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

Improving the consistency of experimental swine dysentery inoculation strategies

Swine dysentery (SD) caused by pathogenic Brachyspira spp. is an economic challenge for the swine industry. In research settings, experimental reproduction of swine dysentery typically relies on intragastric inoculation which has shown variable success. This project aimed to improve the consistency of the experimental inoculation protocol used for swine dysentery in our laboratory. Over six experiments, we evaluated the influence of group housing in inoculated pigs using a frozen-thawed broth culture of strongly hemolytic B. hyodysenteriae strain D19 (Trial A), compared the relative virulence of B. hyodysenteriae strains D19 and G44 (Trial B), compared inoculum volumes (50 mL vs 100 mL) for G44 and B. hampsonii 30446 (Trial C), and performed three independent trials evaluating intragastric inoculation using different oral inoculation methods: oral feed balls (Trial D), and oral syringe bolus of 100 mL (Trial E) or 300 mL (Trial F). Intragastric inoculation with a fresh broth culture of B. hyodysenteriae strain G44 resulted in a shorter incubation period and a higher proportionate duration of mucohemorrhagic diarrhea (MMHD) compared to D19. Intragastric inoculation with either 50 or 100 mL of B. hampsonii 30446 or B. hyodysenteriae (G44) were statistically equivalent. Oral inoculation with 100 mL or 300 mL also yielded similar results to intragastric inoculation but was more expensive due to the additional work and supplies associated with syringe training. Our future research will use intragastric inoculation with 100 mL of a fresh broth culture containing B. hyodysenteriae strain G44 as it yields a high incidence of mucohaemorrhagic diarrhea with a reasonable cost.

Experimental Infection of Pigs with a ST 245 Brachyspira hyodysenteriae Isolated from an Asymptomatic Pig in a Herd with No History of Swine Dysentery

Swine dysentery (SD) is characterized by a severe mucohemorrhagic colitis caused by infection with Brachyspira species. In infected herds the disease causes considerable financial loss due to mortality, slow growth rates, poor feed conversion, and costs of treatment. B. hyodysenteriae is the most common etiological agent of SD and infection is usually associated with disease. However, isolated reports have described low pathogenic strains of B. hyodysenteriae. The aim of this study was to describe an experimental infection trial using a subclinical B. hyodysenteriae isolated from an animal without clinical signs and from a disease-free herd, to evaluate the pathogenicity and clinical pathological characteristics compared to a highly clinical isolate. Forty-eight 5-week-old pigs were divided into three groups: control, clinical and the subclinical isolates. The first detection/isolation of B. hyodysenteriae in samples of the animals challenged with a known clinical B. hyodysenteriae strain (clinical group) occurred 5th day post inoculation. Considering the whole period of the study, 11/16 animals from this group were qPCR positive in fecal samples, and diarrhea was observed in 10/16 pigs. In the subclinical isolate group, one animal had diarrhea. There were SD large intestine lesions in 3 animals at necropsy and positive B. hyodysenteriae isolation in 7/15 samples of the subclinical group. In the control group, no diarrhea, gross/microscopic lesions, or qPCR positivity were observed. Clinical signs, bacterial isolation, macroscopic and histologic lesions were significantly difference among groups, demonstrating low pathogenicity of the subclinical isolate in susceptible pigs.

Whole-Genome Sequencing of Brachyspira hyodysenteriae Isolates From England and Wales Reveals Similarities to European Isolates and Mutations Associated With Reduced Sensitivity to Antimicrobials

Brachyspira hyodysenteriae is the principal cause of swine dysentery, a disease that threatens economic productivity of pigs in many countries as it can spread readily within and between farms, and only a small number of antimicrobials are authorized for treatment of pigs. In this study, we performed whole-genome sequencing (WGS) of 81 B. hyodysenteriae archived at the Animal and Plant Health Agency (APHA) from diagnostic submissions and herd monitoring in England and Wales between 2004 and 2015. The resulting genome sequences were analyzed alongside 34 genomes we previously published. Multi-locus sequence typing (MLST) showed a diverse population with 32 sequence types (STs) among the 115 APHA isolates, 25 of them identified only in England; while also confirming that the dominant European clonal complexes, CC8 and CC52, were common in the United Kingdom. A core-genome SNP tree typically clustered the isolates by ST, with isolates from some STs detected only within a specific region in England, although others were more widespread, suggesting transmission between different regions. Also, some STs were more conserved in their core genome than others, despite these isolates being from different holdings, regions and years. Minimum inhibitory concentrations to commonly used antimicrobials (Tiamulin, Valnemulin, Doxycycline, Lincomycin, Tylosin, Tylvalosin) were determined for 82 of the genome-sequenced isolates; genomic analysis revealed mutations generally correlated well with the corresponding resistance phenotype. There was a major swine dysentery intervention program in 2009–2010, and antimicrobial survival curves showed a significant reduction in sensitivity to tiamulin and valnemulin in isolates collected in and after 2010, compared to earlier isolates. This correlated with a significant increase in post-2009 isolates harboring the pleuromutilin resistance gene tva(A), which if present, may facilitate higher levels of resistance. The reduction in susceptibility of Brachyspira from diagnostic submissions to pleuromutilins, emphasizes the need for prudent treatment, control and eradication strategies.

Retrospective analysis of necrotizing typhlitis cases associated with Brachyspira spp. in British rheas

This paper describes a retrospective analysis of necrotizing typhlitis in common rheas (Rhea americana) diagnosed in the United Kingdom by the Animal & Plant Health Agency (APHA). From January 2008 to January 2020, seven cases of spirochaetal typhlitis associated with Brachyspira spp. were identified using the Veterinary Investigation Diagnosis Analysis database. Gross examination was combined with selective anaerobic culture, polymerase chain reaction, and histopathology to diagnose typhlitis associated with spirochaetal infection. Whole-genome sequencing was subsequently utilized on archived isolates from six of the seven submissions, overcoming issues with traditional testing methods and yielded gains in the identification of Brachyspira to species level. Brachyspira hyodysenteriae, an organism traditionally associated with typhlitis in rheas, was isolated in three sequenced submissions. One of these also demonstrated co-infection with Brachyspira intermedia. Brachyspira suanatina, Brachyspira hampsonii, and Brachyspira alvinipulli were identified by sequencing as single infections in the remaining three animals. This report demonstrates the ability of Brachyspira species other than B. hyodysenteriae to colonize the caeca of rheas presenting with typhlitis. Additionally, the B. alvinipulli isolate harboured a tva(A) gene, indicating higher potential pleuromutilin resistance, which has not previously been described in this Brachyspira species. This study discusses the epidemiology of examined cases and examines the potential role other species may play in these outbreaks.

Differential expression of hemolysin genes in weakly and strongly hemolytic Brachyspira hyodysenteriae strains

Background

Swine dysentery (SD) is a diarrheal disease in fattening pigs that is caused by the strongly hemolytic species Brachyspira (B.) hyodysenteriae, B. hampsonii and B. suanatina. As weakly hemolytic Brachyspira spp. are considered less virulent or even non-pathogenic, the hemolysin is regarded as an important factor in the pathogenesis of SD. Four hemolysin genes (tlyA, tlyB, tlyC, and hlyA) and four putative hemolysin genes (hemolysin, hemolysin activation protein, hemolysin III, and hemolysin channel protein) have been reported, but their role in strong hemolysis is not entirely clear. Our study aimed to assess the transcriptional activity of eight (putative) hemolysin genes in a strongly hemolytic (B204) and a weakly hemolytic (G423) B. hyodysenteriae strain during non-hemolytic and hemolytic growth stages.

Results

Strongly and weakly hemolytic B. hyodysenteriae strains caused hemolysis on blood agar at different growth stages, namely during log phase (B204) and stationary/death phase (G423). During the lag, early log, late log (stationary phase in G423) and death phase (time points 1–4) strains differed in their hemolysin gene transcription patterns. At time point 1, transcription of the putative hemolysin gene was higher in B204 than in G423. At time point 2, tlyA and tlyC were upregulated in B204 during hemolysis. TlyB and hlyA were upregulated in both strains at all time points, but higher transcription rates were observed in the weakly hemolytic strain G423. The transcription activity of the hemolysin channel protein gene was quite similar in both strains, whereas the hemolysin activation protein gene was upregulated in the non-hemolytic stage of B204 at time point 4. Sequence analysis revealed deletions, insertions and single nucleotide polymorphisms in the G423 hlyA promoter, although without altering the transcription activity of this gene.

Conclusion

Our data indicate a combined activity of TlyA and TlyC as the most probable underlying mechanism of strong hemolysis in B. hyodysenteriae. Further studies should verify if the expression of tlyA is upregulated by the putative hemolysin gene. Depending on their immunogenic potential TlyA and TlyC may serve as possible vaccine candidates, especially since vaccines for an effective control of swine dysentery are currently not available.

Identification of Brachyspira species by cpn60 universal target sequencing is superior to NADH oxidase gene sequencing

The pig colon is the habitat of diverse Brachyspira species, of which only a few are of clinical importance. Methods for identification have shifted from phenotypic to molecular testing over the last two decades. Following the emergence of B. hampsonii it became evident that relying on species-specific PCRs carries the risk of overlooking important new species. Consequently, sequencing was proposed as an unbiased alternative for identification of isolates. So far, the main target for identification across species has been the NADH oxidase gene (nox). However, multiple copies of this gene in the genome and potential lateral gene transfer reduce confidence when using this gene. This study compared identification and phylogentic relationship inferred from nox sequencing to that inferred from sequencing of the cpn60 universal target using a collection of 168 isolates from different Brachyspira species. The majority of isolates had an identical identification with both methods. There were a few outliers in the trees with uncertain assignment to a species by BLAST analysis. A few major discrepancies pertained to the pathogenic species B. hampsonii (2), B. pilosicoli (1) and B. suanatina (1). Weakly haemolytic variants of B. hyodysenteriae were assigned to the correct species by both methods. Some of the isolates identified as B. hampsonii also had a weakly haemolytic phenotype.

Testing the efficacy of kitasamycin for use in the control and treatment of swine dysentery in experimentally infected pigs

BACKGROUND

Swine dysentery (SD) caused by Brachyspira hyodysenteriae is an important disease in Australia.

AIM

The aim of this study is to evaluate the macrolide antibiotic kitasamycin for use in SD control.

METHODS

The minimum inhibitory concentrations (MICs) of kitasamycin, tylosin and lincomycin for 32 Australian isolates of B. hyodysenteriae were evaluated. Mutations in the 23S rRNA gene were examined. Isolate '13' with a low kitasamycin MIC was used to challenge weaner pigs. Sixty pigs were housed in 20 pens each containing three pigs: pigs in four pens received 2 kg/tonne of a product containing kitasamycin (3.1% active) prophylactically in their food starting 4 days before B. hyodysenteriae challenge (group 1); pigs in four pens were challenged and received the same dose therapeutically once one pig in a pen showed diarrhoea (group 2); four pens were challenged and received 4 kg/tonne of the product therapeutically (group 3); four pens were challenged but not medicated (group 4); two pens were unmedicated and unchallenged (group 5) and two pens received 2 kg/tonne and were unchallenged (group 6). Pigs were monitored for B. hyodysenteriae excretion and disease.

RESULTS

Macrolide resistance was widespread, and mutations in the 23S rRNA gene were identified in 23 isolates. Four isolates with kitasamycin MICs < 5 μg/mL were considered susceptible. Following experimental challenge, 10 of 12 unmedicated pigs developed SD. No pigs receiving kitasamycin prophylactical or therapeutically developed SD. Medicated pigs shed low numbers of B. hyodysenteriae in their faeces.

CONCLUSIONS

Kitasamycin can help control SD in pigs infected with susceptible isolates of B. hyodysenteriae.

An atypical weakly haemolytic strain of Brachyspira hyodysenteriae is avirulent and can be used to protect pigs from developing swine dysentery

The anaerobic intestinal spirochaete Brachyspira hyodysenteriae colonises the large intestine of pigs and causes swine dysentery (SD), a severe mucohaemorrhagic colitis. SD occurs worldwide, and control is hampered by a lack of vaccines and increasing antimicrobial resistance. B. hyodysenteriae strains typically produce strong beta-haemolysis on blood agar, and the haemolytic activity is thought to contribute to the pathogenesis of SD. Recently, weakly haemolytic variants of B. hyodysenteriae have been identified in Europe and Australia, and weakly haemolytic strain D28 from Belgium failed to cause disease when used experimentally to infect pigs. Moreover, pigs colonised with D28 and then challenged with virulent strongly haemolytic strain B204 showed a delay of 2–4 days in developing SD compared to pigs not exposed to D28. The current study aimed to determine whether Australian weakly haemolytic B. hyodysenteriae strain MU1, which is genetically distinct from D28, could cause disease and whether exposure to it protected pigs from subsequent challenge with strongly haemolytic virulent strains. Three experimental infection studies were undertaken in which no diseases occurred in 34 pigs inoculated with MU1, although mild superficial lesions were found in the colon in 2 pigs in one experiment. In two experiments, significantly fewer pigs exposed to MU1 and then challenged with strongly haemolytic virulent strains of B. hyodysenteriae developed SD compared to control pigs not previously exposed to MU1 (p = 0.009 and p = 0.0006). These data indicate that MU1 lacks virulence and has potential to be used to help protect pigs from SD.

Weakly haemolytic variants of Brachyspira hyodysenteriae newly emerged in Europe belong to a distinct subclade with unique genetic properties

Brachyspira (B.) hyodysenteriae is widespread globally, and can cause mucohaemorrhagic colitis (swine dysentery, SD) with severe economic impact in infected herds. Typical strains of B. hyodysenteriae are strongly haemolytic on blood agar, and the haemolytic activity is believed to contribute to virulence in vivo. However, recently there have been reports of atypical weakly haemolytic isolates of B. hyodysenteriae (whBh). In this study, 34 European whBh and 82 strongly haemolytic isolates were subjected to comparative genomic analysis. A phylogenetic tree constructed using core single nucleotide polymorphisms showed that the whBh formed a distinct sub-clade. All eight genes previously associated with haemolysis in B. hyodysenteriae were present in the whBh. No consistent patterns of amino acid substitutions for all whBh were found in these genes. In contrast, a genome region containing six coding sequences (CDSs) had consistent nucleotide sequence differences between strongly and whBh isolates. Two CDSs were predicted to encode ABC transporter proteins, and a TolC family protein, which may have a role in the export of haemolysins from B. hyodysenteriae. Another difference in this region was the presence of three CDSs in whBh that are pseudogenes in strongly haemolytic isolates. One of the intact CDSs from whBh encoded a predicted PadR-like transcriptional repressor that may play a role in repression of haemolysis functions. In summary, a sub-clade of whBh isolates has emerged in Europe, and several genomic differences, that potentially explain the weakly haemolytic phenotype, were identified. These markers may provide targets for discriminatory molecular tests needed in SD surveillance.

Predominance of a macrolide-lincosamide-resistant Brachyspira hyodysenteriae of sequence type 196 in Swiss pig herds

Worldwide emergence of antimicrobial-resistant Brachyspira (B.) hyodysenteriae led us question whether specific clones are present in Switzerland. Fifty-one B. hyodysenteriae isolates originating from 27 different Swiss pig herds sampled between 2010 and 2017 were characterised. Multilocus sequence typing revealed the presence of four different sequence types (STs) ST6, ST66, ST196 and ST197 with ST196 being predominant. Antimicrobial susceptibility to six different antimicrobial agents was determined by measurement of the minimal inhibitory concentration by broth dilution. Isolates were examined for the presence of point mutations and genes known to be associated with antimicrobial resistance in B. hyodysenteriae by PCR and sequence analysis. Forty-one isolates belonging to ST6 (n = 1), ST66 (n = 4) and ST196 (n = 36) exhibited decreased susceptibility to macrolides and lincomycin associated with an A2058 T/G mutation in the 23S rRNA gene. One isolate of ST66 and five isolates of ST196 exhibited decreased susceptibility to doxycycline associated with a G1058C mutation in the 16S rRNA gene. The Swiss B. hyodysenteriae population is characterised by a low genetic diversity, with macrolide-lincosamide-resistant isolates of ST196 being predominant.

The Efficacy of Two Phytogenic Feed Additives in the Control of Swine Dysentery

Control of swine dysentery with antibiotics is often ineffective due to the resistance of Brachyspira hyodysenteriae. The potential of some herbal-based components against B. hyodysenteriae was previously studied in vitro. This study aims at the evaluation of in vivo efficacy of phytogenic feed additives in the control of swine dysentery

The study involved 64 seven-week old weaned pigs allotted to 4 groups: two were fed on feed supplemented with either Patente Herba® or Patente Herba® Plus, the third received tiamulin (positive control), while the negative control was not given antibiotics or additives. Fecal consistency was recorded daily. The presence of B. hyodysenteriae in the feces was investigated weekly using microbiological assays and the PCR test. Weight gain and feed conversion ratio were calculated for each week, and for the whole experiment.

B. hyodysenteriae was detected in all samples by both methods. The additives showed efficacy in the prevention and control of swine dysentery as only normal and soft stool was observed in the treated groups. By contrast, in the negative control all feces categories were detected. Frequencies of feces categories significantly differed (p<0.001) between feed-supplemented groups and the negative control. Efficacy of both additives in the prevention of SD is comparable to tiamulin, based on insignificant differences in the frequency of the various feces categories.

Beneficial effects of both additives resulted in significantly (p≤0.05) higher weight gain and lower feed conversion ratio in comparison to the negative control. The average weight gains between additive-fed groups and tiamulin-treated group did not differ significantly.

Identification of a New Antimicrobial Resistance Gene Provides Fresh Insights Into Pleuromutilin Resistance in Brachyspira hyodysenteriae, Aetiological Agent of Swine Dysentery

Brachyspira hyodysenteriae is the aetiological agent of swine dysentery, a globally distributed disease that causes profound economic loss, impedes the free trade and movement of animals, and has significant impact on pig health. Infection is generally treated with antibiotics of which pleuromutilins, such as tiamulin, are widely used for this purpose, but reports of resistance worldwide threaten continued effective control. In Brachyspira hyodysenteriae pleuromutilin resistance has been associated with mutations in chromosomal genes encoding ribosome-associated functions, however the dynamics of resistance acquisition are poorly understood, compromising stewardship efforts to preserve pleuromutilin effectiveness. In this study we undertook whole genome sequencing (WGS) and phenotypic susceptibility testing of 34 UK field isolates and 3 control strains to investigate pleuromutilin resistance in Brachyspira hyodysenteriae. Genome-wide association studies identified a new pleuromutilin resistance gene, tva(A) (tiamulin valnemulin antibiotic resistance), encoding a predicted ABC-F transporter. In vitro culture of isolates in the presence of inhibitory or sub-inhibitory concentrations of tiamulin showed that tva(A) confers reduced pleuromutilin susceptibility that does not lead to clinical resistance but facilitates the development of higher-level resistance via mutations in genes encoding ribosome-associated functions. Genome sequencing of antibiotic-exposed isolates identified both new and previously described mutations in chromosomal genes associated with reduced pleuromutilin susceptibility, including the 23S rRNA gene and rplC, which encodes the L3 ribosomal protein. Interesting three antibiotic-exposed isolates harboured mutations in fusA, encoding Elongation Factor G, a gene not previously associated with pleuromutilin resistance. A longitudinal molecular epidemiological examination of two episodes of swine dysentery at the same farm indicated that tva(A) contributed to development of tiamulin resistance in vivo in a manner consistent with that seen experimentally in vitro. The in vitro studies further showed that tva(A) broadened the mutant selection window and raised the mutant prevention concentration above reported in vivo antibiotic concentrations obtained when administered at certain doses. We show how the identification and characterisation of tva(A), a new marker for pleuromutilin resistance, provides evidence to inform treatment regimes and reduce the development of resistance to this class of highly important antimicrobial agents.

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.

Characterization of Brachyspira communities from clinical cases of swine mucohaemorrhagic diarrhea through deep sequencing of the NADH oxidase (nox) gene

Swine dysentery is traditionally associated with Brachyspira hyodysenteriae, but the re-emergence of Brachyspira-associated disease in North America associated with a novel causative species, B. hampsonii, is now a concern for swine producers. The pathogenesis of Brachyspira-associated disease is not completely understood, and it is not known whether mixed infections of Brachyspira spp. are important in disease development. Deep sequencing of partial sequences of the nox gene amplified with genus-specific primers was used to detect Brachyspira spp. in 55 fecal samples from clinical cases of mucohaemorrhagic diarrhea in pigs from Western Canada that had been identified as positive for one or more Brachyspira species using established diagnostic tests. Synthetic mixtures of Brachyspira genomic DNA were included in the study to define detection limits for the technique and identify biases in detection of different species. Multiple species were detected in all clinical cases for which sufficient nox sequence data were generated (n = 47), indicating that mixed species Brachyspira infections are common, although in most cases, one species accounted for at least half of the sequences identified. In all cases, the species detected in the original diagnostic investigation of each case was also detected by nox sequencing. Results from synthetic communities indicated that the method was highly reproducible, but also indicated potential PCR bias against B. hampsonii genomovar I. Deep sequencing of the nox gene target is a suitable method for simultaneous detection of multiple Brachyspira species in clinical case material that may offer advantages over current, more targeted diagnostic approaches for investigating the significance of mixed infections in disease development.

The Spirochete Brachyspira pilosicoli, Enteric Pathogen of Animals and Humans

Brachyspira pilosicoli is a slow-growing anaerobic spirochete that colonizes the large intestine. Colonization occurs commonly in pigs and adult chickens, causing colitis/typhlitis, diarrhea, poor growth rates, and reduced production. Colonization of humans also is common in some populations (individuals living in village and peri-urban settings in developing countries, recent immigrants from developing countries, homosexual males, and HIV-positive patients), but the spirochete rarely is investigated as a potential human enteric pathogen. In part this is due to its slow growth and specialized growth requirements, meaning that it is not detectable in human fecal samples using routine diagnostic methods. Nevertheless, it has been identified histologically attached to the colon and rectum in patients with conditions such as chronic diarrhea, rectal bleeding, and/or nonspecific abdominal discomfort, and one survey of Australian Aboriginal children showed that colonization was significantly associated with failure to thrive. B. pilosicoli has been detected in the bloodstream of elderly patients or individuals with chronic conditions such as alcoholism and malignancies. This review describes the spirochete and associated diseases. It aims to encourage clinicians and clinical microbiologists to consider B. pilosicoli in their differential diagnoses and to develop and use appropriate diagnostic protocols to identify the spirochete in clinical specimens.

An avirulent Brachyspira hyodysenteriae strain elicits intestinal IgA and slows down spread of swine dysentery

Swine dysentery caused by Brachyspira hyodysenteriae, results in substantial economic losses in swine producing countries worldwide. Although a number of different vaccine approaches have been explored with regard to this disease, they show limitations and none of them have reached the market. We here determine the vaccine potential of a weakly haemolytic B. hyodysenteriae strain. The virulence of this strain was assessed in experimental infection trials and its protection against swine dysentery was quantified in a vaccination-challenge experiment using a seeder infection model. Systemic IgG production and local IgA production were monitored in serum and faeces respectively. Across all trials, pigs that were colonized by virulent, strongly haemolytic B. hyodysenteriae strains consistently developed swine dysentery, in contrast to none of the pigs colonized by the weakly haemolytic B. hyodysenteriae vaccine strain. In the seeder vaccination trial nearly all immunised animals developed swine dysentery on subsequent challenge with a virulent strain, but the speed of spread of swine dysentery and faecal score were significantly reduced in animals immunised with the weakly haemolytic strain compared to sham-immunised animals. The IgA response of immunised animals upon challenge with a virulent B. hyodysenteriae strain significantly correlated to a later onset of disease. The correlation between local IgA production and protection induced by a weakly haemolytic B. hyodysenteriae strain provides leads for future vaccine development against swine dysentery.

A review of methods used for studying the molecular epidemiology of Brachyspira hyodysenteriae

Brachyspira (B.) spp. are intestinal spirochaetes isolated from pigs, other mammals, birds and humans. In pigs, seven Brachyspira spp. have been described, i.e. B. hyodysenteriae, B. pilosicoli, B. intermedia, B. murdochii, B. innocens, B. suanatina and B. hampsonii. Brachyspira hyodysenteriae is especially relevant in pigs as it causes swine dysentery and hence considerable economic losses to the pig industry. Furthermore, reduced susceptibility of B. hyodysenteriae to antimicrobials is of increasing concern. The epidemiology of B. hyodysenteriae infections is only partially understood, but different methods for detection, identification and typing have supported recent improvements in knowledge and understanding. In the last years, molecular methods have been increasingly used. Molecular epidemiology links molecular biology with epidemiology, offering unique opportunities to advance the study of diseases. This review is based on papers published in the field of epidemiology and molecular epidemiology of B. hyodysenteriae in pigs. Electronic databases were screened for potentially relevant papers using title and abstract and finally, Barcellos et al. papers were systemically selected and assessed. The review summarises briefly the current knowledge on B. hyodysenteriae epidemiology and elaborates on molecular typing techniques available. Results of the studies are compared and gaps in the knowledge are addressed. Finally, potential areas for future research are proposed.

Characterization of Brachyspira hyodysenteriae isolates from Italy by multilocus sequence typing and multiple locus variable number tandem repeat analysis

AIMS

To evaluate and compare the capabilities of multilocus sequence typing (MLST) and multiple locus variable number tandem repeat analysis (MLVA) techniques to characterize Brachyspira hyodysenteriae isolates and to investigate the relationship between pleuromutilin resistance and genetic variability.

METHODS AND RESULTS

MLST genotyping was performed on 180 B. hyodysenteriae isolates, and the results were evaluated considering profiles from 108 other strains previously reported in the database. In total, 37 sequence types were obtained. The MLVA approach completely characterized 172 strains and grouped the isolates into 22 different profiles. The combination of MLST and MLVA showed a slight increase in the discriminatory power, identifying 33 joint profiles. An antibiotic resistance analysis showed a reduction in the susceptibility to pleuromutilins over time, and a weak association between susceptibility to valnemulin and inclusion in clonal complex 4.

CONCLUSION

MLST and MLVA are reliable methods for characterizing B. hyodysenteriae strains and they have comparable discriminatory power.

SIGNIFICANCE AND IMPACT OF THE STUDY

The genotyping of B. hyodysenteriae isolates and a database of all the genetic profiles collected during the diagnostic activities could support traditional epidemiological investigations in identifying infection sources and routes of transmission among herds, and in developing more effective control measures.

Colonic Spirochetes: What Has Genomics Taught Us?

The 'colonic' spirochetes assigned to the genus Brachyspira are slow-growing anaerobic bacteria. The genus includes both pathogenic and non-pathogenic species, and these variously colonise the large intestines of different species of birds and animals, including humans. Scientific understanding of the physiology and molecular biology of Brachyspira spp. remains very limited compared with that of other pathogenic spirochetes, and there are few descriptions of successful genetic manipulations undertaken to investigate gene function. An important boost to knowledge occurred in 2009 when, for the first time, the whole genome sequence of a Brachyspira strain (Brachyspira hyodysenteriae strain WA1) was obtained. The genomics analysis provided a significant increase in knowledge: for example, a previously unknown ~36 Kb plasmid was discovered and metabolic pathways were constructed. The study also revealed likely acquisition of genes involved in transport and central metabolic functions from other enteric bacterial species. Four subsequent publications have provided a similarly detailed analysis of other Brachyspira genomes, but of these only two included more than one strain of a species (20 strains of B. hyodysenteriae in one and three strains of B. pilosicoli in the other). Since then, more Brachyspira genomes have been made publicly available, with the sequences of at least one representative of each of the nine officially recognised species deposited at public genome repositories. All species have a single circular chromosome varying in size from ~2.5 to 3.3 Mb, with a C + G content of around 27%. In this chapter, we summarise the current knowledge and present a preliminary comparative genomic analysis conducted on 56 strains covering the official Brachyspira species. Besides providing detailed genetic maps of the bacteria, this analysis has revealed gene island rearrangements, putative phenotypes (including antimicrobial drug resistance) and genetic mutation mechanisms that enable brachyspires to evolve and respond to stress. The application of Next-Generation Sequencing (NGS) to generate genomic data from many more Brachyspira species and strains increasing will improve our understanding of these enigmatic spirochetes.

An Investigation into the Etiological Agents of Swine Dysentery in Australian Pig Herds

Swine dysentery (SD) is a mucohemorrhagic colitis, classically seen in grower/finisher pigs and caused by infection with the anaerobic intestinal spirochete Brachyspira hyodysenteriae. More recently, however, the newly described species Brachyspira hampsonii and Brachyspira suanatina have been identified as causing SD in North America and/or Europe. Furthermore, there have been occasions where strains of B. hyodysenteriae have been recovered from healthy pigs, including in multiplier herds with high health status. This study investigated whether cases of SD in Australia may be caused by the newly described species; how isolates of B. hyodysenteriae recovered from healthy herds compared to isolates from herds with disease; and how contemporary isolates compare to those recovered in previous decades, including in their plasmid gene content and antimicrobial resistance profiles. In total 1103 fecal and colon samples from pigs in 97 Australian herds were collected and tested. Of the agents of SD only B. hyodysenteriae was found, being present in 34 (35.1%) of the herds, including in 14 of 24 (58%) herds that had been considered to be free of SD. Multilocus sequence typing applied to 96 isolates from 30 herds and to 53 Australian isolates dating from the 1980s through the early 2000s showed that they were diverse, distinct from those reported in other countries, and that the 2014/16 isolates generally were different from those from earlier decades. These findings provided evidence for ongoing evolution of B. hyodysenteriae strains in Australia. In seven of the 20 herds where multiple isolates were available, two to four different sequence types (STs) were identified. Isolates with the same STs also were found in some herds with epidemiological links. Analysis of a block of six plasmid virulence-associated genes showed a lack of consistency between their presence or absence and their origin from herds currently with or without disease; however, significantly fewer isolates from the 2000s and from 2014/16 had this block of genes compared to isolates from the 1980s and 1990s. It is speculated that loss of these genes may have been responsible for the occurrence of milder disease occurring in recent years. In addition, fewer isolates from 2014/16 were susceptible to the antimicrobials lincomycin, and to a lesser extent tiamulin, than those from earlier Australian studies. Four distinct multi-drug resistant strains were identified in five herds, posing a threat to disease control.