Use of Antibiotics and Antimicrobial Resistance in Veterinary Medicine as Exemplified by the Swine Pathogen Streptococcus suis

Genomic Diversity of Methicillin-Resistant Staphylococcus aureus CC398 Isolates Collected from Diseased Swine in the German National Resistance Monitoring Program GERM-Vet from 2007 to 2019

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) clonal complex 398 (CC398) isolates (n = 178) collected in the national resistance monitoring program GERM-Vet from diseased swine in Germany from 2007 to 2019 were investigated for their genomic diversity with a focus on virulence and antimicrobial resistance (AMR) traits. Whole-genome sequencing was followed by molecular typing and sequence analysis. A minimum spanning tree based on core-genome multilocus sequence typing was constructed, and antimicrobial susceptibility testing was performed. Most isolates were assigned to nine clusters. They displayed close phylogenetic relationships but a wide molecular variety, including 13 spa types and 19 known and four novel dru types. Several toxin-encoding genes, including eta, seb, sek, sep, and seq, were detected. The isolates harbored a wide range of AMR properties mirroring the proportions of the classes of antimicrobial agents applied in veterinary medicine in Germany. Multiple novel or rare AMR genes were identified, including the phenicol-lincosamide-oxazolidinone-pleuromutilin-streptogramin A resistance gene cfr, the lincosamide-pleuromutilin-streptogramin A resistance gene vga(C), and the novel macrolide-lincosamide-streptogramin B resistance gene erm(54). Many AMR genes were part of small transposons or plasmids. Clonal and geographical correlations of molecular characteristics and resistance and virulence genes were more frequently observed than temporal relations. In conclusion, this study provides insight into population dynamics of the main epidemic porcine LA-MRSA lineage in Germany over a 13-year-period. The observed comprehensive AMR and virulence properties, most likely resulting from the exchange of genetic material between bacteria, highlighted the importance of LA-MRSA surveillance to prevent further dissemination among swine husbandry facilities and entry into the human community. IMPORTANCE The LA-MRSA-CC398 lineage is known for its low host specificity and frequent multiresistance to antimicrobial agents. Colonized swine and their related surroundings represent a considerable risk of LA-MRSA-CC398 colonization or infection for occupationally exposed people through which such isolates might be further disseminated within the human community. This study provides insight into the diversity of the porcine LA-MRSA-CC398 lineage in Germany. Clonal and geographical correlations of molecular characteristics and resistance and virulence traits were detected and may be associated with the spread of specific isolates through livestock trade, human occupational exposure, or dust emission. The demonstrated genetic variability underlines the lineage's ability to horizontally acquire foreign genetic material. Thus, LA-MRSA-CC398 isolates have the potential to become even more dangerous for various host species, including humans, due to increased virulence and/or limited therapeutic options for infection control. Full-scale LA-MRSA monitoring at the farm, community, and hospital level is therefore essential.

A tool to enhance antimicrobial stewardship using similarity networks to identify antimicrobial resistance patterns across farms

Antimicrobial resistance (AMR) is one of the major challenges of the century and should be addressed with a One Health approach. This study aimed to develop a tool that can provide a better understanding of AMR patterns and improve management practices in swine production systems to reduce its spread between farms. We generated similarity networks based on the phenotypic AMR pattern for each farm with information on important bacterial pathogens for swine farming based on the Euclidean distance. We included seven pathogens: Actinobacillus suis, Bordetella bronchiseptica, Escherichia coli, Glaesserella parasuis, Pasteurella multocida, Salmonella spp., and Streptococcus suis; and up to seventeen antibiotics from ten classes. A threshold criterion was developed to reduce the density of the networks and generate communities based on their AMR profiles. A total of 479 farms were included in the study although not all bacteria information was available on each farm. We observed significant differences in the morphology, number of nodes and characteristics of pathogen networks, as well as in the number of communities and susceptibility profiles of the pathogens to different antimicrobial drugs. The methodology presented here could be a useful tool to improve health management, biosecurity measures and prioritize interventions to reduce AMR spread in swine farming.

Characterization of integrative and conjugative elements carrying antibiotic resistance genes of Streptococcus suis isolated in China

Streptococcus suis, an emerging zoonotic pathogen, is important reservoirs of antibiotic resistance genes that play critical roles in the horizontal transfer of corresponding resistances. In the present study, 656 antibiotic resistance (AR) genes were detected in 154 of 155 genomes of S. suis strains isolated from the nasopharynx of slaughtered pigs and the lungs of diseased pigs in China. The AR genes were clustered into 11 categories, consisting of tetracycline, macrolides, lincosamide, streptogramin, aminoglycoside, trimethoprim, amphenicols, nucleoside, quinupristin/dalfopristin, glycopeptide, and oxazolidinones resistance genes. In order to investigate the transmission patterns of the AR genes, AR genes-associated the mobile genetic elements (MGEs) were extracted and investigated. Twenty ICEs, one defective ICE, one tandem ICE, and ten prophages were found, which mainly carried tetracycline, macrolides/lincosamides/streptogramin (MLS), and aminoglycosides resistance genes. Three types of DNA cargo with AR genes were integrated into specific sites of ICEs: integrative mobilizable elements (IMEs), cis-IMEs (CIMEs), and transposon Tn916. Obvious differences in AR gene categories were found among the three cargo types. IMEs mainly harbored tetracycline and MLS resistance genes. CIMEs mainly carried aminoglycoside resistance genes, while transposon Tn916 carried only the tet (M) gene. Nearly all AR genes in ICEs were carried by IMEs and CIMEs. IMEs were prevalent and were also detected in additional 29 S. suis genomes. The horizontal transfer of IMEs and CIMEs may play critical role in ICE evolution and AR gene transmission in the S. suis population. Our findings provide novel insights into the transmission patterns of AR genes and the evolutionary mechanisms of ICEs in S. suis.

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.

Genetic diversity and variation in antimicrobial-resistance determinants of non-serotype 2 Streptococcus suis isolates from healthy pigs

Streptococcus suis is a leading cause of bacterial meningitis in South-East Asia, with frequent zoonotic transfer to humans associated with close contact with pigs. A small number of invasive lineages are responsible for endemic infection in the swine industry, causing considerable global economic losses. A lack of surveillance and a rising trend in clinical treatment failure has raised concerns of growing antimicrobial resistance (AMR) among invasive S. suis. Gene flow between healthy and disease isolates is poorly understood and, in this study, we sample and sequence a collection of isolates predominantly from healthy pigs in Chiang Mai province, Northern Thailand. Pangenome characterization identified extensive genetic diversity and frequent AMR carriage in isolates from healthy pigs. Multiple AMR genes were identified, conferring resistance to aminoglycosides, lincosamides, tetracycline and macrolides. All isolates were non-susceptible to three or more different antimicrobial classes, and 75 % of non-serotype 2 isolates were non-susceptible to six or more classes (compared to 37.5 % of serotype 2 isolates). AMR genes were found on integrative and conjugative elements previously observed in other species, suggesting a mobile gene pool that can be accessed by invasive disease isolates. This article contains data hosted by Microreact.

Comparative analysis of Streptococcus suis genomes identifies novel candidate virulence-associated genes in North American isolates

Streptococcus suis is a significant economic and welfare concern in the swine industry. Pan-genome analysis provides an in-silico approach for the discovery of genes involved in pathogenesis in bacterial pathogens. In this study, we performed pan-genome analysis of 208 S. suis isolates classified into the pathogenic, possibly opportunistic, and commensal pathotypes to identify novel candidate virulence-associated genes (VAGs) of S. suis. Using chi-square tests and LASSO regression models, three accessory pan-genes corresponding to S. suis strain P1/7 markers SSU_RS09525, SSU_RS09155, and SSU_RS03100 (>95% identity) were identified as having a significant association with the pathogenic pathotype. The proposed novel SSU_RS09525 + /SSU_RS09155 + /SSU_RS03100 + genotype identified 96% of the pathogenic pathotype strains, suggesting a novel genotyping scheme for predicting the pathogenicity of S. suis isolates in North America. In addition, mobile genetic elements carrying antimicrobial resistance genes (ARGs) and VAGs were identified but did not appear to play a major role in the spread of ARGs and VAGs.

Compositional analysis of the tonsil microbiota in relationship to Streptococcus suis disease in nursery pigs in Ontario

BACKGROUND

The tonsil of the soft palate in pigs is the colonization site of both commensal and pathogenic microbial agents. Streptococcus suis infections are a significant economic problem in the swine industry. The development of S. suis disease remains poorly understood. The purpose of this study was to identify whether the tonsillar microbiota profile in nursery pigs is altered with S. suis disease. Here, the dynamics of the tonsillar microbiota from 20 healthy pigs and 43 diseased pigs with S. suis clinical signs was characterized.

RESULTS

Based on the presence or absence of S. suis in the systemic sites, diseased pigs were classified into confirmed (n = 20) or probable (n = 23) group, respectively. Microbiota composition was assessed using the V3-V4 hypervariable region of the 16S rRNA, and results were analyzed to identify the diversity of the tonsillar microbiota. The taxonomic composition of the tonsil microbiota proved to be highly diverse between individuals, and the results showed statistically significant microbial community structure among the diagnosis groups. The confirmed group had the lowest observed species richness while the probable group had higher phylogenetics diversity level compared to the healthy group. Un-weighted Unifrac also demonstrated that the probable group had a higher beta diversity than both the healthy and the confirmed group. A Dirichlet-multinomial mixture (DMM) model-based clustering method partitioned the tonsil microbiota into two distinct community types that did not correspond with disease status. However, there was an association between Streptococcus suis serotype 2 and DMM community type 1 (p = 0.03). ANCOM-BC identified 24 Streptococcus amplicon sequence variants (ASVs) that were differentially abundant between the DMM community types.

CONCLUSIONS

This study provides a comprehensive analysis of the structure and membership of the tonsil microbiota in nursery pigs and uncovers differences and similarities across varying S. suis disease status. While the overall abundance of Streptococcus was not different among the diagnosis groups, the unique profile of DMM community type 1 and the observed correlation with S. suis serotype 2 could provide insight into potential tonsillar microbiota involvement in S. suis disease.

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.

Effects of fermented wheat bran and yeast culture on growth performance, immunity, and intestinal microflora in growing-finishing pigs

This study was conducted to evaluate the effects of feeding fermented wheat bran (FWB) and yeast culture (YC) on growth performance, immune levels, and intestinal microflora in growing-finishing pigs. In total, 96 crossbred pigs were randomly distributed into four treatments with four replicates pens and six pigs per pen. This study was performed using a 2 × 2 factor design: 1) CON (basal diet), 2) FWB (basal diet + 5% FWB), 3) YC (basal diet + 2% YC), and 4) FWB + YC (basal diet + 5% FWB + 2% YC). Dietary FWB supplementation significantly increased the average daily gain and significantly decreased the feed gain ratio of growing-finishing pigs (P < 0.05). Supplementation of FWB and YC improved the immune capacity and reduced the inflammation level of growing-finishing pigs (P < 0.05). In addition, pigs fed FWB, YC, and FWB + YC diets showed better intestinal development and morphology compared with those CON pigs. The relative abundance of Streptococcus in the FWB group was significantly lower than that in the CON group (P < 0.05), and the relative abundance of probiotics (unclassified_f_Lachnospiraceae, Turicibacter) increased significantly (P < 0.05). Furthermore, the relative abundance of probiotics (Lactobacillus, norank_f_Muribaculaceae) in the YC group was significantly increased compared with the CON group (P < 0.05). The results of this study observed positive effects of FWB and YC on growing-finishing pigs, which provides insights into the application of biological feed in swine industry.

Experimental evaluation of protection and immunogenicity of Streptococcus suis bacterin-based vaccines formulated with different commercial adjuvants in weaned piglets

Streptococcus suis is an important swine pathogen responsible for economic losses to the swine industry worldwide. There is no effective commercial vaccine against S. suis. The use of autogenous (“bacterin”) vaccines to control S. suis outbreaks is a frequent preventive measure in the field, although scientific data on immunogenicity and reduction in mortality and morbidity are scarce. The goal of our study is to experimentally evaluate the immunogenicity and protective efficacy against homologous challenge in weaned piglets of a S. suis serotype 2 bacterin-based vaccine formulated with six different commercial adjuvants (Alhydrogel®, Emulsigen®-D, Quil-A®, Montanide™ ISA 206 VG, Montanide™ ISA 61 VG, and Montanide™ ISA 201 VG). The vaccine formulated with Montanide™ ISA 61 VG induced a significant increase in anti-S. suis antibodies, including both IgG1 and IgG2 subclasses, protected against mortality and significantly reduced morbidity and severity of clinical signs. Vaccines formulated with Montanide ISA 206 VG or Montanide ISA 201 VG also induced a significant increase in anti-S. suis antibodies and showed partial protection and reduction of clinical signs severity. Vaccines formulated with Alhydrogel®, Emulsigen®-D, or Quil-A® induced a low and IgG1-shifted antibody response and failed to protect vaccinated piglets against a homologous challenge. In conclusion, the type of adjuvant used in the vaccine formulation significantly influenced the immune response and efficacy of the vaccine against a homologous challenge.

Stochastic Assessment of the Economic Impact of Streptococcus suis-Associated Disease in German, Dutch and Spanish Swine Farms

The economic assessment of animal diseases is essential for decision-making, including the allocation of resources for disease control. However, that assessment is usually hampered by the lack of reliable data on disease incidence, or treatment and control measures, and that is particularly true for swine production diseases, such as infections caused by Streptococcus suis. Therefore, we deployed a questionnaire survey of clinical swine veterinarians to obtain the input data needed for a stochastic model to calculate the costs caused by S. suis, which was implemented in three of the main swine producing countries in Europe: Germany, the Netherlands and Spain. S. suis-associated disease is endemic in those countries in all production phases, though nursery was the phase most severely impacted. In affected nursery units, between 3.3 and 4.0% of pigs had S. suis-associated disease and the mortalities ranged from 0.5 to 0.9%. In Germany, the average cost of S. suis per pig (summed across all production phases) was 1.30 euros (90% CI: 0.53-2.28), in the Netherlands 0.96 euros (90% CI: 0.27-1.54), and in Spain 0.60 euros (90% CI: 0.29-0.96). In Germany, that cost was essentially influenced by the expenditure in early metaphylaxis in nursery and in autogenous vaccines in sows and nursery pigs; in the Netherlands, by expenditure on autogenous vaccines in sows and nursery pigs; and in Spain, by the expenditures in early metaphylaxis and to a lesser extent by the mortality in nursery pigs. Therefore, the differences in costs between countries can be explained to a great extent by the measures to control S. suis implemented in each country. In Spain and in Germany, use of antimicrobials, predominantly beta-lactams, is still crucial for the control of the disease.

Streptomyces griseocarneus R132 expresses antimicrobial genes and produces metabolites that modulate Galleria mellonella immune system

Actinobacteria is a phylum composed of aerobic, Gram-positive, and filamentous bacteria with a broad spectrum of biological activity, including antioxidant, antitumor, and antibiotic. The crude extract of Streptomyces griseocarneus R132 was fractionated on a C18 silica column and the isolated compound was identified by ¹H and ¹³C nuclear magnetic resonance as 3-(phenylprop-2-enoic acid), also known as trans-cinnamic acid. Antimicrobial activity against human pathogens was assayed in vitro (disk-diffusion qualitative test) and in vivo using Galleria mellonella larvae (RT-qPCR). The methanol fractions 132-F30%, 132-F50%, 132-F70%, and 132-F100% inhibited the Escherichia coli (ATCC 25922) and Staphylococcus aureus (MRSA) growth in vitro the most effectively. Compared with the untreated control (60-80% of larvae death), the fractions and isolated trans-cinnamic acid increased the survival rate and modulated the immune system of G. mellonella larvae infected with pathogenic microorganisms. The anti-infection effect of the S. griseocarneus R132 fermentation product led us to sequence its genome, which was assembled and annotated using the Rast and antiSMASH platforms. The assembled genome consisted of 227 scaffolds represented on a linear chromosome of 8.85 Mb and 71.3% of GC. We detected conserved domains typical of enzymes that produce molecules with biological activity, such as polyketides and non-ribosomal and ribosomal peptides, indicating a great potential for obtaining new antibiotics and molecules with biotechnological application.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02942-1.

Review of the speculative role of co-infections in Streptococcus suis-associated diseases in pigs

Streptococcus suis is one of the most important bacterial swine pathogens affecting post-weaned piglets, causing mainly meningitis, arthritis and sudden death. It not only results in severe economic losses but also raises concerns over animal welfare and antimicrobial resistance and remains an important zoonotic agent in some countries. The definition and diagnosis of S. suis-associated diseases can be complex. Should S. suis be considered a primary or secondary pathogen? The situation is further complicated when referring to respiratory disease, since the pathogen has historically been considered as a secondary pathogen within the porcine respiratory disease complex (PRDC). Is S. suis a respiratory or strictly systemic pathogen? S. suis is a normal inhabitant of the upper respiratory tract, and the presence of potentially virulent strains alone does not guarantee the appearance of clinical signs. Within this unclear context, it has been largely proposed that co-infection with some viral and bacterial pathogens can significantly influence the severity of S. suis-associated diseases and may be the key to understanding how the infection behaves in the field. In this review, we critically addressed studies reporting an epidemiological link (mixed infections or presence of more than one pathogen at the same time), as well as in vitro and in vivo studies of co-infection of S. suis with other pathogens and discussed their limitations and possibilities for improvement and proposed recommendations for future studies.

Inhibitory Effect of Piceatannol on Streptococcus suis Infection Both in vitro and in vivo

Suilysin (SLY) plays a critical role in Streptococcus suis infections making it an ideal target to the combat infection caused by this pathogen. In the present study, we found that piceatannol (PN), a natural compound, inhibits pore-formation by blocking the oligomerization of SLY without affecting the growth of S. suis and the expression of SLY. Furthermore, PN alleviated the J774 cell damage and the expression of the inflammatory cytokine tumor necrosis factor-α (TNF-α) and interleukin-1α (IL-1β) induced by S. suis in vitro. The computational biology and biochemistry results indicated that PN binds to the joint region of D2 and D4 in SLY, and Asn57, Pro58, Pro59, Glu76, Ile379, Glu380, and Glu418 were critical residues involved in the binding. The binding effect between PN and SLY hindered the SLY monomers from forming the oligomers, thereby weakening the hemolytic activity of SLY. This mechanism was also verified by hemolysis analysis and analysis of K_A formation after site-specific mutagenesis. Furthermore, PN protected mice from S. suis infections by reducing bacterial colony formation and the inflammatory response in target organs in vivo. These results indicate that PN is a feasible drug candidate to combat S. suis infections.

Feed additives for the control of post-weaning Streptococcus suis disease and the effect on the faecal and nasal microbiota

Medicated feed is a common strategy to control the occurrence of Streptococcus suis disease in swine production, but feed additives may constitute an alternative to metaphylaxis. In a farm with post-weaning S. suis disease, the following additives were tested: lysozyme (Lys), medium chain fatty acids plus lysozyme (FA + Lys), FA plus a natural anti-inflammatory (FA + antiinf) and amoxicillin (Amox). During the course of the study, FA + antiinf and Amox groups showed lower prevalence of clinical signs compatible with S. suis disease than the rest of the groups. Piglets from the FA + antiinf group showed high diversity and richness in their nasal and faecal microbiota. Diet supplements did not have major effects on the faecal microbiota, where the genus Mitsuokella was the only differentially present in the FA + Lys group. In the nasal microbiota, piglets from FA + antiinf presented higher differential abundance of a sequence variant from Ruminococcaceae and lower abundance of an unclassified genus from Weeksellaceae. In general, we detected more significant changes in the nasal than in the feacal microbiota, and found that parity of the dams affected the microbiota composition of their offspring, with piglets born to gilts exhibiting lower richness and diversity. Our results suggest that additives could be useful to control post-weaning disease when removing antimicrobials in farms.

Synergistic Effect of a Pleuromutilin Derivative with Tetracycline against Streptococcus suis In Vitro and in the Neutropenic Thigh Infection Model

Tetracycline (TET) has been widely used in the treatment of Streptococcus suis (S. suis) infection. However, it was found that the efficacy of many antibiotics in S. suis decreased significantly, especially tetracycline. In this study, GML-12 (a novel pleuromutilin derivative) was used in combination with TET against 12 S. suis isolates. In the checkerboard assay, the TET/GML-12 combination exhibited synergistic and additive effects against S. suis isolates (n = 12). In vitro time-killing assays and in vivo therapeutic experiments were used to confirm the synergistic effect of the TET/GML-12 combination against S. suis strains screened based on an FICI ≤ 0.5. In time-killing assays, the TET/GML-12 combination showed a synergistic effect or an additive effect against three isolates with a bacterial reduction of over 2.4-log10 CFU/mL compared with the most active monotherapy. Additionally, the TET/GML-12 combination displayed potent antimicrobial activity against four isolates in a mouse thigh infection model. These results suggest that the TET/GML-12 combination may be a potential therapeutic strategy for S. suis infection.

Field Study on the Immunological Response and Protective Effect of a Licensed Autogenous Vaccine to Control Streptococcus suis Infections in Post-Weaned Piglets

Streptococcus suis is one of the most important bacterial pathogens in weaned piglets and responsible for serious economic losses to the swine industry. Currently, mostly autogenous vaccines composed of killed bacteria (bacterins) are available. However, immunological and protective data from field studies are missing. We report for the first time a comparative field study on the immunological response induced by an autogenous vaccine applied to either piglets or sows in a farm with recurrent S. suis problems. (I) Piglets from non-vaccinated sows received an autogenous bacterin during the first week and at three weeks of age. (II) Sows received the vaccine at five and three weeks pre-farrowing and piglets were non-vaccinated. Levels, isotype profile and opsonophagocytosis capacity of the serum antibodies induced by vaccination were evaluated. Vaccination of piglets failed to induce an active immune response. Vaccination of sows induced a significant increase in anti-S. suis antibodies, mainly composed of IgG1. However, isotype switching was modulated by the S. suis serotype included in the vaccine formulation. Despite this antibody increase in vaccinated sows, transfer of maternal immunity to piglets was not different from the control group (i.e., piglets from non-vaccinated sows). Notably, levels of maternal antibodies in piglets were already very high with marked opsonophagocytosis capacity at one week of age, independently of the vaccination program. However, their levels decreased by three weeks of age, indicating possible absence of antibodies in the post-weaning high-risk period. These observations correlated with lack of clinical protection in the farm. Overall, a piglet or a sow vaccination program herein mostly failed to induce lasting protection in nursery piglets. An improvement of vaccine formulation or an optimized program may be required.

Enolase and dipeptidyl peptidase IV protein sub-unit vaccines are not protective against a lethal Streptococcus suis serotype 2 challenge in a mouse model of infection

Background

Streptococcus suis is a major swine pathogen causing arthritis, meningitis and sudden death in post-weaning piglets and is also a zoonotic agent. S. suis comprises 35 different serotypes of which the serotype 2 is the most prevalent in both pigs and humans. In the absence of commercial vaccines, bacterins (mostly autogenous), are used in the field, with controversial results. In the past years, the focus has turned towards the development of sub-unit vaccine candidates. However, published results are sometimes contradictory regarding the protective effect of a same candidate. Moreover, the adjuvant used may significantly influence the protective capacity of a given antigen. This study focused on two protective candidates, the dipeptidyl peptidase IV (DPPIV) and the enolase (SsEno). Both proteins are involved in S. suis pathogenesis, and while contradictory protection results have been obtained with SsEno in the past, no data on the protective capacity of DPPIV was available.

Results

Results showed that among all the field strains tested, 86 and 88% were positive for the expression of the SsEno and DPPIV proteins, respectively, suggesting that they are widely expressed by strains of different serotypes. However, no protection was obtained after two vaccine doses in a CD-1 mouse model of infection, regardless of the use of four different adjuvants. Even though no protection was obtained, significant amounts of antibodies were produced against both antigens, and this regardless of the adjuvant used.

Conclusions

Taken together, these results demonstrate that S. suis DPPIV and SsEno are probably not good vaccine candidates, at least not in the conditions evaluated in this study. Further studies in the natural host (pig) should still be carried out. Moreover, this work highlights the importance of confirming results obtained by different research groups.

Antimicrobial susceptibility of Streptococcus suis isolated from diseased pigs, asymptomatic pigs, and human patients in Thailand

Background

Prophylaxis and treatment of emerging zoonotic Streptococcus suis infection in agricultural and healthcare settings mainly rely on antibiotics. However, continued use of antibiotics contributing to emergence and widespread of antibiotic resistant S. suis becomes a significant challenge in many endemic countries, including Thailand. Meanwhile, the knowledge of antibiotic susceptibility patterns of bacterial pathogens is required for overcoming the antimicrobial resistance problem, the information of antibiotic susceptibility of S. suis strains isolated in Thailand remains limited. This study aims to assess the susceptibility of Thai-isolated S. suis strains to different antibiotic classes in order to gain an insight into the distribution of antibiotic-resistant patterns of S. suis strains in different regions of Thailand.

Results

This study revealed the antimicrobial resistance and multidrug resistance of 262 S. suis strains isolated in different regions of Thailand. Susceptibility testing indicated widespread resistance to macrolides and tetracyclines of S. suis strains in the country. Beta-lactam antibiotic drugs (including cefotaxime and ceftiofur), vancomycin, chloramphenicol, as well as florfenicol were potentially the most effective therapeutic drugs for the treatment of S. suis infection in both pigs and humans. High prevalence of intermediate susceptibility of S. suis isolated from asymptomatic pigs for penicillin G, gentamicin, enrofloxacin, and norfloxacin could be the premise of the emergence of S. suis antibiotic resistance. Resistance was also found in S. suis strains isolated from asymptomatic pigs indicating that they could act as reservoirs of antibiotic resistance genes.

Conclusions

To the best of our knowledge, this is the first report on antimicrobial resistance of a large collection of S. suis strains isolated from pigs and humans in Thailand. It revealed the multidrug resistance of S. suis strains in pigs and humans. The information gained from this study raises an awareness and encourage best practices of appropriate antibiotic drug prescribing and use among human health and agriculture sectors.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1732-5) contains supplementary material, which is available to authorized users.

Xylanase and Fermented Polysaccharide of Hericium caputmedusae Reduce Pathogenic Infection of Broilers by Improving Antioxidant and Anti-Inflammatory Properties

Background

Pathogenic infection in broilers has become an important issue in the development of poultry industry. Xylooligosaccharides released from xylan via xylanase and fermented polysaccharide of Hericium caputmedusae (FPHC) have antimicrobial potential against many pathogens.

Objective

We aimed to explore the effects of xylanase and FPHC on pathogenic infection in the broilers (Gallus gallus domesticus).

Methods

Three hundred and thirty 21-day male broilers were assigned into four groups: control group (CG, basic diet), xylanase group (XG, basic diet + xylanase), FPHC group (HG, basic diet + FPHC), and XHG group (basic diet + xylanase + FPHC). Average daily feed intake (ADFI) and daily gain (ADG) were measured. Microflora from broiler feces was analyzed using 16S rRNA sequencing. Serum tumor necrosis factor- (TNF-) α, interleukin-1β (IL-1β), IL-1 receptor antagonist (IL-1ra), IL-10, total antioxidant capacity (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) contents were detected using kits. The variables were compared using the Student t-test between two groups.

Results

Microbiological investigations showed that 75% of broilers were affected by bacterial pathogens in the CG group, most notably by coagulase-negative staphylococci. Comparatively, 15%, 26%, and 5% of broilers were affected by bacterial pathogens in the XG, HG, and XHG groups, respectively. Xylanase and FPHC treatment increased the ratio of ADG to ADFI and antioxidant capacity by increasing the levels of T-AOC, SOD, and GSH-Px and reducing the levels of MDA (P < 0.05). Xylanase and FPHC treatment improved anti-inflammatory capacity by increasing serum levels of IL-1ra and IL-10 and reducing the levels of IL-1β and TNF-α. On the other hand, the treatment increased probiotic concentration of Bacillus licheniformis, Bacillus subtilis, and Lactobacillus plantarum (P < 0.05), which were also proved in cell culture.

Conclusions

Xylanase and FPHC ameliorate pathogen infection by increasing antioxidant and anti-inflammatory activities of broilers via the increase of probiotics.

Pharmacokinetic-pharmacodynamic modeling of tylosin against Streptococcus suis in pigs

BACKGROUND

The aim of this study was to optimize the dosage regimen of tylosin against S.suis in Pigs using pharmacokinetic-pharmacodynamic (PK-PD) modeling. The antibacterial activity of tylosin against S.suis CVCC606 was investigated in Mueller Hinton (MH) broth and serum. The objectives of this investigation were to study the PD data of tylosin against S.suis CVCC606 and the PK data of tylosin in healthy and diseased model of pigs and formulate a rational dosage regimen for the treatment of pig streptococcosis.

RESULTS

The minimum inhibitory concentrations (MIC) were 0.25 μg/mL, and the minimal bactericidal concentrations (MBC) were 1 μg/mL in MH broth and serum. The killing curve showed time-dependent activity and weak concentration-dependent antibacterial activity. A pig pneumoniae model of S. suis infection was built by inoculating subcutaneously with S. suis CVCC606. Tylosin was (10 mg/kg b.w) administered intramuscularly (IM) to the healthy and S.suis infected pigs, The pharmacokinetic properties, including area under the curve(AUC), peak concentration (C_max) and time to reach C_max (T_max), were determined in plasma using UV-HPLC method. The AUC, C_max and T_max in plasma of healthy and infected pigs were 10.80 ± 2.20 and 10.30 ± 3.46 μg.h/mL, 2.06 ± 0.43 and 2.37 ± 0.38 μg/mL, 1.95 ± 0.22 and 1.58 ± 0.49 h, respectively.

CONCLUSIONS

The in vivo PK and in vitro PD data were integrated to determine the surrogate marker of antibacterial activity, C_max/MIC, AUC/MIC and T_>MICwere 8.90, 43.21, 8.86 for healthy pigs, and 9.76, 41.18, 7.56 for infected pigs, respectively. Ex vivo AUC/MIC data were integrated with ex vivo bacterial count to calculate the values for bacteriostatic and bactericidal action, which were 10.67 h and 49.66 h for healthy pigs, 11.73 h and 43.03 h for pigs infected with S.suis. A dosage regimen of 5.32-19.50 mg/kg b.w. every 24 h should be sufficient for tylosin against S.suis.

The inflammatory response and neuronal injury in Streptococcus suis meningitis

BACKGROUND

Many of the currently used models of bacterial meningitis have limitations due to direct inoculation of pathogens into the cerebrospinal fluid or brain and a relatively insensitive assessment of long-term sequelae. The present study evaluates the utility of a Streptococcus (S.) suis intranasal infection model for the investigation of experimental therapies in meningitis.

METHODS

We examined the brains of 10 piglets with S. suis meningitis as well as 14 control piglets by histology, immunohistochemistry and in-situ tailing for morphological alterations in the hippocampal dentate gyrus and microglial activation in the neocortex.

RESULTS

In piglets with meningitis, the density of apoptotic neurons was significantly higher than in control piglets. Moreover, scoring of microglial morphology revealed a significant activation of these cells during meningitis. The slight increase in the density of dividing cells, young neurons and microglia observed in piglets suffering from meningitis was not statistically significant, probably because of the short time frame between onset of clinical signs and organ sampling.

CONCLUSIONS

The morphological changes found during S. suis meningitis are in accordance with abnormalities in other animal models and human autopsy cases. Therefore, the pig should be considered as a model for evaluating effects of experimental therapeutic approaches on neurological function in bacterial meningitis.

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.