In vitro susceptibility of Brachyspira hyodysenteriae strains isolated in pigs in northern Italy between 2005 and 2022

Pleuromutilins (tiamulin and valnemulin) are often used to treat swine dysentery due to recurrent resistance to macrolides and lincosamides. Recently, reduced susceptibility of B. hyodysenteriae to pleuromutilin has been reported. 536 strains of B. hyodysenteriae were isolated from symptomatic pigs weighing 30-150 kg in northern Italy between 2005 and 2022. B. hyodysenteriae was isolated by standard methods and confirmed by PCR. The minimum inhibitory concentration (MIC) to doxycycline, lincomycin, tiamulin, tylosin, tylvalosine and valnemulin was evaluated according to CLSI procedures and MIC data were reported as MIC 50 and MIC 90. The temporal trend of the MIC values was evaluated by dividing the data into two groups (2005-2013 and 2014-2022). Comparison of the distribution in frequency classes in the two periods was performed using Pearson's chi-squared test (p < 0.01). MIC 50 was close to the highest values tested for lincomycin and tylosin, while MIC 90 was close to the highest values tested for all antibiotics. 71.7% of the strains were susceptible to tylvalosin, while 75%-80.4% had reduced susceptibility to valnemulin and tiamulin, respectively. The difference in the distribution of MIC classes was statistically significant in the two periods for doxycycline, tiamulin, tylvalosin and valnemulin, and more MIC classes above the epidemiological cut-off were observed in 2014-2022 compared with 2005-2013. The evaluation of the trends during the period considered shows a decreasing rate of wild-type strains with MIC values below the epidemiological cut-off over time and confirms the presence of resistant strains in northern Italy.

Antimicrobial susceptibility of U.S. porcine Brachyspira isolates and genetic diversity of B. hyodysenteriae by multilocus sequence typing

Swine dysentery, caused by Brachyspira hyodysenteriae and the newly recognized Brachyspira hampsonii in grower-finisher pigs, is a substantial economic burden in many swine-rearing countries. Antimicrobial therapy is the only commercially available measure to control and prevent Brachyspira-related colitis. However, data on antimicrobial susceptibility trends and genetic diversity of Brachyspira species from North America is limited. We evaluated the antimicrobial susceptibility profiles of U.S. Brachyspira isolates recovered between 2013 and 2022 to tiamulin, tylvalosin, lincomycin, doxycycline, bacitracin, and tylosin. In addition, we performed multilocus sequence typing (MLST) on 64 B. hyodysenteriae isolates. Overall, no distinct alterations in the susceptibility patterns over time were observed among Brachyspira species. However, resistance to the commonly used antimicrobials was seen sporadically with a higher resistance frequency to tylosin compared to other tested drugs. B. hampsonii was more susceptible to the tested drugs than B. hyodysenteriae and B. pilosicoli. MLST revealed 16 different sequence types (STs) among the 64 B. hyodysenteriae isolates tested, of which 5 STs were previously known, whereas 11 were novel. Most isolates belonged to the known STs: ST93 (n = 32) and ST107 (n = 13). Our findings indicate an overall low prevalence of resistance to clinically important antimicrobials other than tylosin and bacitracin, and high genetic diversity among the clinical Brachyspira isolates from pigs in the United States during the past decade. Further molecular, epidemiologic, and surveillance studies are needed to better understand the infection dynamics of Brachyspira on swine farms and to help develop effective control measures.

Carriage of Brachyspira hyodysenteriae on common insect vectors

The interactions of likely insect and murine vectors of the causative agent of swine dysentery, Brachyspira hyodysenteriae, were investigated. Insects were collected and analysed from 3 pig farms positive for B hyodysenteriae. Within these farms, several Musca domestica and Orphyra adult fly, Blatta sp. cockroach digestive tracts and hover fly (Eristalis sp) pupal form contents were positive in a standard PCR assay for B hyodysenteriae, whereas all other insect samples on these and case control farms were negative. In challenge exposure studies, B hyodysenteriae DNA was detected in the digestive tract of cockroaches and M domestica flies from day 1 post-inoculation with cultured B hyodysenteriae, for up to 5 days or 10 days respectively, while control non-inoculated insects remained negative. Isolates consistent with B hyodysenteriae were only cultured from frass samples of these inoculated cockroach and flies on days 1-3 post-inoculation. Isolates consistent with B hyodysenteriae were detected by analysis of agar plates exposed to live B hyodysenteriae-inoculated adult flies wandering and feeding on these plates for 20 min per day. In generational challenge inoculation studies, B hyodysenteriae was detected in the adult emergent flies, and internal components of fly pupae on days 1-7 of the pupation period, after being inoculated with B hyodysenteriae as larvae. Five-week-old conventional mice (C3H) that consumed 2 meals of B hyodysenteriae-infected flies remained negative for B hyodysenteriae throughout the next 10 days. The results indicated that pathogenic Brachyspira sp have a limited ability to internally colonise likely insect vectors and do not readily transmit infection to mice. However, the insect vectors analysed were demonstrably capable of mechanical carriage and likely on-farm involvement in consequence.

Brachyspira hyodysenteriae isolate multilocus sequence type dashboard

This focus article has been prepared by Susanna Williamson, Emma Stubberfield and Anna Brzozowska of the APHA and Jill Thomson of SRUC - Veterinary Consulting Services, Edinburgh.

The tva(A) Gene from Brachyspira hyodysenteriae Confers Decreased Susceptibility to Pleuromutilins and Streptogramin A in Escherichia coli

The tva(A) gene suspected to confer resistance to pleuromutilins in Brachyspira hyodysenteriae was tested for functionality in Escherichia coli AG100A and Staphylococcus aureus RN4220. Expression of the cloned tva(A) gene conferred decreased susceptibility to pleuromutilin (P) and streptogramin A (SA) antibiotics in E. coli and had a minor effect in S. aureus The finding provides evidence of the direct association of tva(A) with the PSA resistance phenotype.

Phylogenetic diversity, antimicrobial susceptibility and virulence gene profiles of Brachyspira hyodysenteriae isolates from pigs in Germany

Swine dysentery (SD) is an economically important diarrheal disease in pigs caused by different strongly hemolytic Brachyspira (B.) species, such as B. hyodysenteriae, B. suanatina and B. hampsonii. Possible associations of epidemiologic data, such as multilocus sequence types (STs) to virulence gene profiles and antimicrobial susceptibility are rather scarce, particularly for B. hyodysenteriae isolates from Germany. In this study, B. hyodysenteriae (n = 116) isolated from diarrheic pigs between 1990 and 2016 in Germany were investigated for their STs, susceptibility to the major drugs used for treatment of SD (tiamulin and valnemulin) and genes that were previously linked with virulence and encode for hemolysins (tlyA, tlyB, tlyC, hlyA, BHWA1_RS02885, BHWA1_RS09085, BHWA1_RS04705, and BHWA1_RS02195), outer membrane proteins (OMPs) (bhlp16, bhlp17.6, bhlp29.7, bhmp39f, and bhmp39h) as well as iron acquisition factors (ftnA and bitC). Multilocus sequence typing (MLST) revealed that 79.4% of the isolates belonged to only three STs, namely ST52 (41.4%), ST8 (12.1%), and ST112 (25.9%) which have been observed in other European countries before. Another 24 isolates belonged to twelve new STs (ST113-118, ST120-123, ST131, and ST193). The temporal distribution of STs revealed the presence of new STs as well as the regular presence of ST52 over three decades (1990s-2000s). The proportion of strains that showed resistance to both tiamulin und valnemulin (39.1%) varied considerably among the most frequent STs ranging from 0% (0/14 isolates resistant) in ST8 isolates to 46.7% (14/30), 52.1% (25/48), and 85.7% (6/7) in isolates belonging to ST112, ST52, and ST114, respectively. All hemolysin genes as well as the iron-related gene ftnA and the OMP gene bhlp29.7 were regularly present in the isolates, while the OMP genes bhlp17.6 and bhmp39h could not be detected. Sequence analysis of hemolysin genes of selected isolates revealed co-evolution of tlyB, BHWA1_RS02885, BHWA1_RS09085, and BHWA1_RS02195 with the core genome and suggested independent evolution of tlyA, tlyC, and hlyA. Our data indicate that in Germany, swine dysentery might be caused by a limited number of B. hyodysenteriae clonal groups. Major STs (ST8, ST52, and ST112) are shared with other countries in Europe suggesting a possible role of the European intra-Community trade of pigs in the dissemination of certain clones. The identification of several novel STs, some of which are single or double locus variants of ST52, may on the other hand hint towards an ongoing diversification of the pathogen in the studied area. The linkage of pleuromutilin susceptibility and sequence type of an isolate might reflect a clonal expansion of the underlying resistance mechanism, namely mutations in the ribosomal RNA genes. A linkage between single virulence-associated genes (VAGs) or even VAG patterns and the phylogenetic background of the isolates could not be established, since almost all VAGs were regularly present in the isolates.

Comparison of Brachyspira hyodysenteriae Isolates Recovered from Pigs in Apparently Healthy Multiplier Herds with Isolates from Herds with Swine Dysentery

Swine dysentery (SD) is a mucohaemorrhagic colitis of grower/finisher pigs classically resulting from infection by the anaerobic intestinal spirochaete Brachyspira hyodysenteriae. This study aimed to determine whether B. hyodysenteriae isolates from pigs in three healthy German multiplier herds supplying gilts to other farms differed from isolates from nine German production herds with SD. Isolates were subjected to whole genomic sequencing, and in silico multilocus sequence typing showed that those from the three multiplier herds were of previously undescribed sequence types (ST132, ST133 and ST134), with all isolates from the same herd having the same ST. All isolates were examined for the presence of 332 genes encoding predicted virulence or virulence lifestyle associated factors, and these were well conserved. Isolates from one multiplier herd were atypical in being weakly haemolytic: they had 10 amino acid substitutions in the haemolysin III protein and five in the haemolysin activation protein compared to reference strain WA1, and had a disruption in the promoter site of the hlyA gene. These changes likely contribute to the weakly haemolytic phenotype and putative lack of virulence. These same isolates also had nine base pair insertions in the iron metabolism genes bitB and bitC and lacked five of six plasmid genes that previously have been associated with colonisation. Other overall differences between isolates from the different herds were in genes from three of five outer membrane proteins, which were not found in all the isolates, and in members of a block of six plasmid genes. Isolates from three herds with SD had all six plasmid genes, while isolates lacking some of these genes were found in the three healthy herds-but also in isolates from six herds with SD. Other differences in genes of unknown function or in gene expression may contribute to variation in virulence; alternatively, superior husbandry and better general health may have made pigs in the two multiplier herds colonised by "typical" strongly haemolytic isolates less susceptible to disease expression.

Analysis of Multiple Brachyspira hyodysenteriae Genomes Confirms That the Species Is Relatively Conserved but Has Potentially Important Strain Variation

The intestinal spirochete Brachyspira hyodysenteriae is an important pathogen in swine, causing mucohemorrhagic colitis in a disease known as swine dysentery. Based on the detection of significant linkage disequilibrium in multilocus sequence data, the species is considered to be clonal. An analysis of the genome sequence of Western Australian B. hyodysenteriae strain WA1 has been published, and in the current study 19 further strains from countries around the world were sequenced with Illumina technology. The genomes were assembled and aligned to over 97.5% of the reference WA1 genome at a percentage sequence identity better than 80%. Strain regions not aligned to the reference ranged between 0.2 and 2.5%. Clustering of the strain genes found on average 2,354 (88%) core genes, 255 (8.6%) ancillary genes and 77 (2.9%) unique genes per strain. Depending on the strain the proportion of genes with 100% sequence identity to WA1 ranged from 85% to 20%. The result is a global comparative genomic analysis of B. hyodysenteriae genomes revealing potential differential phenotypic markers for numerous strains. Despite the differences found, the genomes were less varied than those of the related pathogenic species Brachyspira pilosicoli, and the analysis supports the clonal nature of the species. From this study, a public genome resource has been created that will serve as a repository for further genetic and phenotypic studies of these important porcine bacteria. This is the first intra-species B. hyodysenteriae comparative genomic analysis.

Sequence types and pleuromutilin susceptibility of Brachyspira hyodysenteriae isolates from Italian pigs with swine dysentery: 2003-2012

Swine dysentery is a mucohaemorrhagic colitis of pigs caused by infection with Brachyspira hyodysenteriae. The disease can be controlled by treatment with antimicrobial agents, with the pleuromutilins tiamulin and valnemulin being widely used. In recent years, the occurrence of B. hyodysenteriae with reduced susceptibility to these drugs has been increasing. The aim of this study was to determine temporal changes in genetic groups and pleuromutilin susceptibility amongst B. hyodysenteriae isolates from Italy. Multilocus sequence typing (MLST) was performed on 108 isolates recovered from 87 farms in different regions of Italy from 2003 to 2012, and their minimum inhibitory concentrations (MICs) for tiamulin and valnemulin were determined. Logistic regression was performed to assess associations between susceptibility to the two antimicrobial agents and genetic group, year and region of isolation. The isolates were allocated to 23 sequence types (STs), with five clonal clusters (Ccs) and seven singletons. More than 50% of isolates were resistant to both pleuromutilins (MIC >2.0 µg/mL for tiamulin and >1.0 µg/mL for valnemulin). All 10 isolates in ST 83 were resistant; these were first isolated in 2011 and came from nine farms, suggesting recent widespread dissemination of a resistant strain. Significant associations were found between the proportion of pleuromutilin susceptible isolates and the genetic group and year of isolation. Although resistant isolates were found in all Ccs, isolates in Ccs 2 and 7 were over five times more likely to be susceptible than those in the other Ccs. A significant trend in the reduction of susceptibility over time also was observed.

Understanding the molecular epidemiology and global relationships of Brachyspira hyodysenteriae from swine herds in the United States: a multi-locus sequence typing approach

Outbreaks of mucohemorrhagic diarrhea in pigs caused by Brachyspira hyodysenteriae in the late 2000s indicated the re-emergence of Swine Dysentery (SD) in the U.S. Although the clinical disease was absent in the U.S. since the early 1990s, it continued to cause significant economic losses to other swine rearing countries worldwide. This study aims to fill the gap in knowledge pertaining to the re-emergence and epidemiology of B. hyodysenteriae in the U.S. and its global relationships using a multi-locus sequence typing (MLST) approach. Fifty-nine post re-emergent isolates originating from a variety of sources in the U.S. were characterized by MLST, analyzed for epidemiological relationships (within and between multiple sites of swine systems), and were compared with pre re-emergent isolates from the U.S. Information for an additional 272 global isolates from the MLST database was utilized for international comparisons. Thirteen nucleotide sequence types (STs) including a predominant genotype (ST93) were identified in the post re-emergent U.S. isolates; some of which showed genetic similarity to the pre re-emergent STs thereby suggesting its likely role in the re-emergence of SD. In the U.S., in general, no more than one ST was found on a site; multiple sites of a common system shared a ST; and STs found in the U.S. were distinct from those identified globally. Of the 110 STs characterized from ten countries, only two were found in more than one country. The U.S. and global populations, identified as clonal and heterogeneous based on STs, showed close relatedness based on amino acid types (AATs). One predicted founder type (AAT9) and multiple predicted subgroup founder types identified for both the U.S. and the global population indicate the potential microevolution of this pathogen. This study elucidates the strain diversity and microevolution of B. hyodysenteriae, and highlights the utility of MLST for epidemiological and surveillance studies.

Mutations in the 50S ribosomal subunit of Brachyspira hyodysenteriae associated with altered minimum inhibitory concentrations of pleuromutilins

Brachyspira hyodysenteriae, the causative agent of swine dysentery, is responsible for severe mucohaemorrhagic colitis with considerable financial loss to worldwide swine production. Antimicrobial resistance against macrolides and lincosamides is widespread and the mechanisms are well known. Currently, the most common treatment for swine dysentery is the use of pleuromutilins and resistance to these drugs also is increasingly being reported. Although resistance mechanisms against pleuromutilins are less clear than for other drugs, they seem to involve alterations of the peptidyl transferase centre (PTC), including ribosomal RNA and the ribosomal protein L3. The present study was conducted to examine molecular mechanisms of resistance on a representative set of B. hyodysenteriae field strains with different resistance patterns. In total, we identified 24 single nucleotide polymorphisms (SNPs) in the 23S rRNA gene and genes of the ribosomal proteins L3, L4, L2 and L22. The SNP in the ribosomal protein gene L3 at position 443 led to an amino acid substitution of asparagine (Asn) by serine (Ser) at position 148, significantly associated with MICs for pleuromutilins. Based on this SNP a correct assignment of 71% of the strains with respect to a threshold of >0.625 μg tiamulin/ml was reached. Unexpectedly low MICs in some of the Asn-strains were explained by a second SNP at position 2535 of the 23S rRNA. Our results clearly show the associations between MICs for pleuromutilins and mutations in their binding site. A complete list of SNPs that influence MICs of B. hyodysenteriae strains is needed to enable the interpretation of future molecular susceptibility testing.

Estimating diagnostic test accuracies for Brachyspira hyodysenteriae accounting for the complexities of population structure in food animals

For swine dysentery, which is caused by Brachyspira hyodysenteriae infection and is an economically important disease in intensive pig production systems worldwide, a perfect or error-free diagnostic test (“gold standard”) is not available. In the absence of a gold standard, Bayesian latent class modelling is a well-established methodology for robust diagnostic test evaluation. In contrast to risk factor studies in food animals, where adjustment for within group correlations is both usual and required for good statistical practice, diagnostic test evaluation studies rarely take such clustering aspects into account, which can result in misleading results. The aim of the present study was to estimate test accuracies of a PCR originally designed for use as a confirmatory test, displaying a high diagnostic specificity, and cultural examination for B. hyodysenteriae. This estimation was conducted based on results of 239 samples from 103 herds originating from routine diagnostic sampling. Using Bayesian latent class modelling comprising of a hierarchical beta-binomial approach (which allowed prevalence across individual herds to vary as herd level random effect), robust estimates for the sensitivities of PCR and culture, as well as for the specificity of PCR, were obtained. The estimated diagnostic sensitivity of PCR (95% CI) and culture were 73.2% (62.3; 82.9) and 88.6% (74.9; 99.3), respectively. The estimated specificity of the PCR was 96.2% (90.9; 99.8). For test evaluation studies, a Bayesian latent class approach is well suited for addressing the considerable complexities of population structure in food animals.

Dissemination of clonal groups of Brachyspira hyodysenteriae amongst pig farms in Spain, and their relationships to isolates from other countries

Background

Swine dysentery (SD) is a widespread diarrhoeal disease of pigs caused by infection of the large intestine with the anaerobic intestinal spirochaete Brachyspira hyodysenteriae. Understanding the dynamics of SD, and hence being able to develop more effective measures to counter its spread, depends on the ability to characterise B. hyodysenteriae variants and trace relationships of epidemic strains.

Methodology/Principal Findings

A collection of 51 Spanish and 1 Portuguese B. hyodysenteriae isolates was examined using a multilocus sequence typing (MLST) scheme based on the sequences of seven conserved genomic loci. The isolates were allocated to 10 sequence types (STs) in three major groups of descent. Isolates in four of the STs were widely distributed in farms around Spain. One farm was infected with isolates from more than one ST. Sequence data obtained from PubMLST for 111 other B. hyodysenteriae strains from other countries then were included in the analysis. Two of the predominant STs that were found in Spain also were present in other European countries. The 73 STs were arranged in eleven clonal complexes (Cc) containing between 2 and 26 isolates. A population snapshot based on amino acid types (AATs) placed 75% of the isolates from 32 of the 48 AATs into one major cluster. The founder type AAT9 included 22 isolates from 10 STs that were recovered in Spain, Australia, Sweden, Germany, Belgium, the UK, Canada, and the USA.

Conclusions/Significance

This MLST scheme provided sufficient resolution power to unambiguously characterise B. hyodysenteriae isolates, and can be recommended as a routine typing tool that rapidly enables comparisons of isolates. Using this method it was shown that some of the main genetic lineages of B. hyodysenteriae in Spain also occurred in other countries, providing further evidence for international transmission. Finally, analysis of AATs appeared useful for deducing putative ancestral relationships between strains.

Analysis of bacterial load and prevalence of mixed infections with Lawsonia intracellularis, Brachyspira hyodysenteriae and/or Brachyspira pilosicoli in German pigs with diarrhoea

Lawsonia (L.) intracellularis, Brachyspira (B.) hyodysenteriae and B. pilosicoli are important pathogens in domestic pig production world-wide, responsible for porcine intestinal adenomatosis, swine dysentery, and porcine intestinal spirochetosis, respectively. Conventional PCR is the major diagnostic tool in the detection of the three pathogens, but the sole detection of bacterial DNA might lead to misinterpretations of results with respect to their clinical relevance, especially with mixed infections. Thus, the present study targeted the detection and quantification of the three pathogens in samples from herds with a case history of diarrhoea. Herds and samples were selected by the practitioners on a voluntary basis. Results were based on 1176 individual samples from 95 herds from Southern Germany. The pathogens were detected simultaneously by multiplex real-time PCR. The overall prevalence for L. intracellularis, B. hyodysenteriae and B. pilosicoli was 12.6%, 8.4% and 3.2% in faecal samples and 48.4%, 24.2% and 31.6% in herds, respectively. Sixty one percent, 82.6%, and 73.4% of herds positive for L. intracellularis, B. hyodysenteriae, and B. pilosicoli, respectively, had mixed infections. Median log values of DNA equivalents/g of faeces for L. intracellularis, B. hyodysenteriae and B. pilosicoli were 3.3, 5.9 and 3.2, with maxima of 8.3, 8.0 and 6.3, respectively. Within herd prevalence of B. hyodysenteriae and B. pilosicoli as well as the load of B. hyodysenteriae were significantly associated with the severity of diarrhoea.

Genome sequence of the pathogenic intestinal spirochete brachyspira hyodysenteriae reveals adaptations to its lifestyle in the porcine large intestine

Brachyspira hyodysenteriae is an anaerobic intestinal spirochete that colonizes the large intestine of pigs and causes swine dysentery, a disease of significant economic importance. The genome sequence of B. hyodysenteriae strain WA1 was determined, making it the first representative of the genus Brachyspira to be sequenced, and the seventeenth spirochete genome to be reported. The genome consisted of a circular 3,000,694 base pair (bp) chromosome, and a 35,940 bp circular plasmid that has not previously been described. The spirochete had 2,122 protein-coding sequences. Of the predicted proteins, more had similarities to proteins of the enteric Escherichia coli and Clostridium species than they did to proteins of other spirochetes. Many of these genes were associated with transport and metabolism, and they may have been gradually acquired through horizontal gene transfer in the environment of the large intestine. A reconstruction of central metabolic pathways identified a complete set of coding sequences for glycolysis, gluconeogenesis, a non-oxidative pentose phosphate pathway, nucleotide metabolism, lipooligosaccharide biosynthesis, and a respiratory electron transport chain. A notable finding was the presence on the plasmid of the genes involved in rhamnose biosynthesis. Potential virulence genes included those for 15 proteases and six hemolysins. Other adaptations to an enteric lifestyle included the presence of large numbers of genes associated with chemotaxis and motility. B. hyodysenteriae has diverged from other spirochetes in the process of accommodating to its habitat in the porcine large intestine.

SmpB: A novel outer membrane protein present in some Brachyspira hyodysenteriae strains

A novel outer membrane protein-encoding gene was identified in Brachyspira hyodysenteriae. The predicted protein, SmpB, was encoded by a gene that contains regions of identity with that encoding the previously identified lipoprotein SmpA. However, the majority of the reading frame encoding SmpA and SmpB share no detectable similarity. Analysis of several strains revealed that B. hyodysenteriae harbours either smpA or the newly identified gene smpB, but not both. smpB encodes for a slightly larger protein than smpA, 17.6 and 16.8 kDa, respectively. The predicted proteins share an identical leader sequence and the first 10 amino acids of the mature protein, however, the remainder of the predicted protein sequence shows no similarity. It is hypothesised that smpA and smpB are present on the same area of the chromosome. The proteins are antigenically unique, as antisera raised against a strain of B. hyodysenteriae that expresses SmpA cannot detect SmpB and vice versa. Although the presence of an identical leader peptide suggests identical localisation of SmpA and SmpB, it is not known if the two predicted proteins share similar function.

Characterization of Brachyspira hyodysenteriae isolates from Korea

This study was done to characterize diversity in 10 Brachyspira hyodysenteriae isolates in Korea. The isolates were compared with 14 well-characterized non-Korean strains of various Brachyspira species. All Korean isolates showed strong beta haemolysis and had blunt cell ends with 7-14 periplasmic flagella. They produced indole, and did not ferment fructose. They were alpha-glucosidase positive and alpha-galatosidase negative using the APIZYM kit. Using polyclonal antisera raised in rabbits against recognized serotypes, all isolates showed a strong reaction to B. hyodysenteriae antisera E, A and B. Using multilocus enzyme electrophoresis (MLEE) with 15 enzymes and 5 buffer systems, the Korean and non-Korean isolates were divided into 22 electrophoretic types (ETs) and 5 divisions (A, B, C, D and E). Division A corresponded to B. hyodysenteriae, B to B. innocens, C to B. intermedia, D to B. murdochii and E to B. pilosicoli. The 10 Korean isolates of B. hyodysenteriae were relatively diverse, being divided into 9 ETs within MLEE division A. They were all distinct from the non-Korean strains.

Brachyspira hyodysenteriae and other strongly -haemolytic and indole-positive spirochaetes isolated from mallards (Anas platyrhynchos)

The aims of the current study were to collect intestinal spirochaetes (genus Brachyspira) from farmed and wild mallards (Anas platyrhynchos) and to identify and classify those isolates that phenotypically resembled Brachyspira hyodysenteriae, an enteric pathogen of pigs. The isolation rate of Brachyspira spp. was high from both farmed (93 %) and wild mallards (78 %). In wild mallards, it appeared that Brachyspira spp. were more likely to be found in migratory birds (multivariate analysis: RR = 1.8, 95 % CI 1.1-3.1) than in mallards sampled in a public park. Pure cultures of putative B. hyodysenteriae were obtained from 22 birds. All five isolates from farmed mallards and ten randomly selected isolates with this phenotype were used for further studies. All isolates from farmed mallards and two of the isolates from wild mallards were PCR-positive for the tlyA gene of B. hyodysenteriae. Two isolates from farmed mallards were selected for pulsed field gel electrophoresis (PFGE) and randomly amplified polymorphic DNA (RAPD) analysis. These isolates clustered with the type and reference strains of B. hyodysenteriae. 16S rDNA sequence analysis performed on 11 of the strains showed that they were all closely related to each other and to the B. hyodysenteriae-Brachyspira intermedia cluster. Three of the mallard isolates had 16S rDNA sequences that were identical to those of B. hyodysenteriae strains R1 and NIV-1 previously isolated from common rheas (Rhea americana). To conclude, the isolates from farmed mallards and two isolates from wild mallards were classified as B. hyodysenteriae based on the fact that they could not be differentiated by any of the applied methods from type, reference and field strains of B. hyodysenteriae. The remaining isolates could not be assigned irrefutably to any of the presently recognized Brachyspira species. These results point to a broader host spectrum of B. hyodysenteriae than is generally recognized, and to the presence in mallards of strongly beta-haemolytic and indole-producing spirochaetes that possess many, but not all, of the currently recognized characteristics of B. hyodysenteriae.

Immunomagnetic separation of the intestinal spirochaetes Brachyspira pilosicoli and Brachyspira hyodysenteriae from porcine faeces

Porcine intestinal spirochaetes are fastidious anaerobic organisms and, as a consequence, it has been necessary to develop various protocols to enhance their isolation from or detection in faeces. Immunomagnetic separation (IMS) is a method developed recently to improve separation of target cells from mixed cell suspensions. The purpose of the present study was to compare the relative sensitivity of IMS for isolation of Brachyspira pilosicoli and Brachyspira hyodysenteriae with current routine diagnostic methods (culture on selective media and PCR) for detection of these micro-organisms in pig faeces. Neither direct nor indirect IMS methods enhanced the sensitivity of detection of either organism when performed with the recommended washings during sample processing. Performance of the IMS procedure without washing gave sensitivity at levels similar to direct culture onto selective medium. Further development of IMS techniques is required to improve isolation rates of Brachyspira species from faecal samples.

Further characterization of porcine Brachyspira hyodysenteriae isolates with decreased susceptibility to tiamulin

Brachyspira hyodysenteriae is the causative agent of swine dysentery, a severe diarrhoeal disease in pigs. Few drugs are available to treat the disease, owing to both antimicrobial resistance and withdrawal of drugs authorized for use in pigs. Tiamulin is the drug of choice in many countries, but isolates with decreased susceptibility have recently been reported. The mechanism of tiamulin resistance in B. hyodysenteriae is not known and this facet is essential to understand the dissemination of the trait. To study the resistance epidemiology of B. hyodysenteriae, further characterization of a set of isolates from Germany (n = 16) and the UK (n = 6) with decreased susceptibility to tiamulin was performed. The relatedness between the isolates was studied by comparing PFGE patterns, and the in vitro susceptibility to five other antimicrobials (aivlosin, doxycycline, salinomycin, chloramphenicol and avilamycin) was also determined. For comparison of the antimicrobial-susceptibility pattern, Swedish (n = 20) and British (n = 4) tiamulin-susceptible isolates were tested. The German isolates represented several different PFGE patterns, indicating that tiamulin usage has been sufficient to select clones with decreased tiamulin susceptibility at different farms in Germany. The PFGE pattern for the six British isolates with decreased tiamulin susceptibility was identical to that of the German isolates, and they had a similar antimicrobial-susceptibility pattern, except for resistance to aivlosin, which was only found in a few German isolates. No other co-resistance with tiamulin was found.

Brachyspira hyodysenteriae contains eight linked gene copies related to an expressed 39-kDa surface protein

A tandemly linked set of four open reading frames (ORFs), identified as vspA-D (variable surface protein) had been identified from previous cloning and sequencing of clones from a genomic library constructed from Brachyspira hyodysenteriae strain B204. The predicted translation products of these closely related genes were homologous to (but not identical with) a characterized 39-kDa surface-exposed membrane protein from this animal pathogen. Additional screening of the genomic library has been performed to retrieve what are believed to be additional vsp genes including the one expected to encode this 39-kDa protein. Four new vsp genes have been identified and found to be associated in a second set of four tandemly linked alleles. This new gene cluster of 7481 nucleotides is not adjacent to the original vspA-D gene cluster described but does appear to have arisen from a gene (region) duplication event. The new vsp genes (identified as vspE-H) are oriented parallel to one another and appear to have a set of similar but distinct regulatory elements that may control separate expression of their ORFs. The four adjacent ORFs are of similar size (361-390 codons) and share from 83% to 90% identity in their amino acid sequence. The organization and homologies of these highly conserved multiple gene copies are discussed.

The use of culture, pooled samples and PCR for identification of herds infected with Brachyspira hyodysenteriae

The sensitivity of culturing Brachyspira hyodysenteriae was determined after sampling with swabs from porcine fecal specimens inoculated with tenfold dilutions of a field strain of these microbes. After storage of swabs, Brachyspira hyodysenteriae was recovered throughout the first 3 weeks after inoculation from feces with more than 140 cells/g. Viable spirochetes could still be recovered after up to 83 days of storage from feces, with 1.4 x 10(6) cells or more per gram. Culture for Brachyspira spp. was performed on 285 rectal swabs, which were pooled in batches of five. The number of pooled samples positive for B. hyodysenteriae corresponded with the sum results of individual analysis of the corresponding collections of five samples. A PCR system based on the tlyA gene of B. hyodysenteriae was developed and tested on primary cultures of pooled samples. The results of the PCR assay showed a 97% correlation with the culture results. The prevalence of Brachyspira spp. was determined in five swine herds and found to be highest among breeding gilts and boars aged 13-16 weeks and among 6-12-week-old weaned pigs. In contrast, Brachyspira spp. were only rarely found in sows, which may reflect the development of immunity by adult pigs to all species of the genus.

Brachyspira (Serpulina) hyodysenteriae gyrB mutants and interstrain transfer of coumermycin A(1) resistance

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.

Cloning of a beta-hemolysin gene of Brachyspira (Serpulina) hyodysenteriae and its expression in Escherichia coli

Brachyspira (Serpulina) hyodysenteriae induces a mucohemorrhagic diarrheal disease in pigs. The production of a beta-hemolysin has been considered a major virulence attribute of this organism. Previous reports have failed to correlate a specific cloned gene sequence with a purified beta-hemolytic protein sequence. Thus, questions still remain concerning the structural gene sequence of the hemolysin. To answer this question unequivocally, the beta-hemolytic toxin was purified from extracts of log-phase spirochetes, and the N-terminal amino acid sequence was determined (K-D-V-V-A-N-Q-L-N-I-S-D-K) and compared with the translated sequences of previously cloned genes, tlyA to tlyC. The lack of homology between tlyA to tlyC translated sequences and the purified beta-hemolytic toxin sequence resulted in the study that is reported here. A degenerate probe was designed based on the N-terminal amino acid sequence of the purified beta-hemolysin and used to screen a B. hyodysenteriae genomic library. Three overlapping clones were identified, and one was sequenced to reveal an open reading frame coding for a putative 8.93-kDa polypeptide containing the N-terminal sequence of the purified beta-hemolysin. To distinguish this gene from the tlyA to tlyC genes, it has been designated hlyA. A hemolysis-negative Escherichia coli strains containing hlyA was beta-hemolytic on blood agar media. Also, the hemolytic activity of the recombinant protein had identical protease and lipase sensitivities and electrophoretic mobility to those of native B. hyodysenteriae beta-hemolysin. Based on sequence analysis, the translated protein had a pI of 4.3, an alpha-helical structure, and a phosphopantetheine binding motif. Hybridization analysis of genomic DNA indicated that the hlyA gene was present in B. hyodysenteriae and B. intermedia but was not detected in B. innocens, B. pilosicoli, or B. murdochii under high-stringency conditions. The location of hlyA on the chromosomal map was distinct from the locations of tlyA, tlyB, and tlyC.

The spirochete FlaA periplasmic flagellar sheath protein impacts flagellar helicity

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.

Identification of the gene encoding BmpB, a 30 kDa outer envelope lipoprotein of Brachyspira (Serpulina) hyodysenteriae, and immunogenicity of recombinant BmpB in mice and pigs

A gene encoding a 30kDa outer envelope protein of the intestinal spirochaete Brachyspira (Serpulina) hyodysenteriae, was cloned and expressed in Escherichia coli strain XLOLR. Five phagemids containing DNA inserts encoding the protein were established and one clone (pSHA) was sequenced. An 816bp hypothetical open reading frame (ORF) was identified, with a potential ribosome binding site (AGGAG), and putative -10 (TATAAT) and -35 (TTGAAA) promoter regions upstream from the ATG start of the ORF. A 12bp inverted repeat sequence, possibly serving as a transcription terminator, was identified downstream from the TAA stop codon. Analysis of the amino acid sequence identified a 19 residue hydrophobic signal peptide, incorporating a potential signal peptidase cleavage site and membrane lipoprotein lipid attachment site. Further analysis of the amino acid usage of this lipoprotein, designated BmpB, showed its possible outer membrane localisation. Comparison of the gene encoding the lipoprotein, bmpB, with GenBank nucleotide sequences showed that it has homology with the gene (plp3) encoding Plp3, an outer membrane lipoprotein of Pasteurella haemolytica (54% identity in 735bp). Comparison of the deduced amino acid sequence with the SWISS-PROT amino acid database revealed greatest homology with the outer membrane lipoproteins (Plp1, 2, 3) of P. haemolytica (34% identity in 242 aa, 37% identity in 250 aa, and 39% identity in 272 aa, respectively), and lipoproteins (rcsF and lipoprotein-28) of E. coli (40% identity in 267 aa and 36% identity in 263 aa, respectively). Three of the recombinant E. coli clones (pSHA, pSHD, and pSHE) were formalinised and used to immunise mice. A bacterin preparation of one recombinant E. coli clone (pSHA) was used to immunise pigs. Sera from these mice and pigs recognised the 30kDa lipoprotein in outer membrane preparations of B. hyodysenteriae, indicating the immunogenicity of recombinant BmpB. Sera from pigs naturally infected with B. hyodysenteriae also reacted with recombinant BmpB expressed in E. coli.

Prevalence of Brachyspira species isolated from diarrhoeic pigs in Brazil

Pathogenic intestinal spirochaetes of pigs include Brachyspira (formerly Serpulina) hyodysenteriae, the cause of swine dysentery, and Brachyspira pilosicoli, the cause of porcine colonic spirochetosis (PCS). The purpose of this study was to assess the relative importance of Brachyspira species in diarrhoeal disease of growing pigs on farms in southern Brazil. The intensity and pattern of haemolysis, the production of indole and the hydrolysis of hippurate by reference and field porcine intestinal spirochaetes were compared with 16S-ribosomal RNA (mRNA)- and 23S-rRNA-based polymerase chain reaction assays for the identification of B hyodysenteriae and B pilosicoli. Between July and October 1998, 206 rectal swabs were taken from pigs on 17 farms with a history of diarrhoea developing within 30 days after they had been moved from nursery to growing facilities. Of 49 beta-haemolytic spirochaetes that were cultured, 29 (59.2 per cent) were grown in pure culture for phenotypic and genotypic characterisation, leaving 20 untyped. Of the 29 typed isolates, eight isolates obtained from six farms were identified as B hyodysenteriae, and 15 isolates obtained from seven other farms were identified as B pilosicoli; the remaining six isolates were identified as weakly beta-haemolytic commensal spirochaetes. There was complete agreement between the results of the phenotypic and genotypic analyses.

Detection of same sized 4.3 Kb extrachromosomal DNA elements in weakly beta-haemolytic human intestinal spirochaetes and Serpulina pilosicoli of swine origin

Agarose gel electrophoresis of total DNA from Italian strains of weakly beta-haemolytic human intestinal spirochaetes (w beta HIS) and porcine Serpulina pilosicoli reference strain P43/6/78 showed an extrachromosomal band having the same size and migrating at 4.3 Kb. The same results were observed after agarose gel electrophoresis of DNA obtained from the supernatant fluids of the spirochaetal cultures analysed. Swine Serpulina hyodysenteriae reference strain P18A was comparatively analysed and a 6.5 Kb extrachromosomal DNA element was found, as expected. Furthermore, S. hyodysenteriae reference strain P18A differed from all the other spirochaetes tested and had a higher number of flagella (8-12) at each cell end and was strongly beta-haemolytic. To the best of our knowledge, this is the first report on the detection of a band of extrachromosomal DNA having the same size in w beta HIS and S. pilosicoli from swine origin.

Isolation, oxygen sensitivity, and virulence of NADH oxidase mutants of the anaerobic spirochete Brachyspira (Serpulina) hyodysenteriae, etiologic agent of swine dysentery

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.

Characterization of a periplasmic ATP-binding cassette iron import system of Brachyspira (Serpulina) hyodysenteriae

The nucleotide sequence of the pathogenic spirochete Brachyspira hyodysenteriae bit (for "Brachyspira iron transport") genomic region has been determined. The bit region is likely to encode an iron ATP-binding cassette transport system with some homology to those encountered in gram-negative bacteria. Six open reading frames oriented in the same direction and physically linked have been identified. This system possesses a protein containing ATP-binding motifs (BitD), two hydrophobic cytoplasmic membrane permeases (BitE and BitF), and at least three lipoproteins (BitA, BitB, and BitC) with homology to iron periplasmic binding proteins. These periplasmic binding proteins exhibit lipoprotein features. They are labeled by [(3)H]palmitate when tested in recombinant Escherichia coli, and their signal peptides are typical for substrates of the type II secretory peptidase. The FURTA system and Congo red assay indicate that BitB and BitC are involved in iron binding. The Bit system is detected only in B. hyodysenteriae and is absent from B. innocens and B. pilosicoli.

Sequence characterization of two new members of a multi-gene family in Serpulina hyodysenteriae (B204) with homology to a 39 kDa surface exposed protein: vspC and D

Previous cloning and sequencing of clones from a genomic library constructed from Serpulina hyodysenteriae B204 had identified a tandem pair of open reading frames, identified as vspA and vspB (variable surface protein) expected to encode proteins with homology to ( but not identical with) a 39 kDa surface exposed membrane protein from this animal pathogen. Additional screening of the genomic library was performed to retrieve the remainder of the vspB gene using new oligonucleotide probes based upon the cloned gene sequences. Not only was this goal met but we also discovered two more adjacent and related vsp genes (vspC and vspD) and have completely sequenced them. They are all in a parallel orientation and appear to have a set of similar but distinct regulatory elements that may control separate expression of their open reading frames (ORFs). Thus, there are four contiguous vsp genes which are predicted to encode a family of structurally conserved proteins. The four adjacent open reading frames (ORFs) are of similar size (384-389 codons) and share from 83% to 90% identity in their amino acid sequence. Preliminary data suggests there may be yet another homologous gene copy in a distal location of S. hyodysenteriae that faithfully encodes the 39 kDa surface protein. The organization and homologies of these highly conserved multiple gene copies are discussed.

Analysis of Serpulina hyodysenteriae strain variation and its molecular epidemiology using pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) was applied as a molecular typing tool for the spirochaete Serpulina hyodysenteriae, the agent of swine dysentery. Analysis of a collection of 40 mainly Australian isolates, previously characterized by other methods, divided these into 23 PFGE types. This confirmed that there are many strains of the spirochaete in Australia. PFGE was more discriminatory for strain typing than both multilocus enzyme electrophoresis and serotyping. It had similar discriminatory power to restriction endonuclease analysis, but the results of PFGE were easier to interpret. When applied to 29 isolates collected from 4 farms over periods of up to 8 years, 2 PFGE patterns were found on 3 farms, and a single pattern on the other. In each case a new strain had apparently emerged as a variant of an original parent strain. PFGE was found to be a powerful technique for investigating the molecular epidemiology of swine dysentery outbreaks.

Genetic basis of macrolide and lincosamide resistance in Brachyspira (Serpulina) hyodysenteriae

Macrolide antibiotic resistance is widespread among Brachyspira hyodysenteriae (formerly Serpulina hyodysenteriae) isolates. The genetic basis of macrolide and lincosamide resistance in B. hyodysenteriae was elucidated. Resistance to tylosin, erythromycin and clindamycin in B. hyodysenteriae was associated with an A-->T transversion mutation in the nucleotide position homologous with position 2058 of the Escherichia coli 23S rRNA gene. The nucleotide sequences of the peptidyl transferase region of the 23S rDNA from seven macrolide and lincosamide resistant and seven susceptible strains of Brachyspira spp. were determined. None of the susceptible strains were mutated whereas all the resistant strains had a mutation in position 2058. Susceptible strains became resistant in vitro after subculturing on agar containing 4 micrograms ml-1 of tylosin. Sequencing of these strains revealed an A-->G transition mutation in position 2058.

Detection of extrachromosomal DNA in Italian isolates of weakly beta-haemolytic human intestinal spirochaetes

Weakly beta-haemolytic human intestinal spirochaetes (w beta HIS) isolated in Italy showed an extrachromosomal band migrating at 4.3 kb after agarose gel electrophoresis of total DNA. The band was observed within 4 strains (HRM2, HRM4, HRM7 and HRM14) among the 7 w beta HIS analysed and was resistant to proteinase K and RNase treatment, whereas after purification it was completely digested by incubation with DNaseI. The origin, the structure and the significance of this extrachromosomal DNA are at present unknown. In addition to w beta HIS, the reference strain P18A of Serpulina hyodysenteriae was comparatively analysed and a 6.5 Kb extrachromosomal DNA element was found, as expected. This finding proves that the experimental conditions we used while searching for extrachromosomal DNA within w beta HIS were appropriate. To the best of our knowledge, this is the first report on the detection of extrachromosomal DNA from w beta HIS.

Characterization of a haemolysin from Mycobacterium tuberculosis with homology to a virulence factor of Serpulina hyodysenteriae

Scrutiny of sequence data from the Mycobacterium leprae genome sequencing project identified the presence of a gene encoding a 268-amino-acid polypeptide which is highly similar to a pore-forming haemolysin/cytotoxin virulence determinant, TlyA, from the swine pathogen Serpulina hyodysenteriae. Using degenerate oligonucleotide primers based on the TlyA sequences, the Mycobacterium tuberculosis homologue was amplified and this product was used to obtain the clone and sequence a 2.5 kb fragment containing the whole M. tuberculosis tlyA gene. tlyA encodes a 267-amino-acid protein with a predicted molecular mass of 28 kDa. TlyA homologues were identified by PCR in M. leprae, Mycobacterium avium and Mycobacterium bovis BCG, but appeared absent in Mycobacterium smegmatis, Mycobacterium vaccae, Mycobacterium kansasii, Mycobacterium chelonae and Mycobacterium phlei. The M. tuberculosis gene appeared to be the first gene in an operon containing at least two other genes. Introduction of the M. tuberculosis tlyA gene into M. smegmatis using a mycobacterial shuttle expression plasmid converted non-haemolytic cells into those exhibiting significant haemolytic activity. Similarly, inducible haemolytic activity was observed in sonicated bacteria when tlyA was expressed as a His6-tagged fusion protein in Escherichia coli. tlyA mRNA was detected in both M. tuberculosis and M. bovis BCG using RT-PCR, confirming that this gene is expressed in organisms cultured in vitro.

Identification of a linked set of genes in Serpulina hyodysenteriae (B204) predicted to encode closely related 39-kilodalton extracytoplasmic proteins

A tandem pair of nearly identical genes from Serpulina hyodysenteriae (B204) were cloned and sequenced. The full open reading frame of one gene and the partial open reading frame of the neighboring gene appear to encode secreted proteins which are homologous to, yet distinct from, the 39-kDa extracytoplasmic protein purified from the membrane fraction of S. hyodysenteriae. We have designated these newly identified genes vspA and vspB (for variable surface protein).

Evidence for Serpulina hyodysenteriae being recombinant, with an epidemic population structure

The population structure of Serpulina hyodysenteriae was investigated using multilocus enzyme electrophoresis. A total of 231 isolates were divided into 50 electrophoretic types (ETs), with a mean genetic diversity of 0.29 for the number of ETs and 0.23 for the number of isolates. Subsets of isolates from two Australian states (71 isolates from Victoria and 68 isolates from Queensland) exhibited as much genetic variation as the entire collection. The calculated index of association (IA) for the number of ETs (0.29 +/- 0.17) was not significantly different from zero, and hence provided evidence for the occurrence of significant genetic recombination accounting for the observed variation between strains. In contrast, the IA for the number of isolates (3.93 +/- 0.03) was significantly different from zero, with seven of the 50 ETs (ETs 4, 6, 13, 14, 20, 33 and 35) containing 51% of all the isolates. Even when multiple isolates from the same farm were removed from the analysis, the IA value for the number of isolates remained significantly greater than zero (IA 9.87 +/- 0.04), indicating that it was not biased by their inclusion. The results suggest that S. hyodysenteriae has an epidemic population structure.

Specific detection of Serpulina hyodysenteriae and potentially pathogenic weakly beta-haemolytic porcine intestinal spirochetes by polymerase chain reaction targeting 23S rDNA

A 2470-bp section of the 23S ribosomal DNA from Serpulina hyodysenteriae and five biochemically different groups of weakly beta-haemolytic porcine intestinal Serpulina strains was sequenced. The similarity between the sequenced strains was high (96.85% to 99.84%). A phylogenetic tree was estimated by the maximum likelihood method. The sequenced strains formed three groups. Serpulina hyodysenteriae and biochemical group II ('S. intermedius') formed a cluster, but 20 nucleotide positions were different between the two, suggesting that biochemical group II is a separate species. Another cluster consisted of the closely related biochemical group IIIa ('S. murdochii') and IIIb/c (S. innocens) (99.84% similarity), while biochemical group IV (S. pilosicoli) constituted a separate group with a relatively low similarity (96.85% to 97.01%) to the other groups. Three primer pairs were designed for specific PCR detection of the clinically important S. hyodysenteriae and biochemical group II and IV. PCR amplification was accomplished with DNA extracted from bacterial colonies by a simple boiling procedure, and with DNA extracted directly from porcine stool samples using a bead beating extraction procedure. The level of detection for the direct extraction and amplification method was 5 x 10(5) cells added g-1 normal faeces.

Sub-specific differentiation of intestinal spirochaete isolates by macrorestriction fragment profiling

Macrorestriction fragment profile analysis by PFGE was used to distinguish intestinal spirochaetes, some of which were isolated from cases of swine dysentery and intestinal spirochaetosis in humans, pigs, mice, chickens and dogs. Macrorestriction fragment profiles using SmaI and SacII restriction enzymes were produced and used in statistical analysis. This permitted the division of the isolates into two major clusters. One cluster contained isolates which were identified as Serpulina pilosicoli and the second cluster contained isolates identified as Serpulina hyodysenteriae by immunoblotting with species-specific mAbs. Both species contained sub-specific groups, although these rarely correlated with the source of the isolates. We conclude that PFGE is capable of sub-specific differentiation of intestinal spirochaetes, but that the current species contain a large variety of genotypes among which cross-species transmission may be feasible.

Characterization of flaA- and flaB- mutants of Serpulina hyodysenteriae: both flagellin subunits, FlaA and FlaB, are necessary for full motility and intestinal colonization

Motility of Serpulina hyodysenterlae is thought to play a pivotal role in the enteropathogenicity of this spirochete. To test this, a series of isogenic mutants containing specifically disrupted flagellar alleles (flaA1 and flaB1) were constructed and examined for virulence and ability to colonize the intestinal tract of mice. Mice challenged with the wild-type, parent strain showed a dose-related response to the challenge organism. In contrast, all flagellar mutant strains demonstrated aberrant motility in vitro and a significantly reduced ability to colonize and infect mice. To some extent, this degree of reduction in colonizing ability was dependent on the wild-type background strain used for mutant construction. A flaB1- strain generated from a 'laboratory isolate' was unable to colonize the mouse gut even at high challenge doses, although its parent was virulent for mice. However, when the same parent strain was 'animal-passed' prior to disruption of flaB1, the resulting flaB1- strain was able to transiently colonize the mouse gut and induce intestinal lesions. A comparison of a series of flagellar mutants constructed using the animal-passed parent strain further revealed that specific inactivation of flaB1 resulted in a more pronounced reduction in virulence and colonizing ability than that which occurred with two flaA1 mutants. Taken together, these data suggest that motility is an essential virulence factor of S. hyodysenteriae and that both sheath and core flagellin subunits, FlaA and FlaB, are necessary for full motility and intestinal colonization.

Identification of the swine pathogen Serpulina hyodysenteriae in rheas (Rhea americana)

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.

The phylogeny of intestinal porcine spirochetes (Serpulina species) based on sequence analysis of the 16S rRNA gene

Four type or reference strains and twenty-two field strains of intestinal spirochetes isolated from Swedish pig herds were subjected to phylogenetic analysis based on 16S rRNA sequences. Almost complete (>95%) 16S rRNA sequences were obtained by solid-phase DNA sequencing of in vitro-amplified rRNA genes. The genotypic patterns were compared with a previously proposed biochemical classification scheme, comprising beta-hemolysis, indole production, hippurate hydrolysis, and alpha-galactosidase, alpha-glucosidase, and beta-glucosidase activities. Comparison of the small-subunit rRNA sequences showed that the strains of the genus Serpulina were closely related. Phylogenetic trees were constructed, and three clusters were observed. This was also confirmed by signature nucleotide analysis of the serpulinas. The indole-producing strains, including the strains of S. hyodysenteriae and some weakly beta-hemolytic Serpulina strains, formed one cluster. A second cluster comprised weakly beta-hemolytic strains that showed beta-galactosidase activity but lacked indole production and hippurate-hydrolyzing capacity. The second cluster contained two subclusters with similar phenotypic profiles. A third cluster involved strains that possessed a hippurate-hydrolyzing capacity which was distinct from that of the former two clusters, because of 17 unique nucleotide positions of the 16S rRNA gene. Interestingly, the strains of this third cluster were found likely to have a 16S rRNA structure in the V2 region of the molecule different from that of the serpulinas belonging to the other clusters. As a consequence of these findings, we propose that the intestinal spirochetes of this phenotype (i.e., P43/6/78-like strains) should be regarded as a separate Serpulina species. Furthermore, this cluster was found to be by far the most homogeneous one. In conclusion, the biochemical classification of porcine intestinal spirochetes was comparable to that by phylogenetic analysis based on 16S rRNA sequences..

Differentiation of intestinal spirochaetes by multilocus enzyme electrophoresis analysis and 16S rRNA sequence comparisons

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.

Characterization of Serpulina hyodysenteriae isolates of serotypes 8 and 9 by random amplification of polymorphic DNA analysis

A PCR-based DNA fingerprinting method termed RAPD (Random Amplification of Polymorphic DNA), or AP-PCR (for Arbitrary Primed PCR) was used to detect sequence diversity among reference strains and isolates of Serpulina hyodysenteriae. RAPD fingerprinting of 20 S. hyodysenteriae isolates of serotypes 8 or 9 from Quebec was generated with 2 different 10-base primers used independently. Reference strains and field isolates belonging to serotypes 8 or 9 revealed polymorphisms in RAPD fingerprints with both primers. Interspecies polymorphisms were observed by RAPD analysis of S. hyodysenteriae representing serotypes 1 to 9, S.innocens, and 5 other weakly beta-hemolytic intestinal spirochetes. A dendrogram based on the analysis of RAPD profiles of the strains tested with one of the primers (#17), permitted the clustering of these strains into 11 divisions. The predominance of particular RAPD profiles among S. hyodysenteriae isolates isolated from cases of swine dysentery in different herds suggested that certain S. hyodysenteriae types could be epidemiologically important. Our results indicate that RAPD could be used as a typing method for S. hyodysenteriae and as an epidemiological method for identifying spirochetes isolated from swine.

Inactivation of Serpulina hyodysenteriae flaA1 and flaB1 periplasmic flagellar genes by electroporation-mediated allelic exchange

Serpulina hyodysenteriae, the etiologic agent of swine dysentery, contains complex periplasmic flagella which are composed of multiple class A and class B polypeptides. To examine the role these proteins play in flagellar synthesis, structure, and function and to develop strains which may provide insight into the importance of motility in the etiology of this pathogen, we constructed specific periplasmic flagellar mutations in S. hyodysenteriae B204. The cloned flaA1 and flaB1 genes were disrupted by replacement of internal fragments with chloramphenicol and/or kanamycin gene cassettes. Following delivery of these suicide plasmids into S. hyodysenteriae, homologous recombination and allelic exchange at the targeted chromosomal flaA1 and flaB1 genes was verified by PCR, sequence, and Southern analysis. The utility of a chloramphenicol resistance gene cassette for targeted gene disruption was demonstrated and found more amenable than kanamycin as a selective marker in S. hyodysenteriae. Immunoblots of cell lysates of the flagellar mutants with antiserum raised against purified FlaA or FlaB confirmed the absence of the corresponding sheath or core protein. Both mutations selectively abolished expression of the targeted gene without affecting synthesis of the other flagellar polypeptide. flaA1 and flaB1 mutant strains exhibited altered motility in vitro and were less efficient in movement through a liquid medium. Paradoxically, isogenic strains containing specifically disrupted flaA1 or flaB1 alleles were capable of assembling periplasmic flagella that were morphologically normal as evidenced by electron microscopy. This is the first report of specific inactivation of a motility-associated gene in spirochetes.

Distribution of the smpA gene from Serpulina hyodysenteriae among intestinal spirochaetes

Forty intestinal spirochaete strains were investigated for nucleotide sequences related to the smpA locus from Serpulina hyodysenteriae by Southern hybridization of chromosomal DNA using the smpA locus from S. hyodysenteriae strain P18A as a probe and by PCR using primers internal to the smpA gene. The intensity of the hybridization signal at high stringency and positive PCR results suggested that 12 S. hyodysenteriae strains possessed a similar nucleotide sequence. PCR was negative for another 12 S. hyodysenteriae strains and the hybridization signal obtained from 11 of these was weak and one was negative. All S. hyodysenteriae strains hybridized under low stringency conditions. These results indicated that there is variation among the smpA loci of S. hyodysenteriae strains. Among seven strains of S. innocens, and the proposed species 'S. intermedius' and 'S. murdochii', hybridization was weak and no PCR products were obtained, suggesting that these species have sequences related to, but divergent from, the smpA sequences of strains of S. hyodysenteriae. Both gene probe hybridization and PCR analysis of nine strains of the proposed new genus 'Anguillina', including isolates from pigs and humans, gave negative results.

DNA probe and polymerase chain reaction procedure for the specific detection of Serpulina hyodysenteriae

Serpulina (Treponema) hyodysenteriae, a Gram-negative anaerobic spirochete, is the causative agent of swine dysentery, a mucohaemorrhagic diarrheal disease in which lesions are confined to the large intestine of pigs. A DNA probe and polymerase chain reaction (PCR) amplification procedures which are specific, rapid , and sensitive for the detection of S.hyodysenteriae have been developed. Clone pF12 from a plasmid library of S.hyodysenteriae B204 genomic DNA was identified as a clone specific for S.hyodysenteriae but not for S.innocens by differential hybridization screening with S.hyodysenteriae and S.innocens genomic DNA probes. A DNA probe consisting of a 1.3 kb restriction fragment from pF12 was found to be highly specific for S. hyodysenteriae and detected 10(5) bacterial cells. A PCR procedure using primers derived from this fragment yielded a single product which was specifically generated for S.hyodysenteriae template DNA and not for other control cells DNA. PCR provided increased sensitivity with the direct detection of as few as 10 S.hyrodysenteriae cells. The PCR procedure could detect S.hyodysenteriae cells in seeded faecal matter. Moreover the PCR assay was able to detect most S. hyodysenteriae field isolates of serotypes 8 and 9. These tools have diagnostic application in veterinary microbiology.

Isolation of extracytoplasmic proteins from Serpulina hyodysenteriae B204 and molecular cloning of the flaB1 gene encoding a 38-kilodalton flagellar protein

Extracytoplasmic proteins were released from Serpulina (Treponema) hyodysenteriae (strain B204) by treatment of whole cells with a nonionic detergent (Tween 20). Centrifugation of the Tween 20-released proteins at 100,000 x g sedimented 10 major extracytoplasmic proteins with approximate molecular masses of 44, 43.5, 42, 39, 38, 34, 33.5, 33, 31, and 29 kDa. Treatment of the sedimented fraction with 6 M urea solubilized all of the proteins except the 39-kDa protein. Peptide sequences were obtained for the purified 42-, 39-, 38-, 34-, 31-, and 29-kDa proteins. The peptide sequences of the 42-, 38-, and 31-kDa proteins indicate that they likely are components of the periplasmic flagella. The amino-terminal peptide sequence of the 38-kDa protein was used to design an oligonucleotide probe and to clone an S. hyodysenteriae DNA fragment containing the gene encoding this protein. The predicted 290-amino-acid protein sequence derived from the cloned gene was highly homologous to those of several other bacterial flagellar proteins and is preceded by consensus sigma D nucleotide sequences found upstream of other flagellar genes. On the basis of its similarity to the FlaB proteins of other spirochetes, we propose to designate the cloned S. hyodysenteriae gene flaB1 and its encoded protein FlaB1. Vaccination of pigs with FlaB1 or its recombinant counterpart did not protect them from an experimental challenge.

Characterization of Serpulina hyodysenteriae isolates of serotypes 8 and 9 from Quebec by restriction endonuclease fingerprinting and ribotyping

This study was undertaken to assess the discriminatory value of restriction endonuclease fingerprinting (REF) analysis and ribotyping of 21 Serpulina hyodysenteriae isolates of serotypes 8 and 9. For REF analysis, DNAs were digested with the BglII restriction enzyme and the resultant fragments were separated by polyacrylamide gel electrophoresis. For ribotyping, hybridization of BglII genomic fragments with a probe of rrnB operon using an Escherichia coli rDNA probe was performed on all isolates. Although many isolates shared a common pattern by BglII REF and BglII ribotyping analysis, differences among some S. hyodysenteriae isolates were observed. REF and ribotyping using BglII restriction enzyme, were not specific for serotypes. The predominance of an REF and a ribotype pattern among S. hyodysenteriae isolates from Quebec suggested that epidemiologically important S. hyodysenteriae types occur in different swine herds.

Antimicrobial susceptibility testing of Serpulina hyodysenteriae

The macrobroth dilution technique was used to test the in-vitro effectiveness of 4 commonly used antimicrobial agents against 23 Australian isolates and 7 overseas strains of Serpulina hyodysenteriae. Minimum inhibitory concentrations and minimum bactericidal concentrations were determined. The growth of 90% of isolates was inhibited by dimetridazole at a concentration of 4 micrograms/mL, and by tiamulin at 8 micrograms/mL. Australian isolates resistant to both antimicrobial agents were identified. Lincomycin was less effective than these antimicrobial agents, with 90% of isolates requiring a concentration of 128 micrograms/mL for inhibition of growth, and 54% being susceptible at 64 micrograms/mL. Tylosin did not prevent the growth of the majority of S hyodysenteriae isolates tested, and 90% were resistant to concentrations of > or = 128 micrograms/mL. Resistant isolates came from different geographical areas. Resistance was not related to overall genetic background of the spirochaetes, and was not correlated with the presence of plasmids or the serogroup of the isolates.