Development of loop-mediated isothermal amplification to detect Streptococcus suis and its application to retail pork meat in Japan

Study on the Effect of Phillyrin on Streptococcus suis In Vivo and In Vitro

As a zoonotic pathogen, S. suis serotype 2 (SS2) can cause severe diseases in both pigs and humans, and develop resistance to antibiotics. Plant natural compounds are regarded as promising alternatives to conventional antibiotics. Phillyrin is the major bioactive components of Chinese herbal medicine Forsythia suspensa. In this study, we explored the activity and action mechanism of phillyrin against SS2. The results showed that phillyrin could disrupt membrane integrity, destroy intracellular structures, and increase the exosmosis of DNA. Results of PCR revealed that phillyrin affected bacterial-virulence-related genes' expression levels. Meanwhile, phillyrin significantly decreased the adhesion activity, inhibited lactate dehydrogenase (LDH) secretion, and reduced biofilm formation of SS2 in Newborn pig trachea epithelial (NPTr) cells. Furthermore, phillyrin protected tight junction protein of NPTr cells from SS2. We reported that phillyrin (0.1 mg/kg) treatment after bacterial challenge significantly improved the survival rate, ameliorated pulmonary inflammation, and inhibited the accumulation of multiple cytokines (IL-1, IL-6, IL-8, and TNF-α). Molecular docking showed that phillyrin had a good binding activity with the Ala88 and Asp111 of suilysin (SLY), one of the most important virulence factors of SS2. Collectively, phillyrin possesses antibacterial and anti-inflammatory activities, and is a promising candidate for preventing SS2 infection.

Integrating loop-mediated isothermal amplification with lateral flow assay to achieve a highly sensitive method for detecting Streptococcus suis Genome in raw pork

Streptococcus suis (S.suis), a zoonotic foodborne pathogen prevalent in Southeast Asia, poses a substantial threat to human and animal health because of its ability to cause severe and life-threatening illnesses. To address this challenge, a rapid and highly sensitive detection platform for S. suis in raw pork was developed by integrating loop-mediated isothermal amplification (LAMP) and a lateral flow assay (LFA), S. suis LAMP-LFA. LAMP reactions targeting the S. suis glutamate dehydrogenase (gdh) gene were optimized for specific detection of S. suis within 45 min at an isothermal temperature of 65 °C. The assay exhibited marked sensitivity, with a detection limit of 100 fg for genomic DNA extracted from S. suis cultures. Notably, this method showed no cross-reactivity with other bacterial contaminants commonly found in raw pork. The resulting LAMP amplicons were effectively detected using LFA, with a test limit of 101 CFU per 25 g of raw pork. S. suis LAMP-LFA proved to be highly specific and reliable, with no false-positives detected in spiked pork samples or pork samples containing other bacterial contaminants. Due to its high sensitivity, specificity, and rapid turnaround time, the proposed technique has immense potential as a field-deployable screening test for S. suis detection in raw pork, contributing to enhanced food safety and public health protection.

Contamination of Streptococcus suis and S. suis Serotype 2 in Raw Pork and Edible Pig Organs: A Public Health Concern in Chiang Mai, Thailand

Streptococcus suis is one of the most important zoonotic pathogens causing serious diseases in both pigs and humans, especially serotype 2. In northern Thailand, there is a notable prevalence of S. suis infection in humans and transmission has occurred mainly through the consumption of raw pork products. Despite the continued practice of consuming raw pork in this region, limited data exist regarding S. suis contamination in such products. Therefore, this study aimed to assess the prevalence of S. suis and S. suis serotype 2 in retail raw pork meat and edible pig organs sold in Chiang Mai city, Thailand. A total of 200 samples, comprising raw pork meat and edible pig organs, were collected from nine fresh markets in Chiang Mai city between May and July 2023. Samples were prepared and cultured in Todd-Hewitt broth. Bacterial DNA was extracted and tested for any serotypes of S. suis and serotype 2 using loop-mediated isothermal amplification (LAMP) techniques. The study revealed contaminations of S. suis and serotype 2 at rates of 84% and 34%, respectively, with a higher prevalence observed in pig organs compared to raw pork. Both S. suis and serotype 2 were detected across all nine fresh markets investigated. The prevalence of S. suis remained consistently high throughout the study period, whereas serotype 2 showed peaks in May and July. These high rates of contamination indicate that people who consume or work in close contact with raw pork or edible pig organs are at a high risk of S. suis infection. Urgent implementation and maintenance of food safety campaigns and public health interventions are crucial for disease prevention and control.

Multiple Drug Resistant Streptococcus Strains-An Actual Problem in Pig Farms in Western Romania

Streptococci are a type of bacteria that can cause severe illnesses in humans and animals. Some typical species like S. suis, or atypical species like S. porcinus and, S. dysgalactiae subsp. dysgalactiae, can cause infections like septicemia, meningitis, endocarditis, arthritis, and septic shock. S. suis is considered a newly emerging zoonotic pathogen. Although human streptococcal infection outbreaks are rare, it is appropriate to review the main streptococcal species isolated in pig farms in western Romania, due to the high degree of antibiotic resistance among most isolates commonly used in human treatment. This study examines the resistance patterns of these isolates over 5 years (2018-2023). The research investigated the antimicrobial susceptibility of 267 strains of Streptococcus spp. isolated from pigs, primarily from lung and brain tissues. This report is the first to describe the distribution of atypical Streptococcus species (SDSE, S. porcinus, S. hyovaginalis, S. pluranimalium, S. canis) in Romania, as well as the antibiotic resistance profile of these potentially zoonotic species. It is important to re-evaluate and consider the high rates of resistance of S. suis to tetracyclines, lincosamides, macrolides, and aminoglycosides, as well as the high recovery rates of S. suis from the lungs and brain when treating swine diseases.

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.

Rapid Diagnostic of Streptococcus suis in Necropsy Samples of Pigs by thrA-Based Loop-Mediated Isothermal Amplification Assay

Streptococcus (S.) suis presents a serious threat to the pig industry as well as food safety and public health. Although several LAMP assays have been developed for the identification of S. suis, no universal assay is so far available for the field-suitable examination of clinical pig specimens. Based on the thrA housekeeping gene, a new loop-mediated isothermal amplification (LAMP) assay was developed and validated for the detection of S. suis in the brain and joints of pigs. For this LAMP assay, two different methods for the extraction of DNA from brain and joint swabs were compared. Using the LPTV boiling method, the detection limit of LAMP was 1.08 CFU/reaction, while the detection limit was 53.8 CFU/reaction using a commercial DNA extraction kit. The detection limits of thrA-LAMP in combination with the LPTV boiling method were 104-105 CFU/swab in the presence of brain tissue and 103-104 CFU/swab in the presence of joint tissue. The diagnostic quality criteria of LAMP were determined by the examination of 49 brain swabs and 34 joint swabs obtained during routine diagnostic necropsies. Applying the LPTV boiling method to brain swabs, the sensitivity, specificity, and positive and negative predictive values of thrA-LAMP were 88.0, 95.8, 95.7, and 88.5% using cultural investigation as a reference method, and 76.7, 100, 100, and 73.1% using real-time PCR as a reference method. Based on these results, the thrA-LAMP assay combined with the LPTV boiling method is suitable for rapid detection of S. suis from brain swabs.

Development of Two Loop-Mediated Isothermal Amplification Assays for Rapid Detection of ermB and mefA Genes in Streptococcus suis

Streptococcus suis is an important zoonotic pathogen that poses a serious threat to the pig industry and human health. The massive use of macrolides has led to the emergence of resistance in S. suis, and S. suis is suspected to be a reservoir of antimicrobial resistance genes. The mechanism to macrolide resistance in S. suis is mainly due to ermB and mefA. In this study, loop-mediated isothermal amplification (LAMP) methods were developed to detect ermB and mefA genes in S. suis through turbidimetry detection. The sensitivity and specificity of the LAMP reactions were determined. All results of LAMP and polymerase chain reaction (PCR) assay were compared to determine whether LAMP method was accurate and reliable. The results showed that all 100 nonstreptococcus clinical isolates tested negative, indicating the high specificity of LAMP assays. The detection limit of LAMP assay was 1 fg per reaction, and 10²-10⁴-fold lower than those of conventional PCR methods. Evaluation of the performance of the LAMP assay in S. suis clinical strains revealed a good consistency between LAMP and PCR assays. In conclusion, LAMP assays are specific, sensitive, and rapid methods to detect ermB and mefA in S. suis.

Development of a recombinase polymerase amplification assay for rapid detection of Streptococcus suis type 2 in nasopharyngeal swab samples

Streptococcus suis serotype 2 (SS2), an emerging zoonotic pathogen, may induce severe infections and symptoms manifested as septicemia, meningitis and even death both in human and pigs. The aim of this article was to develop a new methodology as real-time recombinase polymerase amplification (RT-RPA) assay targeting cps2J gene for the detection of SS2 (or SS1/2). The sensitivity and reproducibility of RT-RPA results were evaluated and compared with a real-time quantitative PCR (RT-qPCR). The established RT-RPA reaction could be completed in 20 minutes with distinguishable specificity against the predominant S. suis infection serotypes of 3, 4, 5, 7, 9, 14, and 31. Lower detection limit for RT-RPA was 10² genomic DNA copies per reaction. The specimen performance of RT-RPA was tested in nasopharyngeal swab samples with the sensitivity and specificity as 97.5% and 100%, respectively. Thus, this RT-RPA method is a rapid and potential molecular diagnostic tool for SS2 detection.

Rapid Detection of mrp, epf, and sly Genes by Loop-Mediated Isothermal Amplification in Streptococcus suis

Streptococcus suis remains a serious threat to the worldwide swine industry and human health. In this study, rapid assays for the detection of three common virulence-related factors (mrp, epf, and sly) were developed, evaluated, and applied. Loop-mediated isothermal amplification (LAMP) primers were designed using Primer Explorer V5 software. The sensitivity and specificity of the LAMP assays were determined based on sample turbidity. For all three genes, LAMP assays were performed at 62°C with a reaction time of 60 min. The detection limit of conventional polymerase chain reaction (PCR) was 1 ng/μL, 10 pg/μL, and 100 fg/μL for the epf, sly, and mrp genes, respectively. For the LAMP assays, the detection limits were 10 pg/μL, 10 fg/μL, and 100 fg/μL for epf, sly, and mrp, respectively, representing sensitivities 100-1000 times higher than those of the PCR assay. Furthermore, when the LAMP assays were applied to clinical strains, the results were consistent with those of the PCR assay, confirming the LAMP assays as rapid and reliable detection techniques. In conclusion, the LAMP assays described in this study have the potential to become standard methods to detect the virulence factors mrp, epf, and sly. To the best of our knowledge, this is the first study to report the application of LAMP to detect the mrp, epf, and sly genes.

Contamination of Streptococcus suis in pork and edible pig organs in central Thailand

Background and Aim

Streptococcus suis is an important zoonotic pathogen that can cause serious diseases in both swine and humans worldwide, especially in Asian countries. Since the majority of human cases reported in Thailand were infected by the consumption of a raw pork dish, the microbial food safety hazard associated with raw meat has been a matter of concern. Therefore, this study aimed to investigate the contamination by S. suis in pork and edible pig organs sold in central Thailand.

Materials and Methods

In total, 88 raw pork and pig organ samples were purchased from markets, butcher shops, and supermarkets in central Thailand. The samples were examined using the loop-mediated isothermal amplification (LAMP) technique. LAMP reactions used for the detection of the DNA of S. suis (LAMP_SS) and S. suis serotype 2 or 1/2 (LAMP_SS2) were carried out according to previous studies.

Results

The percentage of LAMP_SS-positive samples was as high as 85.23% (75/88) while the percentage of LAMP_SS2-positive samples was 17.05% (15/88). The percentages of LAMP_SS- and LAMP_SS2-positive samples were relatively high in both pig organs (lung and heart) and meat (sliced pork and minced pork) compared with the previous report. Except one supermarket, LAMP_SS-positive samples were found in all sources investigated in this study. The pork and pig organs obtained from the markets and the butcher shops additionally gave positive results for LAMP_SS2.

Conclusion

Using LAMP techniques, high rate contamination of S. suis was found in raw pork and edible pig organs sold at different sources in central Thailand. The cross-contamination could have occurred through slaughtering, meat cutting, and meat handling processes. Therefore, consumers and people involved in the pig production industry should be aware of the potential hazards of S. suis infection; food safety education is crucial to prevent further infection.

Complete Genome Sequence of Streptococcus ruminantium sp. nov. GUT-187T (=DSM 104980T =JCM 31869T), the Type Strain of S. ruminantium, and Comparison with Genome Sequences of Streptococcus suis Strains

Streptococcus ruminantium sp. nov. of type strain GUT-187^T, previously classified as Streptococcus suis serotype 33, is a recently described novel streptococcal species. This study was designed to determine the complete genome sequence of S. ruminantium GUT-187^T using a combination of Oxford Nanopore and the Illumina platform, and to compare this sequence with the genomes of 27 S. suis representative strains. The genome of GUT-187^T was 2,090,539 bp in size, with a GC content of 40.01%. This genome contained 1,961 predicted protein coding DNA sequences (CDSs); of these, 1,685 (85.9%) showed similarity with S. suis CDSs. Of the remaining 276 CDSs, 81 (29.3%) showed some degree of similarity with CDSs of other streptococcal species. The genome of GUT-187^T contained no intact prophage. The numbers of prophages and CRISPR spacers, as well as the presence or absence of genes encoding CRISPR-associated proteins, differed in S. ruminantium and S. suis. A phylogenetic analysis indicates that GUT-187^T may be outgroup to the S. suis strains in our sample, thereby justifying its classification as distinct species. Gene mapping indicated 10.2 times of massive genome rearrangements in average occurred between S. ruminantium and S. suis. There was no significant statistical difference in clusters of orthologous group distribution between S. ruminantium and S. suis.

Methods for the detection and characterization of Streptococcus suis: from conventional bacterial culture methods to immunosensors

One of the most important zoonotic pathogens worldwide, Streptococcus suis is a swine pathogen that is responsible for meningitis, toxic shock and even death in humans. S. suis infection develops rapidly with nonspecific clinical symptoms in the early stages and a high fatality rate. Recently, much attention has been paid to the high prevalence of S. suis as well as the increasing incidence and its epidemic characteristics. As laboratory-acquired infections of S. suis can occur and it is dangerous to public health security, timely and early diagnosis has become key to controlling S. suis prevalence. Here, the techniques that have been used for the detection, typing and characterization of S. suis are reviewed and the prospects for future detection methods for this bacterium are also discussed.

Development of PCR for identifying Streptococcus parasuis, a close relative of Streptococcus suis

Streptococcus parasuis has recently been removed taxonomically from Streptococcus suis, a zoonotic pathogen. S. parasuis has been detected in healthy pigs and in diseased pigs, which suggests that S. parasuis is involved in the normal microbiota of pigs and has potential pathogenicity. However, the pathogenicity of S. parasuis in pigs is unclear because of the lack of appropriate detection methods that discriminate S. parasuis from S. suis. In this study, we developed a PCR method that is specific for S. parasuis. The detection limit of the PCR was 350 CFU per reaction. Bacteria isolated from the saliva of eight pigs were collected and examined by PCR. Sixty-four isolates positive for PCR were obtained from the samples of all pigs. Thirteen of the 64 isolates were genetically confirmed as S. parasuis, and biologically and biochemically had nearly the same features of known S. parasuis strains, which suggested that strains positive for PCR were S. parasuis. Among the 64 isolates, 28 isolates were serotypes 20, 22, or 26 in the S. suis serotyping scheme. The remaining 36 isolates were untypeable, which suggested the presence of novel serotypes or a capsule-negative form. Therefore, the PCR method described in this study is a useful tool for identifying S. parasuis, and can be used in etiological studies on this bacterium.

Survival of Streptococcus suis, Streptococcus dysgalactiae and Trueperella pyogenes in dry-cured Iberian pork shoulders and loins

Dry-cured hams, shoulders and loins of Iberian pigs are highly appreciated in national and international markets. Salting, additive addition and dehydration are the main strategies to produce these ready-to-eat products. Although the dry curing process is known to reduce the load of well-known food borne pathogens, studies evaluating the viability of other microorganisms in contaminated pork have not been performed. In this work, the efficacy of the dry curing process to eliminate three swine pathogens associated with pork carcass condemnation, Streptococcus suis, Streptococcus dysgalactiae and Trueperella pyogenes, was evaluated. Results of this study highlight that the dry curing process is a suitable method to obtain safe ready-to-eat products free of these microorganisms. Although salting of dry-cured shoulders had a moderate bactericidal effect, results of this study suggest that drying and ripening were the most important stages to obtain dry-cured products free of these microorganisms.

Current Taxonomical Situation of Streptococcus suis

Streptococcus suis, a major porcine pathogen and an important zoonotic agent, is considered to be composed of phenotypically and genetically diverse strains. However, recent studies reported several “S. suis-like strains” that were identified as S. suis by commonly used methods for the identification of this bacterium, but were regarded as distinct species from S. suis according to the standards of several taxonomic analyses. Furthermore, it has been suggested that some S. suis-like strains can be assigned to several novel species. In this review, we discuss the current taxonomical situation of S. suis with a focus on (1) the classification history of the taxon of S. suis; (2) S. suis-like strains revealed by taxonomic analyses; (3) methods for detecting and identifying this species, including a novel method that can distinguish S. suis isolates from S. suis-like strains; and (4) current topics on the reclassification of S. suis-like strains.

An accurate assay for HCV based on real-time fluorescence detection of isothermal RNA amplification

Hepatitis C virus (HCV) is one of the common reasons of liver fibrosis and hepatocellular carcinoma (HCC). Early, rapid and accurate HCV RNA detection is important to prevent and control liver disease. A simultaneous amplification and testing (SAT) assay, which is based on isothermal amplification of RNA and real-time fluorescence detection, was designed to optimize routine HCV RNA detection. In this study, HCV RNA and an internal control (IC) were amplified and analyzed simultaneously by SAT assay and detection of fluorescence using routine real-time PCR equipment. The assay detected as few as 10 copies of HCV RNA transcripts. We tested 705 serum samples with SAT, among which 96.4% (680/705) showed consistent results compared with routine real-time PCR. About 92% (23/25) discordant samples were confirmed to be same results as SAT-HCV by using a second real-time PCR. The sensitivity and specificity of SAT-HCV assay were 99.6% (461/463) and 100% (242/242), respectively. In conclusion, the SAT assay is an accurate test with a high specificity and sensitivity which may increase the detection rate of HCV. It is therefore a promising tool to diagnose HCV infection.