Antimicrobial susceptibility of Brachyspira hyodysenteriae determined by a broth microdilution method

In Vitro Antibacterial Activity of Microbial Natural Products against Bacterial Pathogens of Veterinary and Zoonotic Relevance

Antimicrobial resistance (AMR) is considered one of the greatest threats to both human and animal health. Efforts to address AMR include implementing antimicrobial stewardship programs and introducing alternative treatment options. Nevertheless, effective treatment of infectious diseases caused by bacteria will still require the identification and development of new antimicrobial agents. Eight different natural products were tested for antimicrobial activity against seven pathogenic bacterial species (Brachyspira sp., Chlamydia sp., Clostridioides sp., Mannheimia sp., Mycobacterium sp., Mycoplasma sp., Pasteurella sp.). In a first pre-screening, most compounds (five out of eight) inhibited bacterial growth only at high concentrations, but three natural products (celastramycin A [CA], closthioamide [CT], maduranic acid [MA]) displayed activity at concentrations <2 µg/mL against Pasteurella sp. and two of them (CA and CT) also against Mannheimia sp. Those results were confirmed by testing a larger collection of isolates encompassing 64 Pasteurella and 56 Mannheimia field isolates originating from pigs or cattle, which yielded MIC90 values of 0.5, 0.5, and 2 µg/mL against Pasteurella and 0.5, 4, and >16 µg/mL against Mannheimia for CA, CT, and MA, respectively. CA, CT, and MA exhibited higher MIC50 and MIC90 values against Pasteurella isolates with a known AMR phenotype against commonly used therapeutic antimicrobial agents than against isolates with unknown AMR profiles. This study demonstrates the importance of whole-cell antibacterial screening of natural products to identify promising scaffolds with broad- or narrow-spectrum antimicrobial activity against important Gram-negative veterinary pathogens with zoonotic potential.

Bacterial heavy metal resistance related to environmental conditions

Contaminated water bodies such as rivers provide reservoirs for bacterial resistance. This field study tested the water quality and the bacterial resistance to heavy metals of Qishan River water pollution. Wastewater discharged to environmental surface waters is a major pathway of heavy metals and heavy metal-resistant bacteria. Contaminated water bodies such as rivers provide reservoirs for bacterial resistance. This field study tested the water quality and bacterial resistance to heavy metals of Qishan River water pollution. Guided by our research hypothesis that an overall increase in downstream heavy metal resistance levels was following an increase in human settlements were eight sites sampled along the Qishan River. These were situated upstream and downstream to the confluence of the Qishan River with the Kaoping River. In the laboratory bacterial heavy metal resistance was bio-assayed by disk diffusion and micro-dilution with six widely used heavy metals. The comparison of bacterial resistance was among Qishan River upstream sites (sites 1-6) and downstream sites (sites 7-9). Multi-drug-resistant bacteria and co-resistance against heavy metals and antibacterials appeared at site 8. This research discusses the correlation between environmental factors, and antibacterial and heavy metal resistance. The results provide stakeholders and authorities responsible for environmental pollution with a reference for risk assessment and management of bacterial resistance.

Riverine antibacterial resistance gradient determined by environmental factors

Polluted waterbodies such as rivers provide a pathway or reservoir for bacterial resistance. We studied water quality and bacterial antibacterial resistance along the subtropical Qishan River in Taiwan as a case study of environmental resistance spread in a pristine rural area. Human settlement densities increased generally from pristine mountain sites to the more polluted lowlands. Accordingly, as a working hypothesis, we expected the antibacterial resistance level to increase downstream. We collected sediment samples from 8 stations along the Qishan river and where the Qishan river reaches the Kaoping river. The samples were processed in the lab for bacteriological and physicochemical analysis. Antibacterial resistance was tested with common antibacterial. A comparison was made among the sites where isolates began to occur at the upstream (sites 1-6) with the downstream, including site 7 (Qishan town), site 8 (wastewater treatment plant), and site 9 (Kaoping river). The results of multivariate analysis for bacteriological and physicochemical parameters showed increasing water pollution levels downstream of the Qishan river. Bacterial isolates including Escherichia coli, Klebsiella pneumoniae, Serratia marcescens, Enterobacter sp., Acinetobacter sp., Staphylococcus spp., and Bacillus spp. were analyzed and tested in the study. Their percentage of occurrence varied at each site. The resistance level was determined from the growth inhibition zone diameter (disk diffusion) and the minimum inhibitory concentration (micro-dilution). The results indicated that antibacterial resistance was related to certain environmental factors. Besides, the usage pattern of different classes of antibacterial in different sections could alter trends of their resistance. Bacteria were found with increased resistance to antibacterial used in agriculture through the downstream sites. The WWTP discharging wastewater was demonstrated to be a hotspot of resistance in aquatic environments. In conclusion, bacterial resistance against antibacterial from the Qishan river has become a potential public health threat. This study could assist authorities by providing a reference for risk assessment and management of water quality in Kaohsiung city and southern Taiwan.

Porcine intestinal glycosphingolipids recognized by Brachyspira hyodysenteriae

Swine dysentery caused by Brachyspira hyodysenteriae is a disease present worldwide with an important economic impact on the farming business, resulting in an increased use of antibiotics. In the present study, we investigated the binding of B. hyodysenteriae to glycosphingolipids from porcine small intestinal epithelium in order to determine the glycosphingolipids involved in B. hyodysenteriae adhesion. Specific interactions between B. hyodysenteriae and two non-acid glycosphingolipids were obtained. These binding-active glycosphingolipids, were characterized by mass spectrometry as lactotetraosylceramide (Galβ3GlcNAcβ3Galβ4Glcβ1Cer) and the B5 glycosphingolipid (Galα3Galβ4GlcNAcβ3Galβ4Glcβ1Cer). Comparative binding studies using structurally related reference glycosphingolipids showed that B. hyodysenteriae binding to lactotetraosylceramide required an unsubstituted terminal Galβ3GlcNAc sequence, while for binding to the B5 pentaosylceramide the terminal Galα3Galβ4GlcNAc sequence is the minimum element recognized by the bacteria. Binding of Griffonia simplicifolia IB4 lectin to pig colon tissue sections from healthy control pig and B. hyodysenteriae infected pigs showed that in the healthy pigs the Galα3Gal epitope was mainly present in the lamina propria. In contrast, in four out of five pigs with swine dysentery there was an increased expression of Galα3Gal in the goblet cells and in the colonic crypts, where B. hyodysenteriae also was present. The one pig that had recovered by the time of necropsy had the Galα3Gal epitope only in the lamina propria. These data are consistent with a model where a transient increase in the carbohydrate sequence recognized by the bacteria occur in colonic mucins during B. hyodysenteriae infection, suggesting that the mucins may act as decoys contributing to clearance of the infection. These findings may lead to novel strategies for treatment of B. hyodysenteriae induced swine dysentery.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): antimicrobial-resistant Brachyspira hyodysenteriae in swine

Brachyspira hyodysenteriae (B. hyodysenteriae) was identified among the most relevant antimicrobial-resistant (AMR) bacteria in the EU for swine in a previous scientific opinion. Thus, it has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on its eligibility to be listed, Annex IV for its categorisation according to disease prevention and control rules as in Article 9, and Article 8 for listing animal species related to the bacterium. The assessment has been performed following a methodology previously published. The outcome is the median of the probability ranges provided by the experts, which indicates whether each criterion is fulfilled (lower bound ≥ 66%) or not (upper bound ≤ 33%), or whether there is uncertainty about fulfilment. Reasoning points are reported for criteria with uncertain outcome. According to the assessment here performed, it is uncertain whether AMR B. hyodysenteriae can be considered eligible to be listed for Union intervention according to Article 5 of the AHL (33-66% probability). According to the criteria in Annex IV, for the purpose of categorisation related to the level of prevention and control as in Article 9 of the AHL, the AHAW Panel concluded that the bacterium does not meet the criteria in Sections 1, 2 and 3 (Categories A, B and C; 1-10%, 10-33% and 10-33% probability of meeting the criteria, respectively) and the AHAW Panel was uncertain whether it meets the criteria in Sections 4 and 5 (Categories D and E, 50-90% and 33-66% probability of meeting the criteria, respectively). The main animal species to be listed for AMR B. hyodysenteriae according to Article 8 criteria are pigs and some species of birds, such as chickens and ducks.

Implementation and evaluation of different eradication strategies for Brachyspira hyodysenteriae

Background

Brachyspira infections are causing major losses to the pig industry and lead to high antimicrobial use. Treatment of Brachyspira (B.) hyodysenteriae infections may be problematic due to the high level of antimicrobial resistance. The present study implemented and evaluated farm-specific eradication programmes for B. hyodysenteriae in 10 different infected pig farms in Belgium.

Results

Ten pig farms clinically infected with B. hyodysenteriae volunteered to implement a farm-specific eradication programme. The programme depended on the farm and management characteristics, antimicrobial susceptibility of the B. hyodysenteriae strain and the motivation of the farmer. Two farms practiced total depopulation, six farms partial depopulation and two farms antimicrobial medication without depopulation. In addition, all farms implemented biosecurity measures, and faeces samples were tested for the presence of B. hyodysenteriae at 6, 9 and 12 months after the start of the program. Single Brachyspira isolates from before and after the programme were typed using multilocus sequence typing (MLST).Eradication was successful in four farms. Two of them (farrow-to-finish and finishing herd) had applied total depopulation and respected a vacancy period of at least 3 weeks. A third farm (gilt farm) practised partial depopulation, the rooms remained empty for 28 days and changed the source of breeding gilts. The fourth farm practised partial depopulation, the stables remained empty for 3 weeks, and used antimicrobial medication. The eradication programme was not successful in six farms. Two of the latter farms only used medication without partial depopulation. Four farms practiced partial depopulation, one of them combined it with antimicrobial medication. The cleaning and disinfection procedures, rodent control, stand-empty period and/or other biosecurity measures in the six farms were not always implemented properly. In two of three farms, isolates belonging to the same MLST type were found before and after eradication.

Conclusions

Total depopulation or partial depopulation combined with implementing strict biosecurity measures allowed eradication of B. hyodysenteriae from clinically infected pig farms. Programmes based on antimicrobials without depopulation or partial depopulation without strictly adhering to all suggested biosecurity measures were not successful. Stockmanship and motivation of the farmer to permanently maintain high biosecurity standards are essential for success.

Antimicrobial Resistance in Clostridium and Brachyspira spp. and Other Anaerobes

This article describes the antimicrobial resistance to date of the most frequently encountered anaerobic bacterial pathogens of animals. The different sections show that antimicrobial resistance can vary depending on the antimicrobial, the anaerobe, and the resistance mechanism. The variability in antimicrobial resistance patterns is also associated with other factors such as geographic region and local antimicrobial usage. On occasion, the same resistance gene was observed in many anaerobes, whereas some were limited to certain anaerobes. This article focuses on antimicrobial resistance data of veterinary origin.

Antimicrobial resistance in Brachyspira - An increasing problem for disease control

Across all bacterial species the continuing reduction in susceptibility to antimicrobial agents is a critical and increasing threat for disease control. This mini-review outlines the extent of this problem amongst anaerobic intestinal spirochaetes of the genus Brachyspira, of which there are currently nine officially recognised species. These include some important pathogens that may cause colitis with diarrhoea and/or dysentery in various mammalian and avian species, but most notably in pigs and in adult chickens. The most economically significant pathogen is Brachyspira hyodysenteriae, the spirochaete which causes swine dysentery in countries throughout the world. Control of infections with Brachyspira species has long relied on the prophylactic or therapeutic use of antimicrobials, but increasingly strains with reduced susceptibility and sometimes multidrug resistance to previously effective antimicrobial agents are being encountered. In this mini-review we outline these problems and explain the extent and molecular basis of the emerging resistance. Future control will rely on developing and applying standardised methods for measuring antimicrobial susceptibility; improving surveillance of resistance using traditional phenotypic as well as genomic analysis of known resistance determinants; improving understanding of the molecular basis of resistance to different drug classes; improving farmer and veterinarian education about prudent antimicrobial use so as to reduce selective pressure on the emergence of resistance; and developing alternatives to antimicrobials as a means to control these infections.

Isolation and antimicrobial susceptibility of Brachy -spira species from feces of layer chickens in Germany

Objective: Anaerobic spirochetes of the genus Brachyspira are important pathogens causing swine dysentery (Brachyspira [B.] hyodysenteriae) and porcine intestinal spirochetosis (B. pilosicoli, PIS). In addition, avian intestinal spirochetosis (AIS) is caused by B. pilosicoli, B. intermedia and B. alvinipulli. Despite the economic impact of AIS, the disease has not received appropriate attention in Germany. This study was aimed at identifying Brachyspira spp. in Germany and determining their antimicrobial susceptibility. Material and methods: From 2009 to 2013, a total of 71 fecal swabs were obtained from clinically healthy layer hens from eight different commercial flocks. Brachyspira spp. culture was performed in trypticase soybean agar added with 5% sheep blood. Species determination was conducted by PCRs targeting the NADH-gen and the 16S rDNA or by nox-gene sequencing. Antimicrobial susceptibility to macrolides, lincosamides and pleuromutilins was tested by a microdilution assay. Results: Brachyspira spp. were isolated from 40 (56.3%) swabs distributed over all eight flocks. In 26 cases, the following species were determined by PCR: B. pilosicoli (n = 16), B. intermedia (2), B. innocens (3), B. murdochii (1), mixtures of B. pilosicoli/B. intermedia (2), B. innocens/B. intermedia (1), B. innocens/B. murdochii (1). Remaining isolates were characterized by noxgene sequencing as B. “pulli” (n = 9), B. alvinipulli (3), B. intermedia (1) and as not identifiable (1). Antimicrobial susceptibility testing of 37 isolates revealed minimal inhibitory concentrations 90 (MIC90) of > 128 mg/l (tylosin), 64 mg/l (lincomycin), 8 mg/l (tiamulin) and 4 mg/l (valnemulin), respectively. Comparing to breakpoints applied to pigs, these values lie within the range of resistance. Conclusion The demonstration of different Brachyspira spp., particularly B. pilosicoli, intermedia and alvinipulli in commercial layers, indicates the need of further research to assess their potential role in causing AIS in German poultry flocks. The increased antimicrobial resistance of Brachyspira spp. isolates to tylosin and pleuromutilins is likely associated with extensive use of these drugs in poultry medicine.

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.

In vitro susceptibility of Brachyspira hyodysenteriae to a commercial citrus fruit extract

Brachyspira hyodysenteriae is the main etiological agent of swine dysentery (SD). Nowadays, treatment and control of SD is increasingly difficult due to the emergence of antimicrobial resistance together with the restrictions on the use of antibiotics in veterinary practice. The aim of this study was to evaluate, as an alternative in the control of this disease, the antimicrobial activity and the main mechanism of action of BIOCITRO, a citrus extract commercialized as raw material and used as feed additive, against B. hyodysenteriae. Ten isolates of B. hyodysenteriae were used to assess the minimum inhibitory and minimum bactericidal concentrations (MIC and MBC) of BIOCITRO by broth microdilution method. Moreover, stationary phase cultures of two B. hyodysenteriae strains were subjected for 90min to four different concentrations of BIOCITRO and compared with the untreated controls by flow cytometry (FC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results showed that BIOCITRO has a relevant bacteriostatic and bactericidal effect against B. hyodysenteriae with MIC and MBC values ranging from 32 to 128partspermillion (ppm). It induces damage in at least 35% and 76% of the bacterial cells when exposed to 128 and 256ppm of BIOCITRO respectively as revealed by the intake of propidium iodide by FC. Relevant changes in the structure of the bacterial cells were observed by SEM and confirmed by FTIR. According to these results, BIOCITRO seems to be a satisfactory alternative to the use of antibiotics in the control of SD.

A review of the current state of antimicrobial susceptibility test methods for Brachyspira

The re-emergence of swine dysentery (Brachyspira-associated muco-haemorrhagic colitis) since the late 2000s has illuminated diagnostic challenges associated with this genus. The methods used to detect, identify, and characterize Brachyspira from clinical samples have not been standardized, and laboratories frequently rely heavily on in-house techniques. Particularly concerning is the lack of standardized methods for determining and interpreting the antimicrobial susceptibility of Brachyspira spp. The integration of laboratory data into a treatment plan is a critical component of prudent antimicrobial usage. Therefore, the lack of standardized methods is an important limitation to the evidence-based use of antimicrobials. This review will focus on describing the methodological limitations and inconsistencies between current susceptibility testing schemes employed for Brachyspira, provide an overview of what we do know about the susceptibility of these organisms, and suggest future directions to improve and standardize diagnostic strategies.

Comparison of agar dilution and antibiotic gradient strip test with broth microdilution for susceptibility testing of swine Brachyspira species

Production-limiting diseases in swine caused by Brachyspira are characterized by mucohemorrhagic diarrhea ( B. hyodysenteriae and “ B. hampsonii”) or mild colitis ( B. pilosicoli), while B. murdochii is often isolated from healthy pigs. Emergence of novel pathogenic Brachyspira species and strains with reduced susceptibility to commonly used antimicrobials has reinforced the need for standardized susceptibility testing. Two methods are currently used for Brachyspira susceptibility testing: agar dilution (AD) and broth microdilution (BMD). However, these tests have primarily been used for B. hyodysenteriae and rarely for B. pilosicoli. Information on the use of commercial susceptibility testing products such as antibiotic gradient strips is lacking. Our main objective was to validate and compare the susceptibility results, measured as the minimum inhibitory concentration (MIC), of 6 antimicrobials for 4 Brachyspira species ( B. hyodysenteriae, “ B. hampsonii”, B. pilosicoli, and B. murdochii) by BMD and AD (tiamulin, valnemulin, lincomycin, tylosin, and carbadox) or antibiotic gradient strip (doxycycline) methods. In general, the results of a high percentage of all 4 Brachyspira species differed by ±1 log2 dilution or less by BMD and AD for tiamulin, valnemulin, lincomycin, and tylosin, and by BMD and antibiotic gradient strip for doxycycline. The carbadox MICs obtained by BMD were 1–5 doubling dilutions different than those obtained by AD. BMD for Brachyspira was quicker to perform with less ambiguous interpretation of results when compared with AD and antibiotic gradient strip methods, and the results confirm the utility of BMD in routine diagnostics.