Streptococcus suis serotype 2 strains isolated in Argentina (South America) are different from those recovered in North America and present a higher risk for humans

Streptococcus suis serotype 4: a population with the potential pathogenicity in humans and pigs

Streptococcus suis is a major bacterial pathogen in pigs and an emerging zoonotic pathogen. Different S. suis serotypes exhibit diverse characteristics in population structure and pathogenicity. Surveillance data highlight the significance of S. suis serotype 4 (SS4) in swine streptococcusis, a pathotype causing human infections. However, except for a few epidemiologic studies, the information on SS4 remains limited. In this study, we investigated the population structure, pathogenicity, and antimicrobial characteristics of SS4 based on 126 isolates, including one from a patient with septicemia. We discovered significant diversities within this population, clustering into six minimum core genome (MCG) groups (1, 2, 3, 4, 7-2, and 7-3) and five lineages. Two main clonal complexes (CCs), CC17 and CC94, belong to MCG groups 1 and 3, respectively. Numerous important putative virulence-associated genes are present in these two MCG groups, and 35.00% (7/20) of pig isolates from CC17, CC94, and CC839 (also belonging to MCG group 3) were highly virulent (mortality rate ≥ 80%) in zebrafish and mice, similar to the human isolate ID36054. Cytotoxicity assays showed that the human and pig isolates of SS4 strains exhibit significant cytotoxicity to human cells. Antimicrobial susceptibility testing showed that 95.83% of strains isolated from our labs were classified as multidrug-resistant. Prophages were identified as the primary vehicle for antibiotic resistance genes. Our study demonstrates the public health threat posed by SS4, expanding the understanding of SS4 population structure and pathogenicity characteristics and providing valuable information for its surveillance and prevention.

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.

Serotypes, Virulence-Associated Factors, and Antimicrobial Resistance of Streptococcus suis Isolates Recovered From Sick and Healthy Pigs Determined by Whole-Genome Sequencing

Streptococcus suis is ubiquitous in swine, and yet, only a small percentage of pigs become clinically ill. The objective of this study was to describe the distribution of serotypes, virulence-associated factor (VAF), and antimicrobial resistance (AMR) genes in S. suis isolates recovered from systemic (blood, meninges, spleen, and lymph node) and non-systemic (tonsil, nasal cavities, ileum, and rectum) sites of sick and healthy pigs using whole-genome sequencing. In total, 273 S. suis isolates recovered from 112 pigs (47 isolates from systemic and 136 from non-systemic sites of 65 sick pigs; 90 isolates from non-systemic sites of 47 healthy pigs) on 17 Ontario farms were subjected to whole-genome sequencing. Using in silico typing, 21 serotypes were identified with serotypes 9 (13.9%) and 2 (8.4%) as the most frequent serotypes, whereas 53 (19.4%) isolates remained untypable. The relative frequency of VAF genes in isolates from systemic (Kruskal–Wallis, p < 0.001) and non-systemic (Kruskal–Wallis, p < 0.001) sites in sick pigs was higher compared with isolates from non-systemic sites in healthy pigs. Although many VAF genes were abundant in all isolates, three genes, including dltA [Fisher's test (FT), p < 0.001], luxS (FT, p = 0.01), and troA (FT, p = 0.02), were more prevalent in isolates recovered from systemic sites compared with non-systemic sites of pigs. Among the isolates, 98% had at least one AMR gene, and 79% had genes associated with at least four drug classes. The most frequently detected AMR genes were tetO conferring resistance to tetracycline and ermB conferring resistance to macrolide, lincosamide, and streptogramin. The wide distribution of VAFs genes in S. suis isolates in this study suggests that other host and environmental factors may contribute to S. suis disease development.

The global emergence of a novel Streptococcus suis clade associated with human infections

Streptococcus suis, a ubiquitous bacterial colonizer in pigs, has recently extended host range to humans, leading to a global surge of deadly human infections and three large outbreaks since 1998. To better understand the mechanisms for the emergence of cross-species transmission and virulence in human, we have sequenced 366 S. suis human and pig isolates from 2005 to 2016 and performed a large-scale phylogenomic analysis on 1,634 isolates from 14 countries over 36 years. We show the formation of a novel human-associated clade (HAC) diversified from swine S. suis isolates. Phylogeographic analysis identified Europe as the origin of HAC, coinciding with the exportation of European swine breeds between 1960s and 1970s. HAC is composed of three sub-lineages and contains several healthy-pig isolates that display high virulence in experimental infections, suggesting healthy-pig carriers as a potential source for human infection. New HAC-specific genes are identified as promising markers for pathogen detection and surveillance. Our discovery of a human-associated S. suis clade provides insights into the evolution of this emerging human pathogen and extend our understanding of S. suis epidemics worldwide.

Meningitis due to Streptococcus suis in Two Patients with Occupational Exposure from Northeastern Brazil

Streptococcus suis is an emerging zoonotic agent that causes bacterial meningitis. S. suis is an encapsulated Gram-positive, facultative anaerobic bacterium. This infection usually manifests in humans as meningitis, endocarditis, septicemia, and/or arthritis. The primary groups at risk for S. suis infection are individuals occupationally exposed to pigs and/or pork, for example, farmers, butchers, and hunters. Herein, we report two cases of meningitis related to S. suis with occupational exposure from the Ceará state, northeastern Brazil.

Streptococcus suis: An Underestimated Emerging Pathogen in Hungary?

Streptococcus suis (S. suis) is an emerging zoonotic pathogen, demonstrated as an etiological agent in human infections in increasing frequency, including diseases like purulent meningitis, sepsis, uveitis-endophtalmitis and arthritis. Due to the increased availability and utility of novel diagnostic technologies in clinical microbiology, more studies have been published on the epidemiology of S. suis, both in veterinary and human medicine; however, there are no comprehensive data available regarding human S. suis infections from East-Central European countries. As a part of our study, data were collected from the National Bacteriological Surveillance (NBS) system on patients who had at least one positive microbiological result for S. suis, corresponding to an 18-year study period (2002-2019). n = 74 S. suis strains were isolated from invasive human infections, corresponding to 34 patients. The number of affected patients was 1.89 ± 1.53/year (range: 0-5). Most isolates originated from blood culture (63.5%) and cerebrospinal fluid (18.9%) samples. Additionally, we present detailed documentation of three instructive cases from three regions of the country and with three distinctly different outcomes. Hungary has traditional agriculture, the significant portion of which includes the production and consumption of pork meat, with characteristic preparation and consumption customs and unfavorable epidemiological characteristics (alcohol consumption, prevalence of malignant diseases or diabetes), which have all been described as important predisposing factors for the development of serious infections. Clinicians and microbiologist need to be vigilant even in nonendemic areas, especially if the patients have a history of occupational hazards or having close contact with infected pigs.

The bacteriocin from the prophylactic candidate Streptococcus suis 90-1330 is widely distributed across S. suis isolates and appears encoded in an integrative and conjugative element

The Gram-positive α-hemolytic Streptococcus suis is a major pathogen in the swine industry and an emerging zoonotic agent that can cause several systemic issues in both pigs and humans. A total of 35 S. suis serotypes (SS) have been identified and genotyped into > 700 sequence types (ST) by multilocus sequence typing (MLST). Eurasian ST1 isolates are the most virulent of all S. suis SS2 strains while North American ST25 and ST28 strains display moderate to low/no virulence phenotypes, respectively. Notably, S. suis 90–1330 is an avirulent Canadian SS2-ST28 isolate producing a lantibiotic bacteriocin with potential prophylactic applications. To investigate the suitability of this strain for such purposes, we sequenced its complete genome using the Illumina and PacBio platforms. The S. suis 90–1330 bacteriocin was found encoded in a locus cargoed in what appears to be an integrative and conjugative element (ICE). This bacteriocin locus was also found to be widely distributed across several streptococcal species and in a few Staphylococcus aureus strains. Because the locus also confers protection from the bacteriocin, the potential prophylactic benefits of using this strain may prove limited due to the spread of the resistance to its effects. Furthermore, the S. suis 90–1330 genome was found to code for genes involved in blood survival, suggesting that strain may not be a benign as previously thought.

Combination Therapy Strategies Against Multiple-Resistant Streptococcus Suis

Streptococcus suis is a major swine pathogen, an emerging zoonotic agent responsible for meningitis, endocarditis and septicaemia followed by deafness in humans. The development of antimicrobial resistance in S. suis increases the risk for therapeutic failure in both animals and humans. In this study, we report the synergism of combination therapy against multi-resistant S. suis isolates from swine. Twelve antibiotic profiles were determined against 11 S. suis strains. To investigate their synergistic/antagonistic activity, checkerboard assay was performed for all the possible combinations. In-vitro killing curves and in-vivo treatment trials were used to confirm the synergistic activity of special combinations against S. suis dominant clones. In this study, 11 S. suis isolates were highly resistant to erythromycin, clindamycin, trimethoprim/sulfamethoxazole, and tetracycline with ratios of 80–100%, and the resistance percentages to enrofloxacin, florfenicol, and spectinomycin were ~50%. The checkerboard data identified two combination regimens, ampicillin plus apramycin and tiamulin plus spectinomycin which gave the greatest level of synergism against the S. suis strains. In-vitro kill-curves showed a bacterial reduction of over 3-logCFU with the use of combination treatments, whilst the application of mono-therapies achieve less than a 2-logCFU cell killing. In-vivo models confirm that administration of these two combinations significantly reduced the number of bacterial cells after 24 h of treatment. In conclusions, the combinations of ampicillin plus apramycin and tiamulin plus spectinomycin showed the greatest synergism and may be potential strategies for treatment of multi-resistant S. suis in animal.

Effects of Environmental and Management-Associated Factors on Prevalence and Diversity of Streptococcus suis in Clinically Healthy Pig Herds in China and the United Kingdom

Streptococcus suis, a global zoonosis of pigs, shows regional differences in the prevalence of human-associated disease for Asian and non-Asian countries. The isolation rates and diversities of S. suis on tonsils of healthy slaughter pigs in China and the United Kingdom were studied for effects of geography, temperature, pig age, and farm type. Isolates underwent analysis of molecular serotype and multilocus sequence type and virulence-associated genotyping. Although we found no significant difference in positive isolation rates between Chinese and UK farms, the prevalences of serotypes previously associated with human disease were significantly greater in the Chinese collection (P = 0.003). A significant effect of temperature was found on the positive isolation rate of the Chinese samples and the prevalence of human disease-associated serotypes in the UK S. suis population (China, P = 0.004; United Kingdom, P = 0.024) and on the prevalence of isolates carrying key virulence genes in China (P = 0.044). Finally, we found marked diversity among S. suis isolates, with statistically significant temperature effects on detection of multiple strain types within individual pigs. This study highlighted the high carriage prevalence and diversity of S. suis among clinically healthy pig herds of China and the United Kingdom. The significant effect of temperature on prevalence of isolation, human disease-associated serotypes, and diversity carried by individual pigs may shed new light on geographic variations in human S. suis-associated disease.IMPORTANCEStreptococcus suis is a global zoonotic pathogen and also a normal colonizer mainly carried on the tonsil of pigs. Thus, it is important to study the effect of environmental and management-associated factors on the S. suis populations in clinically healthy pigs. In this research, we investigated the similarities and differences between the S. suis populations obtained from different pig ages, seasons, and farm management systems and discovered the relationship between high climatic temperature and the prevalence of S. suis.

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.

Genotypic diversity of Streptococcus suis strains isolated from humans in Thailand

The purpose of this study is to characterize Streptococcus suis isolates recovered from human infections regarding serotype distribution, genotypic profile, clinical manifestations, and epidemiology. A total of 668 S. suis isolates recovered from human infections in Thailand were characterized based on serotyping by multiplex PCR and co-agglutination, genotypic profiles by multilocus sequence typing, and PCR for virulence-associated genes, as well as review of medical records. Serotype 2 (94.6%) was predominant, followed by serotype 14 (4.5%), 24 (0.45%), 5 (0.3%), and 4 (0.15%). Multilocus sequence typing analyses revealed seven clonal complexes (CC): CC1 (56.43%), CC104 (31.74%), CC233/379 (5.4%), CC25 (4.5%), CC28 (0.9%), CC221/234 (0.6%), CC94 (0.15%), and two singletons. The CC1 group contained serotype 2 and 14 isolates, while CC25, 28, 104, and 233/379 consisted of serotype 2 isolates only. CC221/234 contained serotype 5 and 24 isolates, whereas the single serotype 4 isolate belonged to CC94. Two singletons contained serotype 5 (ST235) and 2 (ST236) isolates. Our data showed that ST1 isolates were more associated with meningitis than those of other STs (p < 0.001). The major route of infection was shown to be close contact with infected pigs or contaminated raw pork-derived products, including occupational exposure and recent consumption of raw pork products. This study revealed a relatively large number of CCs of S. suis causing human infection in Thailand. Among them, CC1 followed by CC104, with serotype 2 isolates, are predominant. Food safety campaigns and public health interventions would be important for controlling the S. suis infection in humans.

Streptococcus suis serotype 9 endocarditis and subsequent severe meningitis in a growing pig despite specific bactericidal humoral immunity

INTRODUCTION

. Meningitis and endocarditis are common pathologies of Streptococcussuis infections in pigs and humans. S. suis serotype 9 strains contribute substantially to health problems in European pig production, and immune prophylaxis against this serotype is very difficult.

CASE PRESENTATION

. We report the clinical course and histopathological picture of a 10-week-old growing pig following experimental intravenous infection with S. suis serotype 9. The piglet showed rapid onset of severe clinical signs of meningitis 11 days post-intravenous challenge following prime-booster vaccination. Histopathological findings revealed a diffuse fibrinosuppurative leptomeningitis. Additionally, a polyphasic endocarditis valvularis thromboticans with numerous bacterial colonies was diagnosed. Bacteriological culture of the brain and the mitral valve confirmed association with the challenge strain. However, virulent serotype 2 and 9 strains were killed in the blood of this piglet ex vivo prior experimental infection.

CONCLUSION

. Endocarditis induced by S. suis infection might develop and persist despite the presence of high specific bactericidal activity in the blood. Severe leptomeningitis is a putative sequela of such an endocarditis.