Streptococcus suis is a major swine pathogen responsible for important economic losses to the swine industry worldwide. It is also an emerging zoonotic agent of meningitis and streptococcal toxic shock-like syndrome. Since the recent recognition of the high prevalence of S. suis human disease in southeast and east Asia, the interest of the scientific community in this pathogen has significantly increased. In the last few years, as a direct consequence of these intensified research efforts, large amounts of data on putative virulence factors have appeared in the literature. Although the presence of some proposed virulence factors does not necessarily define a S. suis strain as being virulent, several cell-associated or secreted factors are clearly important for the pathogenesis of the S. suis infection. In order to cause disease, S. suis must colonize the host, breach epithelial barriers, reach and survive in the bloodstream, invade different organs, and cause exaggerated inflammation. In this review, we discuss the potential contribution of different described S. suis virulence factors at each step of the pathogenesis of the infection. Finally, we briefly discuss other described virulence factors, virulence factor candidates and virulence markers for which a precise role at specific steps of the pathogenesis of the S. suis infection has not yet been clearly established.

Virulence factors involved in the pathogenesis of the infection caused by the swine pathogen and zoonotic agent Streptococcus suis

Post-weaning diarrhea (PWD) is one of the most serious threats for the swine industry worldwide It is commonly associated with the proliferation of enterotoxigenic Escherichia coli in the pig intestine Colistin, a cationic antibiotic, is widely used in swine for the oral treatment of intestinal infections caused by E coli, and particularly of PWD However, despite the effectiveness of this antibiotic in the treatment of PWD, several studies have reported high rates of colistin resistant E coli in swine Furthermore, this antibiotic is considered of very high importance in humans, being used for the treatment of infections due to multidrug-resistant (MDR) Gram-negative bacteria (GNB) Moreover, the recent discovery of the mcr-1 gene encoding for colistin resistance in Enterobacteriaceae on a conjugative stable plasmid has raised great concern about the possible loss of colistin effectiveness for the treatment of MDR-GNB in humans Consequently, it has been proposed that the use of colistin in animal production should be considered as a last resort treatment only Thus, to overcome the economic losses, which would result from the restriction of use of colistin, especially for prophylactic purposes in PWD control, we believe that an understanding of the factors contributing to the development of this disease and the putting in place of practical alternative strategies for the control of PWD in swine is crucial Such alternatives should improve animal gut health and reduce economic losses in pigs without promoting bacterial resistance The present review begins with an overview of risk factors of PWD and an update of colistin use in PWD control worldwide in terms of quantities and microbiological outcomes Subsequently, alternative strategies to the use of colistin for the control of this disease are described and discussed Finally, a practical approach for the control of PWD in its various phases is proposed

/pdf/post-weaning-diarrhea-in-pigs-risk-factors-and-non-colistin-4ybjppee5z.pdf

Post weaning diarrhea in pigs: risk factors and non‑colistin‑based control strategies

Streptococcus suis (S. suis) is a family of pathogenic gram-positive bacterial strains that represents a primary health problem in the swine industry worldwide. S. suis is also an emerging zoonotic pathogen that causes severe human infections clinically featuring with varied diseases/syndromes (such as meningitis, septicemia, and arthritis). Over the past few decades, continued efforts have made significant progress toward better understanding this zoonotic infectious entity, contributing in part to the elucidation of the molecular mechanism underlying its high pathogenicity. This review is aimed at presenting an updated overview of this pathogen from the perspective of molecular epidemiology, clinical diagnosis and typing, virulence mechanism, and protective antigens contributing to its zoonosis.

https://www.tandfonline.com/doi/pdf/10.4161/viru.28595

Streptococcus suis infection: An emerging/reemerging challenge of bacterial infectious diseases?

Critical Streptococcus suis Virulence Factors: Are They All Really Critical?

SUMMARY: Environmental mastitis is the most common and costly form of mastitis in modern dairy herds where contagious transmission of intramammary pathogens is controlled through implementation of standard mastitis prevention programmes. Environmental mastitis can be caused by a wide range of bacterial species, and binary classification of species as contagious or environmental is misleading, particularly for Staphylococcus aureus, Streptococcus uberis and other streptococcal species, including Streptococcus agalactiae. Bovine faeces, the indoor environment and used pasture are major sources of mastitis pathogens, including Escherichia coli and S. uberis. A faeco‐oral transmission cycle may perpetuate and amplify the presence of such pathogens, including Klebsiella pneumoniae and S. agalactiae. Because of societal pressure to reduce reliance on antimicrobials as tools for mastitis control, management of environmental mastitis will increasingly need to be based on prevention. This requires a reduction in environmental exposure through bedding, pasture and pre‐milking management and enhancement of the host response to bacterial challenge. Efficacious vaccines are available to reduce the impact of coliform mastitis, but vaccine development for gram‐positive mastitis has not progressed beyond the “promising” stage for decades. Improved diagnostic tools to identify causative agents and transmission patterns may contribute to targeted use of antimicrobials and intervention measures. The most important tool for improved uptake of known mastitis prevention measures is communication. Development of better technical or biological tools for management of environmental mastitis must be accompanied by development of appropriate incentives and communication strategies for farmers and veterinarians, who may be confronted with government‐mandated antimicrobial use targets if voluntary reduction is not implemented.

/pdf/an-update-on-environmental-mastitis-challenging-perceptions-2rxyyhkng7.pdf

An update on environmental mastitis: Challenging perceptions

Streptococcus suis is one of the most important pathogens in pigs and is also an emerging zoonotic agent. After crossing the epithelial barrier, S. suis causes bacteraemia, resulting in meningitis, endocarditis and bronchopneumonia. Since the host environment seems to be an important regulatory component for virulence, we related expression of virulence determinants of S. suis to glucose availability during growth and to the sugar metabolism regulator catabolite control protein A (CcpA). We found that expression of the virulence-associated genes arcB, representing arcABC operon expression, cps2A, representing capsular locus expression, as well as sly, ofs, sao and epf, differed significantly between exponential and early stationary growth of a highly virulent serotype 2 strain. Deletion of ccpA altered the expression of the surface-associated virulence factors arcB, sao and eno, as well as the two currently proven virulence factors in pigs, ofs and cps2A, in early exponential growth. Global expression analysis using a cDNA expression array revealed 259 differentially expressed genes in early exponential growth, of which 141 were more highly expressed in the CcpA mutant strain 10ΔccpA and 118 were expressed to a lower extent. Interestingly, among the latter genes, 18 could be related to capsule and cell wall synthesis. Correspondingly, electron microscopy characterization of strain 10ΔccpA revealed a markedly reduced thickness of the capsule. This phenotype correlated with enhanced binding to porcine plasma proteins and a reduced resistance to killing by porcine neutrophils. Taken together, our data demonstrate that CcpA has a significant effect on the capsule synthesis and virulence properties of S. suis.

/pdf/role-of-glucose-and-ccpa-in-capsule-expression-and-virulence-41mrh7tigo.pdf

Role of glucose and CcpA in capsule expression and virulence of Streptococcus suis.

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

Rapid detection of Streptococcus uberis in raw milk by loop-mediated isothermal amplification.

Weaning of piglets causes stress due to environmental, behavioral, and nutritional stressors and can lead to postweaning diarrhea and impaired gut development. The diet changes experienced during weaning require extensive adaptation of the digestive system. A well-developed piglet that had creep-feed experience before weaning performs better after weaning. In the current study, the effect of providing sow-fed piglets with a supplemental nutrient-dense complex milk replacer (NDM) on gut development and growth performance was studied. Litters of sows with similar parities (3.6 ± 0.8) and similar numbers of live born piglets (13.5 ± 0.3) were assigned to 1 of 2 groups: 1 group of piglets had ad libitum access to NDM from Day 2 through 21 after birth, whereas the other group was used as controls. Nutrient-dense complex milk replacer-fed piglets were shown to be significantly heavier after 21 d of supplementation compared with the control piglets. At Day 21, 3 piglets from each litter were euthanized for morphological and functional analyses of the intestinal tract. The small intestines of NDM-fed piglets had significantly higher weights (g) as well as significantly higher relative weight:length ratios (g//cm) compared with the small intestines of control piglets ( < 0.05). Morphometric analysis demonstrated that villi length and numbers of goblet cells did not differ between groups. However, NDM-fed piglets had deeper crypts ( < 0.001) and an increased expression of the cell-proliferation marker proliferating cell nuclear antigen in crypts ( < 0.05), suggesting higher cell-proliferation rates. The gene encoding IGF-1 showed a tendency to higher gene expression in the jejunum from NDM-fed piglets ( = 0.07) compared with the jejunum from control piglets, suggesting that IGF-1 might be involved in the regulation of cell proliferation and intestinal growth. Finally, as a result of dietary fiber in NDM, piglets showed significantly increased concentrations of metabolic fermentation products. This suggests differences in metabolic activity in the colon between treatment groups. In conclusion, providing sow-fed piglets with NDM before weaning stimulates intestinal proliferation, leading to increased circular growth. Nutrient-dense complex milk replacer supplementation might, therefore, help piglets through the transition period at weaning by increased BW and increased capacity for uptake of nutrients.

Supplementation of piglets with nutrient-dense complex milk replacer improves intestinal development and microbial fermentation

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Role of glucose and CcpA in capsule expression and virulence of Streptococcus suis.

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

Rapid detection of Streptococcus uberis in raw milk by loop-mediated isothermal amplification.

Supplementation of piglets with nutrient-dense complex milk replacer improves intestinal development and microbial fermentation