Distribution of serotypes of Streptococcus suis isolated from diseased pigs in Spain

Comparative Genome Analysis of Two Streptococcus suis Serotype 8 Strains Identifies Two New Virulence-Associated Genes

Streptococcus suis is an important zoonotic pathogen that can cause meningitis and septicemia in swine and humans. Among numerous pathogenic serotypes, S. suis serotype 8 has distinctive characteristics such as a high detection rate and causing multi-host infection. There is no complete genome of serotype 8 strains so far. In this study, the complete genome of two S. suis serotype 8 strains, virulent strain 2018WUSS151 and non-virulent strain WUSS030, were sequenced. Comparative genomic analysis showed that the homology of the two genomes reaches 99.68%, and the main difference is the distinctive prophages. There are 83 genes unique to virulent strain 2018WUSS151, including three putative virulence-associated genes (PVGs). Two PVGs, padR and marR, are passenger genes in ISSsu2 family transposons that are able to form circular DNA intermediates during transposition, indicating the possibility of horizontal transmission among S. suis strains. The deletion mutant of PVGs marR or atpase attenuated the virulence of serotype 2 virulent SC070731 in a mouse infection model, confirming their role in S. suis virulence. These findings contribute to clarifying the genomic characterization of S. suis serotype 8 and S. suis pathogenesis.

Invasive Bacterial Infections of the Musculoskeletal and Central Nervous System during Pig Rearing: Detection Frequencies of Different Pathogens and Specific Streptococcus suis Genotypes

Locomotor and central nervous system disorders occur during pig rearing, but there is no systematic recording of the different causative agents in Germany. Joint and meningeal swabs, kidneys, lungs, and eight different lymph nodes per pig were cultured, and isolated pathogens were identified using polymerase chain reactions (PCRs). The cps and pathotype of Streptococcus suis (S. suis) isolates were determined using multiplex-PCR. S. suis was the most important pathogen in the infected joints (70.8%) and meningeal swabs (85.4%) and was most frequently detected in both sites in suckling and weaning piglets. To elucidate the possible portal of entry of S. suis, eight different lymph nodes from 201 pigs were examined in a prospective study. S. suis was detected in all examined lymph nodes (n = 1569), including the mesenteric lymph nodes (15.8%; n = 121/765), with cps 9 (37.2%; n = 147) and cps 2 (24.3%; n = 96) being the most dominating cps types. In piglets with a systemic S. suis infection, different lymph nodes are frequently infected with the invasive S. suis strain, which does not help clarify the portal of entry for S. suis.

Epidemiology and genetic diversity of Streptococcus suis in smallhold swine farms in the Philippines

This study aimed to determine the presence and characteristics of locally circulating strains of Streptococcus suis, the most important streptococcal pathogen in swine. Oral swab samples were collected from pigs from 664 representative smallhold farms across nine provinces in the Philippines. Isolates were identified and characterized using PCR assays. The study revealed an isolation rate of 15.8% (105/664, 95% CI: 13.0-18.6) among the sampled farms. Two hundred sixty-nine (269) S. suis isolates were recovered from 119 unique samples. Serotype 31 was the most prevalent (50/269, 95% CI: 13.9-23.2) among the other serotypes identified: 5, 6, 8, 9, 10, 11, 15, 16, 17, 21, 27, 28, and 29. The detection of the three 'classical' S. suis virulence-associated genes showed that 90.7% (244/269, 95% CI: 87.2-94.2) were mrp-/epf-/sly-. Multilocus sequence typing (MLST) analysis further revealed 70 novel sequence types (STs). Notably, several local isolates belonging to these novel STs formed clonal complexes (CC) with S. suis strains recovered from Spain and USA, which are major pork-exporting countries to the Philippines. This study functionally marks the national baseline knowledge of S. suis in Philippines.

The characteristics of population structure and antimicrobial resistance of Streptococcus suis serotype 8, a non-negligible pathotype

Streptococcus suis, the leading causative agent of swine streptococcosis, is considered as a severe zoonotic and foodborne pathogen for humans. Characteristics of population structure and pathogenicity of S. suis vary significantly by serotypes. As one of the main pathogenic serotypes causing clinical disease in pigs, very little is known about the pathogenicity, population structure, and antimicrobial resistance of S. suis serotype 8 (SS8). In this study, the genome of 26 SS8 strains isolated from healthy and diseased pigs was sequenced. Together with 38 sequences from NCBI, we found that SS8 population was clustered into 12 sequence types (ST) and 4 minimum core genome (MCG) groups, linked to the geographical distribution. Noteworthily, 10 strains belonged to MCG group 1 which was defined to possess the capacity to cause global outbreaks in our previous study. We found that 75% (9/12) of representative SS8 strains were virulent in mice and zebrafish, including all ST1241 strains. No virulence indicators were identified from 67 putative virulence-associated genes mainly identified among pathogenic serotype 2 strains. Instead, we found that the genotype of some of these genes was correlated to their evolution. All 26 isolates were classified as multidrug-resistant strains by antimicrobial susceptibility testing. The high carrying rate of tetO and ermB, mainly disseminated by integrative mobilizable elements, contributed to the prevalent resistance phenotypes to macrolides, lincosamides and tetracyclines. These findings indicated that the pathogenic potential of SS8 cannot be ignored and provided valuable information for SS8 surveillance.

Genomic and pathogenic investigations of Streptococcus suis serotype 7 population derived from a human patient and pigs

Streptococcus suis is one of the important emerging zoonotic pathogens. Serotype 2 is most prevalent in patients worldwide. In the present study, we first isolated one S. suis serotype 7 strain GX69 from the blood culture of a patient with septicemia complicated with pneumonia in China. In order to deepen the understanding of S. suis serotype 7 population characteristics, we investigated the phylogenetic structure, genomic features, and virulence of S. suis serotype 7 population, including 35 strains and 79 genomes. Significant diversities were revealed in S. suis serotype 7 population, which were clustered into 22 sequence types (STs), five minimum core genome (MCG) groups, and six lineages. Lineages 1, 3a, and 6 were mainly constituted by genomes from Asia. Genomes of Lineages 2, 3b, and 5a were mainly from Northern America. Most of genomes from Europe (41/48) were clustered into Lineage 5b. In addition to strain GX69, 13 of 21 S. suis serotype 7 representative strains were classified as virulent strains using the C57BL/6 mouse model. Virulence-associated genes preferentially present in highly pathogenic S. suis serotype 2 strains were not suitable as virulence indicators for S. suis serotype 7 strains. Integrative mobilizable elements were widespread and may play a critical role in disseminating antibiotic resistance genes of S. suis serotype 7 strains. Our study confirmed S. suis serotype 7 is a non-negligible pathotype and deepened the understanding of the population structure of S. suis serotype 7, which provided valuable information for the improved surveillance of this serotype.

Antimicrobial susceptibility of cinnamon and red and common thyme essential oils and their main constituent compounds against Streptococcus suis

Streptococcus suis is an emerging zoonotic pathogen causing different diseases, in both humans and pigs. Generally, the control of this pathogen is based on antimicrobial therapy, but the development of bacterial resistance has led one to look for new options. In this sense, the essential oils (EOs) constitute a promising alternative. The activity of cinnamon, common thyme and red thyme EOs and their main active compounds (cinnamaldehyde and thymol) against S. suis isolates from pigs (n = 50) and humans (n = 6) was determined by the broth microdilution method. MIC_50-90, MBC_50-90 and the bactericidal index (BI) (minimal bactericidal concentration (MBC)/minimal inhibitory concentration (MIC)) were calculated. Also, the time-kill curve of each product against the S. suis P1/7 European reference strain was determined. No differences in the MIC or MBC values were observed between all the tested products, which suggest a homogeneous behaviour of S. suis, independently of their origin, organ of isolation or resistance profile. All the products showed a concentration-dependent and time-dependent killing activity and achieved the virtual eradication of S. suis at supra-inhibitory concentrations within the first 5 min of exposure, except cinnamaldehyde that showed only bacteriostatic effect. It suggests that these products could be utilized as antimicrobials in veterinary medicine for the control of this zoonotic pathogen.

Antimicrobial activity of selected essential oils against Streptococcus suis isolated from pigs

The inhibitory potential by contact and vapor of basil, cinnamon, clove, peppermint, oregano, rosemary, common thyme, and red thyme essential oils (EOs) against 20 strains of Streptococcus suis was determined by the disk diffusion test. The broth microdilution method was used to determine the minimal inhibitory and minimal bactericidal concentration (MIC and MBC) of the four selected oils. Furthermore, the bactericidal power (ratio MBC/MIC) was calculated. The EOs with the major potential in the disk diffusion method were red thyme, common thyme, oregano, and cinnamon (∅ mean 16.5–34.2 mm), whereas cinnamon did not show vapor activity. In the microdilution test, all the EOs showed notable antimicrobial activity (MIC₉₀ and MBC₉₀ 312.5–625 μg·ml⁻¹) and a strong bactericidal power (ratio = 1). This is the first study that selects essential oils against S. suis. New studies about the possible synergic effect of EOs with antibiotics and about toxicity and efficacy in in vivo conditions are recommended.

Streptococcus suis - The "Two Faces" of a Pathobiont in the Porcine Respiratory Tract

Streptococcus (S.) suis is a frequent early colonizer of the upper respiratory tract of pigs. In fact, it is difficult to find S. suis-free animals under natural conditions, showing the successful adaptation of this pathogen to its porcine reservoir host. On the other hand, S. suis can cause life-threatening diseases and represents the most important bacterial cause of meningitis in pigs worldwide. Notably, S. suis can also cause zoonotic infections, such as meningitis, septicemia, endocarditis, and other diseases in humans. In Asia, it is classified as an emerging zoonotic pathogen and currently considered as one of the most important causes of bacterial meningitis in adults. The “two faces” of S. suis, one of a colonizing microbe and the other of a highly invasive pathogen, have raised many questions concerning the interpretation of diagnostic detection and the definition of virulence. Thus, one major research challenge is the identification of virulence-markers which allow differentiation of commensal and virulent strains. This is complicated by the high phenotypic and genotypic diversity of S. suis, as reflected by the occurrence of (at least) 33 capsular serotypes. In this review, we present current knowledge in the context of S. suis as a highly diverse pathobiont in the porcine respiratory tract that can exploit disrupted host homeostasis to flourish and promote inflammatory processes and invasive diseases in pigs and humans.

Effect of Simultaneous Exposure of Pigs to Streptococcus suis Serotypes 2 and 9 on Their Colonization and Transmission, and on Mortality

The distribution of Streptococcus suis serotypes isolated from clinically infected pigs differs between geographical areas, and varies over time. In several European countries, predomination of serotype 2 has changed to serotype 9. We hypothesize a relation, with one serotype affecting the other in colonization and invasion. The aim of this study was to evaluate whether simultaneous exposure of pigs to serotypes 2 and 9 affects colonization and transmission of each type, and mortality. Thirty-six caesarean-derived/colostrum-deprived piglets were randomly assigned to three groups, and there housed pair-wise. At six weeks old, one pig per pair was inoculated with either one (serotype 2 or 9; mono-group) or two serotypes simultaneously (dual-group); the other pig was contact-exposed. Tonsillar and nasal samples were collected within three weeks post inoculation. Bacterial loads in samples were quantified using multiplex real-time polymerase chain reaction (PCR). Transmission rates of the serotypes among pigs were estimated using a mathematical Susceptible-Infectious (SI) model. Bacterial loads and transmission rates did not differ significantly between serotypes. Compared to the mono-group, in the dual-group the average serotype 2 load in tonsillar samples from contact pigs was reduced on days 1 to 4 and on day 6. Simultaneous exposure to the serotypes reduced the mortality hazard 6.3 times (95% C.I.: 2.0–19.8) compared to exposure to serotype 2 only, and increased it 6.6 times (95% C.I.: 1.4–30.9) compared to exposure to serotype 9 only. This study indicates that serotype 2 load and mortality were affected in pigs exposed to these two serotypes.

Simultaneous Quantification and Differentiation of Streptococcus suis Serotypes 2 and 9 by Quantitative Real-Time PCR, Evaluated in Tonsillar and Nasal Samples of Pigs

Invasive Streptococcus suis (S. suis) infections in pigs are often associated with serotypes 2 and 9. Mucosal sites of healthy pigs can be colonized with these serotypes, often multiple serotypes per pig. To unravel the contribution of these serotypes in pathogenesis and epidemiology, simultaneous quantification of serotypes is needed. A quantitative real-time PCR (qPCR) targeting cps2J (serotypes 2 and 1/2) and cps9H (serotype 9) was evaluated with nasal and tonsillar samples from S. suis exposed pigs. qPCR specifically detected serotypes in all pig samples. The serotypes loads in pig samples estimated by qPCR showed, except for serotype 9 in tonsillar samples (correlation coefficient = 0.25), moderate to strong correlation with loads detected by culture (correlation coefficient > 0.65), and also in pigs exposed to both serotypes (correlation coefficient > 0.75). This qPCR is suitable for simultaneous differentiation and quantification of important S. suis serotypes.

Characterization of the immune response and evaluation of the protective capacity of rSsnA against Streptococcus suis infection in pigs

The efforts made to develop vaccines against Streptococcus suis have failed because of lack of common antigens cross-reactive against different serotypes of this species. The cell wall-anchored proteins can be good vaccine candidates due to their high expression and accessibility to antibodies, among these, a cell-wall protein, DNA-nuclease (SsnA), present in most of the S. suis serotypes and clinical isolates collected from infected pigs, was selected. An experimental challenge against S. suis serotype 2 in a pig model was used to validate the efficacy of recombinant SsnA combined with aluminium hydroxide plus Quil A as adjuvants, previously tested in mice by our research group with good results. In our study, clinical characteristics, bacterial load and spread, haematological and immunological parameters and the antibody response, including the opsonophagocytosis analysis of the sera were evaluated. Moreover the composition of peripheral blood leukocyte populations was studied in infected animals. The results show that the immunization of piglets with rSsnA elicits a significant humoral antibody response. However, the antibody response is not reflected in protection of pigs that are challenged with a virulent strain in our conventional vaccination model. Further studies are necessary to evaluate the use of rSsnA as a vaccine candidate for swine.

Streptococcus suis, an important pig pathogen and emerging zoonotic agent-an update on the worldwide distribution based on serotyping and sequence typing

Streptococcus suis is an important pathogen causing economic problems in the pig industry. Moreover, it is a zoonotic agent causing severe infections to people in close contact with infected pigs or pork-derived products. Although considered sporadic in the past, human S. suis infections have been reported during the last 45 years, with two large outbreaks recorded in China. In fact, the number of reported human cases has significantly increased in recent years. In this review, we present the worldwide distribution of serotypes and sequence types (STs), as determined by multilocus sequence typing, for pigs (between 2002 and 2013) and humans (between 1968 and 2013). The methods employed for S. suis identification and typing, the current epidemiological knowledge regarding serotypes and STs and the zoonotic potential of S. suis are discussed. Increased awareness of S. suis in both human and veterinary diagnostic laboratories and further establishment of typing methods will contribute to our knowledge of this pathogen, especially in regions where complete and/or recent data is lacking. More research is required to understand differences in virulence that occur among S. suis strains and if these differences can be associated with specific serotypes or STs.

Effect of spatial separation of pigs on spread of Streptococcus suis serotype 9

The spread of an infectious agent in a population can be reduced by interfering in the infectiousness or susceptibility of individuals, and/or in their contact structure. The aim of this study was to quantify the effect of prevention of direct contact between infectious and susceptible pigs on the transmission of Streptococcus suis (S. suis). In three replicate experiments, S. suis-free pigs were housed in boxes either in pairs (25 pairs) or alone (15 pigs). The distance between the boxes was ±1 m. At 7 weeks of age, one pig of each pair was inoculated intranasally with S. suis serotype 9; the other pigs were exposed to S. suis by either direct (pairs) or indirect contact (individually housed pigs). Tonsillar brush and saliva swab samples from all pigs were collected regularly for 4 weeks post inoculation to monitor colonization with S. suis. All inoculated pigs became infected, and their pen mates became colonized within 2 days. Thirteen indirectly exposed pigs became positive within 7-25 days after exposure. The rate of direct transmission βdir was estimated to be 3.58 per pig per day (95% CI: 2.29-5.60). The rate of indirect transmission increased in time, depending on the cumulative number of days pigs tested positive for the presence of S. suis. The estimate β'ind was 0.001 (95% CI: 0.0006-0.0017) new infections per pig per day for each day that an infected pig was tested positive for S. suis. We conclude that prevention of direct contact reduces the rate at which susceptible pigs become colonized. Simulation studies using these parameters showed, however, that such intervention measure would not limit S. suis serotype 9 spread in a commercial pig farm to a relevant extent, implying that spatial separation of groups op pigs within a compartment would not be effective on a farm.

Homologous whole bacterin vaccination is not able to reduce Streptococcus suis serotype 9 strain 7997 transmission among pigs or colonization

Streptococcus suis (S. suis) is an important porcine pathogen worldwide, and antibiotics are often applied to treat or prevent clinical signs. Vaccination could be an alternative measure to reduce the abundant use of antimicrobials. The aim of this study was to determine the effect of vaccination with homologues whole bacterin vaccine containing S. suis serotype 9 strain 7997 on transmission of this serotype among pigs and on mucosal colonization. Caesarean derived, colostrum deprived pigs (N=50) were housed pair wise. Thirteen pairs were vaccinated intramuscularly with 2-3×10(9) colony forming units (CFU) inactivated S. suis serotype 9 per dose and α-tocopherolactetaat as adjuvant at 3 and 5 weeks of age; twelve pairs served as non-vaccinated controls. At 7 weeks of age, one pig of each pair was intranasally inoculated with 1-2×10(9)CFU of the homologues strain, whereas the other pig of each pair was contact-exposed. Tonsil brushings and saliva swabs were collected for 4 weeks, and tested for the presence of S. suis by bacteriological culture. No differences in number of S. suis in the tonsils or saliva samples or in clinical signs were observed between vaccinated and control pigs. In all pairs, transmission between inoculated and contact exposed pigs occurred, and no difference was observed in rate at which this occurred. The estimated transmission rate parameter β between vaccinated pigs was β(v)=5.27/day, and for non-vaccinated pigs β(nv)=2.77/day (P=0.18). It was concluded that vaccination against S. suis serotype 9 did not reduce transmission, nor colonization and that there were no indications that protection against clinical signs was induced.

Streptococcus suis: an emerging zoonotic pathogen

Streptococcus suis is a major porcine pathogen worldwide, and can be transmitted to human beings by close contact with sick or carrier pigs. S suis causes meningitis, septicaemia, endocarditis, arthritis, and septic shock in both pigs and human beings, and mortality is high. Human infection with S suis occurs mainly among certain risk groups that have frequent exposure to pigs or pork. Outbreaks of human S suis infection are uncommon, although several outbreaks have occurred in China in recent years. In July, 2005, the largest outbreak of human S suis infection occurred in Sichuan province, China, where 204 people were infected and 38 of them died. There have been 409 cases of human S suis infection worldwide, most of which have occurred in China, Thailand, and the Netherlands, and these infections have led to 73 deaths. This review provides background information on the biology and molecular characteristics of this Gram-positive bacterium, and describes the clinical signs, pathology, epidemiology, diagnosis, and treatment of human infection with S suis.