Brachyspira in dogs: risk factors of shedding in central Germany and longitudinal study of an infected kennel

BACKGROUND

Brachyspira (B.) pilosicoli is a zoonotic pathogen, able to infect different animal species such as pigs, poultry, and rodents, causing intestinal spirochetosis. An association of gastrointestinal clinical signs, such as diarrhea, with the isolation of B. pilosicoli from fecal samples or rectal swabs has not been proven in dogs. Other Brachyspira species commonly isolated from dogs, such as "B. canis" and "B. pulli", are considered commensals. This study investigated the occurrence of different Brachyspira species in rectal swabs and fecal samples in an independent canine cohort in central Germany. These included samples from shelter dogs, hunting dogs, and dogs presenting at regional small animal practices with various clinical signs. Data about the dogs, including potential risk factors for Brachyspira isolation, were obtained using a standardized questionnaire. The study also longitudinally investigated a colony of Beagle dogs for Brachyspira over 5 years.

RESULTS

The rate of Brachyspira spp. isolation was 11% and included different Brachyspira species ("B. canis", "B. pulli", and B. pilosicoli). "B. canis" was detected in 18 dogs, whereas B. pilosicoli was only isolated from 1 dog in the independent cohort (not including the Beagle colony). Risk factors for shedding Brachyspira and "B. canis" were being less than 1 year of age and shelter origin. Gastrointestinal signs were not associated with the shedding of Brachyspira. B. pilosicoli and "B. canis" were isolated from several dogs of the same Beagle colony in 2017 and again in 2022, while Brachyspira was not isolated at multiple sampling time points in 2021.

CONCLUSIONS

Shedding of B. pilosicoli in dogs appears to be uncommon in central Germany, suggesting a low risk of zoonotic transmission from dogs. Commensal status of "B. canis" and "B. pulli" is supported by the results of this study. Findings from the longitudinal investigation of the Beagle colony agree with an asymptomatic long-term colonization of dogs with "B. canis" and B. pilosicoli and suggest that introducing new animals in a pack can trigger an increased shedding of B. pilosicoli.

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.

Molecular characterization of antimicrobial resistance in Brachyspira species isolated from UK chickens: Identification of novel variants of pleuromutilin and beta-lactam resistance genes

Brachyspira species are Gram negative, anaerobic bacteria that colonise the gut of many animals, including poultry. In poultry, Brachyspira species can be commensal (B. innocens, B. murdochii, 'B. pulli') or pathogenic (B. pilosicoli, B. intermedia, B. alvinipulli or rarely B. hyodysenteriae), the latter causing avian intestinal spirochaetosis (AIS). Antimicrobial therapy options for treatment is limited, frequently involving administration of the pleuromutilin, tiamulin, in water. In this study 38 Brachyspira isolates from chickens in the UK, representing both commensal and pathogenic species, were whole genome sequenced to identify antimicrobial resistance (AMR) mechanisms and the minimum inhibitory concentration (MIC) to a number of antimicrobials was also determined. We identified several new variants of blaOXA in B. pilosicoli and B. pulli isolates, and variations in tva which led to two new tva variants in B.murdochii and B.pulli. A number of isolates also harboured mutations known to encode AMR in the 16S and 23S rRNA genes. The percentage of isolates that were genotypically multi-drug resistance (MDR) was 16%, with the most common resistance profile being: tetracycline, pleuromutilin and beta-lactam, which were found in three 'B. pulli' and one B. pilosicoli. There was good correlation with the genotype and the corresponding antibiotic MIC phenotypes: pleuromutilins (tiamulin and valnemulin), macrolides (tylosin and tylvalosin), lincomycin and doxycycline. The occurrence of resistance determinants identified in this study in pathogenic Brachyspira, especially those which were MDR, is likely to impact treatment of AIS and clearance of infections on farm.

Clinical and Pathologic Factors Associated With Colonic Spirochete (Brachyspira pilosicoli and Brachyspira aalborgi) Infection: A Comprehensive Systematic Review and Pooled Analysis

OBJECTIVES

This study aims to determine what pathologic and clinical factors differentiate Brachyspira species that may be useful to clinicians and pathologists.

METHODS

We identified 21 studies of Brachyspira infection with individual patient information (n = 113) and conducted a pooled analysis comparing each species.

RESULTS

There were differences in the pathologic and clinical profiles of each Brachyspira species. Patients infected with Brachyspira pilosicoli infection were more likely to have diarrhea, fever, HIV, and immunocompromised conditions. Those patients infected with Brachyspira aalborgi were more likely to have lamina propria inflammation.

CONCLUSIONS

Our novel data provide potential insights into the pathogenic mechanism(s) and the specific risk factor profile of Brachyspira species. This may be clinically useful when assessing and managing patients.

Antimicrobial susceptibility of western Canadian Brachyspira isolates: Development and standardization of an agar dilution susceptibility test method

The re-emergence of Brachyspira-associated disease in pigs since the late 2000s has illuminated some of the diagnostic challenges associated with this genus; notably, the lack of standardized antimicrobial susceptibility testing (AST) methods and interpretive criteria. Consequently, laboratories have relied heavily on highly variable in-house developed methods. There are currently no published investigations describing the antimicrobial susceptibility of Brachyspira isolates collected from pigs in Canada. The first objective of this study was therefore to develop a standardized protocol for conducting agar dilution susceptibility testing of Brachyspira spp., including determining the optimal standardized inoculum density, a key test variable that impacts test performance. The second objective was to determine the susceptibility of a collection of western Canadian Brachyspira isolates using the standardized methodology. After assessing multiple media, an agar dilution test was standardized in terms of starting inoculum (1-2 × 108 CFU/ml), incubation temperature and time, and assessed for repeatability. The antimicrobial susceptibility of a collection of clinical porcine Brachyspira isolates (n = 87) collected between 2009-2016 was then determined. This method was highly reproducible; repeat susceptibility testing yielded identical results 92% of the time. Although most of the isolates had very low MICs to the commonly used antimicrobials to treat Brachyspira-associated infections, several isolates with elevated MICs (>32 μg/ml) for tiamulin, valnemulin, tylosin, tylvalosin, and lincomycin were identified. Overall, this study underscores the importance of establishing CLSI approved clinical breakpoints for Brachyspira to facilitate the interpretation of test results and support the evidence-based selection of antimicrobials in swine industry.

JMM Profile: Brachyspira species: the causative agent of Avian Intestinal Spirochaetosis

The genus Brachyspira includes nine officially recognised species, several of which are pathogenic to mammals and birds. B. pilosicoli, B. intermedia, and B. alvinipulli are the causative agents of avian intestinal spirochaetosis (AIS), a gastrointestinal disease in poultry caused by the colonisation of the caeca and/ or colo-rectum by Brachyspira. AIS primarily affects layer hens and broiler breeders over the age of 15 weeks. The severity of symptoms can vary but typically presents as reduced growth rates, delayed onset of lay, reduced egg production, faecally stained eggs, and diarrhoea. This disease is estimated to cost the UK laying industry £18 million per annum. Brachyspira colonisation in humans is common in populations from developing countries and HIV-positive patients; however, it is rarely investigated as a human pathogen.