Characterization of Erysipelothrix rhusiopathiae strains isolated from recent swine erysipelas outbreaks in Japan

A field comparison study of two vaccine protocols against Erysipelothrix rhusiopathiae in two types of swine breeds in Spain

Erysipelas still causes large economic losses to pig industry. Maternal immunity is critical to prevent erysipelas in young animals, thus, intensive vaccination protocols or practices focused on the improvement of the maternally derived immunity could provide substantial benefits. The present study evaluates potential changes in antibodies levels in sows and their offspring using two types of tests (commercial ELISA, Ingenasa or rSpaA415 ELISA) when two different vaccination programs (before farrowing or after farrowing) against Erysipelothrix rhusiopathiae were applied to sows from Iberian (A) or conventional Large White-Landrace (B) pig farms. The results showed a statistical correlation between titers found in sows and their one-week old piglets in both tests. The overall mean of (log) antibody titers in farm B measured by the commercial ELISA test was significantly higher in pre-farrowing vaccinated sows compared to the post-farrowing vaccine protocol (p = 0.0278). Additionally, using the rSpaA415 ELISA test, the overall mean of (log) antibody titers was significantly higher in pre-farrowing sows (p = 0.0056) compared to sows following post-farrowing vaccine protocol (p = 0.0003) or non- vaccinated sows. None of the above-mentioned differences were found in farm A. The overall mean of (log) antibody titers in piglets from the pre-farrowing vaccination protocol was significantly higher than piglets from the post-farrowing vaccination protocol in farm A (p = 0.0059; rSpaA415 ELISA) and farm B (p = 0.0168 and p = 0.0098 for the commercial and rSpaA415 ELISA data, respectively). Additionally, higher proportion of piglets from pre-farrowing vaccinated sows remained seropositive during the post-weaning period (days 42 to 84) compared to piglets from non-vaccinated or post-farrowing vaccinated groups in both farms A and B.

Phenotypic and Genotypic Characterization of a Highly Virulent Erysipelothrix rhusiopathiae Strain

Erysipelothrix rhusiopathiae is responsible for erysipelas infection in pigs. Outbreaks of E. rhusiopathiae have increased in several countries, including China, over the past two decades. An E. rhusiopathiae strain (ML101) was isolated and characterized from dead pig tissue sample collected from a farm experiencing an outbreak of E. rhusiopathiae, which was responsible for the deaths of 146 sows and 308 fattening pigs within a week. Spleen swelling, gastric and bladder mucosa bleeding, and submandibular lymph node swelling and bleeding were observed through necropsy. ML101 was identified as serotype 1a via molecular analysis and immunological assays. Studies in mice demonstrated that the minimal lethal dose per animal was less than 10 colony-forming units (CFU). Notably, the minimal lethal dose in piglets was also less than 10 CFU, which is lower than that of any E. rhusiopathiae strain reported to date. The challenged piglets showed typical acute erysipelas symptoms, such as pyrexia, hemorrhage, depression, complete inappetence, reddening, and purpling skin on the buttock. Evidence of efficient horizontal transmission was observed, as healthy pigs were infected and died when cohoused with challenged piglets. Whole-genome sequencing revealed that ML101 contained a 77 kb genomic island (GI), carrying a Tn916 transposon and a multidrug resistance gene cluster (aadE-apt-spw-lsa(E)-lnu(B)-aadE-sat4-aphA3). A retrospective analysis of E. rhusiopathiae isolates via PCR indicated that the GI has been widely distributed since 2010, when outbreaks were more frequently reported in China. This study demonstrated that the highly virulent E. rhusiopathiae is responsible for the erysipelas outbreak and indicates that relevant genes located within the transmissible genetic elements may play roles in virulence. Therefore, epidemiological monitoring needs to be emphasized to better prevent and control erysipelas in the swine industry, and live attenuated vaccines should be used with caution.

Population Structure and Genomic Characteristics of Australian Erysipelothrix rhusiopathiae Reveals Unobserved Diversity in the Australian Pig Industry

Erysipelothrix rhusiopathiae is a bacterial pathogen that is the causative agent of erysipelas in a variety of animals, including swine, emus, turkeys, muskox, caribou, moose, and humans. This study aims to investigate the population structure and genomic features of Australian isolates of E. rhusiopathiae in the Australian pig industry and compare them to the broader scope of isolates worldwide. A total of 178 isolates (154 Australian, seven vaccine isolates, six international isolates, and 11 of unknown origin) in this study were screened against an MLST scheme and publicly available reference isolates, identifying 59 new alleles, with isolates separating into two main single locus variant groups. Investigation with BLASTn revealed the presence of the spaA gene in 171 (96%) of the isolates, with three main groups of SpaA protein sequences observed amongst the isolates. Novel SpaA protein sequences, categorised here as group 3 sequences, consisted of two sequence types forming separate clades to groups 1 and 2, with amino acid variants at positions 195 (D/A), 303 (G/E) and 323(P/L). In addition to the newly identified groups, five new variant positions were identified, 124 (S/N), 307 (Q/R), 323 (P/L), 379 (M/I), and 400 (V/I). Resistance screening identified genes related to lincomycin, streptomycin, erythromycin, and tetracycline resistance. Of the 29 isolates carrying these resistance genes, 82% belonged to SpaA group 2-N101S (n = 22) or 2-N101S-I257L (n = 2). In addition, 79% (n = 23) of these 29 isolates belonged to MLST group ST 5. Our results illustrate that Australia appears to have a unique diversity of E. rhusiopathiae isolates in pig production industries within the wider global context of isolates.

Screening immune adjuvants for an inactivated vaccine against Erysipelothrix rhusiopathiae

In this study, we screened adjuvants for an inactivated vaccine against Erysipelothrix rhusiopathiae (E. rhusiopathiae). Inactivated cells of E. rhusiopathiae strain HG-1 were prepared as the antigen in five adjuvanted inactivated vaccines, including a mineral-oil-adjuvanted vaccine (Oli vaccine), aluminum-hydroxide-gel-adjuvanted vaccine (Alh vaccine), ISA201-biphasic-oil-emulsion-adjuvanted vaccine (ISA201 vaccine), GEL02-water-soluble-polymer-adjuvanted vaccine (GEL vaccine), and IMS1313-water-soluble-nanoparticle-adjuvanted vaccine (IMS1313 vaccine). The safety test results of subcutaneous inoculation in mice showed that Oli vaccine had the most severe side effects, with a combined score of 35, followed by the ISA201 vaccine (25 points), Alh vaccine (20 points), GEL vaccine (10 points), and IMS1313 vaccine (10 points). A dose of 1.5LD₅₀ of strain HG-1 was used to challenge the mice intraperitoneally, 14 days after their second immunization. The protective efficacy of Oli vaccine and Alh vaccine was 100% (8/8), whereas that of the other three adjuvanted vaccines was 88% (7/8). Challenge with 2.5LD₅₀ of strain HG-1 resulted in a 100% survival rate, demonstrating the 100% protective efficacy of the Oli vaccine, followed by the GEL vaccine (71%, 5/7), IMS1313 vaccine (57%, 4/7), ISA201 vaccine (43%, 3/7), and Alh vaccine (29%, 2/7). Challenge with 4LD₅₀ of strain HG-1 showed 100% (7/7) protective efficacy of the Oli vaccine and 71% (5/7) protective efficacy of the GEL vaccine, whereas the protective efficacy of other three adjuvanted vaccine was 14% (1/7). The Alh and GEL vaccines were selected for comparative tests in piglets, and both caused minor side effects. A second immunization with these two adjuvanted vaccines conferred 60 and 100% protective efficacy, respectively, after the piglets were challenged via an ear vein with 8LD₁₀₀ of strain HG-1. After challenge with 16LD₁₀₀ of strain HG-1, the Alh and GEL vaccines showed 40% and 100% protective efficacy, respectively. Our results suggested that GEL is the optimal adjuvant for an inactivated vaccine against E. rhusiopathiae.

The Swine Erysipelas Vaccine SER-ME Effectively Protects Pigs against Challenge with the Erysipelothrix rhusiopathiae M203/I257 SpaA-Type Variant

Simple Summary

Swine erysipelas caused by the Erysipelothrix rhusiopathiae occurred frequently among pigs in Japan mostly by the serovar 1a variant featured by two amino acids in the surface protective antigen A protein. To determine if current vaccines are effective against the variant infection in pigs, one inactivated vaccine, SER-ME containing serovar 2a as the immunogen, was representatively evaluated. All vaccinated pigs survived without any apparent clinical signs after lethal challenge with the Fujisawa reference strain or the variant. This indicates that the serovar 2a immunogen of SER-ME vaccine effectively protects pigs against the E. rhusiopathiae variant and was not related to the emergences of the variant.

Abstract

Erysipelothrix rhusiopathiae causes swine erysipelas (SE). Sporadic SE outbreaks in Japan are mostly caused by the E. rhusiopathiae serovar 1a variant featured by methionine (M) and isoleucine (I) at amino acid positions 203 and 257 of the surface protective antigen (Spa) A protein (M203/I257 SpaA-type). To determine if current vaccines are effective against infection with this variant in pigs, one representative inactivated vaccine, SER-ME (containing E. rhusiopathiae serovar 2a), was evaluated. All vaccinated pigs survived without any apparent clinical signs after lethal challenge with the Fujisawa reference strain or the variant. This indicates that the SER-ME vaccine effectively protects pigs against the infection of E. rhusiopathiae M203/I257 SpaA-type variant. Current vaccines in Japan, including SER-ME, suggest that outbreaks in Japan are unlikely caused by vaccine failure.

Comparative study of the phenotype and virulence of recent serovar 1a, 1b, and 2a isolates of Erysipelothrix rhusiopathiae in Japan

Erysipelothrix rhusiopathiae causes swine erysipelas (SE) and is classified -into 16 serovars based on cell surface antigens. Our previous study suggested that recent SE outbreaks were mostly caused by serovar 1a of E. rhusiopathiae with the surface protective antigen (Spa)A protein characterized by methionine and isoleucine at positions 203 and 257 (M203/I257 SpaA). In this study, four recent E. rhusiopathiae isolates comprising two serovar 1a with M203/I257 SpaA strains (2012 Miyazaki and 2012 Chiba), one serovar 1b strain (2015 Miyazaki), and one serovar 2a strain (2012 Nagano) were compared with each other and with the serovar 1a Fujisawa reference strain regarding in vitro phenotypes and in vivo virulence in mice and pigs. The serovar 1b and 2a strains, which are the less prevalent strains in the field in Japan, showed lower growth in liquid culture and lower virulence in animals than the serovar 1a variants. Adhesion of the serovar 2a strain to porcine endothelial cells was weaker than that of the serovar 1a and 1b strains. Several advantages of serovar 1a strains were found, but no plausible cause of the M203/I257 SpaA type variants to be selected for the most prevalent strains among serovar 1a strains was identified in this study.

Characterization of Erysipelothrix rhusiopathiae Isolates from Diseased Pigs in 15 Chinese Provinces from 2012 to 2018

Erysipelothrix rhusiopathiae can cause erysipelas in animals and erysipeloid in humans. Since its recurrence in 2012, swine erysipelas has caused serious losses within the pig industry in China. The aim of this study was to perform multilocus sequence typing and understand the virulence and antimicrobial susceptibility of E. rhusiopathiae isolates in China. Multilocus sequence typing (MLST) of a total of 120 strains was performed, and as a result, three different sequence types were identified, of which ST48 was the main one. Five isolates of each MLST type were randomly selected to be used to challenge mice. ST48 was associated with a higher virulence. Antimicrobial susceptibility was tested using a microdilution technique and, to analyze the resistance mechanism, six strains were selected for genome sequencing. A comparison of the six genomes indicated the presence of a suspected macrolide resistance gene, namely, Erm(A)-like, in erythromycin-resistant strains, which increased the minimum inhibitory concentration (MIC) of erythromycin against E. coli C600 at least four-fold. In addition, three mutations (gyrA86T-I, gyrA90D-N, and parC81S-I) were observed in the quinolone resistance-determining regions (QRDRs) of gyrA and parC in quinolone-resistant strains. After the gyrA gene with the 86T-I mutation or the parC gene with the 81S-I mutation was transfected into E. coli C600, the MIC of enrofloxacin against this strain increased at least two-fold. Our findings provide a theoretical basis for developing antibacterial drugs and may contribute to the clinical prevention and control of E. rhusiopathiae.

A PCR assay to specifically detect serovar 1a strains of Erysipelothrix rhusiopathiae and differentiate them from serovar 2 strains possessing an intact ERH_1440 gene

The Erysipelothrix rhusiopathiae ERH_1440 gene, which encodes CDP-glycerol:poly (glycerophosphate) glycerophosphotransferase, is conserved in serovar 1a strains. The gene is usually missing or truncated in other serovar strains and therefore has been used for PCR detection of serovar 1a strains. We have previously reported a rare case of an E. rhusiopathiae serovar 2 strain possessing an intact ERH_1440. In this study, we analyzed three additional serovar 2 strains with an intact ERH_1440 and developed a new PCR assay for the specific detection and differentiation of serovar 1a strains from these serovar 2 strains. PCR with primers designed based on serovar 1a-specific gene sequences upstream of ERH_1440 showed 100% specificity for four hundred thirty Erysipelothrix strains isolated from extensive origins.

First Report of Genetic Variability of Erysipelothrix sp. Strain 2 in Turkeys Associated to Vero Cells Morphometric Alteration

Erysipelas is a disease caused by the Erysipelothrix genus, whose main species is the E. rhusiopathiae, the causative agent of animal erysipelas and human erysipeloid. We isolated Erysipelothrix sp. strain 2 (ES2) from turkey's organs during an outbreak in Brazilian commercial and breeder flocks with sepsis and high mortality levels. We studied 18 flocks, accounting for 182 samples, being eight flocks (84 samples) as ES2 positive with individuals demonstrating clinical symptoms and high mortality. We obtained the genetic variability of 19 samples with PFGE and found two clones, both from the same flock but different samples, and two clusters. Interestingly, we found 15 strains with high genetic variability among and within flocks. We have found a positive association between the proximity of ES2 positive turkey flocks and commercial swine sites through epidemiological analysis. We infected Vero cells with two different isolates and three distinct concentrations of ES2. After performing the morphometry, we recorded enlargement of the nucleus and nucleolus. Moreover, we performed fluorescence assays that resulted in apoptotic and necrotic cells. We demonstrated that ES2 could multiply in the extracellular medium and invade and survive inside Vero cells. For the first time, our finds show that ES2 may have similar behavior as E. rhusiopathiae as a facultative intracellular microorganism, which may represent a hazard for humans.

Serovars and SpaA Types of Erysipelothrix rhusiopathiae Isolated from Pigs in Japan from 2012 to 2019

Erysipelothrix rhusiopathiae causes swine erysipelas (SE), which results in considerable economic loss on pig farms. During SE outbreaks that occurred sporadically from 2008 to 2011 in Japan, new E. rhusiopathiae strains were isolated with a specific surface protective antigen (Spa)A protein characterized by methionine at position 203 and isoleucine at position 257 (M203/I257 SpaA type). To determine whether strains with the M203/I257 SpaA type are still prevalent in Japan, we collected 79 strains of E. rhusiopathiae from pigs showing various SE symptoms from 2012 to 2019 and classified them based on serovar typing, spaA gene sequence analysis, and lineage typing. We found that the majority of recent E. rhusiopathiae strains (59/79) belonged to the serovar 1a strain, and that the M203/I257 SpaA type (56/59) was predominant continuing from 2008 to 2011. Furthermore, serovar 1a strains with IVb-1 and IVb-2 lineages that had been isolated in specific regions of Japan were no longer local but were found across Japan. The pathogenicity of recent isolates tested in mice was not significantly changed when compared to that of previously isolated strains. Our results suggest that recent SE outbreaks were not due to changes in the SpaA protein or to altered virulence of E. rhusiopathiae but were rather caused by the persistent presence of E. rhusiopathiae with the M203/I257 SpaA type.

Potential risk factors of swine erysipelas outbreak in Northeast Mainland China

Swine erysipelas is a common infectious disease that affects the pig-breeding industry. The purpose of this study was to elucidate the risk factors and their role in the prevalence of swine erysipelas so that one may be able to better prevent and control the swine erysipelas outbreaks in Northeast China. Using spatial clusters, the study area was divided into two parts: South Central Mainland China (hot spots) and Northeast Mainland China (potential outbreak areas). We investigated a total of 31 environmental factors and used the lasso regression and k-fold cross-validation methods to determine the main factors involved. Seven risk factors were determined to have a major impact on swine erysipelas. Multiple logistic regression was used to examine the contribution of these seven risk factors to the outbreak from 2008 to 2018, in the two research regions. In South Central Mainland China, where swine erysipelas was most prevalent, the extreme maximum temperature [OR = 1.143 (95%CI: 1.032-1.342)], total precipitation [OR = 2.298 (95%CI: 1.410-5.112)] and precipitation ≥0.1 mm [OR = 2.396 (95%CI: 1.329-5.941)] exhibited positive effects. The maximum wind speed [OR = 0.550 (95%CI: 0.303-0.775)] and concentration of O3-8H-90 per [OR = 0.876 (95%CI: 0.747-0.980)] exhibited negative effects. Summer was the main season for the erysipelas epidemic in South Central Mainland China. In Northeast China, only the total precipitation [OR = 1.048 (95%CI: 0.900-0.989)] was positively correlated with the prevalence of swine erysipelas, whereas the other factors were not significant. There was no obvious seasonal feature for the epidemic. Through the comparison and analysis of risk factors between the two research regions, more attention should be given to the impacts of high temperature and precipitation on the swine erysipelas epidemic in Northeast China.

Erysipelothrix Spp.: Past, Present, and Future Directions in Vaccine Research

Erysipelothrix spp. comprise a group of small Gram-positive bacteria that can infect a variety of hosts including mammals, fish, birds, reptiles and insects. Among the eight Erysipelothrix species that have been described to date, only Erysipelothrix rhusiopathiae plays a major role in farmed livestock where it is the causative agent of erysipelas. E. rhusiopathiae also has zoonotic potential and can cause erysipeloid in humans with a clear occupational link to meat and fish industries. While there are 28 known Erysipelothrix serovars, over 80% of identified isolates belong to serovars 1 or 2. Vaccines to protect pigs against E. rhusiopathiae first became available in 1883 as a response to an epizootic of swine erysipelas in southern France. The overall vaccine repertoire was notably enlarged between the 1940s and 1960s following major outbreaks of swine erysipelas in the Midwest USA and has changed little since. Traditionally, E. rhusiopathiae serovar 1a or 2 isolates were inactivated (bacterins) or attenuated and these types of vaccines are still used today on a global basis. E. rhusiopathiae vaccines are most commonly used in pigs, poultry, and sheep where the bacterium can cause considerable economic losses. In addition, erysipelas vaccination is also utilized in selected vulnerable susceptible populations, such as marine mammals in aquariums, which are commonly vaccinated at regular intervals. While commercially produced erysipelas vaccines appear to provide good protection against clinical disease, in recent years there has been an increase in perceived vaccine failures in farmed animals, especially in organic outdoor operations. Moreover, clinical erysipelas outbreaks have been reported in animal populations not previously considered at risk. This has raised concerns over a possible lack of vaccine protection across various production species. This review focuses on summarizing the history and the present status of E. rhusiopathiae vaccines, the current knowledge on protection including surface antigens, and also provides an outlook into future directions for vaccine development.

Genomic and Immunogenic Protein Diversity of Erysipelothrix rhusiopathiae Isolated From Pigs in Great Britain: Implications for Vaccine Protection

Erysipelas, caused by the bacterium Erysipelothrix rhusiopathiae, is re-emerging in swine and poultry production systems worldwide. While the global genomic diversity of this species has been characterized, how much of this genomic and functional diversity is maintained at smaller scales is unclear. Specifically, while several key immunogenic surface proteins have been identified for E. rhusiopathiae, little is known about their presence among field strains and their divergence from vaccines, which could result in vaccine failure. Here, a comparative genomics approach was taken to determine the diversity of E. rhusiopathiae strains in pigs in Great Britain over nearly three decades, as well as to assess the field strains’ divergence from the vaccine strain most commonly used in British pigs. In addition, the presence/absence and variability of 13 previously described immunogenic surface proteins was determined, including SpaA which is considered a key immunogen. We found a high diversity of E. rhusiopathiae strains in British pigs, similar to the situation described in European poultry but in contrast to swine production systems in Asia. Of the four clades of E. rhusiopathiae found globally, three were represented among British pig isolates, with Clade 2 being the most common. All British pig isolates had one amino acid difference in the immunoprotective domain of the SpaA protein compared to the vaccine strain. However, we were able to confirm using in silico structural protein analyses that this difference is unlikely to compromise vaccine protection. Of 12 other known immunogenic surface proteins of E. rhusiopathiae examined, 11 were found to be present in all British pig isolates and the vaccine strain, but with highly variable degrees of conservation at the amino acid sequence level, ranging from 0.3 to 27% variant positions. Moreover, the phylogenetic incongruence of these proteins suggests that horizontal transfer of genes encoding for antigens is commonplace for this bacterium. We hypothesize that the sequence variants in these proteins could be responsible for differences in the efficacy of the immune response. Our results provide the necessary basis for testing this hypothesis through in vitro and in vivo studies.

Wild boars: A potential source of Erysipelothrix rhusiopathiae infection in Japan

The potential role of wild boars as a source of erysipelas infection was investigated. An ELISA test of wild boar serum samples from 41 prefectures in Japan revealed that proportions of the Erysipelothrix rhusiopathiae-positive samples were very high in all the prefectures, and the mean positive rate was 95.6% (1312/1372). Serovars of E. rhusiopathiae isolates from wild boars were similar to those of previously reported swine isolates, and all serovar isolates tested were found to be pathogenic to mice. These results suggest that wild boars in Japan constitute a reservoir of E. rhusiopathiae and may pose risks to other animals.

Multiplex PCR assay for the simultaneous detection and differentiation of clonal lineages of Erysipelothrix rhusiopathiae serovar 1a strains currently circulating in Japan

The species Erysipelothrix rhusiopathiae displays genetic heterogeneity; however, E. rhusiopathiae serovar 1a strains currently circulating in Japan exhibit remarkably low levels of genetic diversity and group into clonal sublineages of Lineage IVb (IVb-1 and IVb-2). In the present study, based on whole genome sequencing data, we designed primers for a multiplex PCR assay to simultaneously detect and differentiate the sublineages of E. rhusiopathiae strains. Among the one hundred and twenty-seven isolates of various serovar strains, including isolates from a wide range of hosts and geographic origins, the PCR assay could successfully detect and differentiate the serovar 1a strains belonging to the sublineages.

Clonal Lineages of Erysipelothrix rhusiopathiae Responsible for Acute Swine Erysipelas in Japan Identified by Using Genome-Wide Single-Nucleotide Polymorphism Analysis

Erysipelothrix rhusiopathiae causes swine erysipelas, an important infectious disease in the swine industry. In Japan, the incidence of acute swine erysipelas due to E. rhusiopathiae serovar 1a has recently increased markedly. To study the genetic relatedness of the strains from the recent cases, we analyzed 34 E. rhusiopathiae serovar 1a swine isolates collected between 1990 and 2011 and further investigated the possible association of the live Koganei 65-0.15 vaccine strain (serovar 1a) with the increase in cases. Pulsed-field gel electrophoresis analysis revealed no marked variation among the isolates; however, sequencing analysis of a hypervariable region in the surface-protective antigen A gene (spaA) revealed that the strains isolated after 2007 exhibited the same spaA genotype and could be differentiated from older strains. Phylogenetic analysis based on genome-wide single-nucleotide polymorphisms (SNPs) revealed that the Japanese strains examined were closely related, showing a relatively small number of SNPs among them. The strains were classified into four major lineages, with Koganei 65-0.15 (lineage III) being phylogenetically separated from the other three lineages. The strains isolated after 2007 and the two older strains constituted one major lineage (lineage IV) with a specific spaA genotype (M203/I257-SpaA), while the recent isolates were further divided into two geographic groups. The remaining older isolates belonged to either lineage I, with the I203/L257-SpaA type, or lineage II, with the I203/I257-SpaA type. These results indicate that the recent increased incidence of acute swine erysipelas in Japan is associated with two sublineages of lineage IV, which have independently evolved in two different geographic regions.IMPORTANCE Using large-scale whole-genome sequence data from Erysipelothrix rhusiopathiae isolates from a wide range of hosts and geographic origins, a recent study clarified the existence of three distinct clades (clades 1, 2, and 3) that are found across multiple continents and host species, representing both livestock and wildlife, and an "intermediate" clade between clade 2 and the dominant clade 3 within the species. In this study, we found that the E. rhusiopathiae Japanese strains examined exhibited remarkably low levels of genetic diversity and confirmed that all of the Japanese and Chinese swine isolates examined in this study belong to clonal lineages within the intermediate clade. We report that spaA genotyping of E. rhusiopathiae strains is a practical alternative to whole-genome sequencing analysis of the E. rhusiopathiae isolates from eastern Asian countries.

Serotypes and Spa types of Erysipelothrix rhusiopathiae isolates from British pigs (1987 to 2015)

Erysipelothrix spp. cause a range of clinical signs in pigs and at least 28 different Erysipelothrix spp. serotypes have been identified. In this study, 128 isolates of Erysipelothrix spp. from pigs in Great Britain from 1987 to 2015 were characterised by serotyping and multiplex real time PCR assays targeting the surface protective antigen (Spa) and the main genotypes (Erysipelothrix rhusiopathiae, Erysipelothrix tonsillarum and Erysipelothrix spp. strain 2). All 128 British isolates were characterised as E. rhusiopathiae and were classified as serotypes 1a (n=21), 1b (n=17), 2 (n=75), 5 (n=2), 9 (n=2), 10 (n=2), 11 (n=4) and 15 (n=1), while four isolates were untypeable. All isolates were positive for the spa A gene. Serotypes 1a, 1b and 2 constituted 88.3% of the isolates; current serotype 2 based vaccines should protect against these isolates.

Experimental induction of necrotic enteritis in chickens by a netB-positive Japanese isolate of Clostridium perfringens

Necrotic enteritis (NE) is one of the most important bacterial diseases in terms of economic losses. Clostridium perfringens necrotic enteritis toxin B, NetB, was recently proposed as a new key virulent factor for the development of NE. The goal of this work was to develop a necrotic enteritis model in chickens by using a Japanese isolate of C. perfringens. The Japanese isolate has been found to contain netB gene, which had the same nucleotide and deduced amino acid sequences as those of prototype gene characterized in Australian strain EHE-NE18, and also expressed in vitro a 33-kDa protein identified as NetB toxin by nano-scale liquid chromatographic tandem mass spectrometry. In the challenge experiment, broiler chickens fed a commercial chicken starter diet for 14 days post-hatch were changed to a high protein feed mixed 50:50 with fishmeal for 6 days. At day 21 of age, feed was withheld for 24 hr, and each chicken was orally challenged twice daily with 2 ml each of C. perfringens culture (10⁹ to 10¹⁰ CFU) on 5 consecutive days. The gross necrotic lesions were observed in 90 and 12.5% of challenged and control chickens, respectively. To our knowledge, this is the first study that demonstrated that a netB-positive Japanese isolate of C. perfringens is able to induce the clinical signs and lesions characteristic of NE in the experimental model, which may be useful for evaluating the pathogenicity of field isolates, the efficacy of a vaccine or a specific drug against NE.

Pathogenic characterization of Erysipelothrix rhusiopathiae Met-203 type SpaA strains from chronic and subacute swine erysipelas in Japan

To characterize the Erysipelothrix rhusiopathiae Met-203 type surface protective antigen (Spa) A strains causing swine erysipelas in Japan, the nucleotide sequence of the hypervariable region of the spaA gene was determined in 80 E. rhusiopathiae (serotype 1a) isolates collected from pigs with chronic and subacute swine erysipelas in 14 prefectures in 2008-2014. In this study, 14 (17.5%) isolates were Met-203 type SpaA strains. We confirmed the pathogenicity of a Met-203 type SpaA strain in specific-pathogen-free pigs. In this experiment, the two challenged pigs displayed arthritis, urticaria and other clinical signs, but recovered within 10 days. Our results reveal the existence of the E. rhusiopathiae Met-203 type strains that have been causing chronic erysipelas in Japan.

Genomic analysis of the multi-host pathogen Erysipelothrix rhusiopathiae reveals extensive recombination as well as the existence of three generalist clades with wide geographic distribution

Background

Knowledge about how bacterial populations are structured is an important prerequisite for studying their ecology and evolutionary history and facilitates inquiry into host specificity, pathogenicity, geographic dispersal and molecular epidemiology. Erysipelothrix rhusiopathiae is an opportunistic pathogen that is currently reemerging in both the swine and poultry industries globally. This bacterium sporadically causes mortalities in captive marine mammals, and has recently been implicated in large-scale wildlife die-offs. However, despite its economic relevance and broad geographic and host distribution, including zoonotic potential, the global diversity, recombination rates, and population structure of this bacterium remain poorly characterized. In this study, we conducted a broad-scale genomic comparison of E. rhusiopathiae based on a diverse collection of isolates in order to address these knowledge gaps.

Results

Eighty-three E. rhusiopathiae isolates from a range of host species and geographic origins, isolated between 1958 and 2014, were sequenced and assembled using both reference-based mapping and de novo assembly. We found that a high proportion of the core genome (58 %) had undergone recombination. Therefore, we used three independent methods robust to the presence of recombination to define the population structure of this species: a phylogenetic tree based on a set of conserved protein sequences, in silico chromosome painting, and network analysis. All three methods were broadly concordant and supported the existence of three distinct clades within the species E. rhusiopathiae. Although we found some evidence of host and geographical clustering, each clade included isolates from diverse host species and from multiple continents.

Conclusions

Using whole genome sequence data, we confirm recent suggestions that E. rhusiopathiae is a weakly clonal species that has been shaped extensively by homologous recombination. Despite frequent recombination, we can reliably identify three distinct clades that do not clearly segregate by host species or geographic origin. Our results provide an essential baseline for future molecular epidemiological, ecological and evolutionary studies of E. rhusiopathiae and facilitate comparisons to other recombinogenic, multi-host bacteria.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2643-0) contains supplementary material, which is available to authorized users.

A combinational approach of multilocus sequence typing and other molecular typing methods in unravelling the epidemiology of Erysipelothrix rhusiopathiae strains from poultry and mammals

Erysipelothrix rhusiopathiae infections re-emerged as a matter of great concern particularly in the poultry industry. In contrast to porcine isolates, molecular epidemiological traits of avian E. rhusiopathiae isolates are less well known. Thus, we aimed to (i) develop a multilocus sequence typing (MLST) scheme for E. rhusiopathiae, (ii) study the congruence of strain grouping based on pulsed-field gel electrophoresis (PFGE) and MLST, (iii) determine the diversity of the dominant immunogenic protein SpaA, and (iv) examine the distribution of genes putatively linked with virulence among field isolates from poultry (120), swine (24) and other hosts (21), including humans (3). Using seven housekeeping genes for MLST analysis we determined 72 sequence types (STs) among 165 isolates. This indicated an overall high diversity, though 34.5% of all isolates belonged to a single predominant ST-complex, STC9, which grouped strains from birds and mammals, including humans, together. PFGE revealed 58 different clusters and congruence with the sequence-based MLST-method was not common. Based on polymorphisms in the N-terminal hyper-variable region of SpaA the isolates were classified into five groups, which followed the phylogenetic background of the strains. More than 90% of the isolates harboured all 16 putative virulence genes tested and only intI, encoding an internalin-like protein, showed infrequent distribution. MLST data determined E. rhusiopathiae as weakly clonal species with limited host specificity. A common evolutionary origin of isolates as well as shared SpaA variants and virulence genotypes obtained from avian and mammalian hosts indicates common reservoirs, pathogenic pathways and immunogenic properties of the pathogen.

Development of an SNP-based PCR assay for rapid differentiation of a Japanese live vaccine strain from field isolates of Erysipelothrix rhusiopathiae

The differentiation of vaccine from non-vaccine isolates is important for disease control. Based on single nucleotide polymorphisms identified by comparison of the genomes of the Koganei 65-0.15 vaccine strain and a reference strain of Erysipelothrix rhusiopathiae, we developed a PCR assay that can differentiate the vaccine strain from field isolates.

Characterization of Erysipelothrix rhusiopathiae strains isolated from acute swine erysipelas outbreaks in Eastern China

Recently, a series of acute swine erysipelas outbreaks occurred in Eastern China. Eight strains isolated from cases of septicemia were determined as serotype 1a, and 4 of the isolates were resistant to acriflavine. One isolate strain named HX130709 was attenuated on agar media containing acriflavine dye. The 432-bp hypervariable region in spaA gene of the field and attenuated strains were amplified and sequenced. It was further compared with the vaccine strain G4T10, and thus, the eight field strains can be divided into four spaA-types. The partial spaA gene analysis also showed that no point mutations occurred among different archived passages of HX130709 during the attenuation. Results of pulsed-field gel electrophoresis showed that eight distinct patterns with 22 to 30 DNA fragment bands were produced from field strains, and twelve distinct patterns with 23 to 27 DNA fragment bands were produced from different passages of the attenuated strains. Mouse pathogenicity test showed that the mortality of the mice infected with 10(4) CFU field strains was 100% and the attenuation of strain HX130709 occurred between 46 and 50 passages. All the field and attenuated strains were highly sensitive to β-lactam antibiotics, tetracyclines and macrolides. So, we can make conclusions that the acute swine erysipelas outbreaks in Eastern China were caused by serotype 1a E. rhusiopathiae strains with different biochemical characteristics, and the virulence of serotype 1a E. rhusiopathiae strains is unrelated with some point mutations in 432-bp hypervariable region of the spaA gene.

Presence and new genetic environment of pleuromutilin-lincosamide-streptogramin A resistance gene lsa(E) in Erysipelothrix rhusiopathiae of swine origin

Erysipelothrix rhusiopathiae is a Gram-positive bacillus that causes erysipelas in swine. In recent years, erysipelas infection among swine in China has been increasing. A combined resistance phenotype to pleuromutilins, lincosamides, and streptogramin A (PLSA phenotype) was found in some E. rhusiopathiae isolates. The aim of this study was to identify the resistance genes responsible for the PLSA phenotype in E. rhusiopathiae strains and to map the genetic environment of the identified resistance gene. A total of 46 E. rhusiopathiae isolates from 31 pig farms in China were studied. Minimum inhibitory concentrations (MICs) of 11 antimicrobial agents were determined by broth microdilution method. Seven were highly resistant to tiamulin (MICs 32 μg/ml) and clindamycin (MICs 64 μg/ml). Resistance genes responsible for the PLSA phenotype were screened by PCR. The lsa(E), spw, lnu(B), aadE and aphA3 genes were detected in strains had the PLSA phenotype, whereas none was detected in susceptible strains. The genetic environment of lsa(E) gene was determined by whole-genome sequencing and overlapping PCR assays. A novel multiresistance gene cluster, orf1-aadE-apt-spw-lsa(E)-lnu(B)-rec-orf2-orf1-aadE-sat4-aphA3, was found. Horizontal gene transfer experiments and whole-genome sequencing suggested that the lsa(E)-carrying multiresistance gene cluster was located in the chromosome. This is the first molecular characterization of PLSA resistance in E. rhusiopathiae. The lsa(E), spw and lnu(B) genes were found in E. rhusiopathiae for the first time. A novel lsa(E)-carrying multiresistance gene cluster was found. The location of lsa(E) in different gene cluster facilitates its persistence and dissemination.

Prevalence of Met-203 type spaA variant in Erysipelothrix rhusiopathiae isolates and the efficacy of swine erysipelas vaccines in Japan

Since 2009, erysipelas infection among pigs in Japan has been increasing. This study investigated the prevalence, and characteristics of Erysipelothrix rhusiopathiae isolates in Japan from 2008 to 2010 and assessed the efficacy of current commercial erysipelas vaccines. Based on polymorphisms in a 432-bp hypervariable region in the surface protective antigen A (spaA) gene, 34 isolates were classified into three groups: (i) Group 1 with methionine at position 203 (Met-203) and isoleucine at position 257 (Ile-257) (18 isolates of serotype 1a and one untypable isolate). (ii) Group 2 with Ile-257 (12 isolates of serotypes 1a, 1b, 2, 10 and 11), and (iii) Group 3 with alanine at position 195 (Ala-195) and Ile-257 (three isolates of serotype 1a). Isolates with Met-203 were highly pathogenic in mice and pigs, causing death in the pig and LD50 values of 0.45-1.45 CFU per mouse. One live and three inactivated commercial E. rhusiopathiae vaccines were evaluated for efficacy against a Met-203 isolate. Almost all mice and pigs that received vaccine survived, while non-vaccinated controls all died within 5 days of the challenge. This indicates that swine erysipelas vaccines might be still effective in protecting animals against the recently prevalent Met-203 isolates in Japan.

Protection of immunized mice and swine to challenge exposure with Erysipelothrix rhusiopathiae strains obtained from recent swine erysipelas outbreaks in Japan

The aim of the study was to investigate the protective effect provided by immunization with commercial erysipelas vaccines in mice and conventional pigs to challenge with the field strains (serotype 1a) ofErysipelothrix rhusiopathiae. Sequence analysis of surface protective antigen (spaA) gene revealed that the strains were different from those reported previously. A total of 150 mice immunized subcutaneously with live or inactivated vaccines were protected against challenge exposure to one reference and four field strains. Seven conventional pigs immunized intramuscularly with inactivated vaccines developed specific antibodies against the SpaA protein ofE. rhusiopathiaeand were protected against challenge with two field strains. Our study is the first to demonstrate that the commercially available vaccines could protect animals against challenge with the most recently isolated SpaA-type strains ofE. rhusiopathiae.