Population structure, genetic diversity and pathotypes of Streptococcus suis isolated during the last 13 years from diseased pigs in Switzerland

Guanosine enhances the bactericidal effect of ceftiofur sodium on Streptococcus suis by activating bacterial metabolism

The emergence and rapid development of antibiotic resistance poses a serious threat to global public health. Streptococcus suis (S. suis) is an important zoonotic pathogen, and the development of its antibiotic resistance has made the infections difficult to treat. The combination of non-antibiotic compounds with antibiotics is considered a promising strategy against multidrug-resistant bacteria. However, the mechanism by which metabolites act as antibiotic adjuvant remains unclear. Here, we found that guanosine metabolism was repressed in multidrug-resistant S. suis. Exogenous guanosine promoted the antibacterial effects of ceftiofur sodium (CEF) in vitro and in vivo. Furthermore, we demonstrated that exogenous guanosine promoted the biosynthesis of purine pathway, TCA cycle and bacterial respiration, which make bacteria more sensitive to the killing effect of antibacterial. In addition, the function of the cell membrane is affected by guanosine and the accumulation of antimicrobials in the bacteria increased. Bacterial-oxidative stress and DNA damage induced by guanosine is also one of the mechanisms by which the antibacterial effect is enhanced. These results suggest that guanosine is a promising adjuvant for antibacterial drugs and provide new theoretical basis for the clinical treatment of S. suis infection.

Current prevalence and therapeutic strategies for porcine Streptococcus suis in China

Porcine Streptococcus suis is a zoonotic bacterial pathogen that poses serious threats to both human and animal health. S. suis is ubiquitously transmitted from the swine industry to the environments and human communities. However, the ambiguous epidemiological patterns and the escalating risk of antimicrobial resistance render S. suis infections a considerable challenge. Here, we review the current prevalence of S. suis infection worldwide, including identified bacterial strains, routes of infection, and transformation of resistance genes. This comprehensive overview of the prevalent patterns in S. suis offers detailed insights into therapeutic approaches for porcine infections and alternative strategies to address emerging resistant strains, highlighting potential multitarget prevention and treatment options to combat S. suis infection.

Serotype distribution and antimicrobial susceptibility of Streptococcus suis isolates from porcine diagnostic samples in Hungary, 2020-2023

BACKGROUND

Streptococcus suis (S. suis) is a major swine pathogen and a significant zoonotic agent, causing substantial economic losses in the swine sector and having considerable public health importance. The control and management of S. suis-related conditions has become increasingly challenging due to the multitude of involved serotypes with varying antimicrobial resistance patterns. Here, we report the serological distribution and antimicrobial susceptibility of S. suis isolates isolated form clinical samples of Hungarian large-scale swine farms.

RESULTS

Between 2020 and 2023, altogether 296 S. suis isolates were obtained from diseased pigs of 64 Hungarian pig operations. Serotyping of the isolates was carried out by using molecular methods (cps-typing). The isolated strains belonged to 24 single cps-types. The most frequently detected cps-types during the four years of this passive survey were 9 (19.6%), 2 (19.3%), 1/2 (18.9%) and 7 (14.5%). The brain, spleen, endocardial valve thrombus and lung proved to be the most frequent site of S. suis strain isolation, and animals 29-75 days of age were affected in the highest proportion. Antimicrobial susceptibility testing of the isolates was performed by determining the minimal inhibitory concentration for 15 antimicrobial agents of veterinary and human importance using a commercial microdilution assay. More than 90% of the tested isolates proved to be susceptible to the examined beta-lactams, cephalosporins and florfenicol, as well as to rifampicin, trimethoprim/sulfamethoxazole and vancomycin. Phenotypic resistance profiles (resistotypes) of clindamycin-tetracyclin (3.8%), clindamycin-erythromycin-tetracyclin (8.4%) and clindamycin-erythromycin-tetracyclin-trimethoprim / sulfamethoxazole (3.8%) were most frequently detected. Vancomycin resistance was observed in the case of 1 S. suis strain.

CONCLUSIONS

The dominance of S. suis cps-types 9, 2, 1/2 and 7 in Hungary over the four years of this study aligns with previous reports from several countries worldwide. The presence of highly susceptible S. suis isolates suggests a prudent antibiotic usage and treatment practice in the surveyed Hungarian swine operations. In contrary, the presence of several resistotypes could indicate the problem of antibiotic resistance in the future.

Comparative genome analysis of Streptococcus suis serotype 5 strains from humans and pigs revealed pathogenic potential of virulent, antimicrobial resistance, and genetic relationship

Streptococcus suis is a causative agent of swine and human infections. Genomic analysis indicated that eight S. suis serotype 5 strains recovered from human patients and pigs carried many virulence-associated genes and markers defining pathogenic pathotypes. The strains were sequence types diverse and clustered within either minimum core genome group 3 (MCG-3) or MCG-7-3. Almost all the serotype 5 strains were non-susceptible to penicillin, ceftriaxone, erythromycin, and levofloxacin. Resistance to tetracycline and clindamycin was observed in all strains. The antimicrobial resistance genes tet(O), tet(O/W/32/O), tet(W), tet(44), erm(B), ant(6)-Ia, lsaE, and lnuB were found in these strains. Moderate-to-large numbers of substitutions were observed in three penicillin-binding proteins (PBP)-PBP1A, PBP2B, and PBP2X-in the penicillin-non-susceptible serotype 5 isolates that were involved in β-lactam-non-susceptibility. Comparative genomics between the serotype 5 and 2 strains revealed that only 15 genes absent from the serotype 2 strains were shared by all the serotype 5 strains. However, some additional genes were present only in some of the serotype 5 strains. This study highlighted the pathogenic potential of virulent serotype 5 strains in humans and pigs and the need for increased monitoring of penicillin-non-susceptibility in S. suis serotypes other than for serotype 2.

Streptococcus suis strains with novel and previously undescribed capsular loci circulate in Europe

Streptococcus suis (S. suis) causes serious diseases in pigs, and certain serotypes also pose a risk to humans. The expression of capsular polysaccharides (CPS) is considered an important virulence property of the pathogen. Recently, some serotypes have been reclassified as other organisms, while novel S. suis serotypes are being described. Although the CPS can be typed by serological methods using antisera, the presence of unique sequences for each capsular polysaccharide synthesis locus (cps locus) enables convenient PCR-based serotyping. In this study, we characterized 33 non-serotypeable S. suis strains obtained from diseased pigs in the Czech Republic by sequencing and analyzing the cps locus. Phylogenetic analysis of cpn60 confirmed that all isolates belong to the S. suis species. Four isolates had cps loci similar to the previously described reference S. suis serotypes. Eleven isolates were classified as recently described novel cps loci (NCLs). Nine isolates had substitutions, insertions and/or deletions in their cps loci and showed only partial similarity to the already described NCLs. Another eight isolates had previously undescribed cps locus structures and were proposed as novel NCLs. One isolate had lost the genes encoding capsule biosynthesis. Only four sequence types (ST) had two isolates each; the rest had unique STs. Two isolates harbored the classical virulence associated genes (VAGs) mrp and sly. Another isolate had only the mrp gene, while a different isolate harbored only the sly gene. This study provides insight into untypeable isolates in the Czech Republic, highlighting the genetic diversity and potential for novel serotype identification.

Identification and genomic analyses of a Streptococcus suis ST25 strain associated with the first human septicemia in mainland China

Streptococcus suis (S. suis) is a Gram-positive bacterium and the main culprit behind zoonotic outbreaks, posing a serious threat to public health. The prevalent strains in China are mainly of sequence types (ST) 1 and 7, with few cases of human infections caused by other sequence type being reported. This study presents the first isolation of a ST25 strain from the blood of a septicemic patient. A 57-year-old febrile patient was admitted to a hospital in Hainan of China, diagnosed as septicemia and hepatic dysfunction. A strain of S. suis was isolated from blood culture and confirmed to be serotype 2 and ST25 through 16S rRNA sequencing and whole-genome sequencing, and its genome was further analyzed for gene functions and presence of drug resistance genes. The full-length genome of strain HN28 spans 2,280,124 bp and encodes a total of 2291 proteins. Genes annotated in COG, GO, KEGG, CAZy, and PHl databases accounted for 75.38 %, 69.14 %, 55.35 %, 4.58 %, and 11.87 % of the total predicted proteins, respectively. Virulence factor analysis revealed the presence of seven putative virulence genes in strain HN28. Analysis using the CARD database identified 51 resistance genes in HN28, alongside abundant exocytosis systems. These findings underscore the occurrence of S. suis infections in humans caused by less common ST, emphasizing the need for enhanced epidemiological investigations and monitoring of S. suis infections in the human population.

Genetic diversity and antimicrobial susceptibility of Streptococcus suis from diseased Swiss pigs collected between 2019 - 2022

Streptococcus suis is an important pathogen causing severe disease in pigs and humans, giving rise to economic losses in the pig production industry. Out of 65 S. suis isolates collected from diseased pigs in Switzerland between 2019 and 2022, 57 isolates were thoroughly examined by phenotypic and whole genome sequence (WGS) based characterization. The isolates' genomes were sequenced allowing for a comprehensive analysis of their distribution in terms of serovar, sequence type (ST), clonal complex (CC), and classical virulence markers. Antimicrobial resistance (AMR) genes were screened, and phenotypic susceptibility to eight classes of antimicrobial agents was examined. Serovar 6, devoid of any resistance genes, was found to be most prevalent, followed by serovars 1, 3, 1/2, and 9. Thirty STs were identified, with ST1104 being the most prevalent. Serovar 2 and serovar 1/2 were associated with CC1, potentially containing the most virulent variants. Based on single nucleotide polymorphism (SNP) analyses, fifteen isolates belonged to one of seven putative transmission clusters each consisting of two or three isolates. High phenotypic AMR rates were detected for tetracyclines (80%) and macrolides (35%) and associated with the resistance genes tet(O) and erm(B), respectively. In contrast, susceptibility to β-lactam antibiotics and phenicols was high. Determination of phenotypic AMR profiling, including the minimum inhibitory concentrations (MICs) of the tested antimicrobial agents, sets a baseline for future studies. The study provides valuable insights into the genetic diversity and antimicrobial susceptibility of Swiss S. suis isolates, facilitating the identification of emerging clones relevant to public health concerns.

Genomic epidemiology in Streptococcus suis: Moving beyond traditional typing techniques

Streptococcus suis is a bacterial gram-positive pathogen that causes invasive infections in swine and is also a zoonotic disease agent. Traditional molecular typing techniques such as ribotyping, multilocus sequence typing, pulse-field gel electrophoresis, or randomly amplified polymorphic DNA have been used to investigate S. suis population structure, evolution, and genetic relationships and support epidemiological and virulence investigations. However, these traditional typing techniques do not fully reveal the genetically heterogeneous nature of S. suis strains. The high-resolution provided by whole-genome sequencing (WGS), which is now more affordable and more commonly available in research and clinical settings, has unlocked the exploration of S. suis genetics at full resolution, permitting the determination of population structure, genetic diversity, identification of virulent clades, genetic markers, and other bacterial features of interest. This approach will likely become the new gold standard for S. suis strain typing as WGS instruments become more widely available and traditional typing techniques are gradually replaced.

Virulence genes, resistome and mobilome of Streptococcus suis strains isolated in France

Streptococcus suis is a leading cause of infection in pigs, causing extensive economic losses. In addition, it can also infect wild fauna, and can be responsible for severe infections in humans. Increasing antimicrobial resistance (AMR) has been described in S. suis worldwide and most of the AMR genes are carried by mobile genetic elements (MGEs). This contributes to their dissemination by horizontal gene transfer. A collection of 102 strains isolated from humans, pigs and wild boars in France was subjected to whole genome sequencing in order to: (i) study their genetic diversity, (ii) evaluate their content in virulence-associated genes, (iii) decipher the mechanisms responsible for their AMR and their association with MGEs, and (iv) study their ability to acquire extracellular DNA by natural transformation. Analysis by hierarchical clustering on principal components identified a few virulence-associated factors that distinguish invasive CC1 strains from the other strains. A plethora of AMR genes (n=217) was found in the genomes. Apart from the frequently reported erm(B) and tet(O) genes, more recently described AMR genes were identified [vga(F)/sprA, vat(D)]. Modifications in PBPs/MraY and GyrA/ParC were detected in the penicillin- and fluoroquinolone-resistant isolates respectively. New AMR gene-MGE associations were detected. The majority of the strains have the full set of genes required for competence, i.e for the acquisition of extracellular DNA (that could carry AMR genes) by natural transformation. Hence the risk of dissemination of these AMR genes should not be neglected.

Characterization of pig tonsils as niches for the generation of Streptococcus suis diversity

Streptococcus suis is a gram-positive bacterium that causes meningitis, septicemia, endocarditis, and other disorders in pigs and humans. We obtained 42 and 50 S. suis isolates from lesions of porcine endocarditis and palatine tonsils, respectively, of clinically healthy pigs in Japan; we then determined their sequence types (STs) by multilocus sequence typing (MLST), cps genotypes, serotypes, and presence of classical major virulence-associated marker genes (mrp, epf, and sly). The 42 isolates from endocarditis lesions were assigned to a limited number of STs and clonal complexes (CCs). On the other hand, the 50 isolates from tonsils were diverse in these traits and seemingly in the degree of virulence, suggesting that tonsils can accommodate a variety of S. suis isolates. The goeBURST full algorithm using tonsil isolates obtained in this study and those retrieved from the database showed that major CCs as well as many other clusters were composed of isolates originating from different countries, and some of the STs were very similar to each other despite the difference in country of origin. These findings indicate that S. suis with not only different but also similar mutations in the genome have survived in tonsils independently across different geographical locations. Therefore, unlike the lesions of endocarditis, the tonsils of pigs seemingly accommodate various S. suis lineages. The present study suggests that S. suis acquired its diversity by natural mutations during colonization and persistence in the tonsils of pigs.

Prevalence of Streptococcus suis serotype 2 isolated from pigs: A systematic review and meta-analysis

Background and Aim

Among Streptococcus suis serotypes, S. suis serotype 2 is the most significant serotype that causes serious diseases in pigs and humans worldwide. The present study aimed to estimate the global prevalence of S. suis serotype 2 isolated from pigs, determine its trend, and explore the factors associated with this serotype.

Materials and Methods

We retrieved relevant published studies from PubMed, Scopus, and the Web of Science. The retrieved citations were screened for possible inclusion. Relevant data were then extracted from the included studies. The random-effects model was used for all meta-analyses. A subgroup meta-analysis was used to assess the heterogeneity of the prevalence for four characteristics (continents, sampling organs, reporting unit, and pig's health status). A cumulative meta-analysis was performed to determine the cumulative prevalence over time. Meta-regression analysis was used to determine the trend of pooled prevalence of S. suis serotype 2 over time.

Results

Of 600 articles retrieved, 36 studies comprising a total sample size of 6939 isolates or samples from 16 countries of four continents were included for meta-analysis. The pooled prevalence of S. suis serotype 2 isolated from pigs was 13.6% (95% confidence interval [CI], 10.7%-17.1%), with high heterogeneity among the included studies (Cochran's Q, 431.6; p < 0.001; I2 = 91.9%; Table-1). No statistical significance was observed among subgroups of the four characteristics examined. However, the pooled prevalence of S. suis serotype 2 was as high as 16.0% (95% CI, 12.5%-20.3%; n = 16) in diseased pigs compared with 9.9% (95% CI, 5.6%-17.0%; n = 15) in healthy pigs. The pooled prevalence of S. suis serotype 2 isolated from pigs did not significantly decrease over time [regression coefficient = -0.020 (95% CI, 0.046-0.006, p = 0.139)]. The pooled prevalence of S. suis serotype 2 isolated from pigs fluctuated slightly between 13.2% and 17.8% from 2007 to 2023, although the pooled prevalence gradually decreased from 30.6% in 1987 to over 20% in 2003.

Conclusion

The global prevalence of S. suis serotype 2 isolated from pigs was estimated to be 13.6% (approximately 10% in healthy pigs and around 16% in diseased pigs). S. suis serotype 2 isolated from pigs did not change significantly over time. These results indicate that S. suis serotype 2 remains a problem for the pig industry and poses a threat to human health.

Streptococcus suis Research Update: Serotype Prevalence and Antimicrobial Resistance Distribution in Swine Isolates Recovered in Spain from 2020 to 2022

This study aimed to update the Streptococcus suis serotype distribution in Spain by analysing 302 clinical isolates recovered from diseased pigs between 2020 and 2022. The main objectives were to identify prevalent serotypes, differentiate specific serotypes 1, 14, 2, and 1/2, investigate specific genotypic and phenotypic antimicrobial resistance features, and explore associations between resistance genes and phenotypic resistances. Serotypes 9 (21.2%), 1 (16.2%), 2 (15.6%), 3 (6%), and 7 (5.6%) were the most prevalent, whereas serotypes 14 and 1/2 corresponded with 4.3% and 0.7% of all isolates. Antimicrobial resistance genes, including tet(O), erm(B), lnu(B), lsa(E), tet(M), and mef(A/E), were analysed, which were present in 85.8%, 65.2%, 7%, 7%, 6.3%, and 1% of the samples, respectively. Susceptibility testing for 18 antimicrobials revealed high resistance levels, particularly for clindamycin (88.4%), chlortetracycline (89.4%), and sulfadimethoxine (94.4%). Notably, seven significant associations (p < 0.0001) were detected, correlating specific antimicrobial resistance genes to the observed phenotypic resistance. These findings contribute to understanding the S. suis serotype distribution and its antibiotic resistance profiles in Spain, offering valuable insights for veterinary and public health efforts in managing S. suis-associated infections.

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.

Mycobacteriosis in slaughter pigs from South Africa from 1991 to 2002: Mycobacterium spp. diversity and Mycobacterium avium complex genotypes

Introduction

Mycobacterium avium complex (MAC) bacteria are the most prominent etiological agents of lymphadenitis in pigs. M. avium subspecies hominissuis (MAH) is a member of MAC and has been reported in many parts of the world to be the most prevalent non-tuberculous mycobacteria (NTM) to cause mycobacteriosis in humans, mainly in children. Thus, the economic and zoonotic impact of MAC species are increasingly being recognized. In South Africa, little is known about the distribution of NTM and the molecular epidemiology of M. avium in pigs.

Materials and methods

In this study, lymph nodes including mandibular, mesenteric, submandibular, and retropharyngeal, with tuberculosis-like lesions were collected during routine meat inspection of slaughter pigs with no disease symptoms (n = 132), between 1991 and 2002. These pigs were slaughtered at 44 abattoirs distributed across seven of the nine South African provinces. Mycobacterial culture, polymerase chain reaction (PCR), and sequencing of the Mycobacterium specific 577 bp 16S rRNA gene fragment were performed for species and subspecies identification.

Results

The majority of the isolates (each per sample); 114 (86.4%) were identified as MAH, 8 (6%) as MAA/M. avium subsp. silvaticum, 4 (3%) were Mycobacterium tuberculosis, 2 (1.5%) as Mycobacterium intracellulare, and 1 (0.75%) as Mycobacterium bovis. The other isolates were identified as Mycobacterium lentiflavum (0.75%), Mycobacterium novocastrense (0.75%), and a Micrococcus spp. (0.75%). Using an eight-marker MLVA typing tool, we deciphered at least nine MIRU VNTR INMV types of MAH and MAA.

Discussion

Identification of known zoonotic mycobacteria, including MAH, MAA, M. intracellulare, M. bovis, and M. tuberculosis, from slaughter pigs has a potential public health impact and also strengthens recognition of the potential economic impact of MAC. This study has also for the first time in South Africa, revealed MAC MIRU VNTR INMV genotypes which will aid in the future epidemiological investigation of MAC in South Africa.

Magistral Phage Preparations: Is This the Model for Everyone?

Phage therapy is increasingly put forward as a promising additional tool to help curb the global antimicrobial resistance crisis. However, industrially manufactured phage medicinal products are currently not available on the European Union and United States markets. In addition, it is expected that the business purpose-driven phage products that are supposed to be marketed in the future would mainly target commercially viable bacterial species and clinical indications, using fixed phage cocktails. hospitals or phage therapy centers aiming to help all patients with difficult-to-treat infections urgently need adequate phage preparations. We believe that national solutions based on the magistral preparation of personalized (preadapted) phage products by hospital and academic facilities could bring an immediate solution and could complement future industrially manufactured products. Moreover, these unlicensed phage preparations are presumed to be more efficient and to elicit less bacterial phage resistance issues than fixed phage cocktails, claims that need to be scientifically substantiated as soon as possible. Just like Belgium, other (European) countries could develop a magistral phage preparation framework that would exist next to the conventional medicinal product development and licensing pathways. However, it is important that the current producers of personalized phage products are provided with pragmatic quality and safety assurance requirements, which are preferably standardized (at least at the European level), and are tiered based on benefit-risk assessments at the individual patient level. Pro bono phage therapy providers should be supported and not stopped by the imposition of industry standards such as Good Manufacturing Practice requirements. Keywords: antimicrobial resistance; antibiotic resistance; bacterial infection; bacteriophage therapy; magistral preparation.

Population structure and genetic diversity of Streptococcus suis isolates obtained from the United States

Diseases caused by the zoonotic pathogen Streptococcus suis are an extensive economic problem as well as an animal welfare concern for the global swine industry. Previous studies have evaluated the genomic diversity and population structure of S. suis isolates, however, the majority of these studies utilized isolates obtained from countries other than the U.S. This study applied whole genome sequencing and cgMLST-based typing to evaluate the population structure and genetic relatedness among S. suis isolates obtained within the U.S. The established high-resolution phylogenomic framework revealed extensive genomic variation and diversity among the sampled S. suis isolates, with isolates from the U.S. and from countries outside the U.S. found interspersed in the phylogeny. S. suis isolates obtained within the U.S. did not cluster by state or geographic location, however, isolates with similar serotypes, both obtained from within and outside the U.S., generally clustered together. Average nucleotide identity (ANI) values determined for the S. suis genomes were extensively broad, approaching the recommended species demarcation value, and correlated with the phylogenetic group distribution of the cgMLST-based tree. Numerous antimicrobial resistance (AMR) elements were identified among both U.S. and non-U.S. isolates with ble, tetO, and ermB genes identified as the most prevalent. The epf, mrp, and sly genes, historically used as markers for virulence potential, were also observed in the genomes of isolates that grouped together forming a subclade of clonal complex 1 (CC1) isolates. Collectively, the data in this report provides critical information needed to address potential biosurveillance needs and insights into the genetic diversity and population structure of S. suis isolates obtained within the U.S.

Genomic characterization and virulence of Streptococcus suis serotype 4 clonal complex 94 recovered from human and swine samples

Streptococcus suis is a zoonotic pathogen that causes invasive infections in humans and pigs. Herein, we performed genomic analysis of seven S. suis serotype 4 strains belonging to clonal complex (CC) 94 that were recovered from a human patient or from diseased and clinically healthy pigs. Genomic exploration and comparisons, as well as in vitro cytotoxicity tests, indicated that S. suis CC94 serotype 4 strains are potentially virulent. Genomic analysis revealed that all seven strains clustered within minimum core genome group 3 (MCG-3) and had a high number of virulence-associated genes similar to those of virulent serotype 2 strains. Cytotoxicity assays showed that both the human lung adenocarcinoma cell line and HeLa cells rapidly lost viability following incubation for 4 h with the strains at a concentration of 106 bacterial cells. The human serotype 4 strain (ID36054) decreased cell viability profoundly and similarly to the control serotype 2 strain P1/7. In addition, strain ST1689 (ID34572), isolated from a clinically healthy pig, presented similar behaviour in an adenocarcinoma cell line and HeLa cells. The antimicrobial resistance genes tet(O) and ermB that confer resistance to tetracyclines, macrolides, and lincosamides were commonly found in the strains. However, aminoglycoside and streptothricin resistance genes were found only in certain strains in this study. Our results indicate that S. suis CC94 serotype 4 strains are potentially pathogenic and virulent and should be monitored.

Evaluation of pathotype marker genes in Streptococcus suis isolated from human and clinically healthy swine in Thailand

BACKGROUND

Streptococcus suis is a zoonotic pathogen that causes substantial economic losses in the pig industry and contributes to human infections worldwide, especially in Southeast Asia. Recently, a multiplex polymerase chain reaction (PCR) process was developed to distinguish disease-associated and non-disease-associated pathotypes of S. suis European strains. Herein, we evaluated the ability of this multiplex PCR approach to distinguish pathotypes of S. suis in Thailand.

RESULTS

This study was conducted on 278 human S. suis isolates and 173 clinically healthy pig S. suis isolates. PCR identified 99.3% of disease-associated strains in the human isolates and 11.6% of non-disease-associated strains in the clinically healthy pig isolates. Of the clinically healthy pig S. suis isolates, 71.1% were classified as disease-associated. We also detected undetermined pathotype forms in humans (0.7%) and pigs (17.3%). The PCR assay classified the disease-associated isolates into four types. Statistical analysis revealed that human S. suis clonal complex (CC) 1 isolates were significantly associated with the disease-associated type I, whereas CC104 and CC25 were significantly associated with the disease-associated type IV.

CONCLUSION

Multiplex PCR cannot differentiate non-disease-associated from disease-associated isolates in Thai clinically healthy pig S. suis strains, although the method works well for human S. suis strains. This assay should be applied to pig S. suis strains with caution. It is highly important that multiplex PCR be validated using more diverse S. suis strains from different geographic areas and origins of isolation.

Characterisation of Streptococcus suis Isolates in the Czech Republic Collected from Diseased Pigs in the Years 2018-2022

As in other countries, in the Czech Republic, Streptococcus suis infection in pigs is considered an economically significant disease for the pig industry, though little is known about its population structure. We collected S. suis isolates from 144 farms in the years 2018-2022. All samples were taken from animals suffering from symptoms indicating possible S. suis infection. Serotyping revealed the presence of 23 different serotypes, and 18.94% were non-typable strains. The most common was S7 (14.96%), while other serotypes had frequencies of less than 10%. Sequence typing identified 56 different sequence types, including 31 newly assigned sequence types together with 41 new alleles in genes in the MLST schema. A large portion of isolates (25.70%) were of unknown sequence type. The most common sequence types were ST29 (14.77%) and ST28 (10.04%); the other sequence types had frequencies of less than 10%. In total, 100 different combinations of serotypes and sequence types were identified. Among them, S7ST29 was found in 72 isolates, representing 13.63% of all isolates, and was significantly associated with the central nervous system. Many other isolates of particular serotype and sequence type combinations were found in a few cases, and a number of isolates were non-typable.

Comparative virulence and antimicrobial resistance distribution of Streptococcus suis isolates obtained from the United States

Streptococcus suis is a zoonotic bacterial swine pathogen causing substantial economic and health burdens to the pork industry worldwide. Most S. suis genome sequences available in public databases are from isolates obtained outside the United States. We sequenced the genomes of 106 S. suis isolates from the U.S. and analyzed them to identify their potential to function as zoonotic agents and/or reservoirs for antimicrobial resistance (AMR) dissemination. The objective of this study was to evaluate the genetic diversity of S. suis isolates obtained within the U.S., for the purpose of screening for genomic elements encoding AMR and any factors that could increase or contribute to the capacity of S. suis to transmit, colonize, and/or cause disease in humans. Forty-six sequence types (STs) were identified with ST28 observed as the most prevalent, followed by ST87. Of the 23 different serotypes identified, serotype 2 was the most prevalent, followed by serotype 8 and 3. Of the virulence genes analyzed, the highest nucleotide diversity was observed in sadP, mrp, and ofs. Tetracycline resistance was the most prevalent phenotypic antimicrobial resistance observed followed by macrolide-lincosamide-streptogramin B (MLSB) resistance. Numerous AMR elements were identified, many located within MGE sequences, with the highest frequency observed for ble, tetO and ermB. No genes encoding factors known to contribute to the transmission, colonization, and/or causation of disease in humans were identified in any of the S. suis genomes in this study. This includes the 89 K pathogenicity island carried by the virulent S. suis isolates responsible for human infections. Collectively, the data reported here provide a comprehensive evaluation of the genetic diversity among U.S. S. suis isolates. This study also serves as a baseline for determining any potential risks associated with occupational exposure to these bacteria, while also providing data needed to address public health concerns.

Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry in veterinary medicine: Recent advances (2019-present)

Matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry (MS) has become a valuable laboratory tool for rapid diagnostics, research, and exploration in veterinary medicine. While instrument acquisition costs are high for the technology, cost per sample is very low, the method requires minimal sample preparation, and analysis is easily conducted by end-users requiring minimal training. Matrix-assisted laser desorption ionization-time-of-flight MS has found widespread application for the rapid identification of microorganisms, diagnosis of dermatophytes and parasites, protein/lipid profiling, molecular diagnostics, and the technique demonstrates significant promise for 2D chemical mapping of tissue sections collected postmortem. In this review, an overview of the MALDI-TOF technique will be reported and manuscripts outlining current uses of the technology for veterinary science since 2019 will be summarized. The article concludes by discussing gaps in knowledge and areas of future growth.

Streptococcal autolysin promotes dysfunction of swine tracheal epithelium by interacting with vimentin

Streptococcus suis serotype 2 (SS2) is a major zoonotic pathogen resulting in manifestations as pneumonia and septic shock. The upper respiratory tract is typically thought to be the main colonization and entry site of SS2 in pigs, but the mechanism through which it penetrates the respiratory barrier is still unclear. In this study, a mutant with low invasive potential to swine tracheal epithelial cells (STECs) was screened from the TnYLB-1 transposon insertion mutant library of SS2, and the interrupted gene was identified as autolysin (atl). Compared to wild-type (WT) SS2, Δatl mutant exhibited lower ability to penetrate the tracheal epithelial barrier in a mouse model. Purified Atl also enhanced SS2 translocation across STEC monolayers in Transwell inserts. Furthermore, Atl redistributed the tight junctions (TJs) in STECs through myosin light chain kinase (MLCK) signaling, which led to increased barrier permeability. Using mass spectrometry, co-immunoprecipitation (co-IP), pull-down, bacterial two-hybrid and saturation binding experiments, we showed that Atl binds directly to vimentin. CRISPR/Cas9-targeted deletion of vimentin in STECs (VIM KO STECs) abrogated the capacity of SS2 to translocate across the monolayers, SS2-induced phosphorylation of myosin II regulatory light chain (MLC) and MLCK transcription, indicating that vimentin is indispensable for MLCK activation. Consistently, vimentin null mice were protected from SS2 infection and exhibited reduced tracheal and lung injury. Thus, MLCK-mediated epithelial barrier opening caused by the Atl-vimentin interaction is found to be likely the key mechanism by which SS2 penetrates the tracheal epithelium.

Streptococcus suis serotype 2 (SS2), an emerging zoonotic agent, can breach the respiratory barrier and cause invasive disease in pigs. Here, we identified the novel role of autolysin Atl in penetration of the respiratory barrier by SS2 and its systemic dissemination and identified its binding partner, vimentin, a type III intermediate filament protein. Atl contributed to the MLCK-triggered redistribution of tight junctions to open the tracheal epithelial barrier. Knockout of vimentin abolished the ability of SS2 to penetrate the monolayer barrier and the activation of MLCK. Furthermore, vimentin null mice were protected from infection by intranasally administered SS2. This study is the first to demonstrate that the interaction between the GBS Bsp-like domain of Atl and vimentin promotes MLCK-mediated dysfunction of the epithelial barrier, which may provide theoretical information for prophylactic and/or therapeutic treatments against diseases caused by similar respiratory pathogens.

Effects of l-Serine on Macrolide Resistance in Streptococcus suis

Streptococcus suis is an important zoonotic pathogen. Due to the indiscriminate use of macrolides, S. suis has developed a high level of drug resistance, which has led to a serious threat to human and animal health. However, it takes a long time to develop new antibacterial drugs. Therefore, we consider the perspective of bacterial physiological metabolism to ensure that the development of bacterial resistance to existing drugs is alleviated and bacterial susceptibility to drugs is restored. In the present study, an untargeted metabolomics analysis showed that the serine catabolic pathway was inhibited in drug-resistant S. suis. The addition of l-serine restored the fungicidal effect of macrolides on S. suisin vivo and in vitro by enhancing the serine metabolic pathway. Further studies showed that l-serine, stimulated by its serine catabolic pathway, inhibited intracellular H₂S production, reduced Fe-S cluster production, and restored the normal occurrence of the Fenton reaction in cells. It also attenuated the production of glutathione, an important marker of the intracellular oxidation-reduction reaction. All these phenomena eventually contribute to an increase in the level of reactive oxygen species, which leads to intracellular DNA damage and bacterial death. Our study provides a potential new approach for the treatment of diseases caused by drug-resistant S. suis.

IMPORTANCE The emergence of antimicrobial resistance is a global challenge. However, new drug development efforts consume considerable resources and time, and alleviating the pressure on existing drugs is the focus of our work. We investigated the mechanism of action of l-serine supplementation in restoring the use of macrolides in S. suis, based on the role of the serine catabolic pathway on reactive oxygen species levels and oxidative stress in S. suis. This pathway provides a theoretical basis for the rational use of macrolides in clinical practice and also identifies a possible target for restoring drug sensitivity in S. suis.

Genomic characterization of Streptococcus parasuis, a close relative of Streptococcus suis and also a potential opportunistic zoonotic pathogen

Streptococcus parasuis (S. parasuis) is a close relative of Streptococcus suis (S. suis), composed of former members of S. suis serotypes 20, 22 and 26. S. parasuis could infect pigs and cows, and recently, human infection cases have been reported, making S. parasuis a potential opportunistic zoonotic pathogen. In this study, we analysed the genomic characteristics of S. parasuis, using pan-genome analysis, and compare some phenotypic determinants such as capsular polysaccharide, integrative conjugative elements, CRISPR-Cas system and pili, and predicted the potential virulence genes by associated analysis of the clinical condition of isolated source animals and genotypes. Furthermore, to discuss the relationship with S. suis, we compared these characteristics of S. parasuis with those of S. suis. We found that the characteristics of S. parasuis are similar to those of S. suis, both of them have "open" pan-genome, their antimicrobial resistance gene profiles are similar and a srtF pilus cluster of S. suis was identified in S. parasuis genome. But S. parasuis still have its unique characteristics, two novel pilus clusters are and three different type CRISPR-Cas system were found. Therefore, this study provides novel insights into the interspecific and intraspecific genetic characteristics of S. parasuis, which can be useful for further study of this opportunistic pathogen, such as serotyping, diagnostics, vaccine development, and study of the pathogenesis mechanism.

Distribution and characterization of Streptococcus suis serotypes isolated from January 2015 to June 2020 from diseased pigs in Québec, Canada

Streptococcus suis is one of the most important swine bacterial pathogens causing economic losses. This report presents the serotype distribution of S. suis recovered from diseased pigs in Québec from January 2015 to June 2020. Serotypes 1/2 and 2 predominated, followed by serotypes 7, 3, 5, 4, 9, 1, and 14. Compared to previously reported data, very few changes could be observed concerning the serotype distribution, indicating a relative stability. Half of the untypable isolates did not belong to the species S. suis sensu stricto, as determined by recN polymerase chain reaction. Less than 10% of "real S. suis" isolates were untypable. The genetic diversity of S. suis serotypes 1, 2, and 14, as analyzed by multilocus sequence typing, was mainly represented by sequence type (ST)1, ST28, ST25, and ST94. All ST1 isolates (considered highly virulent) belonged to either serotype 1 or 14.

Survival patterns of Streptococcus suis serotypes 1 and 14 in porcine blood indicate cross-reactive bactericidal antibodies in naturally infected pigs

Streptococcus suis serotype (cps) 1 and cps14 have been detected in association with severe diseases such as meningitis and polyarthritis in pigs. Though these two cps are very similar, only cps14 is an important zoonotic agent in Asia and only cps1 is described to be associated with diseases in suckling piglets rather than weaning piglets. The main objective of this study was to assess restriction of survival of cps14 and cps1 in porcine blood by IgG and IgM putatively cross-reacting with these two cps. Furthermore, we differentiate recent European cps1/14 strains by agglutination, cpsK sequencing, MLST and virulence-associated gene profiling. Our data confirmed cps1 of clonal complex 1 as an important pathotype causing polyarthritis in suckling piglets in Europe. The experimental design included also bactericidal assays with blood samples drawn at different ages of piglets naturally infected with different S. suis cps types including cps1 but not cps14. We report survival of a cps1 and a cps14 strain (both of sequence type 1) in blood of suckling piglets with high levels of maternal IgG binding to the bacterial surface. In contrast, killing of cps1 and cps14 was recorded in older piglets due to an increase of IgM as demonstrated by specific cleavage of IgM. Heterologous absorption of antibodies with cps1 or cps14 is sufficient to significantly increase the survival of the other cps. In conclusion, IgM elicited by natural S. suis infection is crucial for killing of S. suis cps1 and cps14 in older weaning piglets and has most likely the potential to cross-react between cps1 and cps14.

Mini Review: Clinical Routine Microbiology in the Era of Automation and Digital Health

Clinical microbiology laboratories are the first line to combat and handle infectious diseases and antibiotic resistance, including newly emerging ones. Although most clinical laboratories still rely on conventional methods, a cascade of technological changes, driven by digital imaging and high-throughput sequencing, will revolutionize the management of clinical diagnostics for direct detection of bacteria and swift antimicrobial susceptibility testing. Importantly, such technological advancements occur in the golden age of machine learning where computers are no longer acting passively in data mining, but once trained, can also help physicians in making decisions for diagnostics and optimal treatment administration. The further potential of physically integrating new technologies in an automation chain, combined to machine-learning-based software for data analyses, is seducing and would indeed lead to a faster management in infectious diseases. However, if, from one side, technological advancement would achieve a better performance than conventional methods, on the other side, this evolution challenges clinicians in terms of data interpretation and impacts the entire hospital personnel organization and management. In this mini review, we discuss such technological achievements offering practical examples of their operability but also their limitations and potential issues that their implementation could rise in clinical microbiology laboratories.