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Heat stress (HS) may result in economic losses to pig producers across the USA and worldwide. Despite significant advancements in management practices, HS continues to be a challenge. In this study, an in-feed antibiotic (carbadox, CBX) and antibiotic alternatives ( [XPC], and [SGX] fermentation products) were evaluated in a standard pig starter diet as mitigations against the negative effects of HS in pigs. A total of 100 gilts were obtained at weaning (6.87 ± 0.82 kg BW, 19.36 ± 0.72 d of age) and randomly assigned to dietary treatments (2 rooms/treatment, 2 pens/room, 6 to 7 pigs/pen). After 4 wk of dietary acclimation, half of the pigs in each dietary group (1 room/dietary treatment) were exposed to repeated heat stress conditions (RHS; daily cycles of 19 h at 25°C and 5 h at 40°C, repeated for 9 d), and the remaining pigs were housed at constant thermal neutral temperature (25°C, [NHS]). Pigs subjected to RHS had elevated skin surface temperature ( < 0.05; average 41.7°C) and respiration rate ( < 0.05; 199 breaths per minute (bpm) during HS, and overall reduced ( < 0.05) BW, ADG, ADFI, and G:F regardless of dietary treatment. Independent of diet, RHS pigs had significantly shorter ( < 0.05) jejunum villi on d 3 and d 9 compared to NHS pigs. Heat stress resulted in decreased villus height to crypt depth ratio (V:C) in pigs fed with control diet with no added feed additive (NON) and CBX diets at d 3, whereas the pigs fed diets containing XPC or SGX showed no decrease. Transcriptional expression of genes involved in cellular stress (, , , ), tight junction integrity (, , ), and immune response (, , and ) were measured in the ileum mucosa. Pigs in all dietary treatments subjected to RHS had significantly higher ( < 0.05) transcript levels of and , and an upward trend ( < 0.07) of mRNA expression. RHS pigs had higher ( < 0.05) transcript levels of and in NON diet, in XPC and CBX diets, and in SGX diet compared to the respective diet-matched pigs in the NHS conditions. Neither RHS nor diet affected peripheral natural killer () cell numbers or NK cell lytic activity. In conclusion, pigs subjected to RHS had decreased performance, and supplementation with fermentation products in the feed (XPC and SGX) protected pigs from injury to the jejunum mucosa.

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A novel Coriobacteriaceae bacterium (strain 68-1-3) was isolated from the ileum of the swine intestinal tract using a selective mucus-based medium. Here we present the finished genome sequence for the swine commensal, totaling 1.97 Mb in size.

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A novel anaerobic, mesophilic, amino-acid-fermenting bacterium, designated strain CL-84(T), was isolated from the swine intestinal tract on mucin-based media. Cells were curved rods (0.8-1.2 × 3.5-5.0 µm), stained Gram-negative and were non-motile with no evidence of spores. Strain CL-84(T) produced acetate, propionate, formate and butyrate as the end products of metabolism when grown on serine. Optimum growth occurred at 39 °C and pH 6.5. The major cellular fatty acids were iso-C15:0, iso-C15:0 3-OH, iso-C17:0 and C16:0, distinguishing strain CL-84(T) from closely related species. The DNA G+C content of strain CL-84(T) was 55.1 mol%. 16S rRNA gene sequence analysis showed that strain CL-84(T) shared 90-95% similarity with characterized genera within the phylum Synergistetes, family Synergistaceae. Phylogenetic analysis showed that strain CL-84(T) was related to, but distinct from, Cloacibacillus evryensis. Based on these findings, we propose that strain CL-84(T) represents a novel species of the genus Cloacibacillus. We further propose the name Cloacibacillus porcorum sp. nov. be designated for this species. The type strain is CL-84(T) (=DSM 25858(T)=CCUG 62631(T)). An emended description of the genus Cloacibacillus is provided.

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Little is known about the outer membrane structure of Brachyspira hyodysenteriae and Brachyspira pilosicoli or the role of outer membrane proteins (OMPs) in host colonization and the development of disease. The isolation of outer membrane vesicles from B. hyodysenteriae has confirmed that cholesterol is a significant outer membrane constituent and that it may impart unique characteristics to the lipid bilayer structure, including a reduced density. Unique proteins that have been identified in the B. hyodysenteriae outer membrane include the variable surface proteins (Vsp) and lipoproteins such as SmpA and BmpB. While the function of these proteins remains to be determined, there is indirect evidence to suggest that they may be involved in immune evasion. These data may explain the ability of the organism to initiate chronic infection. OMPs may be responsible for the unique attachment of B. pilosicoli to colonic epithelial cells; however, the only B. pilosicoli OMPs that have been identified to date are involved in metabolism. In order to identify further B. pilosicoli OMPs we have isolated membrane vesicle fractions from porcine strain 95-1000 by osmotic lysis and isopycnic centrifugation. The fractions were free of contamination by cytoplasm and flagella and contained outer membrane. Inner membrane contamination was minimal but could not be completely excluded. An abundant 45-kDa, heat-modifiable protein was shown to have significant homology with B. hyodysenteriae Vsp, and monoclonal antibodies were produced that reacted with five B. pilosicoli-specific membrane protein epitopes. The first of these proteins to be characterized is a unique surface-exposed lipoprotein.

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To further develop genetic techniques for the enteropathogen Brachyspira hyodysenteriae, the gyrB gene of this spirochete was isolated from a lambdaZAPII library of strain B204 genomic DNA and sequenced. The putative protein encoded by this gene exhibited up to 55% amino acid sequence identity with GyrB proteins of various bacterial species, including other spirochetes. B. hyodysenteriae coumermycin A(1)-resistant (Cn(r)) mutant strains, both spontaneous and UV induced, were isolated by plating B204 cells onto Trypticase soy blood agar plates containing 0.5 microg of coumermycin A(1)/ml. The coumermycin A(1) MICs were 25 to 100 microg/ml for the resistant strains and 0.1 to 0.25 microg/ml for strain B204. Four Cn(r) strains had single nucleotide changes in their gyrB genes, corresponding to GyrB amino acid changes of Gly(78) to Ser (two strains), Gly(78) to Cys, and Thr(166) to Ala. When Cn(r) strain 435A (Gly(78) to Ser) and Cm(r) Km(r) strain SH (DeltaflaA1::cat Deltanox::kan) were cultured together in brain heart infusion broth containing 10% (vol/vol) heat-treated (56 degrees C, 30 min) calf serum, cells resistant to chloramphenicol, coumermycin A(1), and kanamycin could be isolated from the cocultures after overnight incubation, but such cells could not be isolated from monocultures of either strain. Seven Cn(r) Km(r) Cm(r) strains were tested and were determined to have resistance genotypes of both strain 435A and strain SH. Cn(r) Km(r) Cm(r) cells could not be isolated when antiserum to the bacteriophage-like agent VSH-1 was added to cocultures, and the numbers of resistant cells increased fivefold when mitomycin C, an inducer of VSH-1 production, was added. These results indicate that coumermycin resistance associated with a gyrB mutation is a useful selection marker for monitoring gene exchange between B. hyodysenteriae cells. Gene transfer readily occurs between B. hyodysenteriae cells in broth culture, a finding with practical importance. VSH-1 is the likely mechanism for gene transfer.

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Spirochete periplasmic flagella (PFs), including those from Brachyspira (Serpulina), Spirochaeta, Treponema, and Leptospira spp., have a unique structure. In most spirochete species, the periplasmic flagellar filaments consist of a core of at least three proteins (FlaB1, FlaB2, and FlaB3) and a sheath protein (FlaA). Each of these proteins is encoded by a separate gene. Using Brachyspira hyodysenteriae as a model system for analyzing PF function by allelic exchange mutagenesis, we analyzed purified PFs from previously constructed flaA::cat, flaA::kan, and flaB1::kan mutants and newly constructed flaB2::cat and flaB3::cat mutants. We investigated whether any of these mutants had a loss of motility and altered PF structure. As formerly found with flaA::cat, flaA::kan, and flaB1::kan mutants, flaB2::cat and flaB3::cat mutants were still motile, but all were less motile than the wild-type strain, using a swarm-plate assay. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis indicated that each mutation resulted in the specific loss of the cognate gene product in the assembled purified PFs. Consistent with these results, Northern blot analysis indicated that each flagellar filament gene was monocistronic. In contrast to previous results that analyzed PFs attached to disrupted cells, purified PFs from a flaA::cat mutant were significantly thinner (19.6 nm) than those of the wild-type strain and flaB1::kan, flaB2::cat, and flaB3::cat mutants (24 to 25 nm). These results provide supportive genetic evidence that FlaA forms a sheath around the FlaB core. Using high-magnification dark-field microscopy, we also found that flaA::cat and flaA::kan mutants produced PFs with a smaller helix pitch and helix diameter compared to the wild-type strain and flaB mutants. These results indicate that the interaction of FlaA with the FlaB core impacts periplasmic flagellar helical morphology.

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Brachyspira (Serpulina) hyodysenteriae, the etiologic agent of swine dysentery, uses the enzyme NADH oxidase to consume oxygen. To investigate possible roles for NADH oxidase in the growth and virulence of this anaerobic spirochete, mutant strains deficient in oxidase activity were isolated and characterized. The cloned NADH oxidase gene (nox; GenBank accession no. U19610) on plasmid pER218 was inactivated by replacing 321 bp of coding sequence with either a gene for chloramphenicol resistance (cat) or a gene for kanamycin resistance (kan). The resulting plasmids, respectively, pCmDeltaNOX and pKmDeltaNOX, were used to transform wild-type B. hyodysenteriae B204 cells and generate the antibiotic-resistant strains Nox-Cm and Nox-Km. PCR and Southern hybridization analyses indicated that the chromosomal wild-type nox genes in these strains had been replaced, through allelic exchange, by the inactivated nox gene containing cat or kan. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western immunoblot analysis revealed that both nox mutant cell lysates were missing the 48-kDa Nox protein. Soluble NADH oxidase activity levels in cell lysates of Nox-Cm and Nox-Km were reduced 92 to 96% compared to the activity level in parent strain B204. In an aerotolerance test, cells of both nox mutants were at least 100-fold more sensitive to oxygen exposure than were cells of the wild-type parent strain B204. In swine experimental infections, both nox mutants were less virulent than strain B204 in that fewer animals were colonized by the mutant cells and infected animals displayed mild, transient signs of disease, with no deaths. These results provide evidence that NADH oxidase serves to protect B. hyodysenteriae cells against oxygen toxicity and that the enzyme, in that role, contributes to the pathogenic ability of the spirochete.

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The NADH oxidase genes (nox) of 18 strains of intestinal spirochaetes were partially sequenced over 1246 bases. Strains examined included 17 representatives from six species of the genus Serpulina, and the type strain 513A(T) of the human intestinal spirochaete Brachyspira aalborgi. Sequences were aligned and used to investigate phylogenetic relationships between the organisms. Nox sequence identities between strains within the genus Serpulina were within the range 86.3-100%, whilst the nox gene of B. aalborgi shared between 78.8-83.0% sequence identity with the nox sequences of the various Serpulina strains. A phenogram produced based on sequence dissimilarities was in good agreement with the current classification of species in the genus Serpulina, although an atypical strongly beta-haemolytic porcine strain (P280/1), previously thought to be S. innocens, appeared distinct from other members of this species. Primer pairs were developed from the nox sequence alignments for use in polymerase chain reaction (PCR) identification of the pathogenic species S. hyodysenteriae (NOX1), S. intermedia (NOX2), and S. pilosicoli (NOX3), and for the combined non-pathogenic species S. innocens and S. murdochii (NOX4). The PCRs were optimised using 80 strains representing all currently described species in the genus Serpulina, as well as the type strain of B. aalborgi. Tests NOX1 and NOX4 specifically amplified DNA from all members of their respective target species, whilst tests NOX2 and NOX3 were less sensitive. NOX2 amplified DNA from all 10 strains of S. intermedia from pigs but from only 4 of 10 strains from chickens, whilst NOX3 amplified DNA from only 18 of 21 S. pilosicoli strains, even at low stringency. Tests NOX1 and NOX4 should prove useful in veterinary diagnostic laboratories, whilst NOX2 and NOX3 require further refinement.

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Strain C1T is an anaerobic spirochaete that causes intestinal disease in chickens. Multilocus enzyme electrophoresis analysis and 16S rRNA sequence comparisons have indicated that this spirochaete is a Serpulina strain. In these investigations, various phenotypic and genomic properties useful for establishing a taxonomic identity for strain C1T were studied. As determined by electron microscopy, cells of the spirochaete measured 8-11 x 0.22-0.34 mum and had a typical spirochaete ultrastructure. Each cell had 22-30 flagella. C1T cells formed weakly beta-haemolytic colonies on trypticase soy agar plates containing 5% bovine blood. The spirochaete reached maximum population densities of 10(9) cells ml-1 with a 2-4 h population doubling time in brain heart infusion broth containing 10% calf serum (BHIS broth). C1T cultures in BHIS broth were positive in tests for hippurate hydrolysis and negative for indole production. Glucosamine, N-acetyglucosamine, glucose, fructose, maltose and mannose were growth substrates for the spirochaete in heart infusion broth containing 7% calf serum (HS broth). During growth in HS broth beneath an O2/N2 (1:99) atmosphere, cells of the spirochaete consumed O2 and glucose and produced H2, CO2, acetate, butyrate and ethanol. Strain C1T DNA had a G+C content of 24.6 mol%. Based on DNA-DNA hybridization analyses, the DNA of strain C1T exhibited 24-39% relative reassociation with DNA of Serpulina hyodysenteriae, Serpulina innocens, Serpulina pilosicoli, Serpulina murdochii and Serpulina intermedia. These results indicate that chicken spirochaete strain C1T has many phenotypic properties common to Serpulina species and, based on DNA hybridization analysis, represents a unique Serpulina species. For this new species the name Serpulina alvinipulli is proposed, for which the type strain is C1T (= ATCC 51933T).

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On the basis of DNA-DNA hybridization data, nine intestinal spirochete strains were grouped into five genospecies. Three of these genospecies were previously recognized Serpulina species, Serpulina hyodysenteriae (type strain, B78), Serpulina innocens (type strain, B256), and Serpulina pilosicoli (type strain, P43/6/78; previously "Anguillina coli"). The other two genospecies were found to be new Serpulina species, for which we propose the names Serpulina intermedia sp. nov. (with type strain PWS/A) and Serpulina murdochii sp. nov. (with type strain 56-150). S. intermedia and S. murdochii cells had a typical spirochete ultrastructure with 22 to 28 periplasmic flagella per cell. Various soluble sugars were growth substrates for S. intermedia and S. murdochii. During growth in basal heart infusion broth supplemented with fetal calf serum beneath an O2-N2 (1:99) atmosphere, cells of these new species consumed oxygen and glucose and produced H2, CO2, acetate, butyrate, and ethanol. The G + C content of the DNA of S. murdochii 56-150T was 27 mol%, and the G + C content of the DNA of S. intermedia PWS/AT was 25 mol%. In addition, a restriction fragment length polymorphism-PCR assay for the detection of intestinal spirochetes was developed. The assay was based on generation and restriction endonuclease analysis (with HinfI, TaqI, Sau3A, and MboII) of a 558-bp amplicon of ribosomal DNA (rDNA) encoding 16S rRNA. The PCR amplification was specific for Serpulina species and Brachyspira aalborgi. Four restriction digest patterns were found for the five Serpulina species. HinfI restriction differentiated S. murdochii and S. innocens from the other species. Sau3A and TaqI restrictions gave unique fragment patterns for S. murdochii and S. pilosicoli, respectively. S. hyodysenteriae and S. intermedia DNAs gave the same fragment pattern regardless of the enzyme tested. B. aalborgi was differentiated from the Serpulina species by MboII digestion of the 16S rDNA amplicon.

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The phenotypic and genetic characteristics of spirochetes isolated from the blood of one U.S. and six French patients with severe clinical disease or impaired immunity were examined. All spirochetes were anaerobic, weakly beta-hemolytic, positive for hippurate hydrolysis, and negative for beta-glucosidase activity. Cell lengths ranged from 4 to 8 microm, and each isolate had between 8 and 12 periplasmic flagella per cell. These features were consistent with the spirochetes' being Serpulina pilosicoli, the agent of intestinal spirochetosis. All isolates were positive in a PCR assay amplifying a portion of the S. pilosicoli 16S rRNA gene, and they all grouped with fecal isolates of S. pilosicoli in multilocus enzyme electrophoresis (MLEE). The blood isolates could be differentiated from each other by MLEE, although the U.S. and two French isolates were closely related. Apparently S. pilosicoli may translocate from the large intestine to establish spirochetemia. The clinical significance of this finding remains uncertain and requires further investigation.

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Serpulina hyodysenteriae B204 cells treated with mitomycin (20 microg of mitomycin/ml of culture broth) lysed and released bacteriophages. Bacteriophage particles, precipitated by using polyethylene glycol and purified by CsC1 density gradient ultracentrifugation, had a buoyant density of 1.375 g/cm3 and consisted of a head (45-nm diameter) and an ultrastructurally simple (noncontractile) tail (64 by 9 nm) composed of at least 13 proteins with molecular masses ranging between 13 and 101 kDa. The purified bacteriophage has been designated VSH-1 (VSH for virus of S. hyodysenteriae). VSH-1 was incapable of lytic growth on any of five intestinal spirochete strains, representing three Serpulina species. VSH-1 nucleic acid was determined to be approximately 7.5 kb in size and to be linear, double-stranded DNA based on differential staining with acridine orange, DNase I sensitivity, electrophoretic mobility, and contour length as measured by electron microscopy. Phage DNA digested by the restriction enzymes SspI, AseI, EcoRV, and AflII gave electrophoretic banding patterns nearly identical to those of digested chromosomal DNA from S. hyodysenteriae. Additionally, VSH-1 DNA fragments hybridized with probes complementary to S. hyodysenteriae chromosomal genes nox and flaA1. When purified bacteriophages induced from cultures of S. hyodysenteriae A203 (deltaflaA1 593-762::cat) were added to growing cells of strain A216 (deltanox 438-760::kan), transductants (Cmr Kmr) were obtained at a frequency of 1.5 x l0(-6) per phage particle (enumerated by electron microscopy). These findings indicate that induced VSH-1 virions package DNA of S. hyodysenteriae and are capable of transferring host genes between cells of that spirochete. To our knowledge, this is the first report of genetic transduction of a spirochete.

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Recently intestinal spirochetes were isolated from rheas in Ohio and Iowa with a necrotizing typhlocolitis. These intestinal spirochetes, strains R1 and NIV-1, were characterized and compared with other intestinal spirochetes, including strains of S. hyodysenteriae. Both rhea spirochetes were indole positive, strongly beta-hemolytic, grew under a 1% O2:99% N2 atmosphere, and were morphologically similar to spirochetes in the genus Serpulina. Analysis of rRNA gene restriction patterns (ribotypes), and immunoblots of whole cell proteins, indicated both spirochetes were similar to Serpulina hyodysenteriae strains from swine. Comparisons of nearly complete sequences (> 1458 bases) of the 16S rRNA gene of the two rhea spirochetes with S. hyodysenteriae strains confirmed that rhea spirochetes R1 and NIV-1 were strains of S. hyodysenteriae. These results indicate that S. hyodysenteriae has a broader host range than previously recognized.

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The phenotypic characteristics of three Serpulina pilosicoli strains isolated from humans with diarrhoea (WesB, Kar, Hrm7) and two porcine S. pilosicoli strains isolated from pigs with intestinal spirochaetosis (1648, 3295), were compared with the type strain of the species P43/6/78T (T = type strain) and other intestinal spirochaetes within the genus Serpulina. All S. pilosicoli strains had a characteristic ultrastructural appearance, displayed similar growth rates, hydrolysed hippurate, lacked beta-glucosidase activity, utilised D-ribose as a growth substrate, and had similar sensitivities to rifampicin and spiramycin. The only consistent phenotypic characteristic that differentiated human strains from porcine strains of S. pilosicoli was that the human strains all utilised the pentose sugar D-xylose. These distinguishing phenotypic traits appear useful for identifying S. pilosicoli.

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Multilocus enzyme electrophoresis (MEE) analysis and comparisons of nearly complete 16S rRNA gene sequences (1416 nucleotide positions) were used to evaluate phylogenetic relationships among Serpulina hyodysenteriae strain B78T, S. innocens strain B256T, Brachyspira aalborgi strain 513AT, and eight uncharacterised strains of swine, avian, and human intestinal spirochaetes. From MEE analysis, nine strains could be assigned to five groups containing other intestinal spirochaetes (genetic distances between groups = 0.6-0.9). Chicken spirochaete strain C1 and B. aalborgi 513AT represented unique electrophoretic types and formed their own MEE groups. Despite MEE differences, the 11 strains had highly similar (96.3-99.9%) 16S rRNA sequences. These findings point out limitations of both MEE analysis and 16S rRNA sequence comparisons when used as solitary techniques for classifying intestinal spirochaetes related to Brachyspira/Serpulina species.

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Phenotypic and genetic traits of porcine intestinal spirochete strain P43/6/78T (= ATCC 51139T) (T = type strain), which is pathogenic and weakly beta-hemolytic, were determined in order to confirm the taxonomic position of this organism and its relationships to previously described species of intestinal spirochetes. In BHIS broth, P43/6/78T cells had a doubling time of 1 to 2 h and grew to a maximum cell density of 2 x 10(9) cells per ml at 37 to 42 degrees C. They hydrolyzed hippurate, utilized D-glucose, D-fructose, sucrose, D-trehalose, D-galactose, D-mannose, maltose, N-acetyl-D-glucosamine, D-glucosamine, pyruvate, L-fucose, D-cellobiose, and D-ribose as growth substrates, and produced acetate, butyrate, ethanol, H2, and CO2 as metabolic products. They consumed substrate amounts of oxygen and had a G+C content (24.6 mol%) similar to that of Serpulina hyodysenteriae B78T (25.9 mol%). Phenotypic traits that could be used to distinguish strain P43/6/78T from S. hyodysenteriae and Serpulina innocens included its ultrastructural appearance (each strain P43/6/78T cell had 8 or 10 periplasmic flagella, with 4 or 5 flagella inserted at each end, and the cells were thinner and shorter and had more pointed ends than S. hyodysenteriae and S. innocens cells), its faster growth rate in liquid media, its hydrolysis of hippurate, its lack of beta-glucosidase activity, and its metabolism of D-ribose. DNA-DNA relative reassociation experiments in which the S1 nuclease method was used revealed that P43/6/78T was related to, but was genetically distinct from, both S. hyodysenteriae B78T (level of sequence homology, 25 to 32%) and S. innocens B256T (level of sequence homology, 24 to 25%). These and previous results indicate that intestinal spirochete strain P43/6/78T represents a distinct Serpulina species. Therefore, we propose that strain P43/6/78 should be designated as the type strain of a new species, Serpulina pilosicoli.

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A prophage was induced from cells of the pathogenic spirochaete Serpulina hyodysenteriae using mitomycin C. Five to seven hours after mitomycin C was added (8 micrograms/ml, final concentration) to S. hyodysenteriae B204 cultures in BHIS broth (OD620 = 0.9) cell lysis was detected as a decrease in culture optical density. Bacteriophage particles attached to whole cells and to cell debris were detected by electron microscopic analysis of negatively stained (2% PTA, pH 7.0) bacteria harvested by centrifugation from mitomycin C treated cultures. The phage particles consisted of a head (45 nm diameter) and a tail (64 nm x 9 nm). Bacteria from untreated cultures lacked phages detectable by electron microscopy. The appearance of bacteriophage particles in mitomycin C treated cultures correlated with the appearance of extrachromosomal DNA, 7-8 kb in size as estimated by agarose gel electrophoresis, in DNA preparations from treated S. hyodysenteriae cells. When cultures of other S. hyodysenteriae strains (B78, B169, A-1, B8044, B6933, Ack300/8, R-1) and S. innocens 4/71 in BHIS were treated with mitomycin C (8-15 micrograms/ml, final concentration), phages similar in morphology and size to the S. hyodysenteriae B204 were induced.

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Strains of Serpulina hyodysenteriae and Serpulina innocens produced a cell-associated sucrase activity when grown in a medium containing sucrose. S. hyodysenteriae B204 sucrase activity cleaved sucrose and, to a lesser extent, raffinose and had a pH optimum of 5.7 to 6.2. This is the first report of an inducible enzyme produced by either S. hyodysenteriae or S. innocens.

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A combined physical and genetic map of the Serpulina hyodysenteriae B78T genome was constructed by using pulsed-field gel electrophoresis and DNA blot hybridizations. The S. hyodysenteriae genome is a single circular chromosome about 3.2 Mb in size. The physical map of the chromosome was constructed with the restriction enzymes BssHII, EclXI, NotI, SalI, and SmaI. The physical map was used to constructed a linkage map for genes encoding rRNA, flagellum subunit proteins, DNA gyrase, NADH oxidase, and three distinct hemolysins. Several flaB2-related loci, encoding core flagellum subunit proteins, were detected and are dispersed around the chromosome. The rRNA gene organization in S. hyodysenteriae is unusual. S. hyodysenteriae has one gene each for 5S (rrf), 16S (rrs), and 23S (rrl) rRNAs. The rrf and rrl genes are closely linked (within 5 kb), while the rrs gene is about 860 kb from the other two rRNA genes. Using a probe for the S. hyodysenteriae gyrA gene, we identified a possible location for the chromosomal replication origin. The size and genetic organization of the S. hyodysenteriae chromosome are different from those of previously characterized spirochetes.

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The enteropathogenicity of Serpulina hyodysenteriae B78, the type strain of the species, was compared with S. hyodysenteriae B204, a known pathogenic strain, in 7 week-old pigs. Clinical signs of swine dysentery were observed in 11/18 pigs (61.1%) inoculated with S. hyodysenteriae strain B204. However, in pigs inoculated with S. hyodysenteriae B78, only 1/21 (4.8%) of the pigs became infected. The 21 pigs inoculated with strain B78 included four pigs which received 5-fold higher numbers of S. hyodysenteriae B78 cells than were normally used in test inoculations. None of the four pigs became infected. Restriction fragment length polymorphism (RFLP) analysis, using a randomly cloned piece of S. hyodysenteriae B204 genomic DNA as the probe (pSRM5), was found to be useful in distinguishing S. hyodysenteriae strains. RFLP analysis confirmed that the one S. hyodysenteriae B78-inoculated pig that exhibited clinical signs of swine dysentery was infected with S. hyodysenteriae B78, and not by contamination with S. hyodysenteriae B204. These results indicate that S. hyodysenteriae B78 is only weakly pathogenic and should not be used in experimental infections of swine or in studies of virulence determinants where use of a pathogenic strain of S. hyodysenteriae would be crucial.

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