Development of an unambiguous and discriminatory multilocus sequence typing scheme for the Streptococcus zooepidemicus group

An Overview of Infectious and Non-Infectious Causes of Pregnancy Losses in Equine

Equine breeding plays an essential role in the local economic development of many countries, and it has experienced rapid growth in China in recent years. However, the equine industry, particularly large-scale donkey farms, faces a significant challenge with pregnancy losses. Unfortunately, there is a lack of systematic research on abortion during equine breeding. Several causes, both infectious and non-infectious, of pregnancy losses have been documented in equines. The infectious causes are viruses, bacteria, parasites, and fungi. Non-infectious causes may include long transportation, ingestion of mycotoxins, hormonal disturbances, twinning, placentitis, umbilical length and torsion, etc. In current review, we discuss the transmission routes, diagnostic methods, and control measures for these infectious agents. Early detection of the cause and appropriate management are crucial in preventing pregnancy loss in equine practice. This review aims to provide a comprehensive understanding of the potential causes of abortion in equines, including infectious agents and non-infectious factors. It emphasizes the importance of continued research and effective control measures to address this significant challenge in the equine industry.

Streptococcus equi subsp. zooepidemicus: High molecular diversity of Argentinian strains isolated from mares with endometritis

Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) is a mucosal commensal of the lower genital tract in horses and is the most isolated bacterium causing endometritis in mares. The aim of this study was to determine the molecular diversity of S. zooepidemicus obtained from endometritis in mares in Buenos Aires province, Argentina. Thirty isolates obtained from the uterus of mares in 2005 and 2017 were studied. The MLST scheme was applied to identify the Argentinian genotypes and the clonal relationships and patterns of evolutionary descent were identified using the eBURST algorithm - goeBURST. Twenty six different Sequence types (STs) were identified, being only 11 of them previously reported in horses and also, from several host species and tissues. The other 15 STs were reported in Argentinian reproductive strains of mares in our study for the first time. The genotypes obtained from uterus in Argentina were not evenly distributed when all the published S. zooepidemicus STs were analysed, thus, it was not possible to establish that the same lineage circulates in our equine population. The fact that the identified genotypes were also reported in other countries, diverse samples and host species suggest that there is not a host, and an anatomical niche adaptation. Finally, the isolation of the same genotype in the vagina/clitoris and the uterus of the same mare highlights the versatility of S. zooepidemicus and its role as an opportunistic pathogen.

Streptococcus zooepidemicus in dogs: Exploring a canine pathogen through multilocus sequence typing

Streptococcus equi. subsp. zooepidemicus (S. zooepidemicus) associated diseases in dogs have emerged as a significant concern over recent decades. S. zooepidemicus occurs sporadically in dog populations globally, with increased prevalence in shelters/kennels. This study used multilocus sequence typing (MLST) of 149 independent canine S. zooepidemicus isolates to assess associations between sequence type and breed, country of origin, disease severity, sampling type, year, and behaviour within an outbreak. No clear associations for breed, country, sampling type and year were determined in this study. ST-10 and 123 strains were present within all disease categories, from no clinical signs to severe disease. Assessment of S. zooepidemicus infection in 3 UK outbreaks at the same location found ST-10, 18, 123 strains, and a ST-173 strain in a US outbreak, were associated with haemorrhagic pneumonia and persisted in kennelled populations over time. The ST-173 clonal complex has been noted to have severe virulence capabilities in dogs and other species. S. zooepidemicus seems to thrive in environments with a high risk of transmissibility, overcrowding, stress and naïve populations, particularly for those in shelters/kennels. MLST alone cannot determine the virulence phenotype of S. zooepidemicus in dogs. However, a level of conservancy and diversity within ST allelic loci aids the opportunity to cause severe disease in dogs. Thus, further research into whole genome sequencing and characterising the virulence factors of S. zooepidemicus is warranted in dogs.

Multi-locus sequence typing and in vitro antimicrobial resistance of equine Streptococcus equi subspecies zooepidemicus strains

Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) is one of the most important pathogens frequently associated with the main causes of equine infertility. In this study, we surveyed 22 strains of S. zooepidemicus collected during 2021 from cervico-uterine swabs of mares with endometritis. The genetic variability of the isolated strains was studied by multi-locus sequence typing (MLST) from whole-genome sequencing (WGS) data. The average length of reconstructed genomes was 2,088,286 bp (95% CI: 2,061,569 bp-2,114,967 bp), which was expected for S. zooepidemicus genomes. The assembled genomes were assigned to sequence types (STs) using the S. zooepidemicus scheme targeting seven loci (arcC, nrdE, proS, spi, tdk, tpi, yqiL) available in PubMLST database. MLST revealed a wide variability of STs with two (9.1%) novel STs identified in this study, precisely ST521 with two isolates and ST522 with one isolate. Furthermore, 4/22 (18.2%) isolates were assigned to ST92, 3/22 (13.6%) to ST205, 2/22 (9.1%) to ST475, and one strain (4.5%) for each of the following STs: ST10, ST30, ST39, ST49, ST101, ST132, ST147, ST314, ST369, ST467. Isolates were also tested for antimicrobial resistance using Kirby-Bauer disk diffusion method. Resistance to amoxicillin-clavulanate, ampicillin, amikacin, gentamicin, streptomycin, enrofloxacin, sulfamethoxazole-trimethoprim, tetracycline, oxytetracycline represented the most common resistance profile (13/22, 59.1%). No correlation between specific ST and antimicrobial resistance profile was found. Our study provides a comprehensive insight into the epidemiology, ST diversity and antimicrobial resistance profile of S. zooepidemicus strains, isolated in Italy, causing subfertility problems in mares.

Complete genome sequencing and comparative genomic analysis of three donkey Streptococcus equi subsp. equi isolates

Introduction

Streptococcus equi subspecies equi (S. equi) is the causative agent of strangles, which is one of the most common and highly contagious respiratory infectious illnesses in horses. Streptococcus equi (S. equi) is a horse-specific pathogen that originated from the closely related zoonotic pathogen Streptococcus equi subspecies zooepidemicus (S. zooepidemicus). Despite decades of research, the movement of genetic material across host-restricted diseases remains a mystery.

Methods

Three S. equi donkey isolates (HTP133, HTP232, and HT1112) were recently isolated from a strangles epidemic on donkey farms in China's Xinjiang Province. In this study, we performed a comprehensive comparative analysis of these isolates using whole genome sequencing and compared them to the published genomic sequences of equine strain S. equi 4047 to uncover evidence of genetic events that shaped the evolution of these donkey S. equi isolates' genomes.

Results

Whole genome sequencing indicated that both strains were closely related, with comparable gene compositions and a high rate of shared core genomes (1788-2004). Our comparative genomic study indicated that the genome structure is substantially conserved across three donkey strains; however, there are several rearrangements and inversions when compared to the horse isolate S. equi 4047. The virulence factors conveyed by genomic islands and prophages, in particular, played a key role in shaping the pathogenic capacity and genetic diversity of these S. equi strains. Furthermore, we discovered that the HT133 isolate had a strong colonization ability and increased motility; the HT1112 isolates had a significantly higher ability for antimicrobial resistance and biofilm formation, and the HT232 isolate gained pathogenic specialization by acquiring a bacteriophage encoding hyaluronate lyase.

Discussion

In summary, our findings show that genetic exchange across S. equi strains influences the development of the donkey S. equi genome, offering important genetic insights for future epidemiological studies of S. equi infection.

Streptococcus equi subspecies zooepidemicus - a case report of sudden death in a German sow farm

A farm in North-West Germany experienced a high morbidity and mortality in their sow herd. Sows showed fever, lethargy, oedema, mucosal discharge and dyspnoea. Necropsy revealed a severe fibrinous and purulent polyserositis. Haematological and histological examinations confirmed septicaemia. Streptococcus equi subspecies zooepidemicus was isolated in high yields from major organs. Sequence typing of this isolate (21/455) revealed a new sequence type showing a significantly higher proliferation rate in comparison to two other isolates. Other infectious agents (influenza A virus, Porcine Reproductive and Respiratory Syndrome Virus, Porcine Circovirus 2, african swine fever virus, classical swine fever virus, Actinobacillus pleuropneumoniae) were excluded by routine diagnostic examinations. A climate check revealed an insufficient air supply in the area for the gestating sows. This case describes the first disease outbreak in swine due to S. zooepidemicus in Germany.

Severe Streptococcus equi Subspecies zooepidemicus Outbreak from Unpasteurized Dairy Product Consumption, Italy

During November 2021-May 2022, we identified 37 clinical cases of Streptococcus equi subspecies zooepidemicus infections in central Italy. Epidemiologic investigations and whole-genome sequencing showed unpasteurized fresh dairy products were the outbreak source. Early diagnosis by using sequencing technology prevented the spread of life-threatening S. equi subsp. zooepidemicus infections.

Strangles in equines: An overview

Strangles, caused by Streptococcus equi subspecies equi, is a highly infectious respiratory disease affecting horses and other equines. The disease is economically important and compromises the productivity of equine farm significantly. The disease is characterized by pyrexia, mucopurulent nasal discharge, and abscess formation in the lymph nodes of the head and neck of horses. The disease transmission occurs either directly by coming in contact with infectious exudates or indirectly via fomite transmission. Besides this, carrier animals are the primary and most problematic source of disease infection. The organism not only initiates outbreaks but also makes the control and prevention of the disease difficult. The diagnosis of strangles is best done by isolating and characterizing the bacteria from nasal discharge, pus from abscesses, and lymphoid tissues or by using PCR. ELISA can also be used to detect serum protein M (SeM) antibodies for diagnosis. The most popular treatment for strangles is with penicillin; however, the treatment is affected by the stage, feature and severity of the disease. Prevention and control of strangles can be achieved through vaccination and good hygiene practices. Basically, this review describes the global prevalence of S. equi, as well as general aspects of the disease, like pathogenesis, diagnosis, treatment, prevention, control and management of the disease.

Outbreak of Pathogenic Streptococcus equi subsp. zooepidemicus in Guinea Pigs Farms of The Andean Region

Streptococcus zooepidemicus is an emerging zoonotic pathogen involved in septicemic infections in humans and livestock. Raising guinea pigs in South America is an important economic activity compared to raising them as pets in other countries. An outbreak of severe lymphadenitis was reported in guinea pigs from farms in the Andean region. S. zooepidemicus was isolated from multiple cervical and mandibular abscesses. Isolate was characterized by multilocus sequence typing and phylogenetic analysis. This is the first molecular characterization of a highly pathogenic strain, showing major important virulence factors such as the M-like protein genes szP and mlpZ, the fimbrial subunit protein gene fszF, and the protective antigen-like protein gene spaZ. Additionally, this guinea pig strain was phylogenetically related to equines but distant from zoonotic and pig isolates reported in other countries.

Molecular Features and Antimicrobial Susceptibilities of Streptococcus equi ssp. equi Isolates from Strangles Cases in Indonesia

Strangles, caused by Streptococcus equi ssp. equi (S. equi equi), is a highly infectious and frequent disease of equines worldwide. No data are available regarding the molecular epidemiology of strangles in Indonesia. This study aimed to characterize S. equi equi isolates obtained from suspected strangles cases in Indonesia in 2018. Isolates originated from seven diseased horses on four different farms located in three provinces of Indonesia. Whole genome sequences of these isolates were determined and used for seM typing, multilocus sequence typing (MLST), and core genome MLS typing (cgMLST). Genomes were also screened for known antimicrobial resistance genes and genes encoding for the recombinant antigens used in the commercial Strangvac^® subunit vaccine. All seven S. equi equi isolates from Indonesia belonged to ST179 and carried seM allele 166. Isolates differed from each other by only 2 to 14 cgSNPs and built an exclusive sub-cluster within the Bayesian Analysis of Population Structure (BAPS) cluster 2 (BAPS-2) of the S. equi equi cgMLST scheme. All isolates revealed predicted amino acid sequence identity to seven and high similarity to one of the eight antigen fragments contained in Strangvac^®. Furthermore, all isolates were susceptible to beta-lactam antibiotics penicillin G, ampicillin, and ceftiofur. Our data suggest that the horses from this study were affected by strains of the same novel sublineage within globally distributed BAPS-2 of S. equi equi. Nevertheless, penicillin G can be used as a first-choice antibiotic against these strains and Strangvac^® may also be protective against Indonesian strains.

Characterization of Streptococcus equi subsp. zooepidemicus isolates containing lnuB gene responsible for the L phenotype

Within the framework of the β-hemolytic streptococci surveillance carried out by the National Reference Laboratory from Uruguay, three putative Streptococcus equi subsp. zooepidemicus (SEZ) were received from different health centers. Being these the first reports associated with human infections in Uruguay, the objective of this work was to confirm their identification, to determine their genetic relationship and to study their antibiotic susceptibility. Using four different methods, they were identified as SEZ, a subspecies which has been described as the etiologic agent of rare and severe zoonosis in a few cases in other countries. The three isolates presented different pulsotypes by PFGE; however, two of them appeared to be related and were confirmed as ST431 by MLST, while the remaining isolate displayed ST72. Their resistance profile exhibited an unexpected feature: despite all of them were susceptible to macrolides, they showed different levels of resistance to clindamycin, i.e. they had the so-called "L phenotype". This rare trait is known to be due to a nucleotidyl-transferase, encoded by genes of the lnu family. Although this phenotype was previously described in a few SEZ isolates, its genetic basis has not been studied yet. This was now analyzed by PCR in the three isolates and they were found to contain a lnuB gene. The lnuB sequence was identical among the three isolates and with many lnuB sequences deposited in data banks. In conclusion, for the first time in Uruguay, three SEZ isolates recovered from non-epidemiologically related cases of human invasive infection were identified. Moreover, this is the first report about the presence of a lnu gene in the S. equi species, revealing the active lateral spread of the lnuB in a new streptococcal host.

Comparison of PCR-HRM, colorimetric LAMP and culture based diagnostic assays in the detection of endometritis caused by Streptococcus equi subsp. zooepidemicus in mares

Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) is one of the causative agents of equine endometritis. In this study, a panel of different bacterial species, and colonies derived from bacteriological cultures of 38 clinical samples, were subjected to Loop-Mediated Isothermal Amplification (LAMP) assay and PCR, followed by high-resolution melt (HRM) curve analysis. All clinical samples were genotyped into three distinct groups based on HRM curve analysis. Differences in melting curve profiles were a reflection of DNA variation in sorD gene which was confirmed by DNA sequencing. A mathematical model based on Genetic Confidence Percentage (GCP) was used in HRM curve analysis and a cut-off point value was established which differentiated S. zooepidemicus isolates without requiring visual interpretation of curve profiles. The accuracy of PCR-HRM and bacterial culture in detection of S. zooepidemicus were identical with 100% sensitivity and specificity, while LAMP assay had similar specificity but a lower sensitivity (89.5%). PCR-HRM and LAMP assay provided an effective detection method with a turn-around time of six hours for PCR-HRM and 120 min for LAMP assay, compared to a minimum three days that was required when routine bacteriological culture method was used. In summary, results indicate that LAMP had the quickest turnaround, and HRM curve analysis could potentially be used for genotyping without DNA sequencing. Any mare suspected of endometritis will benefit from developed rapid diagnostic tests for detection of S. zooepidemicus and proper treatment prior to being bred and will mitigate unnecessary treatment and antibiotic resistance.

Differences in the Accessory Genomes and Methylomes of Strains of Streptococcus equi subsp. equi and of Streptococcus equi subsp. zooepidemicus Obtained from the Respiratory Tract of Horses from Texas

Streptococcus equi subsp. equi (SEE) is a host-restricted equine pathogen considered to have evolved from Streptococcus equi subsp. zooepidemicus (SEZ). SEZ is promiscuous in host range and is commonly recovered from horses as a commensal. Comparison of a single strain each of SEE and SEZ using whole-genome sequencing, supplemented by PCR of selected genes in additional SEE and SEZ strains, was used to characterize the evolution of SEE. But the known genetic variability of SEZ warrants comparison of the whole genomes of multiple SEE and SEZ strains. To fill this knowledge gap, we utilized whole-genome sequencing to characterize the accessory genome elements (AGEs; i.e., elements present in some SEE strains but absent in SEZ or vice versa) and methylomes of 50 SEE and 50 SEZ isolates from Texas. Consistent with previous findings, AGEs consistently found in all SEE isolates were primarily from mobile genetic elements that might contribute to host restriction or pathogenesis of SEE. Fewer AGEs were identified in SEZ because of the greater genomic variability among these isolates. The global methylation patterns of SEE isolates were more consistent than those of the SEZ isolates. Among homologous genes of SEE and SEZ, differential methylation was identified only in genes of SEE encoding proteins with functions of quorum sensing, exopeptidase activity, and transitional metal ion binding. Our results indicate that effects of genetic mobile elements in SEE and differential methylation of genes shared by SEE and SEZ might contribute to the host specificity of SEE.

IMPORTANCE Strangles, caused by the host-specific bacterium Streptococcus equi subsp. equi (SEE), is the most commonly diagnosed infectious disease of horses worldwide. Its ancestor, Streptococcus equi subsp. zooepidemicus (SEZ), is frequently isolated from a wide array of hosts, including horses and humans. A comparison of the genomes of a single strain of SEE and SEZ has been reported, but sequencing of further isolates has revealed variability among SEZ strains. Thus, the importance of this study is that it characterizes genomic and methylomic differences of multiple SEE and SEZ isolates from a common geographic region (viz., Texas). Our results affirm many of the previously described differences between the genomes of SEE and SEZ, including the role of mobile genetic elements in contributing to host restriction. We also provide the first characterization of the global methylome of Streptococcus equi and evidence that differential methylation might contribute to the host restriction of SEE.

Zoonotic infection and clonal dissemination of Streptococcus equi subspecies zooepidemicus sequence type 194 isolated from humans in Thailand

Streptococcus equi subsp. zooepidemicus (SEZ) is a zoonotic pathogen associated with diseases in a wide range of animals as well as in humans. SEZ sequence type (ST) 194 strains have been associated with outbreaks in China, the USA, and Canada and have caused high mortality in pigs. Nevertheless, human infection by this ST has never been reported. This study conducted a retrospective analysis of 18 SEZ strains from human patients in Thailand during 2005-2020. The study revealed clonal dissemination of ST194 with the identical pulsotype in human patients throughout Thailand. Clinical manifestation was mainly septicemia (61.1%), while 72.2% had a history of eating raw pork products. There were six fatal cases (33.3%). Antimicrobial susceptibility testing revealed that all strains were susceptible to penicillin, ampicillin, cefotaxime, erythromycin, levofloxacin, clindamycin, chloramphenicol, tetracycline and vancomycin. Virulence-associated genes, including bifA, szM, szP, sdzD, spaZ, and fszF, were present in all tested strains. Some representative genes in four pathogenicity islands found in the swine outbreak SEZ-ATCC35246 (ST194) strain were detected in these SEZ strains. Whole-genome sequencing analysis of three representative SEZs in this study revealed no acquired antimicrobial-resistant genes and they contained the same virulence factors. The single-nucleotide polymorphism phylogenetic tree demonstrated that the current strains were clustered with swine ST194 strains. The results should be highlighted as a public health concern, especially to those who may directly or indirectly have contact with livestock or companion animals or have consumed raw meat products as risk factors for infections with SEZ.

An Outbreak Associated with Streptococcus equi Subsp. zooepidemicus in Layers: Evidence of Fecal Transmission

Major disease outbreaks caused by Streptococcus equi subsp. zooepidemicus seldom are reported in poultry. Besides acute septicemia, infection can result in a subacute or chronic form of disease with described mortality rates of 11% to 80%. Previously, the source of infection in poultry was linked to horses in which this bacterium can be present as an opportunistic pathogen on mucus membranes. The main route of spreading and being maintained within a poultry flock, after entering the stable, however, remains unclear. This case report describes an outbreak associated with S. zooepidemicus affecting a flock of 28 500 layer hens housed in an aviary system with free range. Besides sudden deaths, clinical signs of depression were noticed. Between 44 and 61 wk of age a total mortality of 23% was observed. Egg production dropped from 92% to 83%. Bacterial titration revealed substantial numbers of S. zooepidemicus present in the ceca of a healthy chicken. This novel finding hypothesizes that transmission of the infection within the flock might occur through the fecal route.

Differences in the genome, methylome, and transcriptome do not differentiate isolates of Streptococcus equi subsp. equi from horses with acute clinical signs from isolates of inapparent carriers

Streptococcus equi subsp. equi (SEE) is a host-restricted bacterium that causes the common infectious upper respiratory disease known as strangles in horses. Perpetuation of SEE infection appears attributable to inapparent carrier horses because it neither persists long-term in the environment nor infects other host mammals or vectors, and infection results in short-lived immunity. Whether pathogen factors enable SEE to remain in horses without causing clinical signs remains poorly understood. Thus, our objective was to use next-generation sequencing technologies to characterize the genome, methylome, and transcriptome of isolates of SEE from horses with acute clinical strangles and inapparent carrier horses—including isolates recovered from individual horses sampled repeatedly—to assess pathogen-associated changes that might reflect specific adaptions of SEE to the host that contribute to inapparent carriage. The accessory genome elements and methylome of SEE isolates from Sweden and Pennsylvania revealed no significant or consistent differences between acute clinical and inapparent carrier isolates of SEE. RNA sequencing of SEE isolates from Pennsylvania demonstrated no genes that were differentially expressed between acute clinical and inapparent carrier isolates of SEE. The absence of specific, consistent changes in the accessory genomes, methylomes, and transcriptomes of acute clinical and inapparent carrier isolates of SEE indicates that adaptations of SEE to the host are unlikely to explain the carrier state of SEE. Efforts to understand the carrier state of SEE should instead focus on host factors.

Globetrotting strangles: the unbridled national and international transmission of Streptococcus equi between horses

The equine disease strangles, which is characterized by the formation of abscesses in the lymph nodes of the head and neck, is one of the most frequently diagnosed infectious diseases of horses around the world. The causal agent, Streptococcus equi subspecies equi, establishes a persistent infection in approximately 10 % of animals that recover from the acute disease. Such 'carrier' animals appear healthy and are rarely identified during routine veterinary examinations pre-purchase or transit, but can transmit S. equi to naïve animals initiating new episodes of disease. Here, we report the analysis and visualization of phylogenomic and epidemiological data for 670 isolates of S. equi recovered from 19 different countries using a new core-genome multilocus sequence typing (cgMLST) web bioresource. Genetic relationships among all 670 S. equi isolates were determined at high resolution, revealing national and international transmission events that drive this endemic disease in horse populations throughout the world. Our data argue for the recognition of the international importance of strangles by the Office International des Épizooties to highlight the health, welfare and economic cost of this disease. The Pathogenwatch cgMLST web bioresource described herein is available for tailored genomic analysis of populations of S. equi and its close relative S. equi subspecies zooepidemicus that are recovered from horses and other animals, including humans, throughout the world. This article contains data hosted by Microreact.

SpeS: A Novel Superantigen and Its Potential as a Vaccine Adjuvant against Strangles

Bacterial superantigens (sAgs) are powerful activators of the immune response that trigger unspecific T cell responses accompanied by the release of proinflammatory cytokines. Streptococcus equi (S. equi) and Streptococcus zooepidemicus (S. zooepidemicus) produce sAgs that play an important role in their ability to cause disease. Strangles, caused by S. equi, is one of the most common infectious diseases of horses worldwide. Here, we report the identification of a new sAg of S. zooepidemicus, SpeS, and show that mutation of the putative T cell receptor (TCR)-binding motif (YAY to IAY) abrogated TCR-binding, whilst maintaining interaction with major histocompatibility complex (MHC) class II molecules. The fusion of SpeS and SpeS^Y39I to six S. equi surface proteins using two different peptide linkers was conducted to determine if MHC class II-binding properties were maintained. Proliferation assays, qPCR and flow cytometry analysis showed that SpeS^Y39I and its fusion proteins induced less mitogenic activity and interferon gamma expression when compared to SpeS, whilst retaining Antigen-Presenting Cell (APC)-binding properties. Our data suggest that SpeS^Y39I-surface protein fusions could be used to direct vaccine antigens towards antigen-presenting cells in vivo with the potential to enhance antigen presentation and improve immune responses.

Genetic characterization of Streptococcus equi subspecies zooepidemicus associated with high swine mortality in the United States

High mortality events due to Streptococcus equi subspecies zooepidemicus (Streptococcus zooepidemicus) in swine have not previously been reported in the United States. In September and October 2019, outbreaks with swine mortality up to 50% due to S. zooepidemicus septicaemia were reported in Ohio and Tennessee. Genomic epidemiological analysis revealed that the eight outbreak isolates were clustered together with ATCC 35246, a Chinese strain caused outbreaks with high mortality, also closely related to three isolates from human cases from Virginia, but significantly different from an outbreak-unrelated swine isolate from Arizona and most isolates from other animal species. Comparative genomic analysis on two outbreak isolates and another outbreak-unrelated isolate identified several genomic islands and virulence genes specifically in the outbreak isolates only, which are likely associated with the high mortality observed in the swine population. These findings have implications for understanding, tracking and possibly preventing diseases caused by S. zooepidemicus in swine.

Genetics and Pathogenicity Factors of Group C and G Streptococci

Of the eight phylogenetic groups comprising the genus Streptococcus , Lancefield group C and G streptococci (GCS and GGS, resp.) occupy four of them, including the Pyogenic, Anginosus, and Mitis groups, and one Unnamed group so far. These organisms thrive as opportunistic commensals in both humans and animals but may also be associated with clinically serious infections, often resembling those due to their closest genetic relatives, the group A streptoccci (GAS). Advances in molecular genetics, taxonomic approaches and phylogenomic studies have led to the establishment of at least 12 species, several of which being subdivided into subspecies. This review summarizes these advances, citing 264 early and recent references. It focuses on the molecular structure and genetic regulation of clinically important proteins associated with the cell wall, cytoplasmic membrane and extracellular environment. The article also addresses the question of how, based on the current knowledge, basic research and translational medicine might proceed to further advance our understanding of these multifaceted organisms. Particular emphasis in this respect is placed on streptokinase as the protein determining the host specificity of infection and the Rsh-mediated stringent response with its potential for supporting bacterial survival under nutritional stress conditions.

Genetic diversity of Streptococcus equi subsp. zooepidemicus isolated from horses

Streptococcus equi subsp. zooepidemicus (SEZ) is an opportunistic and zoonotic pathogen of horses. In this study, genetic intraspecies variability of SEZ obtained mainly from respiratory and genital samples of horses was investigated by analysis of the 16S-23S rRNA intergenic spacer region (ISR) and of the 16S rRNA gene. 16S-23S ISR rRNA type A1 was predominant, although a high rate of multiple products (30.5%) was obtained. Phylogenetic analysis of the 16S rRNA gene detected three genogroups (I, II and III). 16S rRNA variable regions V1 and V2 are the most important regions for evaluating SEZ intraspecies variability, but at least V1-V5 regions should be considered to avoid mistakes. Analysis of all 16S rRNA sequences available in databases assigned human SEZ to groups I and III but not to group II. These results show a high genetic variability in SEZ collected from different specimens of horses from various regions of Italy.

Multi-locus sequence typing of Streptococcus equi subspecies zooepidemicus strains isolated from cats

Streptococcus equi subspecies zooepidemicus ( S. zooepidemicus) causes outbreaks of fatal respiratory disease in dog shelters and fatal respiratory and neurologic disease in cat shelters. We conducted multi-locus sequence typing analysis on S. zooepidemicus isolates from 5 Canadian and 3 Israeli cats with severe respiratory and neurologic disease, plus 1 isolate from a clinically normal shelter cat. Our aim was to determine if feline outbreaks are clonal and whether there is commonality between feline and canine strains. ST363 was identified as the causative strain of a Canadian outbreak of S. zooepidemicus-linked disease, and is a double-locus variant of ST173, which was isolated from one of the Israeli cats. ST363 was also isolated from the clinically normal cat, indicative of the potential for enzootic infection in shelters. Strains within the ST173 clonal complex were responsible for 2 large canine outbreaks in the United States and the United Kingdom, as well as the death of 1 cat in the United States outbreak. ST215 was isolated from 2 cats in the Israeli outbreak, and is unrelated to the ST173 complex. We conclude that S. zooepidemicus outbreaks in cat shelters are clonal and that strains within the ST173 clonal complex are pathogenic for both dogs and cats.

Diversity of Streptococcus equi subsp. zooepidemicus strains isolated from the Spanish sheep and goat population and the identification, function and prevalence of a novel arbutin utilisation system

The zoonotic bacterium Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) is a diverse, opportunistic pathogen that can cause mastitis in dairy sheep and goats. We used multilocus sequence typing (MLST) to define the genetic diversity of 60 isolates of S. zooepidemicus, which were recovered from sheep and goats in Spain between 2003 and 2010. We identify a novel clonal complex based on sequence type (ST), ST-236, which accounted for 39 of the 60 isolates. A representative ST-236 strain, S. zooepidemicus strain C7 (SzC7), was sequenced and interrogated for the presence of novel nutritional uptake or utilisation systems, the acquisition of which have previously been shown to be important for environmental adaptation in other streptococcal pathogens. A novel phosphoenolpyruvate sugar phosphotransferase system (PTS), which enabled the utilisation of arbutin, was identified. Functionality of the PTS was confirmed following deletion of the PTS from SzC7. Arbutin is found in multiple animal foodstuffs and we propose that the ability to utilise arbutin may have conferred a selective advantage to strains infecting animals, the diet of which contains this sugar.

Genomic Dissection of an Icelandic Epidemic of Respiratory Disease in Horses and Associated Zoonotic Cases

Iceland is free of the major infectious diseases of horses. However, in 2010 an epidemic of respiratory disease of unknown cause spread through the country’s native horse population of 77,000. Microbiological investigations ruled out known viral agents but identified the opportunistic pathogen Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) in diseased animals. We sequenced the genomes of 257 isolates of S. zooepidemicus to differentiate epidemic from endemic strains. We found that although multiple endemic clones of S. zooepidemicus were present, one particular clone, sequence type 209 (ST209), was likely to have been responsible for the epidemic. Concurrent with the epidemic, ST209 was also recovered from a human case of septicemia, highlighting the pathogenic potential of this strain. Epidemiological investigation revealed that the incursion of this strain into one training yard during February 2010 provided a nidus for the infection of multiple horses that then transmitted the strain to farms throughout Iceland. This study represents the first time that whole-genome sequencing has been used to investigate an epidemic on a national scale to identify the likely causative agent and the link to an associated zoonotic infection. Our data highlight the importance of national biosecurity to protect vulnerable populations of animals and also demonstrate the potential impact of S. zooepidemicus transmission to other animals, including humans.

An epidemic of respiratory disease affected almost the entire native Icelandic horse population of 77,000 animals in 2010, resulting in a self-imposed ban on the export of horses and significant economic costs to associated industries. Although the speed of transmission suggested that a viral pathogen was responsible, only the presence of the opportunistic pathogen Streptococcus zooepidemicus was consistent with the observed clinical signs. We applied genomic sequencing to differentiate epidemic from endemic strains and to shed light on the rapid transmission of the epidemic strain throughout Iceland. We further highlight the ability of epidemic and endemic strains of S. zooepidemicus to infect other animals, including humans. This study represents the first time that whole-genome sequencing has been used to elucidate an outbreak on a national scale and identify the likely causative agent.

Zoonotic necrotizing myositis caused by Streptococcus equi subsp. zooepidemicus in a farmer

BACKGROUND

Streptococcus equi subsp. zooepidemicus is a beta-hemolytic group C streptococcus mainly causing infections in domesticated animals. Here we describe the first case of zoonotic necrotizing myositis caused by this bacterium.

CASE PRESENTATION

The patient was a 73-year-old, previously healthy farmer with two asymptomatic Shetland ponies in his stable. After close contact with the ponies while feeding them, he rapidly developed erythema of his left thigh and sepsis with multiple organ failure. The clinical course was severe and complicated, requiring repetitive surgical excision of necrotic muscle, treatment with vasopressors, mechanical ventilation and continuous venovenous hemofiltration, along with adjunctive hyperbaric oxygen therapy. The patient was discharged from hospital at day 30, without obvious sequelae. The streptococcal isolate was identified as Streptococcus equi by MALDI-ToF MS, and was later assigned subspecies identification as S. equi subsp. zooepidemicus. Multilocus sequence typing identified the strain as a novel sequence type (ST 364), closely related to types previously identified in horses and cattle. A focused proteomic analysis revealed that the ST 364 expressed putative virulence factors similar to that of Streptococcus pyogenes, including homologues of the M protein, streptodornases, interleukin 8-protease and proteins involved in the biosynthesis of streptolysin S.

CONCLUSION

This case illustrates the zoonotic potential of S. equi subsp. zooepidemicus and the importance of early clinical recognition, rapid and radical surgical therapy, appropriate antibiotics and adequate supportive measures when necrotizing soft tissue infection is suspected. The expression of Streptococcus pyogenes-like putative virulence determinants in ST 364 might partially explain the fulminant clinical picture.

Reducing exposure to pathogens in the horse: a preliminary study into the survival of bacteria on a range of equine bedding types

AIMS

To compare the rate of growth of four microbial strains that cause disease in the horse, on four commonly used types of bedding. The moisture-holding capacity of each bedding type was also tested.

METHODS AND RESULTS

Microbial strains included Streptococcus equi, Streptococcus zooepidemicus, Fusobacterium necrophorum, Dichelobacter nodosus and Dermatophilus congolensis. The bedding types tested were Pinus sylvestris (Scots pine shavings), Pinus nigra (Corsican pine shavings), Picea sitchensis (Sitka spruce shavings), Cannabis sativa (hemp) and chopped wheat straw. A suspension of each microbial strain was spread in triplicate on agar media and incubated in its optimal growth conditions. The viable count (colony-forming unit per ml) was determined for each bacterial strain for the five different bedding types. Pinus sylvestris bedding resulted in significantly less (P = 0·001) bacterial growth of all strains tested.

CONCLUSIONS

Factors resulting in the inhibition of bacterial growth include the antibacterial effects reported in the Pinacea family and the physical properties of the bedding substrate. Research is currently focussed on the diagnosis and management of disease. Prevention of disease is also important for matters of biosecurity. Strategies should include the provision of a hygienic environment and the use of specific types of bedding.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bedding choice has implications for global equine health and disease prevention as well as potential benefits in other animal species.

Beta-hemolytic Streptococcus dysgalactiae strains isolated from horses are a genetically distinct population within the Streptococcus dysgalactiae taxon

The pathogenic role of beta-hemolytic Streptococcus dysgalactiae in the equine host is increasingly recognized. A collection of 108 Lancefield group C (n = 96) or L (n = 12) horse isolates recovered in the United States and in three European countries presented multilocus sequence typing (MLST) alleles, sequence types and emm types (only 56% of the isolates could be emm typed) that were, with few exceptions, distinct from those previously found in human Streptococcus dysgalactiae subsp. equisimilis. Characterization of a subset of horse isolates by multilocus sequence analysis (MLSA) and 16S rRNA gene sequence showed that most equine isolates could also be differentiated from S. dysgalactiae strains from other animal species, supporting the existence of a horse specific genomovar. Draft genome information confirms the distinctiveness of the horse genomovar and indicates the presence of potentially horse-specific virulence factors. While this genomovar represents most of the isolates recovered from horses, a smaller MLST and MLSA defined sub-population seems to be able to cause infections in horses, other animals and humans, indicating that transmission between hosts of strains belonging to this group may occur.

Phylogenetic, epidemiological and functional analyses of the Streptococcus bovis/Streptococcus equinus complex through an overarching MLST scheme

Background

The Streptococcus bovis/Streptococcus equinus complex (SBSEC) comprises seven (sub)species classified as human and animal commensals, emerging opportunistic pathogens and food fermentative organisms. Changing taxonomy, shared habitats, natural competence and evidence for horizontal gene transfer pose difficulties for determining their phylogeny, epidemiology and virulence mechanisms. Thus, novel phylogenetic and functional classifications are required. An SBSEC overarching multi locus sequence type (MLST) scheme targeting 10 housekeeping genes was developed, validated and combined with host-related properties of adhesion to extracellular matrix proteins (ECM), activation of the immune responses via NF-KB and survival in simulated gastric juice (SGJ).

Results

Commensal and pathogenic SBSEC strains (n = 74) of human, animal and food origin from Europe, Asia, America and Africa were used in the MLST scheme yielding 66 sequence types and 10 clonal complexes differentiated into distinct habitat-associated and mixed lineages. Adhesion to ECMs collagen I and mucin type II was a common characteristic (23 % of strains) followed by adhesion to fibronectin and fibrinogen (19.7 %). High adhesion abilities were found for East African dairy and human blood isolate branches whereas commensal fecal SBSEC displayed low adhesion. NF-KB activation was observed for a limited number of dairy and blood isolates suggesting the potential of some pathogenic strains for reduced immune activation. Strains from dairy MLST clades displayed the highest relative survival to SGJ independently of dairy adaptation markers lacS/lacZ.

Conclusion

Combining phylogenetic and functional analyses via SBSEC MLST enabled the clear delineation of strain clades to unravel the complexity of this bacterial group. High adhesion values shared between certain dairy and blood strains as well as the behavior of NF-KB activation are concerning for specific lineages. They highlighted the health risk among shared lineages and establish the basis to elucidate (zoonotic-) transmission, host specificity, virulence mechanisms and enhanced risk assessment as pathobionts in an overarching One Health approach.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0735-2) contains supplementary material, which is available to authorized users.

Rapid diagnosis of strangles (Streptococcus equi subspecies equi) using PCR

Strangles is one of the most common equine infectious diseases with serious health, welfare and socio-economic impact. However, the detection of Streptococcus equi subspecies equi can be challenging and persistently infected carriers are common. Furthermore, the use of classical microbiology can result in an underestimation of the prevalence of the disease. The difficulties associated with the slow diagnosis of Strangles can result in rapid spread of the disease. Therefore, rapid and economical diagnostic tests are urgently required. Here, two multiplex assays, were developed and validated for the detection of S. equi and S. equi subspecies zooepidemicus, the most common differential diagnosis. Using 59 S. equi and 59 S. zooepidemicus strains collected from various geographical areas, the PCR tests demonstrated a sensitivity of 95% and a specificity of 98%. Furthermore, the assay can be performed directly from clinical swabs. Thus, the assays designed here provide a rapid, reliable and economical solution for the diagnosis of Strangles.

Risk factors associated with uterine fluid after breeding caused by Streptococcus zooepidemicus

Infectious endometritis is a major cause of infertility in the mare and inflicts major losses on the equine breeding industry. The ability of the mare to eliminate uterine infections has been studied intensively for decades; however, despite identification of several factors contributing to the multifactorial pathogenesis and improved treatment, infectious endometritis remains a significant problem in a subpopulation of broodmares. Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) is one of the most commonly isolated pathogens from the uterus of mares, suffering from infectious endometritis. Its ability to cause chronic latent infection by residing deep within the endometrial tissue has previously been described. The aim of the present study was to correlate different mare risk factors to infectious endometritis and pregnancy rates in broodmares and to investigate whether clonal or genetically distinct S. zooepidemicus strains isolated from mares with endometritis were associated with mare risk factors and the outcome of insemination. Mares (N = 152) were examined after natural cover, and 20% (31 mares) had intrauterine fluid (IUF) accumulation. Fifty-five percent (16 of 29) of the mares with IUF had infectious endometritis, and S. zooepidemicus was isolated in 81% (13 of 16) of these mares. Significantly more resting mares had IUF compared with foaling mares, and the foaling mares had the highest prevalence of positive bacterial growth from the uterine swab. The per-cycle pregnancy rate for the study was 63%. Pregnancy rate was significantly negatively affected by increased age (>12 years) and increased parity (>4), and the lowest pregnancy rate was observed in resting mares compared with foaling, barren, and maiden mares. Up to four S. zooepidemicus isolates were selected from each mare with growth of S. zooepidemicus from the uterine swab sample and further characterized by pulsed-field gel electrophoresis. In total, S. zooepidemicus isolates from 18 mares were analyzed with pulsed-field gel electrophoresis. In 13 mares, the isolates selected from each mare showed a high genetic relatedness within each individual mare, whereas two genetically distinct strains were isolated in five mares. A clonal S. zooepidemicus infection was associated with increased age, high parity, and poor vulvar conformation. Mares with clonal infection had a low pregnancy rate (38%) compared with mares with two strains isolated (80%). In conclusion, the results indicate that clonal S. zooepidemicus endometritis is associated with increased age, parity, and poor vulvar conformation in the broodmare.

Genome specialization and decay of the strangles pathogen, Streptococcus equi, is driven by persistent infection

Strangles, the most frequently diagnosed infectious disease of horses worldwide, is caused by Streptococcus equi. Despite its prevalence, the global diversity and mechanisms underlying the evolution of S. equi as a host-restricted pathogen remain poorly understood. Here, we define the global population structure of this important pathogen and reveal a population replacement in the late 19th or early 20th Century. Our data reveal a dynamic genome that continues to mutate and decay, but also to amplify and acquire genes despite the organism having lost its natural competence and become host-restricted. The lifestyle of S. equi within the horse is defined by short-term acute disease, strangles, followed by long-term infection. Population analysis reveals evidence of convergent evolution in isolates from post-acute disease samples as a result of niche adaptation to persistent infection within a host. Mutations that lead to metabolic streamlining and the loss of virulence determinants are more frequently found in persistent isolates, suggesting that the pathogenic potential of S. equi reduces as a consequence of long-term residency within the horse post-acute disease. An example of this is the deletion of the equibactin siderophore locus that is associated with iron acquisition, which occurs exclusively in persistent isolates, and renders S. equi significantly less able to cause acute disease in the natural host. We identify several loci that may similarly be required for the full virulence of S. equi, directing future research toward the development of new vaccines against this host-restricted pathogen.

Prevalence of Streptococcus dysgalactiae subsp. equisimilis and S. equi subsp. zooepidemicus in a sample of healthy dogs, cats and horses

AIMS

To estimate the prevalence of β-haemolytic Lancefield group C streptococci in healthy dogs, cats and horses; to determine if frequent contact with horses was associated with isolation of these species from dogs and cats; and to characterise recovered S. equi subsp. zooepidemicus isolates by multilocus sequence typing.

METHODS

Oropharyngeal swabs were collected from 197 dogs and 72 cats, and nasopharyngeal swabs from 93 horses. Sampling was carried out at the Massey University Veterinary Teaching Hospital, on sheep and beef farms or on premises where horses were present. All animals were healthy and were categorised as Urban dogs and cats (minimal contact with horses or farm livestock), Farm dogs (minimal contact with horses) and Stable dogs and cats (frequent contact with horses). Swabs were cultured for β-haemolytic Streptococcus spp. and Lancefield group C streptococcal subspecies were confirmed by phenotypic and molecular techniques.

RESULTS

Of the 197 dogs sampled, 21 (10.7 (95% CI= 4.0-25.4)%) tested positive for S. dysgalactiae subsp. equisimilis and 4 (2.0 (95% CI=0.7-5.5)%) tested positive for S. equi subsp. zooepidemicus. All these isolates, except for one S. dysgalactiae subsp. equisimilis isolate in an Urban dog, were from Stable dogs. S. dysgalactiae subsp. equisimilis was isolated from one Stable cat. Of the 93 horses, 22 (23.7 (95% CI=12.3-40.6)%) and 6 (6.5 (95% CI=2.8-14.1)%) had confirmed S. dysgalactiae subsp. equisimilis and S. equi subsp. zooepidemicus isolation respectively. Isolation of S. dysgalactiae subsp. equisimilis from dogs was associated with frequent contact with horses (OR=9.8 (95% CI=2.6-72.8)). Three different multilocus sequence type profiles of S. equi subsp. zooepidemicus that have not been previously reported in dogs were recovered.

CONCLUSIONS AND CLINICAL RELEVANCE

Subclinical infection or colonisation by S. equi subsp. zooepidemicus and S. dysgalactiae subsp. equisimilis occurs in dogs and further research on inter-species transmission and the pathogenic potential of these Lancefield group C streptococci is needed. Complete speciation of β-haemolytic streptococci should be recommended in clinical cases and the possible exposure to horses and their environment should be considered in epidemiological investigations.

Rapid and accurate identification of Streptococcus equi subspecies by MALDI-TOF MS

Streptococcus equi includes very important animal and human pathogens. S. equi subsp. equi (SEE) is a highly pathogenic equine specific subspecies, while S. equi subsp. zooepidemicus (SEZ) and S. equi subsp. ruminatorum are opportunistic pathogens of various animal species and humans. Due to great phenotypic and sequence similarity between three subspecies their discrimination remains difficult. In this study, we aimed to design and validate a novel, Superspectra based, MALDI-TOF MS approach for reliable, rapid and cost-effective identification of SEE and SEZ, the most frequent S. equi subspecies in horses. Superspectra created in this study enabled correct identification of 86 strains belonging to different subspecies of S. equi, isolated from various hosts, infection sites and years. In general, higher average identification accuracy was achieved for SEE (99.0±3.0%) than for SEZ (93.3±7.5%). This result may be attributed to the highly clonal population structure of SEE, as opposed to the diversity of SEZ seen in horses. Importantly strains with atypical colony appearance both within SEE and SEZ did not affect correct identification of the strains by MALDI-TOF MS. Atypical colony variants are often associated with a higher persistence or virulence of S. equi, thus their correct identification using the current method strengthens its potential use in routine clinical diagnostics. In conclusion, reliable identification of S. equi subspecies was achieved by combining a MALDI-TOF MS method with spectra analyses using the SARAMIS database. Additionally, first results on subtyping of SEZ indicated that a more refined discrimination, for example for epidemiological surveys, may be possible.

Using multilocus sequence typing to study bacterial variation: prospects in the genomic era

Multilocus sequence typing (MLST) indexes the sequence variation present in a small number (usually seven) of housekeeping gene fragments located around the bacterial genome. Unique alleles at these loci are assigned arbitrary integer identifiers, which effectively summarizes the variation present in several thousand base pairs of genome sequence information as a series of numbers. Comparing bacterial isolates using allele-based methods efficiently corrects for the effects of lateral gene transfer present in many bacterial populations and is computationally efficient. This 'gene-by-gene' approach can be applied to larger collections of loci, such as the ribosomal protein genes used in ribosomal MLST (rMLST), up to and including the complete set of coding sequences present in a genome, whole-genome MLST (wgMLST), providing scalable, efficient and readily interpreted genome analysis.

Localised mitogenic activity in horses following infection with Streptococcus equi

Streptococcus equi subspecies equi (S. equi) is the causative agent of strangles, a highly contagious upper respiratory disease of equids. Streptococcus equi produces superantigens (sAgs), which are thought to contribute to strangles pathogenicity through non-specific T-cell activation and pro-inflammatory response. Streptococcus equi infection induces abscesses in the lymph nodes of the head and neck. In some individuals, some abscess material remains into the guttural pouch and inspissates over time to form chondroids which can harbour live S. equi. The aim of this study was to determine the sites of sAg production during infection and therefore improve our understanding of their role. Abscess material, chondroids and serum collected from Equidae with signs of strangles were tested in mitogenic assays. Mitogenic sAg activity was only detected in abscess material and chondroids. Our data support the localised in vivo activity of sAg during both acute and carrier phases of S. equi infection.

PinR mediates the generation of reversible population diversity in Streptococcus zooepidemicus

Opportunistic pathogens must adapt to and survive in a wide range of complex ecosystems. Streptococcus zooepidemicus is an opportunistic pathogen of horses and many other animals, including humans. The assembly of different surface architecture phenotypes from one genotype is likely to be crucial to the successful exploitation of such an opportunistic lifestyle. Construction of a series of mutants revealed that a serine recombinase, PinR, inverts 114 bp of the promoter of SZO_08560, which is bordered by GTAGACTTTA and TAAAGTCTAC inverted repeats. Inversion acts as a switch, controlling the transcription of this sortase-processed protein, which may enhance the attachment of S. zooepidemicus to equine trachea. The genome of a recently sequenced strain of S. zooepidemicus, 2329 (Sz2329), was found to contain a disruptive internal inversion of 7 kb of the FimIV pilus locus, which is bordered by TAGAAA and TTTCTA inverted repeats. This strain lacks pinR and this inversion may have become irreversible following the loss of this recombinase. Active inversion of FimIV was detected in three strains of S. zooepidemicus, 1770 (Sz1770), B260863 (SzB260863) and H050840501 (SzH050840501), all of which encoded pinR. A deletion mutant of Sz1770 that lacked pinR was no longer capable of inverting its internal region of FimIV. The data highlight redundancy in the PinR sequence recognition motif around a short TAGA consensus and suggest that PinR can reversibly influence the wider surface architecture of S. zooepidemicus, providing this organism with a bet-hedging solution to survival in fluctuating environments.

Vaccination with a live multi-gene deletion strain protects horses against virulent challenge with Streptococcus equi

Strangles, caused by Streptococcus equi subspecies equi (S. equi) is one of the most frequently diagnosed infectious diseases of horses and there remains a significant need to develop new preventative vaccines. We generated a live vaccine strain of S. equi containing deletions in six genes: sagA, hasA, aroB, pyrC, seM and recA, which was administered to nine Welsh mountain ponies via the intramuscular route. Four vaccinated ponies developed adverse reactions following the first vaccination from which the live vaccine strain was isolated. Two of these ponies were withdrawn from the study and seven ponies received a second vaccination, one of which then developed an adverse reaction. Nine control ponies injected with culture media alone developed no adverse reactions. Following challenge with a virulent strain of S. equi, none of the seven vaccinated ponies had developed clinical signs of strangles eleven days post-challenge, compared to six of nine control ponies over the same period (P=0.0114). A lymph node abscess was identified in one of the seven vaccinated ponies at post-mortem examination, whilst all nine control ponies had at least one lymph node abscess (P=0.0009). Three of the six vaccinated ponies that were protected from strangles had not developed an adverse reaction following vaccination, suggesting that a better understanding of the pro-inflammatory responses to S. equi could lead to the development of a live attenuated vaccine against strangles that is safe for administration via intramuscular injection.

New perspectives for the diagnosis, control, treatment, and prevention of strangles in horses

Strangles, characterized by abscessation of the lymph nodes of the head and neck, is the most frequently diagnosed infectious disease of horses worldwide. The persistence of the causative agent, Streptococcus equi, in a proportion of convalescent horses plays a critical role in the recurrence and spread of disease. Recent research has led to the development of effective diagnostic tests that assist the eradication of S equi from local horse populations. This article describes how these advances have been made and provides advice to assist the resolution and prevention of outbreaks. New perspectives on preventative vaccines and therapeutic interventions are discussed.

Prevalence and disease associations of superantigens szeF, szeN and szeP in the S. zooepidemicus population and possible functional redundancy of szeF

Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) causes a variety of infections in a broad range of species. This study broadens prevalence data for three recently identified novel superantigens (szeF, szeN, and szeP) to define links between their presence and disease type. Screening of 437 strains across 190 sequence types (STs) revealed that 50% of strains contained superantigen genes. Results confirmed that the presence of S. zooepidemicus superantigen genes is significantly associated with non-Strangles lymph node abscessation in the horse (p-value = 0.003) and their absence is associated with uterine infection/abortion (p-value = 0.006). This study also investigated the lack of mitogenicity observed in szeF only. Results show that szeF is polymorphic, with 23 different alleles, and mutations altering the protein sequence. Gene expression differences are not responsible for lack of mitogenic activity in these strains. Taken together, these findings suggest that superantigens are important for S. zooepidemicus pathogenesis but SzeF probably has little involvement.

Streptococcus zooepidemicus and Streptococcus equi evolution: the role of CRISPRs

The host-restricted bacterium Streptococcus equi is the causative agent of equine strangles, the most frequently diagnosed infectious disease of horses worldwide. The disease is characterized by abscessation of the lymph nodes of the head and neck, leading to significant welfare and economic cost. S. equi is believed to have evolved from an ancestral strain of Streptococcus zooepidemicus, an opportunistic pathogen of horses and other animals. Comparison of the genome of S. equi strain 4047 with those of S. zooepidemicus identified examples of gene loss due to mutation and deletion, and gene gain through the acquisition of mobile genetic elements that have probably shaped the pathogenic specialization of S. equi. In particular, deletion of the CRISPR (clustered regularly interspaced short palindromic repeats) locus in the ancestor of S. equi may have predisposed the bacterium to acquire and incorporate new genetic material into its genome. These include four prophages and a novel integrative conjugative element. The virulence cargo carried by these mobile genetic elements is believed to have shaped the ability of S. equi to cause strangles. Further sequencing of S. zooepidemicus has highlighted the diversity of this opportunistic pathogen. Again, CRISPRs are postulated to influence evolution, balancing the need for gene gain over genome stability. Analysis of spacer sequences suggest that these pathogens may be susceptible to a limited range of phages and provide further evidence of cross-species exchange of genetic material among Streptococcus pyogenes, Streptococcus agalactiae and Streptococcus dysgalactiae.

Clones of Streptococcus zooepidemicus from outbreaks of hemorrhagic canine pneumonia and associated immune responses

Acute hemorrhagic pneumonia caused by Streptococcus zooepidemicus has emerged as a major disease of shelter dogs and greyhounds. S. zooepidemicus strains differing in multilocus sequence typing (MLST), protective protein (SzP), and M-like protein (SzM) sequences were identified from 9 outbreaks in Texas, Kansas, Florida, Nevada, New Mexico, and Pennsylvania. Clonality based on 2 or more isolates was evident for 7 of these outbreaks. The Pennsylvania and Nevada outbreaks also involved cats. Goat antisera against acutely infected lung tissue as well as convalescent-phase sera reacted with a mucinase (Sz115), hyaluronidase (HylC), InlA domain-containing cell surface-anchored protein (INLA), membrane-anchored protein (MAP), SzP, SzM, and extracellular oligopeptide-binding protein (OppA). The amino acid sequences of SzP and SzM of the isolates varied greatly. The szp and szm alleles of the closely related Kansas clone (sequence type 129 [ST-129]) and United Kingdom isolate BHS5 (ST-123) were different, indicating that MLST was unreliable as a predictor of virulence phenotype. Combinations of conserved HylC and serine protease (ScpC) and variable SzM and SzP proteins of S. zooepidemicus strain NC78 were protectively immunogenic for mice challenged with a virulent canine strain. Thus, although canine pneumonia outbreaks are caused by different strains of S. zooepidemicus, protective immune responses were elicited in mice by combinations of conserved or variable S. zooepidemicus proteins from a single strain.