Occurrence of dysentery-like diarrhoea associated with Brachyspira suanatina infection on a German fattening pig farm

First molecular detection of Brachyspira suanatina on pig farms in Poland

Introduction

Prior to the 2000s, swine dysentery was considered to be caused only by Brachyspira hyodysenteriae with contributing commensal intestinal anaerobes. Nowadays, it is known that the disease is caused by three strongly beta-haemolytic species of the anaerobic spirochaetal genus Brachyspira, i.e. B. hyodysenteriae and newly emerged B. hampsonii and B. suanatina.

Material and Methods

The present investigation was carried out in November 2022 on nine Polish high-performing finisher pig farms. At every location one fresh pooled faecal sample was collected from 40 randomly selected pigs of between 60 and 110 kg live weight. Nucleic acid extracted from each pooled faecal sample was analysed by an in-house multiplex PCR for Brachyspira spp., which is capable of confirming the Brachyspira genus and detecting and differentiating Brachyspira species.

Results

From a total of nine samples examined, the genetic material of B. suanatina was detected in seven. Non-pathogenic/questionably pathogenic Brachyspira spp. were found in six samples.

Conclusion

To the best of our knowledge, this is the first report on the identification of B. suanatina in pigs outside Scandinavia, Germany and the United Kingdom. Our research not only provides valuable epidemiological data on B. suanatina infection in Europe but also highlights both the importance of modern laboratory diagnostics and the need for thorough investigation across regions, including retrospective studies.

Predictive Power of Long-Read Whole-Genome Sequencing for Rapid Diagnostics of Multidrug-Resistant Brachyspira hyodysenteriae Strains

Infections with Brachyspira hyodysenteriae, the etiological agent of swine dysentery, result in major economic losses in the pig industry worldwide. Even though microbial differentiation of various Brachyspira species can be obtained via PCR, no quick diagnostics for antimicrobial susceptibility testing are in place, which is mainly due to the time-consuming (4 to 7 days) anaerobic growth requirements of these organisms. Veterinarians often rely on a clinical diagnosis for initiating antimicrobial treatment. These treatments are not always effective, which may be due to high levels of acquired resistance in B. hyodysenteriae field isolates. By using long-read-only whole-genome sequencing and a custom-trained Bonito base-calling model, 81 complete B. hyodysenteriae genomes with median Q51 scores and 99% completeness were obtained from 86 field strains. This allowed the assessment of the predictive potential of genetic markers in relation to the observed acquired resistance phenotypes obtained via agar dilution susceptibility testing. Multidrug resistance was observed in 77% and 21% of the tested strains based on epidemiological cutoff and clinical breakpoint values, respectively. The predictive power of genetic hallmarks (genes and/or gene mutations) for antimicrobial susceptibility testing was promising. Sensitivity and specificity for tiamulin [tva(A) and 50SL3^N148S, 99% and 67%], valnemulin [tva(A), 97% and 92%), lincomycin (23S^A2153T/G and lnuC, 94% and 100%), tylvalosin (23S^A2153T/G, 99% and 93%), and doxycycline (16S^G1026C, 93% and 87%) were determined. The predictive power of these genetic hallmarks is promising for use in sequencing-based workflows to speed up swine dysentery diagnostics in veterinary medicine and determine proper antimicrobial use. IMPORTANCE Diagnostics for swine dysentery rely on the identification of Brachyspira species using molecular techniques. Nevertheless, no quick diagnostic tools are available for antimicrobial susceptibility testing due to extended growth requirements (7 to 14 days). To enable practitioners to tailor antimicrobial treatment to specific strains, long-read sequencing-based methods are expected to lead to rapid methods in the future. Nevertheless, their potential implementation should be validated extensively. This mainly implies assessing sequencing accuracy and the predictive power of genetic hallmarks in relation to their observed (multi)resistance phenotypes.

In Vitro Screening of Non-Antibiotic Components to Mitigate Intestinal Lesions Caused by Brachyspira hyodysenteriae, Lawsonia intracellularis and Salmonella enterica Serovar Typhimurium

Swine dysentery, ileitis, and porcine salmonellosis are production-limiting diseases of global importance for swine production. They are caused by infection with Brachyspira hyodysenteriae, Lawsonia intracellularis, and Salmonella enterica serovar Typhimurium, respectively. Currently, the prevention, treatment, and control of these diseases still relies on antimicrobials. The goal of this study was to evaluate the effectiveness of four commercially available non-antimicrobial compounds in preventing lesions caused by the bacteria cited above using an in vitro intestinal culture model. A total of five pigs per pathogen were used and multiple compounds were evaluated. For compound F (a fungal fermented rye), S (a blend of short and medium chain fatty acids), and P (a synergistic blend of short and medium chain fatty acids, including coated butyrates), a total of four explants/pig for each treatment were used, while for compound D (an extract of carob and thyme) only 12 explants/pig for each treatment were used. Explants were exposed to a combination of pathogen only (n = 4/compound/pig), compound only (n = 4/compound/pig), or pathogen and compound (n = 4/compound/pig) and sampled at two time-points. Histopathology and gene expression levels were evaluated to investigate the treatment effect on explants. Short and medium-chain fatty acids, and an extract of carob and thyme, was found to mitigate lesions due to B. hyodysenteriae exposure. A fungal fermented prebiotic increased healthy epithelial coverage when explants were exposed to L. intracellularis or S. Typhimurium. These findings represent a step towards finding alternatives to antimicrobials usage and control of swine dysentery, ileitis, and salmonellosis in pork production.

Mutational analysis of TlyA from Brachyspira hampsonii reveals two key residues conserved in pathogenic bacteria responsible for oligomerization and hemolytic activity

BACKGROUND

TlyA proteins are expressed in a variety of pathogenic bacteria and possess dual hemolytic and ribosomal RNA methyltransferase functions. While the mechanism of TlyA mediated rRNA methylation is well understood, relatively little is known about the mechanism of TlyA induced hemolysis.

METHODS

TlyA protein from the pig pathogen Brachyspira hampsonii was heterologously expressed and purified from an E. coli host. Hemolytic activity and rRNA methylation were assessed in vitro. Site-directed mutagenesis was used to mutate amino acids believed to be involved in TlyA mediated hemolysis.

RESULTS

Purified TlyA-His protein exhibited both hemolytic and rRNA methyltransferase activities in vitro, with partial inhibition of hemolysis observed under reducing conditions. Mutation of cysteine 80 to alanine impaired hemolytic activity. A C27A/C93A mutant was capable of dimerizing under non-reducing conditions, indicating that a C80-C80 disulfide bond is involved in TlyA oligomerization. A mutation conserved in several avirulent Brachyspira species (S9K) completely abolished hemolytic activity of TlyA. This loss of activity was attributed to impaired oligomerization in the S9K mutant, as assessed by ITC and size-exclusion chromatography experiments.

CONCLUSIONS

Oligomeric assembly and hemolytic activity of TlyA from Brachyspira hampsonii is dependent on the formation of an intermolecular C80-C80 disulfide bond and noncovalent interactions involving serine 9. The conservation of these amino acids in TlyA proteins from pathogenic bacteria suggests a correlation between tlyA gene mutations and bacterial virulence.

GENERAL SIGNIFICANCE

Our results further elucidate the mechanisms underlying TlyA mediated hemolysis and provide evidence of a conserved mechanism of oligomerization for TlyA family proteins.

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.

Postweaning mortality in commercial swine production II: review of infectious contributing factors

Postweaning mortality is extremely complex with a multitude of noninfectious and infectious contributing factors. In the current review, our objective is to describe the current state of knowledge regarding infectious causes of postweaning mortality, focusing on estimates of frequency and magnitude of effect where available. While infectious mortality is often categorized by physiologic body system affected, we believe the complex multifactorial nature is better understood by an alternative stratification dependent on intervention type. This category method subjectively combines disease pathogenesis knowledge, epidemiology, and economic consequences. These intervention categories included depopulation of affected cohorts of animals, elimination protocols using knowledge of immunity and epidemiology, or less aggressive interventions. The most aggressive approach to control infectious etiologies is through herd depopulation and repopulation. Historically, these protocols were successful for Actinobacillus pleuropneumoniae and swine dysentery among others. Additionally, this aggressive measure likely would be used to minimize disease spread if either a foreign animal disease was introduced or pseudorabies virus was reintroduced into domestic swine populations. Elimination practices have been successful for Mycoplasma hyopneumoniae, porcine reproductive and respiratory syndrome virus, coronaviruses, including transmissible gastroenteritis virus, porcine epidemic diarrhea virus, and porcine deltacoronavirus, swine influenza virus, nondysentery Brachyspira spp., and others. Porcine circovirus type 2 can have a significant impact on morbidity and mortality; however, it is often adequately controlled through immunization. Many other infectious etiologies present in swine production have not elicited these aggressive control measures. This may be because less aggressive control measures, such as vaccination, management, and therapeutics, are effective, their impact on mortality or productivity is not great enough to warrant, or there is inadequate understanding to employ control procedures efficaciously and efficiently. Since there are many infectious agents and noninfectious contributors, emphasis should continue to be placed on those infectious agents with the greatest impact to minimize postweaning mortality.

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.