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Streptococcus equi Infections in Horses: Guidelines for Treatment, Control, and Prevention of Strangles—Revised Consensus Statement
research-article
Author(s):
A.G. Boyle
1
,
,
J.F. Timoney
2 ,
J.R. Newton
3 ,
M.T. Hines
4 ,
A.S. Waller
3 ,
B.R. Buchanan
5
Publication date (Electronic):
09 February 2018
Publisher:
John Wiley and Sons Inc.
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Abstract
This consensus statement update reflects our current published knowledge and opinion about clinical signs, pathogenesis, epidemiology, treatment, complications, and control of strangles. This updated statement emphasizes varying presentations in the context of existing underlying immunity and carrier states of strangles in the transmission of disease. The statement redefines the “gold standard” for detection of possible infection and reviews the new technologies available in polymerase chain reaction diagnosis and serology and their use in outbreak control and prevention. We reiterate the importance of judicious use of antibiotics in horses with strangles. This updated consensus statement reviews current vaccine technology and the importance of linking vaccination with currently advocated disease control and prevention programs to facilitate the eradication of endemic infections while safely maintaining herd immunity. Differentiation between immune responses to primary and repeated exposure of subclinically infected animals and responses induced by vaccination is also addressed.
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Most cited references87
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Genomic Evidence for the Evolution of Streptococcus equi: Host Restriction, Increased Virulence, and Genetic Exchange with Human Pathogens
Matthew Holden, Zoe Heather, Romain Paillot … (2009)
Introduction Streptococcus equi subspecies equi (S. equi) is the causative agent of equine strangles, characterized by abscessation of the lymph nodes of the head and neck. Rupture of abscesses formed in retropharyngeal lymph nodes into the guttural pouches leads to a proportion of horses becoming persistently infected carriers. These carriers transmit the organism to naïve horses and play an important role in disease spread. S. equi is believed to have evolved from an ancestral strain of Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) [1],[2], which is associated with a wide variety of diseases in horses and other animals including humans. Both of these organisms belong to the same group of streptococci as the human pathogen Streptococcus pyogenes. Previous work has shown that S. equi produces four superantigens (SeeH, SeeI, SeeL and SeeM) [3]–[5], two secreted fibronectin-binding proteins (SFS and FNE) [6],[7], a novel M-protein (SeM) [8], an H-factor-binding protein (Se18.9) [9] and a novel non-ribosomal peptide synthesis system [10], but little is known about other factors that influence differences in the virulence of these closely related streptococci. We determined the complete genome sequence of S. equi strain 4047 (Se4047), a virulent strain isolated from a horse with strangles in the New Forest, England, in 1990 [11] and S. zooepidemicus strain H70 (SzH70), isolated from a nasal swab taken from a healthy Thoroughbred racehorse in Newmarket, England, in 2000 [2]. Using comparative genomic analysis to identify Se4047-specific loci, and subsequent screening of S. equi and S. zooepidemicus strains from around the world, we provide evidence of the genetic events that have shaped the evolution of the S. equi genome, and led to its emergence as a host-restricted pathogen. Results/Discussion General features of the genomes Multilocus sequence typing (MLST) has provided evidence of the close genetic relationship of S. equi and S. zooepidemicus [2]. The genomes of Se4047 (ST-179) and SzH70 (ST-1) support the overall relatedness, but also reveal evidence of genome plasticity that has generated notable diversity. The two genomes are similar in size: the Se4047 genome consists of a circular chromosome of 2,253,793 bp (Figure 1A) encoding 2,137 predicted coding sequences (CDSs), and the SzH70 genome contains a chromosome of 2,149,866 bp (Figure 1B), encoding 1,960 predicted CDSs. Much of the Se4047 genome is orthologous to the SzH70 genome: 1671 Se4047 CDSs have SzH70 orthologs. Of the remaining 466 non-orthologous Se4047 CDSs, 422 are found on mobile genetic elements (MGEs; for details of the regions of variation in the Se4047 and SzH70 genomes see Table S1). 10.1371/journal.ppat.1000346.g001 Figure 1 Schematic circular diagrams of the Se4047 (A) and SzH70 genomes (B). Key for the circular diagrams (outside to inside): scale (in Mb); annotated CDSs colored according to predicted function represented on a pair of concentric circles, representing both coding strands; orthologue matches shared with the Streptococcal species, Se4047 or SzH70, SzMGCS10565, S. uberis 0140J, S. pyogenes Manfredo, S. mutans UA159, S. gordonii Challis CH1, S. sanguinis SK36, S. pneumoniae TIGR4, S. agalactiae NEM316, S. suis P1/7, S. thermophilus CNRZ1066, blue; orthologue matches shared with Lactococcus lactis subspecies lactis, green; G+C% content plot; G+C deviation plot (>0%, olive, 94% identity with prophage sequences present in the published genomes of S. pyogenes, four spacers have identical matches with prophage sequences found in the Se4047 genome (#6 with SEQ0163, #7 with SEQ1743, #8 with SEQ1745 and #15 with SEQ1727 (seeM)) and one spacer (#18) has a near identical match with the Se4047 prophage CDS SEQ0190, differing only at the first nucleotide (C to T). This latter spacer is the only exact match with the spacer sequences of SzMGCS10565 CRISPRs (spacer 9 of CRISPR I) [12]. The limited spacer similarity of SzH70 and SzMGCS10565 may reflect exposure to different phage in their respective host environments. The CRISPR loci of SzH70 and SzMGCS10565 may assist the development of resistance to circulating phage and maintain genome integrity. The CRISPR region of SzH70 was present in 93% (131/140) of S. zooepidemicus isolates examined by PCR, but was absent from all strains of S. equi tested (Figure 4). Deletion of the CRISPR locus from the ancestor of Se4047 is likely to have resulted in increased genome instability and illustrates that in some circumstances gene loss may in turn influence the subsequent rate of gene gain. Both the SzH70 and Se4047 genomes contain distinct integrative conjugative element (ICE) regions. This type of MGE element has been shown to be widely distributed [46], and associated with the transfer of a diverse range of functions. One of the ICE in the Se4047 genome, ICESe2, contained CDSs (SEQ1233-SEQ1246) with similarity to the non-ribosomal peptide synthesis (NRPS) system of Clostridium kluyveri and Yersinia sp. that produce an unnamed siderophore [47] and the ferric iron-binding siderophore yersiniabactin [48], respectively. We have demonstrated that the S. equi NRPS operon is required for the production of an undefined secreted molecule, provisionally named equibactin, which enhances the ability of S. equi to acquire iron [10]. Siderophore biosynthesis has not previously been identified in any streptococci [49]. However, homologues of SEQ1246 and SEQ1243 (present as a pseudogene) are in the genome of S. agalactiae NEM316 serotype III, suggesting that a locus with similarity to the S. equi NRPS operon may have been important to this organism at some time. The ICESe2 locus was present in all of the S. equi isolates, but in none of the diverse collection of S. zooepidemicus isolates examined (Figure 4). Given the importance of iron acquisition to other streptococcal pathogens [50], the acquisition of ICESe2 may have contributed significantly to the increased pathogenesis of this Streptococcus. In particular, we hypothesize that more efficient acquisition of iron could enhance the ability of S. equi to generate lymph node abscessation, which is critical to the establishment of long term carriage and vital to the success of this bacterium. It is intriguing to note that the production of yersiniabactin by Y. pestis is essential to its virulence [51]. It will be important to determine the contribution of ICESe2 to the formation of abscesses in the lymph nodes of horses. A facet of the Se4047 genome suggestive of recent niche adaptation is the large increase in the number of IS elements relative to SzH70 (SzH70 contains 30 whereas Se4047 contains 73; Table S4). In particular there appears to have been an expansion of the IS3-family IS element, ISSeq3: the Se4047 genome contains 40 copies of ISSeq3 whereas SzH70 contains 4 (ISSzo3). An expansion of IS elements has been observed in several host-restricted pathogens, which have recently evolved from generalist ancestors [15],[16]. An evolutionary consequence of niche transit is hypothesized to be that many genes become dispensable, allowing increased inactivation. Niche change is also associated with significant evolutionary bottlenecks, which will be enhanced by repeated acquisition of mobile genetic elements. This leads to small effective population sizes, resulting in lower efficiency of selection, which in turn allows gene mutation and expansion of IS elements through accelerated genetic drift. A corollary of the IS proliferation has been the loss of genes by deletion [15]: several of the previously described examples of gene loss (eg. pilus locus and CRISPR locus) probably occurred through insertion and recombination between IS elements (Table S1). Conclusions The comparison of the genomes of Se4047 and SzH70 provides strong evidence that S. equi has passed through a genetic bottleneck during its evolution from an ancestral S. zooepidemicus strain. We have identified several examples of gene loss that serve to reduce the ancestral capabilities of S. equi and increase the opportunity for genetic change. The acquisition of new mobile genetic elements has been critical to the evolution of S. equi. However, surveillance of the S. zooepidemicus population has identified examples of strains that did not cause strangles, but contain genes encoding phospholipase A2 toxins and superantigens. Therefore, we propose that the key speciation event in the evolution of S. equi was the acquisition of ICESe2, containing a novel NRPS involved in the acquisition of iron, which is the first of its kind to be identified in streptococci. The proposed functional effects that result from the genetic events highlighted by our analysis are summarized in Figure 8. 10.1371/journal.ppat.1000346.g008 Figure 8 Summary of functional loss and gene gain by S. equi. Gene loss (blue): (1) Se4047 has lost the ability to ferment lactose, sorbitol, and ribose, which may reduce its ability to colonize the mucosal surface. (2) Hyaluronate lyase activity is predicted to be reduced in Se4047, which could decrease its ability to invade tissue and provide an explanation for increased levels of hyaluronate capsule. Increased levels of capsule may enhance resistance to phagocytosis, but could also reduce adhesion to the mucosal surface. (3) Truncation of fne and Shr in Se4047 and subsequent synthesis of secreted fibronectin products may decrease the adhesive properties of Se4047 and interfere with fibronectin-dependent attachment mechanisms of competing pathogens. (4) Loss of function of the tetR regulator may lead to constitutive production of longer collagen-binding pili by S. equi. (5) The putative SZO18310 pilus locus of SzH70 has been deleted from the Se4047 genome. (6) Se4047 has lost a Listeria-Bacteroides repeat domain containing surface-anchored protein. Gene gain (red): (7) The acquisition of prophage plays an important evolutionary role through integration of cargo genes. (8) Recirculation and secretion of the integrated ϕSeq1 may kill susceptible competing bacteria such as S. zooepidemicus. (9) ϕSeq2 contains a gene encoding a phospholipase A2 (SlaA) that may enhance virulence. (10) ϕSeq3 and ϕSeq4 encode superantigens SeeH, SeeI, SeeL, and SeeM that target the equine immune system (11). (12) The absence of prophage in S. zooepidemicus may be explained by the presence of CRISPR arrays and competence proteins that confer resistance to circulating phage and maintain genome integrity. (13) The ICESe2 locus may enhance iron acquisition in Se4047 through the production of a potential siderophore, equibactin. (14) Se18.9 binds Factor H and interferes with complement activation. Our study provides strong evidence for genetic exchange between S. equi, S. zooepidemicus and S. pyogenes, which continues to influence the pathogenicity of these important bacteria. The genetic diversity of the S. zooepidemicus population as measured by MLST [2] suggests that further investigation of this species will be likely to identify many more genes of importance to both veterinary and human disease. Materials and Methods Strains growth and DNA isolation Se4047 was isolated from a horse with strangles in the New Forest, England, in 1990 [11], and has been typed as ST-179 by MLST [2]. SzH70 was isolated from a nasal swab taken from a healthy Thoroughbred racehorse in Newmarket, England, in 2000, and has been typed as ST-1 by MLST [2]. Details of all of the isolates examined in this study are presented in Table S3 and are also available on the online MLST database (Available: http://pubmlst.org/szooepidemicus/. Accessed 3 October 2008). For the preparation of DNA for whole genome sequencing Se4047 and SzH70 were grown overnight in Todd Hewitt broth (THB) at 37°C in a 5% CO2 enriched atmosphere. Cells were harvested and chromosomal DNA was extracted according to the method of Marmur [52] with the addition of 5000 units of mutanolysin (Sigma) and 20 µg of RNaseA (Sigma) during the lysis step. For the study of hyaluronate capsule degradation strains were grown overnight on COBA strep select plates (bioMérieux) at 37°C in a 5% CO2 enriched atmosphere, with and without pre-absorption of plates with 50 µl of 40 mg ml−1 hyaluronidase (Sigma cat# H2126). Whole genome sequencing The genome of Se4047 was obtained with ∼8× coverage from m13mp18 and pUC18 genomic shotgun libraries (with insert sizes of 1.4 to 4 kb) using big-dye terminator chemistry on ABI3700 automated sequencers. Large insert BAC libraries (pBACe3.6, with insert sizes of 10–20 kb; and pEpiFos1, with insert sizes of 38–42 kb) were used as scaffolds. The SzH70 genome was obtained with ∼8× coverage from pUC18 and pMAQ1b genomic shotgun libraries (with insert sizes of 2–6 kb) using big-dye terminator chemistry on ABI3700 automated sequencers. A large insert pBACe3.6 library (with insert sizes of 20–23 kb) was used as a scaffold. Repeats were bridged by read-pairs or end-sequenced PCR products. Annotation and analysis The sequence was finished and annotated as described previously using Artemis software to collate data and facilitate annotation [53]. Comparison of the genome sequences was facilitated by using the Artemis Comparison Tool (ACT) [54]. Orthologous proteins were identified as reciprocal best matches using FASTA [55] with subsequent manual curation. Orthology inferred from positional information was investigated using ACT. Pseudogenes had one or more mutations that would prevent correct translation; each of the inactivating mutations was subsequently checked against the original sequencing data. The sequence and annotation of the Se4047 and SzH70 genomes have been deposited in the EMBL database under accession numbers FM204883 and FM204884 respectively. Sequences used for comparative genomic analysis were: S. zooepidemicus MGCS10565 (CP001129) [12], S. uberis 0140J (AM946015) [56], S. pyogenes Manfredo (AM295007) [57], S. thermophilus CNRZ1066 (CP000024) [58], S. suis P1/7 (http://www.sanger.ac.uk/Projects/S_suis/) (Holden et al., unpublished), S. pneumoniae TIGR4 (AE005672) [59], S. sanguinis SK36 (CP000387) [60], S. mutans UA159 (AE014133) [61], S. agalactiae NEM316 (AL732656) [62], S. gordonii str. Challis substr. CH1 (CP000725) [63] and Lactococcus lactis subsp. lactis IL1403 (AE005176) [64]. Prophage Clustering S. pyogenes prophage sequences were extracted from the genomes of S. pyogenes strains Manfredo (AM295007) [57]; SSI-1 (BA000034) [65], SF370 (AE004092) [66], MGAS315 (AE014074) [42], MGAS8232 (AE009949) [59], MGAS10394 (CP000003) [60], MGAS6180 (CP000056) [61], MGAS5005 (CP000017) [67], MGAS2096 (CP000261) [33], MGAS9429 (CP000259) [33], MGAS10270 (CP000260) [33] and MGAS10750 (CP000262) [33]. Prophage CDSs were clustered into homology groups using TribeMCL (Centre for Mathematics and Computer Science and EMBL-EBI) [68] with a cut-off of 1e−50. Sugar fermentation The ability of isolates to ferment lactose, ribose and sorbitol was determined in Purple broth (Becton Dickinson) as previously described [18]. Mitogenicity assays Equine PBMC were purified from heparinised blood by centrifugation on a Ficoll density gradient. PBMC were incubated with S. equi or S. zooepidemicus culture supernatants diluted 1/20. PBMC proliferation was detected by overnight incorporation of 3H thymidine after 3 days of culture. Equine PBMC proliferation is expressed as stimulation index (SI) calculated as follows (experimental response/control response). A SI≥2 was considered as positive. Gene prevalence studies Genomic DNA from a diverse set of 26 S. equi strains and 140 S. zooepidemicus strains was prepared from single colonies grown on COBA strep select plates (bioMérieux) and purified using GenElute spin columns according to manufacturer's instructions (Sigma). The relatedness of MLST STs was determined using ClonalFrame [69]. Gene prevalence was then determined by quantitative PCR (QPCR) using a SYBR green based method with a Techne Quantica instrument. For the QPCR, 10 ng DNA diluted was mixed with 0.3 µM forward and reverse primers (Table S5) and 1× ABsolute QPCR SYBR green mix (Abgene) in a total volume of 20 µl and subjected to thermocycling at 95°C for 15 min, followed by 40 cycles of 95°C for 15 s, 55°C for 30 s and 72°C for 30 s. Dissociation curves were analyzed following a final ramp step from 60°C to 90°C with reads at 0.5°C increments to rule out non-specific amplification. Data were analyzed using Quansoft software (Techne). Crossing point values relative to those for the gyrA house-keeping gene were used to determine gene presence or absence. Reverse transcription and quantitative real-time PCR for recombinase activity The potential for inversion of the promoter region proceeding the recombinase was assessed by comparison of SZO08560 mRNA transcript levels (produced when the promoter region is in the forward orientation) with reverse strand SZO08550 mRNA transcript levels (produced when the promoter region is inverted) in SzH70. SzH70 was grown to log phase in THB with 10% horse sera. A quantitative two-step reverse transcription (RT) PCR procedure was used to analyze levels of SZO08560 and reverse strand SZO08550 transcription relative to the housekeeping gene gyrA. RT was performed using the Verso cDNA kit (Abgene). The RT reaction mixture (20 µl) contained 100 ng total RNA, 2 µM gene-specific primer (ZM474R or ZM476F) (Table S5), 500 µM dNTP mix, 1× cDNA synthesis buffer, 1 µl RT enhancer and 1 µl Verso enzyme mix. RT was performed at 50°C for 30 min and terminated by heating to 95°C for 2 min. Quantitative real time PCR (QPCR) was performed with a Techne Quantica instrument and data analyzed using Quansoft software (Techne). For the QPCR, 6 µl RT reaction mixture diluted 1/1000 was mixed with 0.3 µM forward and reverse primers (Table S5), and 1× ABsolute QPCR SYBR green mix (Abgene) in a total volume of 20 µl and subjected to thermocycling at 95°C for 15 min, followed by 40 cycles of 95°C for 15 s, 55°C for 30 s and 72°C for 30 s. Dissociation curves were analyzed, following a final ramp step from 60°C to 90°C with reads at 0.5°C increments, to rule out non-specific amplification. No-template negative controls were included and reverse transcriptase negative controls to confirm the absence of contaminating DNA from RNA samples. Standard curves (Crossing point vs. log gene copy number) were generated from genomic DNA for each target gene and used to calculate transcript copy number in cDNA samples. SZO08560 and reverse strand SZO08550 transcript copy numbers were normalized to gyrA reference gene copy number to correct for differences in the amount of starting material. Data was expressed as fold difference in normalized SZO08560 transcript level relative to reverse strand SZO08550 transcript level. Phage particle DNA purification, PCR, and sequencing Phage particle DNA was purified according to previously published methods [70]. Se4047 was grown to log phase and treated for 3 hours with mitomycin C. Bacteria were centrifuged at 8,000×g for 15 minutes and the supernatant was sterilized with a 0.45 µm filter (Millipore). The filter-sterilized supernatant was centrifuged at 141,000×g for 4 h at 10°C, and the pellet resuspended in 1 ml phage suspension buffer. 0.5 ml phage particles were treated with 25 U benzonase (Novagen) for 1 h at 37°C and then lysed with 0.5% sodium dodecyl sulfate, 10 mM EDTA and 500 µg of proteinase K (Sigma)/ml for 1 h at 37°C. Phage DNA was extracted with an equal volume of phenol-chloroform-isoamyl alcohol (25∶24∶1) (Sigma), followed by an equal volume of chloroform-isoamyl alcohol (24∶1) (Sigma). Phage DNA was precipitated with 300 mM NaOAc (pH 4.6) (Sigma) and a 2.5-fold volume of ethanol at −20°C overnight, washed with 70% ethanol and suspended in distilled H2O. Prophage induction was detected by PCR with forward and reverse primers (Table S5) that were specific for each recircularized prophage and amplified across the join of prophage ends. Se4047 genomic DNA was used to confirm that the integrated prophage did not generate a PCR product using these primers. PCR products generated from phage particle DNA preparations were purified on QIAquick spin columns (Qiagen) and the sequences of both strands of the PCR fragments were determined using an ABI3100 DNA sequencer with BigDye fluorescent terminators and the primers used in the initial PCR amplification to confirm prophage recircularization. Accession numbers The sequence and annotation of the Se4047 and SzH70 genomes have been deposited in the EMBL database under accession numbers FM204883 and FM204884, respectively. Supporting Information Table S1 Complete list of the differences between the Se4047 and SzH70 genomes. (A) Novel S. equi strain 4047 DNA loci. *Homologue present in SzMGCS10565. (B) Novel S. zooepidemicus strain H70 DNA loci. *Homologue present in SzMGCS10565. (C) Diversified regions of the S. zooepidemicus strain H70 and S. equi strain 4047 genomes. (D) S. equi strain 4047 pseudogenes (includes partial genes). (E) S. zooepidemicus strain H70 pseudogenes (includes partial genes). (1.42 MB DOC) Click here for additional data file. Table S2 Sortase-processed surface proteins of S. zooepidemicus strain H70 and S. equi strain 4047. §Needleman-Wunsch global alignment; % identity given for intact CDSs only. *Orthologue present in SzMGCS10565. †Pseudogene or gene remnant. NP, not present. (0.07 MB DOC) Click here for additional data file. Table S3 Identity of S. equi and S. zooepidemicus isolates studied and stimulation index data. NA, information not available. (0.35 MB DOC) Click here for additional data file. Table S4 Composition of insertion elements in the S. zooepidemicus strain H70 and S. equi strain 4047 genomes. IS elements were grouped into separate isoforms (IS elements with DNA sequence more than 95% identity), numbered accordingly, and given a specific three-letter identifier to designate the species of origin. Truncated IS elements lacking either the 3-prime or 5-prime ends were not included in the table. *Chimeric IS element that appears to have been generated from recombination between ISSeq3 and ISSeq5 elements. (0.04 MB DOC) Click here for additional data file. Table S5 Oligonucleotides used in this study. (0.07 MB DOC) Click here for additional data file. Figure S1 Hyaluronidase treatment of Se4047, SzH70 and ST-57 (JKS115). Colony phenotypes of Se4047, SzH70 and ST-57 (JKS115) grown overnight on COBA selective agar with and without addition of hyaluronidase. (7.65 MB TIF) Click here for additional data file. Figure S2 Alignment of SZO08560 and Sez_1114 Listeria-Bacteroides repeat domains domains. Alignment of protein domains in InlA, (Listeria monocytogenes, ABO32414), SZO08560 (SzH70), Sez_1114 (SzMGCS10565), SSU05_0473 (Streptococcus suis strain 05ZYH33, A4VTK0) and SAN_1519 (Streptococcus agalactiae strain COH1, Q3D8T2) to the Pfam hidden Markov model (HMM) for the Listeria-Bacteroides repeat domain (PF09479). Listeria-Bacteroides repeat domains are a feature of some Bacteroides forsythus proteins and families of internalins of Listeria species. Matches to the highly conserved and less well conserved Listeria-Bacteroides repeat domain residues are shown in dark and light grey respectively. (0.70 MB TIF) Click here for additional data file.
- Record: found
- Abstract: found
- Article: not found
Real-time PCR for detection and differentiation of Streptococcus equi subsp. equi and Streptococcus equi subsp. zooepidemicus.
V Båverud, A Aspán, Magnus S K Johansson (2007)
Strangles is a contagious equine disease caused by Streptococcus equi subsp. equi. In this study, clinical strains of S. equi (n=24) and Streptococcus equi subsp. zooepidemicus (n=24) were genetically characterized by sequencing of the 16S rRNA and sodA genes in order to devise a real-time PCR system that can detect S. equi and S. zooepidemicus and distinguish between them. Sequencing demonstrated that all S. equi strains had the same 16S rRNA sequence, whereas S. zooepidemicus strains could be divided into subgroups. One of these (n=12 strains) had 16S rRNA sequences almost identical with the S. equi strains. Interestingly, four of the strains biochemically identified as S. zooepidemicus were found by sequencing of the 16S rRNA gene to have a sequence homologous with Streptococcus equi subsp. ruminatorum. However, they did not have the colony appearance or the biochemical characteristics of the type strain of S. ruminatorum. Classification of S. ruminatorum may thus not be determined solely by 16S rRNA sequencing. Sequencing of the sodA gene demonstrated that all S. equi strains had an identical sequence. For the S. zooepidemicus strains minor differences were found between the sodA sequences. The developed real-time PCR, based on the sodA and seeI genes was compared with conventional culturing on 103 cultured samples from horses with suspected strangles or other upper respiratory disease. The real-time PCR system was found to be more sensitive than conventional cultivation as two additional field isolates of S. equi and four of S. zooepidemicus were detected.
- Record: found
- Abstract: found
- Article: not found
Sequence variation of the SeM gene of Streptococcus equi allows discrimination of the source of strangles outbreaks.
M Maiden, Carl Robinson, Joshua D Newton … (2006)
Improved understanding of the epidemiology of Streptococcus equi transmission requires sensitive and portable subtyping methods that can rationally discriminate between strains. S. equi is highly homogeneous and cannot be distinguished by multilocus enzyme electrophoretic or multilocus sequence-typing methods that utilize housekeeping genes. However, on sequence analysis of the N-terminal region of the SeM genes of 60 S. equi isolates from 27 strangles outbreaks, we identified 21 DNA codon changes. These resulted in the nonsynonymous substitution of 18 amino acids and allowed the assignment of S. equi strains to 15 distinct subtypes. Our data suggest the presence of multiple epitopes across this region that are subjected to selective immune pressure (nonsynonymous-synonymous substitution rate [d(N)/d(S)] ratio = 3.054), particularly during the establishment of long-term S. equi infection. We further report the application of SeM gene subtyping as a method to investigate potential cases of disease related to administration of a live attenuated S. equi vaccine. SeM gene subtyping successfully differentiated between the vaccine strain and field strains of S. equi responsible for concurrent disease. These results were confirmed by the development and application of a PCR diagnostic test, which identifies the aroA partial gene deletion present in the Equilis StrepE vaccine strain. Although the vaccine strain was found to be responsible for injection site lesions, all seven outbreaks of strangles investigated in recently vaccinated horses were found to be due to concurrent infection with wild-type S. equi and not due to reversion of the vaccine strain.
Author and article information
Contributors
A.G. Boyle:
ORCID: http://orcid.org/0000-0003-4325-1005
boylea@vet.upenn.edu
Journal
Journal ID (nlm-ta): J Vet Intern Med
Journal ID (iso-abbrev): J. Vet. Intern. Med
Journal ID (doi): 10.1111/(ISSN)1939-1676
Journal ID (publisher-id): JVIM
Title:
Journal of Veterinary Internal Medicine
Publisher:
John Wiley and Sons Inc.
(Hoboken
)
ISSN
(Print):
0891-6640
ISSN
(Electronic):
1939-1676
Publication date
(Electronic):
09
February
2018
Publication date
(Print):
Mar-Apr 2018
Volume: 32
Issue: 2
(
doiID:
10.1111/jvim.2018.32.issue-2
)
Pages: 633-647
Affiliations
Author notes
[*]
[*
]Corresponding Author: A.G. Boyle, Department of Clinical Studies, School of Veterinary
Medicine, University of Pennsylvania, New Bolton Center, 382 West Street Road, Kennett
Square, PA 19348; e‐mail:
boylea@
123456vet.upenn.edu
.
Author information
A.G. Boyle
http://orcid.org/0000-0003-4325-1005
Article
Publisher ID: JVIM15043DOI: 10.1111/jvim.15043
PMC ID: 5867011
PubMed ID: 29424487
SO-VID: 35738c77-a11b-44dc-ac69-88e29f0d534d
Copyright © Copyright © 2018 The Authors. Journal of Veterinary Internal Medicine published by
Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.
License:
This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
History
Date
received
: 07
November
2017
Date
revision received
: 14
December
2017
Date
accepted
: 14
December
2017
Page count
Figures: 0,
Tables: 2,
Pages: 15,
Words: 13011
Categories
Subject:
ACVIM Consensus Statement
Subject:
Consensus Statements
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component-id jvim15043
cover-date March/April 2018
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ScienceOpen disciplines: Veterinary medicine
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ScienceOpen disciplines: Veterinary medicine