The six PCR assays confirmed the species identities of 31 of 32 (97%) human isolates and 56 of 84 (67%) poultry isolates as C. jejuni. Twenty eight of 84 (33%) poultry isolates were identified as Campylobacter coli and the remaining human isolate was tentatively identified as Campylobacter upsaliensis based on the degree of similarity of 16S rRNA gene sequences. Four of six published PCR assays showed 100% concordance in their ability to speciate 113 of the 116 (97.4%) isolates; two assays failed to generate a PCR product with four to 10 isolates. A C. coli-specific PCR identified all 28 hippuricase gene (hipO)-negative poultry isolates as C. coli although three isolates confirmed to be C. jejuni by the remaining five assays were also positive in this assay. A PCR-restriction fragment length polymorphism assay based on the 16S rRNA gene was developed, which contrary to the results of the six PCR-based assays, identified 28 of 29 hipO-negative isolates as C. jejuni. DNA sequence analysis of 16S rRNA genes from four hipO-negative poultry isolates showed they were almost identical to the C. jejuni type strain 16S rRNA sequences ATCC43431 and ATCC33560 indicating that assays reliant on 16S rRNA sequence may not be suitable for the differentiation of these two species.

The common ovine Shiga toxin 2-containing Escherichia coli serotypes and human isolates of the same serotypes possess a Stx2d toxin type

Shiga toxin 2 (Stx2) has been reported as the main Shiga toxin associated with human disease. In addition, the Stx2 toxin type can have a profound impact on the degree of tissue damage in animal models. We have characterized the stx(2) subtype of 168 Shiga toxin-producing Escherichia coli (STEC) isolates of which 146 were derived from ovine sources (principally feces and meat) and 22 were isolated from humans. The ovine STEC isolates were of serotypes that have been shown to occur commonly in the gastrointestinal tract of healthy sheep. The major stx(2) subtype in the ovine isolates was shown to be stx(2d-Ount) (119 of 146 [81.5%]) and was predominantly associated with serotypes O75:H(-)/H8/H40, O91:H(-), O123:H(-), O128:H2, and OR:H2. However, 17 of 18 (94.4%) ovine isolates of serotype O5:H(-) possessed a stx(2d-O111/OX3a) subtype. Furthermore, STEC isolates of serotypes commonly found in sheep and recovered from both clinical and nonclinical human infections also contained a stx(2d) (stx(2d-Ount/O111/OX3a)) subtype. These studies suggest that a specific stx(2) subtype(s) associates with serotype and may have important epidemiological implications for tracing sources of E. coli during outbreaks of STEC-associated diseases in humans.

Virulence properties and serotypes of Shiga toxin-producing Escherichia coli from healthy Australian slaughter-age sheep

A group of 1,623 ovine fecal samples recovered from 65 geographically distinct mutton sheep and prime lamb properties across New South Wales, Australia, were screened for the presence of Shiga toxin-producing Escherichia coli (STEC) virulence factors (stx(1), stx(2), eaeA, and ehxA). A subset was cultured for STEC isolates containing associated virulence factors (eaeA and/or ehxA), which were isolated from 17 of 20 (85%) and 19 of 20 (95%) tested prime lamb and mutton sheep properties, respectively. STEC isolates containing stx(1), stx(2), and ehxA were most commonly isolated (19 of 40 flocks; 47.5%), and this profile was observed for 10 different serotypes. Among 90 STEC isolates studied, the most common serotypes were O91:H(-) (22 isolates [24.4%]), O5:H(-) (16 isolates [17.8%]), O128:H2 (11 isolates [12.2%]), O123:H(-) (8 isolates [8.9%]), and O85:H49 (5 isolates [5.6%]). Two isolates (2.2%) were typed as O157:H(-). A total of 78 of 90 STEC isolates (86.7%) expressed Shiga toxin in Vero cell culture and 75 of 84 ehxA-positive isolates (89.3%) expressed enterohemolysin on washed sheep blood agar. eaeA was observed in 11 of 90 (12.2%) ovine STEC isolates, including serotypes O5:H(-), O84:H(-), O85:H49, O123:H(-) O136:H40, and O157:H(-). Although only 2 of 90 isolates were typed as O157:H(-), the predominant serotypes recovered during this study have been recovered from human patients with clinical disease, albeit rarely.

The detection of Shiga toxin-producing Escherichia coli in diagnostic bovine faecal samples using vancomycin-cefixime-cefsulodin blood agar and PCR

The prevalence of complex Shiga toxin-producing Escherichia coli (STEC), i.e. STEC containing accessory virulence factors intimin (eaeA) and/or enterohaemorrhagic E. coli haemolysin (ehxA) and their serotypes were determined in diagnostic bovine faecal samples processed during a 3 months period. The presence of complex STEC was determined using PCR and vancomycin-cefixime-cefsulodin blood agar (BVCCA) using a dual approach which involved (i) direct culture of faecal samples on BVCCA followed by mutiplex PCR of BVCCA positive colonies and (ii) culture of faecal samples enriched in modified EC (mEC) broth (with a complex STEC profile determined by PCR) on BVCCA followed by multiplex PCR of BVCCA positive colonies. Using both techniques complex STEC were isolated from 23 (18.7%) of the 123 faecal samples. Complex STEC were isolated from 14 faecal samples by direct culture on BVCCA and 13 faecal samples yielded complex STEC by culture of mEC broths with a complex STEC profile on BVCCA. Only four samples were positive using both techniques. The serotypes isolated included O5:H-, O26:H-, O26:H11, O91:H21, O111:H-, O111:H8, O104:H11, O113:H21 and O157:H8. This study confirms that non-O157 STEC can be isolated from bovine faeces and that they carry types associated with human disease. This work also demonstrates that the use of a dual approach is advisable to increase the likelihood of isolating complex STEC.

Identification and detection of Actinobacillus pleuropneumoniae by PCR based on the gene apxIVA

The apxIVA gene, a recently discovered RTX determinant of Actinobacillus pleuropneumoniae, was shown to be species-specific. DNA hybridization experiments using probes for various regions of apxIVA revealed that the 3'-terminus of this gene was present in all 14 serotypes of A. pleuropneumoniae but absent from phylogenetically related species. A primer pair spanning this region specifically amplified a 422bp fragment in PCR experiments with DNA from the reference strains of the 14 serotypes and 194 field strains isolated from various geographic locations worldwide. DNA sequence analysis of PCR products derived from all serotypes were identical except in serotypes 3, 8, and 10, which showed minor differences. The PCR did not amplify any product when DNA from 17 different bacterial species closely related to A. pleuropneumoniae was used as template. In addition, the PCR was negative with DNA of several Actinobacillus sp. which were initially characterized as A. pleuropneumoniae using routine phenotypic and serological analyses but which were subsequently shown by 16S rRNA sequence analysis to belong to yet undefined Actinobacillus species. The sensitivity of the PCR was determined to be 10pg of A. pleuropneumoniae DNA. A set of nested primers amplified a 377bp fragment specifically with A. pleuropneumoniae DNA. DNA titration experiments using the flanking and nested primer pairs showed an improved level of sensitivity to approximately 10fg of genomic DNA. The nested PCR was used to monitor the spread of A. pleuropneumoniae in pigs experimentally infected with a virulent serotype 1 strain and housed in a controlled environment facility. A. pleuropneumoniae DNA could be detected by nested PCR in nasal swab samples of infected pigs receiving either a high dose (5x10(5)) or a low dose (1x10(4)) challenge and in unchallenged cohorts that were contact-infected by the inoculated animals. Furthermore, PCR confirmed the presence of A. pleuropneumoniae in 16/17 homogenates from necrotic lung lesions, while the bacterium was successfully recovered from 13 of these lesions by culture.

Oral immunization of swine with attenuated Salmonella typhimurium aroA SL3261 expressing a recombinant antigen of Mycoplasma hyopneumoniae (NrdF) primes the immune system for a NrdF specific secretory IgA response in the lungs

Salmonella typhimurium SL3261 (aroA mutant) expressing a recombinant Mycoplasma hyopneumoniae antigen was used to orally immunize swine against porcine enzootic pneumonia. This construct, designated S. typhimurium aro A SL3261 (pKF1), expressed a recombinant protein containing the carboxy-terminal 11 kDa of a 42 kDa M. hyopneumoniae NrdF ribonucleotide reductase R2 subunit protein. Here we demonstrate that this antigen is present in all seven geographically diverse strains of M. hyopneumoniae tested, and is recognized by the swine immune system after experimental infection with the virulent M. hyopneumoniae Beaufort strain. The immune response of swine orally immunized twice with S. typhimurium SL3261 (pKF1) on day 0 and day 14 was evaluated. Oral immunization with S. typhimurium SL3261 (pKF1) primed the immune system to elicit a significant (P<0.05) secretory IgA response against the 15 kDa NrdF antigen in the respiratory tract of swine, post-challenge, compared to control groups. Blood lymphocytes from swine immunized with S. typhimurium SL3261 (pKF1) proliferated significantly (P<0.05) following stimulation with M. hyopneumoniae whole-cell extracts compared to control groups 14 days post-vaccination. Following challenge with virulent M. hyopneumoniae, swine immunized with S. typhimurium SL3261 (pKF1) showed higher average daily weight gains and reduced lung pathology compared to control groups.