Deletion of sua gene reduces the ability of Streptococcus uberis to adhere to and internalize into bovine mammary epithelial cells

Comparison of Virulence Patterns Between Streptococcus uberis Causing Transient and Persistent Intramammary Infection

The objectives of this study were determined by two experiments including Experiment 1 (EXP1) using Streptococcus uberis obtained from a weekly longitudinal study to compare virulence patterns between transient and persistent intramammary infection (IMI), and Experiment 2 (EXP2) using a stored-known-appearance PFGE strain of a contagious S. uberis to determine a change of virulence patterns after long-term transmission. For EXP1, quarter milk samples from 31 milking cows were aseptically and longitudinally collected once a week for 10 weeks. A total of 14 S. uberis isolates from quarters with 1 and >4 weeks of duration of IMI were categorized as transient and persistent IMI, respectively. For EXP2, 11 isolates of a stored-known-appearance PFGE strain of S. uberis from our previous study (1) were randomly selected, including 5 from transient IMI (1 month) and 6 from persistent IMI (>1 month). The virulence profiles of all isolates were investigated, including sua, hasAB, hasC, gapC, pauA, and CAMP factor or cfu, using PCR. The Kaplan–Meier estimates were used to calculate the duration of IMI in EXP1. Approximately 50% of field S. uberis IMI was spontaneously cured within 1 week, while 25% was not cured within 10 weeks. From EXP1, 4 virulence patterns were found in 14 isolates. The majority of patterns for transient S. uberis did not include hasAB (63.6%), the gene relating to capsule formation. Regardless of transient or persistent IMI, a high similarity of the virulence pattern within a PFGE strain was found in EXP2. Few changes of virulence pattern within a PFGE strain were found or were related to its subsequently changing to transient IMI.

Evaluation of Streptococcus uberis Surface Proteins as Vaccine Antigens to Control S. uberis Mastitis in Dairy Cows

There is no effective vaccine against Streptococcus uberis mastitis in dairy cows. Objectives of this study were (1) to extract S. uberis surface proteins (SUSP) and determine immunoreactivity in vitro and (2) immunogenicity and efficacy in vivo. SUSP was extracted from S. uberis, and their immunoreactivity was tested by western blot. In total, 26 Jersey dairy cows were randomly divided into four groups. Groups 1, 2, and 3 were vaccinated subcutaneously with 4 mg, 1 mg, and 100 μg of SUSP, respectively, with Freund's incomplete adjuvant. Group 4 (control) was injected with placebo. S. uberis UT888 was infused into two contralateral quarters of each cow during early lactation. Somatic cell count (SCC), bacteria count in milk, and mastitis were monitored. Our results show that SUSP contains multiple protein bands, that ranged from 10 to 100 kDa. All vaccinates showed an increased anti-SUSP IgG antibody. The SCC of all experimentally infected quarters increased after challenge but slightly decreased after day 3 with no significant difference among groups. Milk bacterial count was significantly (p < 0.05) reduced in high and medium doses vaccinated groups than low and control groups. In conclusion, SUSP vaccine is immunogenic and showed a promising efficacy to control bovine S. uberis mastitis.

Potential factors involved in the early pathogenesis of Streptococcus uberis mastitis: a review

Bovine mastitis is an inflammation of the mammary gland, which could be the result of allergy, physical trauma, or invasion by pathogens as Streptococcus uberis. This pathogen is an environmental pathogen associated with subclinical and clinical intramammary infection (IMI) in both lactating and non-lactating cows, which can persist in the udder and cause a chronic infection in the mammary gland. In spite of the important economic losses and increased prevalence caused by S. uberis mastitis, virulence factors involved in bacterial colonization of mammary glands and the pathogenic mechanisms are not yet clear. In the last 30 years, several studies have defined adherence and internalization of S. uberis as the early stages in IMI. S. uberis adheres to and invades into mammary gland cells, and this ability has been observed in in vitro assays. Until now, these abilities have not been determined in vivo challenges since they have been difficult to study. Bacterial surface proteins are able to bind to extracellular matrix protein components such as fibronectin, collagen and laminin, as well as proteins in milk. These proteins play a role in adhesion to host cells and have been denominated microbial surface components recognizing adhesive matrix molecules (MSCRAMMs). This article aims to summarize our current knowledge on the most relevant properties of the potential factors involved in the early pathogenesis of S. uberis mastitis.

The Role of Gram-Positive Surface Proteins in Bacterial Niche- and Host-Specialization

Gram-positive bacterial pathogens have an array of proteins on their cell surface that mediate interactions with the host environment. In particular, bacterial cell wall-associated (CWA) proteins play key roles in both colonization and pathogenesis. Furthermore, some CWA proteins promote specialization for host-species or mediate colonization of specific anatomical niches within a host. In this mini review, we provide examples of the many ways by which major pathogens, such as Staphylococci, Streptococci and Listeria monocytogenes, utilize CWA proteins for both host- and niche-specialization. We describe different biological mechanisms mediated by CWA proteins including: the acquisition of iron from hemoglobin in the bloodstream, adherence to and invasion of host cells, and innate immune evasion through binding to the plasma proteins fibrinogen, immunoglobulin G, and complement. We also discuss the limitations of using animal models for understanding the role of specific CWA proteins in host-specialization and how transformative technologies, such as CRISPR-Cas, offer tremendous potential for developing transgenic models that simulate the host environment of interest. Improved understanding of the role of CWA proteins in niche- or host-specificity will allow the design of new therapeutic approaches which target key host–pathogen interactions underpinning Gram-positive bacterial infections.

Relative expression of genes associated with adhesion to bovine mammary epithelial cells by Streptococcus uberis

Streptococcus uberis is one of the most prevalent environmental pathogens of bovine mastitis. Biofilm growth ability by S. uberis looks to depend first upon the adherence of cells to a surface. The S. uberis ability to adhere to mammary gland epithelia might provide an advantage to colonize the lactating mammary gland. The objectives of this study were (a) to select S.uberis strains according to their ability to form biofilm, (b) to determine adherence to and internalization into MAC-T cells and (c) to investigate the expression profile adherence genes in these S. uberis strains. For the assays, the MAC-T bovine mammary epithelial cell line was used. Relative expression of genes acdA, lmb, scpA, sua, fbp and lbp was quantified by RT-qPCR. We observed that the RC38 strain from clinical bovine mastitis showed in the six genes higher values than control in both conditions. While the strain with greater ability to adhere, from clinical mastitis and biofilm producer (RC29) evidenced higher values in group 1 (G₁) (bacteria after the initial contact with MAC-T cells) and decrease in group 2 (G₂) (both adhered and internalized bacteria) than control. Strains with a moderate or strong capacity for biofilm production showed significantly lower relative expression values in the G₂. In all adherence associated genes, strain RC19 showed relative expression values incremented in G_1, while in G₂ decreased expression. In conclusion, we did not find a single profile of relative expression because the relative expression levels of each gene differed depending on the strain and the co-culture stage of S. uberis cells from which RNA was obtained.

Assessment of the potential utility of different regions of Streptococcus uberis adhesion molecule (SUAM) for mastitis subunit vaccine development

Streptococcus uberis is one of the most prevalent pathogens causing clinical and subclinical mastitis worldwide. Among bacterial factors involved in intramammary infections caused by this organism, S. uberis adhesion molecule (SUAM) is one of the main virulence factors identified. This molecule is involved in S. uberis internalization to mammary epithelial cells through lactoferrin (Lf) binding. The objective of this study was to evaluate SUAM properties as a potential subunit vaccine component for prevention of S. uberis mastitis. B epitope prediction analysis of SUAM sequence was used to identify potentially immunogenic regions. Since these regions were detected all along the gene, this criterion did not allow selecting a specific region as a potential immunogen. Hence, four fractions of SUAM (-1fr, 2fr, 3fr and 4fr), comprising most of the protein, were cloned and expressed. Every fraction elicited a humoral immune response in mice as predicted by bioinformatics analysis. SUAM-1fr generated antibodies with the highest recognition ability towards SUAM native protein. Moreover, antibodies against SUAM-1fr produced the highest proportion of internalization inhibition of S. uberis to mammary epithelial cells. In conclusion, SUAM immunogenic and functionally relevant regions were identified and allowed to propose SUAM-1fr as a potential candidate for a subunit vaccine for S. uberis mastitis prevention.

Bifidobacteria and Their Role as Members of the Human Gut Microbiota

Members of the genus Bifidobacterium are among the first microbes to colonize the human gastrointestinal tract and are believed to exert positive health benefits on their host. Due to their purported health-promoting properties, bifidobacteria have been incorporated into many functional foods as active ingredients. Bifidobacteria naturally occur in a range of ecological niches that are either directly or indirectly connected to the animal gastrointestinal tract, such as the human oral cavity, the insect gut and sewage. To be able to survive in these particular ecological niches, bifidobacteria must possess specific adaptations to be competitive. Determination of genome sequences has revealed genetic attributes that may explain bifidobacterial ecological fitness, such as metabolic abilities, evasion of the host adaptive immune system and colonization of the host through specific appendages. However, genetic modification is crucial toward fully elucidating the mechanisms by which bifidobacteria exert their adaptive abilities and beneficial properties. In this review we provide an up to date summary of the general features of bifidobacteria, whilst paying particular attention to the metabolic abilities of this species. We also describe methods that have allowed successful genetic manipulation of bifidobacteria.

Protective effect of anti-SUAM antibodies on Streptococcus uberis mastitis

In the present study, the effect of anti-recombinant Streptococcus uberis adhesion molecule (SUAM) antibodies against S. uberis intramammary infections (IMI) was evaluated using a passive protection model. Mammary quarters of healthy cows were infused with S. uberis UT888 opsonized with affinity purified anti-rSUAM antibodies or hyperimmune sera. Non-opsonized S. uberis UT888 were used as a control. Mammary quarters infused with opsonized S. uberis showed mild-to undetectable clinical symptoms of mastitis, lower milk bacterial counts, and less infected mammary quarters as compared to mammary quarters infused with non-opsonized S. uberis. These findings suggest that anti-rSUAM antibodies interfered with infection of mammary gland by S. uberis which might be through preventing adherence to and internalization into mammary gland cells, thus facilitating clearance of S. uberis, reducing colonization, and causing less IMI.

Correlation of hypothetical virulence traits of two Streptococcus uberis strains with the clinical manifestation of bovine mastitis

Streptococcus uberis is a common cause of clinical and subclinical mastitis in dairy cattle. Several virulence mechanisms have been proposed to contribute to the species' ability to cause disease. Here, virulence characteristics were compared between S. uberis strains FSL Z1-048, which consistently caused clinical mastitis in a challenge model, and FSL Z1-124, which consistently failed to cause disease in the same model, to ascertain whether in vitro virulence characteristics were related to clinical outcome. Macrophages derived from bovine blood monocytes failed to kill FSL Z1-048 whilst reducing survival of FSL Z1-124 by 42.5%. Conversely, blood derived polymorphonuclear cells caused more reduction (67.1 vs. 44.2%, respectively) in the survival of FSL Z1-048 than in survival of FSL Z1-124. After 3 h of coincubation with bovine mammary epithelial cell line BME-UV1, 1000-fold higher adherence was observed for FSL Z1-048 compared to FSL Z1-124, despite presence of a frame shift mutation in the sua gene of FSL Z1-048 that resulted in predicted truncation of the S. uberis Adhesion Molecule (SUAM) protein. In contrast, FSL Z1-124 showed higher ability than FSL Z1-048 to invade BME-UV1 cells. Finally, observed biofilm formation by FSL Z1-124 was significantly greater than for FSL Z1-048. In summary, for several hypothetical virulence characteristics, virulence phenotype in vitro did not match disease phenotype in vivo. Evasion of macrophage killing and adhesion to mammary epithelial cells were the only in vitro traits associated with virulence in vivo, making them attractive targets for further research into pathogenesis and control of S. uberis mastitis.

Role of Streptococcus uberis adhesion molecule in the pathogenesis of Streptococcus uberis mastitis

Adherence to and internalization into mammary epithelial cells are central mechanisms in the pathogenesis of S. uberis mastitis. Through these pathogenic strategies, S. uberis reaches an intracellular environment where humoral host defenses and antimicrobials in milk are essentially ineffective, thus allowing persistence of this pathogen in the mammary gland. We reported that S. uberis expresses a surface adhesion molecule (SUAM) that has affinity for lactoferrin (LF) and a central role adherence to and internalization of S. uberis into bovine mammary epithelial cells. To define the role of SUAM in the pathogenesis of S. uberis mastitis, we created a sua gene deletion mutant clone of S. uberis UT888 (Δsua S. uberis UT888) unable to express SUAM. When tested in vitro, Δsua S. uberis UT888 was defective in adherence to and internalization into bovine mammary epithelial cells. To prove that the absence of SUAM reduces bacterial attachment, subsequent colonization and infection of bovine mammary glands, the wild type S. uberis UT888 and its isogenic Δsua S. uberis UT888 were infused into mammary quarters of dairy cows. Results showed that fewer mammary glands infused with Δsua S. uberis UT888 become infected than those infused with the isogenic parental strain. Furthermore, mammary glands infused with Δsua S. uberis UT888 had less severe clinical symptoms as compared to those infused with the isogenic parental strain. These results suggest that the SUAM mutant clone was less virulent than the isogenic parental strain which further substantiates the role of SUAM in the pathogenesis of S. uberis mastitis.

A targeted gene knockout method using a newly constructed temperature-sensitive plasmid mediated homologous recombination in Bifidobacterium longum

Bifidobacteria are the main component of the human microflora. We constructed a temperature-sensitive (Ts) plasmid by random mutagenesis of the Bifidobacterium-Escherichia coli shuttle vector pKKT427 using error-prone PCR. Mutant plasmids were introduced into Bifidobacterium longum 105-A and, after screening approximately 3,000 colonies, candidate clones that grew at 30 °C but not at 42 °C were selected. According to DNA sequence analysis of the Ts plasmid, five silent and one missense mutations were found in the repB region. The site-directed mutagenesis showed only the missense mutation to be relevant to the Ts phenotype. We designated this plasmid pKO403. The Ts phenotype was also observed in B. longum NCC2705 and Bifidobacterium adolescentis ATCC15703. Single-crossover homologous-recombination experiments were carried out to determine the relationship between the length of homologous sequences encoded on the plasmid and recombination frequency: fragments greater than 1 kb gave an efficiency of more than 10(3) integrations per cell. We performed gene knockout experiments using this Ts plasmid. We obtained gene knockout mutants of the pyrE region of B. longum 105-A, and determined that double-crossover homologous recombination occurred at an efficiency of 1.8 %. This knockout method also worked for the BL0033 gene in B. longum NCC2705.

Molecular characterization of Streptococcus agalactiae and Streptococcus uberis isolates from bovine milk

Streptococci are one among the major mastitis pathogens which have a considerable impact on cow health, milk quality, and productivity. The aim of the present study was to investigate the occurrence and virulence characteristics of streptococci from bovine milk and to assess the molecular epidemiology and population structure of the Indian isolates using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Out of a total of 209 bovine composite milk samples screened from four herds (A-D), 30 Streptococcus spp. were isolated from 29 milk samples. Among the 30 isolates, species-specific PCR and partial 16S rRNA gene sequence analysis identified 17 Streptococcus agalactiae arising from herd A and 13 Streptococcus uberis comprising of 5, 7, and 1 isolates from herds B, C, and D respectively. PCR based screening for virulence genes revealed the presence of the cfb and the pavA genes in 17 and 1 S. agalactiae isolates, respectively. Similarly, in S. uberis isolates, cfu gene was present in six isolates from herd C, the pau A/skc gene in all the isolates from herds B, C, and D, whereas the sua gene was present in four isolates from herd B and the only isolate from herd D. On MLST analysis, all the S. agalactiae isolates were found to be of a novel sequence type (ST), ST-483, reported for the first time and is a single locus variant of the predicted subgroup founder ST-310, while the S. uberis isolates were found to be of three novel sequence types, namely ST-439, ST-474, and ST-475, all reported for the first time. ST-474 was a double locus variant of three different STs of global clonal complex ST-143 considered to be associated with clinical and subclinical mastitis, but ST-439 and ST-475 were singletons. Unique sequence types identified for both S. agalactiae and S. uberis were found to be herd specific. On PFGE analysis, identical or closely related restriction patterns for S. agalactiae ST-483 and S. uberis ST-439 in herds A and B respectively, but an unrelated restriction pattern for S. uberis ST-474 and ST-475 isolates from herds D and C respectively, were obtained. This signifies that the isolates of particular ST may exhibit related PFGE patterns suggesting detection of a faster molecular clock by PFGE than MLST. Since all the isolates of both the species belonged to novel sequence types, their epidemiological significance in global context could not be ascertained, however, evidence suggests that they have uniquely evolved in Indian conditions. Further research would be useful for understanding the role of these pathogens in bovine sub-clinical mastitis and implementing effective control strategies in India.

pGh9:ISS1 transpositional mutations in Streptococcus uberis UT888 causes reduced bacterial adherence to and internalization into bovine mammary epithelial cells

Streptococcus uberis is an important mastitis pathogen that affects dairy cows worldwide. In spite of the economic impact caused by the high prevalence of S. uberis intramammary infections (IMI) in many well-managed dairy herds, pathogenic strategies and associated virulence factors of S. uberis are not well understood. It has been shown that S. uberis attaches to and internalizes into mammary epithelial cells and can survive inside cells for extended periods of time. We hypothesize that early attachment to and internalization into mammary epithelial cells is a critical step for the establishment of intramammary infection. The aim of this study is to identify and characterize chromosomally encoded virulence factors of S. uberis that allow early bacterial attachment to and internalization into mammary epithelial cells. A common approach used to identify virulence factors is by generating random insertion mutants that are defective in adherence to and internalization into mammary epithelial cells using pGh9:ISS1 mutagenesis system. A random insertion mutant library of S. uberis strain UT888 was created using a thermo-sensitive plasmid pGh9:ISS1 carrying ISS1 insertion sequence. Integration of the insertion sequence into the chromosome of these mutant clones was confirmed by PCR and Southern blot. Southern blot analysis of mutant clones also showed that insertional integration was random. Of 1000 random chromosomal insertion mutants of S. uberis strain UT888 screened, 32 had significantly reduced ability to adhere to and internalize into mammary epithelial cells. Chromosomal mapping of insertion sequence integration sites in some of these defective mutants showed integration into penicillin binding protein 2A (pbp2A), sensor histidine kinase, tetR family regulatory protein, phosphoribosylaminoimidazole carboxylase catalytic subunit (purE), lactose phosphotransferase, phosphoribosylamine glycine ligase (purD), and other genes involved in metabolic activities. These proteins may have a significant role in early bacterial colonization of the mammary gland during infection.