Invasion of bovine mammary epithelial cells by Streptococcus dysgalactiae

Clathrin: the molecular shape shifter

Clathrin is best known for its contribution to clathrin-mediated endocytosis yet it also participates to a diverse range of cellular functions. Key to this is clathrin's ability to assemble into polyhedral lattices that include curved football or basket shapes, flat lattices or even tubular structures. In this review, we discuss clathrin structure and coated vesicle formation, how clathrin is utilised within different cellular processes including synaptic vesicle recycling, hormone desensitisation, spermiogenesis, cell migration and mitosis, and how clathrin's remarkable 'shapeshifting' ability to form diverse lattice structures might contribute to its multiple cellular functions.

Infective mastitis due to bovine-associated Streptococcus dysgalactiae contributes to clinical persistent presentation in a murine mastitis model

Background

Mastitis caused by Streptococcus dysgalactiae (GCS) is a major pathology of dairy cows. The mechanisms by which GCS intramammary infection is established and maintained involve not only bacterial adherence and invasion but also modulation of the cytokines and TLR immune response.

Objectives

The study aimed to evaluate characteristics of persistent infection of GCS collected from bovine mastitis milk in a murine mastitis model whose mammary structure is similar to that of dairy cows; dairy cow mastitis can be well simulated by using mice as models. HLJ2019 was tested for its ability to persistently infected mice by intramammary inoculation.

Methods

As antibiotics tested, establish an intramammary infection model in murine, histopathology analyses, relative expression of inflammatory cytokines mRNA and adherence and invasion in mMECs.

Results

It induced a robust inflammatory reaction in the mammary gland, characterized by histopathological changes, increased myeloperoxidase activity and induced expression of inflammatory cytokines (TNF‐α, IL‐6, IFN‐γ, IL‐10, IL‐1α and IL‐1β) and TLR2/4, the exhibited strong LDH release, adhesion and invasive abilities in contact with mMECs.

Conclusion

These results contribute to increase the available information on host‐pathogen interaction and point out the need for further research to expand the knowledge about these interactions for developing new strategies to intervene in the intramammary persistent infection progress.

Genetic diversity and virulence characteristics of Staphylococcus aureus isolates from cases of bovine mastitis

Staphylococcus aureus is one of the major bacterial mastitis pathogens with significant effects on animal and human health. Some studies showed that S. aureus strains that infect different host species are genetically distinct, although most strains can infect a wide range of host species. However, there are no clearly defined clonal patterns of S. aureus strains that are known to infect a specific host. The objectives of this study were to evaluate the clonal diversity and virulence characteristics of S. aureus isolates from cases of bovine mastitis. Bacteriological tests were conducted on milk samples from cases of bovine mastitis from 11 dairy farms including some milk samples from unknown farms in Eastern Tennessee. Overall, a total of 111 S. aureus were isolated and identified, and further evaluated for their genetic diversity by pulsed-field gel electrophoresis (PFGE) and virulence characteristics by PCR. Genotypic virulence factors including staphylococcal enterotoxins, and toxic shock syndrome toxin 1 (tsst-1) were tested by PCR. In addition, the association among several known virulence factors of these isolates based on our current and previous studies in our lab were evaluated. Previously generated data that were included in the analysis of association among virulence factors were the presence of biofilm production associated genes in the ica operon such as icaA, icaD and icaAB, and phenotypic virulence characteristics such as hemolysis on blood agar, slime production and resistance or susceptibility to ten commonly used antimicrobials in dairy farms. The PFGE results showed the presence of 16 PFGE types (designated A - P) throughout farms, of which three pulsotypes, I, M and O were the most frequently isolated PFGE types from most farms. The PFGE type M was the most prevalent of all 16 PFGE types, with 64 isolates being present among nine farms. The PCR results of enterotoxin genes showed that out of the total 111 tested 84 (75.7%) were negative whereas 13 (11.7%), 2 (1.8%), 3 (2.7%), 1 (0.9%) and 8 (7.2%) were positive for seb, seb and sec, sec, see, and tsst-1, respectively. All 111 isolates were negative for sea and sej. Results of the evaluation of I, M and O strains adhesion to and invasion into mammary epithelial cells showed that the total count of each strain of bacteria adhered to and invaded into mammary epithelial cell line (MAC-T cells) was not significantly different (P > 0.05). This may be an indication that there is no significant difference in their ability to establish early host-pathogen interaction and colonization of the host. There were no statistically significant associations among PFGE types and other known virulence factors of these strains. However, PFGE types O and M tend to cluster with β-hemolysin, absence of enterotoxins and susceptibility to antimicrobials. In conclusion, there was not any association between pulsotype and genotypic and phenotypic virulence factors. S. aureus isolates from cases of bovine mastitis had diverse genotypes that possessed variable virulence factors.

Taming the Triskelion: Bacterial Manipulation of Clathrin

The entry of pathogens into nonphagocytic host cells has received much attention in the past three decades, revealing a vast array of strategies employed by bacteria and viruses. A method of internalization that has been extensively studied in the context of viral infections is the use of the clathrin-mediated pathway. More recently, a role for clathrin in the entry of some intracellular bacterial pathogens was discovered. Classically, clathrin-mediated endocytosis was thought to accommodate internalization only of particles smaller than 150 nm; however, this was challenged upon the discovery that Listeria monocytogenes requires clathrin to enter eukaryotic cells. Now, with discoveries that clathrin is required during other stages of some bacterial infections, another paradigm shift is occurring. There is a more diverse impact of clathrin during infection than previously thought. Much of the recent data describing clathrin utilization in processes such as bacterial attachment, cell-to-cell spread and intracellular growth may be due to newly discovered divergent roles of clathrin in the cell. Not only does clathrin act to facilitate endocytosis from the plasma membrane, but it also participates in budding from endosomes and the Golgi apparatus and in mitosis. Here, the manipulation of clathrin processes by bacterial pathogens, including its traditional role during invasion and alternative ways in which clathrin supports bacterial infection, is discussed. Researching clathrin in the context of bacterial infections will reveal new insights that inform our understanding of host-pathogen interactions and allow researchers to fully appreciate the diverse roles of clathrin in the eukaryotic cell.

Effect of heat stress on the interaction of Streptococcus uberis with bovine mammary epithelial cells

Heat stress (HS) negatively affects milk production and has been associated with decreased immune function, and increased rate of intramammary infections (IMI). Research has shown that HS affects gene expression, cell cycle, and cell metabolism in bovine mammary epithelial cells (BMEC). Since BMEC are an initial target of mastitis pathogens, we studied adherence to and internalisation of S. uberis into HS-BMEC, as well as the effect that this interaction has on host cells by measuring HS-BMEC viability and membrane integrity. Results reported in this Research Communication showed that HS reduced cell viability and induced membrane damage. However, these pathological changes, as well as the rate of adherence and internalisation of S. uberis into BMEC, were augmented when S. uberis was cocultured with HS-BMEC. These results may help to understand the pathogenesis of S. uberis IMI as well as the increased susceptibility of mammary glands to IMI in cows subjected to HS.

Lactoferrin affects the adherence and invasion of Streptococcus dysgalactiae ssp. dysgalactiae in mammary epithelial cells

Streptococcus dysgalactiae ssp. dysgalactiae is an important causative agent of bovine mastitis worldwide. Lactoferrin is an innate immune protein that is associated with many functions including immunomodulatory, antiproliferative, and antimicrobial properties. This study aimed to investigate the interactions between lactoferrin and a clinical bovine mastitis isolate, Strep. dysgalactiae ssp. dysgalactiae DPC5345. Initially a deliberate in vivo bovine intramammary challenge was performed with Strep. dysgalactiae DPC5345. Results demonstrated a significant difference in lactoferrin mRNA levels in milk cells between the control and infused quarters 7h postinfusion. Milk lactoferrin levels in the Strep. dysgalactiae DPC5345 infused quarters were significantly increased compared with control quarters at 48h postinfusion. In vitro studies demonstrated that lactoferrin had a bacteriostatic effect on the growth of Strep. dysgalactiae DPC5345 and significantly decreased the ability of the bacteria to internalize into HC-11 mammary epithelial cells. Confocal microscopy images of HC-11 cells exposed to Strep. dysgalactiae and lactoferrin further supported this effect by demonstrating reduced invasion of bacteria to HC-11 cells. The combined data suggest that a bovine immune response to Strep. dysgalactiae infection includes a significant increase in lactoferrin expression in vivo, and based on in vitro data, lactoferrin limits mammary cell invasion of this pathogen by binding to the bacteria and preventing its adherence.

Characterization of the bovine innate immune response in milk somatic cells following intramammary infection with Streptococcus dysgalactiae subspecies dysgalactiae

The innate immune response of milk somatic cells in cows to Streptococcus dysgalactiae ssp. dysgalactiae was investigated by deliberate intramammary challenge. Cows were challenged with 2,500 colony-forming units of Strep. dysgalactiae DPC 5435, previously isolated from a clinical mastitis case. Eight of the 9 cows treated showed clinical signs of mastitis (swollen udders, increased somatic cell score, and clotted milk) within 1 wk of challenge. Messenger RNA levels of IL-1β and toll-like receptor 4 (TLR4) in milk somatic cells increased approximately 40 fold within 48 h of infusion, whereas tumor necrosis factor α increased 16 fold within the same time frame. Interestingly, cows homozygous for the G allele of the C-X-C chemokine receptor type 1 (CXCR1)-777 polymorphism had higher IL-8 and CXCR1 transcript abundance at 24h postinfusion compared with cows homozygous for the C allele. The difference in expression of these genes at this critical time point may influence the severity of disease within different genotypes.

Intracellular fate of strains of Escherichia coli isolated from dairy cows with acute or chronic mastitis

Research on mastitis in dairy cows caused by Escherichia coli has reported the emergence of strains capable of inducing chronic mastitis and that these strains adhered to and internalized into bovine mammary epithelial cells better than strains of E. coli isolated from acute mastitis. To understand mechanisms and strategies used by chronic E. coli strains to survive intracellularly internalization studies using bovine mammary epithelial cells treated with inhibitors of caveolae-mediated endocytosis (CME) and receptor-mediated endocytosis (RME), double immunofluorescence labeling confocal laser and fluorescence microscopy were conducted. Internalization studies showed that strains chronic E. coli strains persisted intracellularly longer than acute E. coli strains. Treatment of bovine mammary epithelial cells CME or RME inhibitors resulted in lower numbers of intracellular E. coli strains associated with chronic or acute mastitis than untreated controls. In addition, when selective CME inhibitors were used significantly fewer chronic E. coli were detected intracellularly than acute E. coli or untreated controls. Confocal laser microscopy showed that chronic E. coli strains colocalized preferentially with caveolae whereas acute strains did so with early endosomes, an early step of RME. These results suggest that strains of E. coli associated with chronic mastitis exploit lipid rafts/CME to internalize into and move through mammary epithelial cells. By exploiting this endocytosis pathway, chronic E. coli strains avoid bactericidal mechanisms such as endosome acidification and endosome-lysosome fusion, thus allowing intracellular survival. Data from this study helps to explain how these strains are capable of causing chronic E. coli mastitis.

Bacteriocins - exploring alternatives to antibiotics in mastitis treatment

Mastitis is considered to be the most costly disease affecting the dairy industry. Management strategies involve the extensive use of antibiotics to treat and prevent this disease. Prophylactic dosages of antibiotics used in mastitis control programmes could select for strains with resistance to antibiotics. In addition, a strong drive towards reducing antibiotic residues in animal food products has lead to research in finding alternative antimicrobial agents. In this review we have focus on the pathogenesis of the mastitis in dairy cows, existing antibiotic treatments and possible alternative for application of bacteriocins from lactic acid bacteria in the treatment and prevention of this disease.

Mammary tissue damage during bovine mastitis: causes and control

Mastitis, an inflammatory reaction of the mammary gland that is usually caused by a microbial infection, is recognized as the most costly disease in dairy cattle. Decreased milk production accounts for approximately 70% of the total cost of mastitis. Mammary tissue damage reduces the number and activity of epithelial cells and consequently contributes to decreased milk production. Mammary tissue damage has been shown to be induced by either apoptosis or necrosis. These 2 distinct types of cell death can be distinguished by morphological, biochemical, and molecular changes in dying cells. Both bacterial factors and host immune reactions contribute to epithelial tissue damage. During infection of the mammary glands, the tissue damage can initially be caused by bacteria and their products. Certain bacteria produce toxins that destroy cell membranes and damage milk-producing tissue, whereas other bacteria are able to invade and multiply within the bovine mammary epithelial cells before causing cell death. In addition, mastitis is characterized by an influx of somatic cells, primarily polymorphonuclear neutrophils, into the mammary gland. With more immune cells migrating into the mammary gland and the breakdown of the blood-milk barrier, damage to the mammary epithelium worsens. It is well known that breakdown of the extracellular matrix can lead to death of the epithelial cells. Meanwhile, polymorphonuclear neutrophils can harm the mammary tissue by releasing reactive oxygen intermediates and proteolytic enzymes. In vitro and in vivo studies suggest that the use of antioxidants and other protective compounds in mastitis control programs is worth investigating, because they may aid in alleviating damage to secretory cells and thus reduce subsequent milk loss.

Intracellular killing of mastitis pathogens by penethamate hydriodide following internalization into mammary epithelial cells

Penethamate hydriodide was highly effective in killing Streptococcus uberis, Streptococcus dysgalactiae subsp. dysgalactiae and Staphylococcus aureus that internalized mammary epithelial cells. At higher concentrations (32 microg/mL to 32 mg/mL), killing rates ranged from 85% to 100%. At lower concentrations (0.032 microg/mL to 3.2 microg/mL), killing rates ranged from 0 to 80%. Results of this proof-of-concept study demonstrated that: (1) penethamate hydriodide is capable of entering mammary epithelial cells and killing intracellular mastitis pathogens without affecting mammary epithelial cell viability, (2) the in vitro model used is capable of quantifying the fate of mastitis pathogens internalized into mammary epithelial cells, and (3) this in vitro model can be used to determine the effectiveness of antibiotics at killing bacteria within the cytoplasm of mammary epithelial cells.

Invasive potential of bacterial isolates associated with subclinical bovine mastitis

This work describes differences in the invasive ability of bacterial isolates associated with mastitis. Invasion ability was determined by the uptake and survival in a primary culture of bovine mammary epithelial cells (BMEC). BMEC were isolated from a healthy lactating cow and characterized by their morphology, immunostaining for cytokeratin and the detection of beta- and kappa-casein mRNAs. Ten bacterial isolates comprising the staphylococcal species Staphylococcus aureus (3), Staphylococcus epidermidis (1), Staphylococcus haemolyticus (1), Staphylococcus equorum (2), Staphylococcus xylosus (1) and Brevibacterium stationis (2) obtained from raw milk of cows with mastitis from backyard farms were assayed for their ability to invade BMEC. Only two S. aureus and one S. epidermidis isolates were able to invade BMEC, at similar levels to the S. aureus control strain ATCC 27543. In conclusion, using the in vitro model of infection used in this study, differences in bacterial invasion capability may be detected.

Streptococcus uberis internalizes and persists in bovine mammary epithelial cells

Streptococcus uberis is one of the most important emerging bovine mastitis pathogens and chronic persistent intramammary infections (IMI) are often described. To define the ability of S. uberis to persist intracellularly, studies on time-dependent internalization and survival of S. uberis strains in bovine mammary epithelial cells were conducted. Two S. uberis strains (UT366 and UT888) and a Staphylococcus aureus strain used as positive control, all isolated from cows with clinical mastitis were cocultured with bovine mammary epithelial cells (MAC-T) and persistent survival in host epithelial cells for extended periods (120 h) studied. Of S. uberis strains tested, UT366 showed highest internalization values at 60 min of incubation whereas at 8 h of incubation the corresponding values for UT888 were the highest. Of both strains of S. uberis tested, UT366 seems to internalize bovine mammary cells more efficiently initially, however, during the first 8 h, UT888 seems to survive intracellularly better than UT366. Results showed that both S. uberis strains could survive intracellularly up to 120 h without apparent loss of host cells viability. S. aureus internalized more efficiently than all strains tested and host cell death was observed after 72 h of incubation. These results indicate that S. uberis can survive within mammary epithelial cells for extended time without apparent loss of host cells viability. Intracellular persistence of S. uberis may be associated with the spread of the infection to deeper tissues and development of persistent IMI.

The ability of Mycobacterium avium subsp. paratuberculosis to enter bovine epithelial cells is influenced by preexposure to a hyperosmolar environment and intracellular passage in bovine mammary epithelial cells

Mycobacterium avium subsp. paratuberculosis is the cause of Johne's disease in cattle and other ruminants. M. avium subsp. paratuberculosis infection of the bovine host is not well understood; however, it is assumed that crossing the bovine intestinal mucosa is important in order for M. avium subsp. paratuberculosis to establish infection. To examine the ability of M. avium subsp. paratuberculosis to infect bovine epithelial cells in vitro, Madin-Darby bovine kidney (MDBK) epithelial cells were exposed to M. avium subsp. paratuberculosis. It was observed that bacteria can establish infection and replicate within MDBK cells. M. avium subsp. paratuberculosis also has been reported to infect mammary tissue and milk, and we showed that M. avium subsp. paratuberculosis infects bovine mammary epithelial cells (MAC-T cell line). Using polarized MAC-T cell monolayers, it was also determined that M. avium subsp. paratuberculosis crosses apical and basolateral surfaces with approximately the same degree of efficiency. Because M. avium subsp. paratuberculosis can be delivered to the naïve host by milk, it was investigated whether incubation of M. avium subsp. paratuberculosis with milk has an effect on invasion of MDBK cells. M. avium subsp. paratuberculosis exposed to milk entered epithelial cells with greater efficiency than M. avium subsp. paratuberculosis exposed to broth medium or water (P < 0.01). Growth of M. avium subsp. paratuberculosis within MAC-T cells also resulted in augmented ability to subsequently infect bovine MDBK cells (P < 0.001). Microarray analysis of intracellular M. avium subsp. paratuberculosis RNA indicates the increased transcription of genes which might be associated with an invasive phenotype.

Adherent and invasive Escherichia coli are associated with persistent bovine mastitis

Bovine mastitis caused by Escherichia coli has traditionally been viewed as a transient infection. However, E. coli can also cause clonal persistent intramammary infection (IMI) in dairy cows. In this study, we explored the possibility that E. coli strains associated with persistent IMI are better able to adhere to, invade, survive and replicate in cultured mammary epithelial cells (MAC-T) than transient strains, and examined their serotype, overall genotype, phylogenetic group, and the presence of known virulence genes. Both transient and persistent E. coli strains adhered to MAC-T cells, but persistent strains invaded MAC-T cells 2.6-63.5 times more than transient strains. Blocking the adhesin/invasin FimH with mannose diminished but did not eliminate adhesion and invasion of any strain. Cytoskeletal and protein kinase inhibitors cytochalasin D, colchicine, genistein and wortmannin dramatically reduced invasion of MAC-T cells by both strains. All of the persistent strains, but only one transient strain, were able to survive and replicate intracellularly in MAC-T cells over 48 h. Transient and persistent strains displayed heterogeneous serotypes and overall genotypes, but similar phylogeny (group A), and lacked virulence genes of invasive E. coli. We have found that E. coli strains associated with persistent IMI are better able to invade and replicate within cultured mammary epithelial cells than transient strains. The invasion process involves the host cytoskeleton and signaling cascades and is not FimH dependent. Our findings suggest that the invasion of mammary epithelial cells and intracellular survival play an important role in the pathogenesis of persistent E. coli mastitis.

The Mig protein ofStreptococcus dysgalactiaeinhibits bacterial internalization into bovine mammary gland epithelial cells

The role of the Mig protein of Streptococcus dysgalactiae in bacterial adhesion and internalization of bovine mammary gland epithelial cells (MAC-T) was investigated with the wild-type and isogenic mig mutant strains. While there was no difference in adhesion between the strains, the wild-type strain exhibited a significantly lower level of invasion than the mutants. The lower level of internalization of the Mig(+) strain is likely due to Mig-mediated interference with uptake of the microorganisms rather than the host protein binding properties of Mig. Avoidance of intimate interactions with the host cells might be an alternative strategy for S. dysgalactiae to survive and persist in the bovine mammary glands.

Interaction of coagulase-negative Staphylococcus species with bovine mammary epithelial cells

Three coagulase-negative Staphylococcus species (CNS) (Staphylococcus epidermidis, Staphylococcus xylosus and Staphylococcus hyicus), from the milk of cows with mastitis, were used to evaluate adherence to and internalization by bovine mammary epithelial cells, and to investigate involvement of host cell signal transduction and host cell cytoskeleton rearrangement on internalization of CNS. S. xylosus showed highest adherence and internalization values of the species evaluated. Host cell cytoskeleton polymerization and protein kinase (PK) phosphorylation were required for internalization of CNS. Both protein kinase C (PKC) and tyrosine kinase (TPK) pathways were involved, but internalization of S. xylosus occurred preferentially through epidermal growth factor TPK activity. S. epidermidis and S. hyicus seemed to exploit other TPK pathways. Results of this study showed that S. xylosus, S. hyicus and S. epidermidis were able to adhere and internalize bovine mammary cells in a process that appeared to be receptor(s) mediated and exploited host signal transduction and cytoskeleton to induce an uptake signal.

Studies about the mechanism of internalization by mammary epithelial cells of Escherichia coli isolated from persistent bovine mastitis

The purpose of this study was to investigate the interaction between Escherichia coli and primary mammary epithelial cell cultures derived from cows with persistent intramammary infection (IMI). Two strains of E. coli, isolated from the milk of two different cows suffering from persistent E. coli IMI were tested for adhesion to and invasion of three primary mammary epithelial cell cultures derived from mammary biopsies of the two infected cows. Intracellular E. coli were detected during five days post infection in vitro. Both strains of E. coli adhered to and invaded monolayers of all three primary mammary epithelial cell cultures. One strain adhered less but invaded more than the other. Comparison with other mammary pathogens indicated that E. coli invaded the cells less efficiently than Staphylococcus aureus, about as efficiently as Streptococcus dysgalactiae and more efficiently than Streptococcus uberis. The mechanism of E. coli invasion was studied using the cytoskeleton disrupting agents colchicine and cytochalasin D. These compounds inhibited the invasion of E. coli. Invasion of E. coli could also be inhibited by the phosphokinase inhibitors genistein and staurosporin in a dose-dependent fashion. Phorbol-myristyl-acetate (PMA) had no effect on the invasion of E. coli. Histology of mammary tissue revealed chronic inflammatory changes in quarters that were persistently infected by E. coli. Intracellular bacteria were not detected in mammary tissue sections. Polymerase chain reaction (PCR) analysis suggested that the two strains of E. coli lacked genes encoding for bundle-forming pili (bfpA), intimin (eae) and translocated intimin receptor (tir), which are characteristic for enteropathogenic E. coli (EPEC).

Adhesion and invasion of Escherichia coli from single and recurrent clinical cases of bovine mastitis in vitro

Seven strains of Escherichia coli, originating from clinical cases of bovine mastitis, and one Salmonella typhimurium control strain were tested for their ability to adhere to, and invade, bovine mammary epithelial cells (MAC-T cells) in vitro. Four of the seven strains were isolated from cows with chronic intramammary infections with recurrent episodes of clinical mastitis and three strains were isolated from single cases of clinical mastitis. Both adhesion and invasion of all strains were dose and time dependent. The four E. coli strains isolated from recurrent cases of clinical mastitis invaded twice as frequently as and three times faster than the strains isolated from single cases of clinical mastitis. By contrast, there was no difference in the amount or speed of adhesion between the two types of strains of E. coli. Adhesion and invasion curves of E. coli resembled a two-step chain reaction, where invasion was the rate-limiting step. Although adhesion and invasion of E. coli has not been demonstrated in vivo yet, the results of the present study may contribute to an understanding of the pathogenesis of chronic intramammary infections caused by E. coli.

M-like proteins of Streptococcus dysgalactiae

Streptococcus dysgalactiae is one of the most important bacterial species isolated from bovine mastitis. To identify potential virulence factors of this species we prepared chromosomal DNA from strain 8215 and constructed a phage display library. By affinity selection of the library against fibrinogen (Fg), we isolated and characterized a gene, called demA, encoding a protein with the molecular mass of approximately 58 kDa, called DemA, displaying both plasma protein binding properties and sequence similarities with the M and M-like proteins of other streptococcal species. Purified recombinant DemA protein was found to completely inhibit Fg-binding to cells of S. dysgalactiae. A continued sequence analysis revealed that the demA gene was preceded by an open reading frame (dmgA) coding for a putative protein, called DmgA, with high similarities to the Mga proteins of Streptococcus pyogenes. By additional cloning, the corresponding dmgA and demA genes from another strain, called Epi9, were isolated and analyzed. These genes, called dmgB and demB, respectively, revealed a high degree of similarity to the corresponding genes in strain 8215. Increased binding of Fg by cells of strain Epi9, grown in an atmosphere with 10% CO(2), was correlated to an enhanced transcription of the demB gene as shown in a Northern blot. Strain 8215 did not respond to CO(2), which could be explained by a nonfunctional dmgA gene due to insertion of an insertion sequence element. Based on sequence similarities of the described proteins to Mga, M, and M-like proteins and the response to elevated level of CO(2), we suggest that the dmg and dem genes are members of a regulon similar to the described mga regulon in S. pyogenes, which encodes several virulence factors in this species.

Role of fibronectin-binding MSCRAMMs in bacterial adherence and entry into mammalian cells

Most bacterial infections are initiated by the adherence of microorganisms to host tissues. This process involves the interaction of specific bacterial surface structures, called adhesins, with host components. In this review, we discuss a group of microbial adhesins known as Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs) which recognize and bind FN. The interaction of bacteria with FN is believed to contribute significantly to the virulence of a number of microorganisms, including staphylococci and streptococci. Several FN-binding MSCRAMMs of staphylococci and streptococci exhibit a similar structural organization and mechanism of ligand recognition. The ligand-binding domain consists of tandem repeats of a approximately 45 amino acid long unit which bind to the 29-kDa N-terminal region of FN. The binding mechanism is unusual in that the repeat units are unstructured and appear to undergo a conformational change upon ligand binding. Apart from supporting bacterial adherence, FN is also involved in bacterial entry into non-phagocytic mammalian cells. A sandwich model has been proposed in which FN forms a molecular bridge between MSCRAMMs on the bacterial surface and integrins on the host cell. However, the precise mechanism of bacterial invasion and the roles of FN and integrins in this process have yet to be fully elucidated.

Bovine S protein (vitronectin) increases phagocytosis of Streptococcus dysgalactiae

The effects of bovine S protein (vitronectin) on phagocytosis of Streptococcus dysgalactiae strains isolated from cattle with mastitis were investigated. Phagocytized streptococci were determined by a fluorometric microassay using glass adherent polymorphonuclear neutrophils (PMN). Preincubation of S. dysgalactiae with bovine S protein significantly increased their phagocytosis by PMN. Bovine S protein had no effect on phagocytic killing of non-S protein binding S. pyogenes cultures. Enzymatic digestion of the bovine S protein binding sites on S. dysgalactiae with pronase resulted in a significative reduction of the effects of S protein on phagocytosis. It could thus be concluded that in addition to its role as a promoter of cellular adhesion and complement inhibitor, bovine S protein may also influence the phagocytosis of S. dysgalactiae during inflammatory processes.

Characterization of mechanisms involved in uptake of Streptococcus dysgalactiae by bovine mammary epithelial cells

Bovine mammary epithelial cells were pretreated with inhibitors of protein kinase activity, actin polymerization and receptor-mediated endocytosis. In addition, mammary epithelial cells and Streptococcus dysgalactiae were pretreated with inhibitors of protein synthesis. Results showed that activity of tyrosine protein kinases, intact microfilaments and de novo eukaryotic protein synthesis was required for uptake of S. dysgalactiae by bovine mammary epithelial cells; a process that appeared to occur via receptor-mediated endocytosis. In contrast, de novo bacterial protein synthesis was not required for uptake of S. dysgalactiae by MAC-T cells. This study provides insight into bacterial and cellular mechanisms involved in early host-pathogen interactions, putting into perspective the role of mammary epithelial cells in the development and establishment of intramammary infections by S. dysgalactiae.

Factors influencing adherence of Streptococcus dysgalactiae to bovine mammary epithelial cell monolayers

Factors that affected adherence of Streptococcus dysgalactiae to monolayers of primary bovine mammary epithelial cells and to a bovine mammary epithelial transformed cell line were evaluated. Cell culture medium inhibited more than 99% of binding of S. dysgalactiae to plastic and was as effective as several blocking agents in decreasing adventitious adherence of this organism to plastic. Adherence of two strains of S. dysgalactiae (UT516 and UT519) was higher to a transformed mammary epithelial cell line (2.85% and 0.83%, respectively) than to primary bovine mammary epithelial cells (0.45% and 0.52%, respectively). Measurement of the extent of bacterial adherence to cell monolayers showed that adherence was affected by inoculum size. This indicated that the process was mediated by saturable cell receptors and allowed selection of bacteria:epithelial cell ratios not approaching saturating conditions (< 1500:1). In addition, reduction of bacterial adherence by more than 90% following cell fixation indicated that cell surface proteins played a major role in this process. Delineation of bacterial and epithelial cell factors influencing adherence of S. dysgalactiae to mammary epithelial cell monolayers resulted in the development of an in vitro method for quantifying bacterial adherence to cell monolayers.

Potential virulence factors of Streptococcus dysgalactiae associated with bovine mastitis

Mastitis caused by environmental pathogens is a major problem that affects many well-managed dairy herds. Among the environmental pathogens, Streptococcus dysgalactiae is isolated frequently from intramammary infections during lactation and during the nonlactating period. In spite of its high prevalence, little is known about factors that contribute to the virulence of S. dysgalactiae. During the last decade, several cell-associated and extracellular factors of S. dysgalactiae have been identified; yet, the relative importance of these factors in the transmission and pathogenesis of mastitis caused by S. dysgalactiae has not been defined. Streptococcus dysgalactiae can interact with several plasma and extracellular host-derived proteins such as immunoglobulin G, albumin, fibronectin, fibrinogen, collagen, vitronectin, plasminogen, and alpha 2-macroglobulin. These interactions are mediated by bacterial surface proteins. This organism also produces hyaluronidase and fibrinolysin which may be involved in promoting dissemination of the organism into host tissue. Streptococcus dysgalactiae adheres to and is internalized by bovine mammary epithelial cells in vitro. Involvement of host cell kinases, intact microfilaments and de novo eukaryotic protein synthesis are required for internalization of S. dysgalactiae into bovine mammary epithelial cells; a process that appeared to occur by a receptor-mediated endocytosis mechanism. However, de novo bacterial protein synthesis was not required for epithelial cell internalization. Furthermore, S. dysgalactiae survived within mammary epithelial cells for extended periods of time without losing viability or damaging the eukaryotic cell. Further research on characterization of host-pathogen interactions that take place during the early stages of mammary gland infection will enhance our understanding of pathogenesis of intramammary infection which may contribute to development of methods to minimize production losses due to mastitis.

Invasion and persistence of Streptococcus dysgalactiae within bovine mammary epithelial cells

Little is known about bacterial and host factors that contribute to the establishment and persistence of intramammary infection by Streptococcus dysgalactiae. Streptococcus dysgalactiae adheres to epithelial cells from the bovine mammary gland and to extracellular matrix proteins in vitro and invades mammary epithelial cell cultures, all of which can be potentially important pathogenic mechanisms. In this study, mechanisms involved in the invasion of Strep. dysgalactiae into epithelial cells from the bovine mammary gland were characterized. Studies were conducted to determine whether Strep. dysgalactiae invaded mammary epithelial cell cultures in a dose-dependent manner and whether mammary epithelial cells that harbored different numbers of Strep. dysgalactiae for varying times were damaged. Bacterial invasion increased as inoculum size increased; however, the number of intracellular bacteria was not proportional to the inoculum size, increased; however, the number of intracellular bacteria was not proportional to the inoculum size, indicating that a finite number of organisms is capable of invading epithelial cells. No net increase in intracellular organisms was detected at any bacterial density evaluated; however, Strep. dysgalactiae remained viable throughout the evaluation. In addition, Strep. dysgalactiae did not appear to cause cell injury at any bacterial density or time point evaluated. These data suggest that Strep. dysgalactiae can survive within mammary epithelial cells for an extended time without losing viability or damaging the eukaryotic cell. This feature may be associated with the development of persistent infection and protection of organisms from antimicrobial drugs and host defense mechanisms and may provide a route for bacterial colonization of subepithelial tissues.

Eukaryotic and prokaryotic cell functions required for invasion of Staphylococcus aureus into bovine mammary epithelial cells

Eukaryotic and prokaryotic cellular functions required for invasion of Staphylococcus aureus into bovine mammary epithelial cells were investigated. Two strains of S. aureus isolated from milk of cows with clinical mastitis, a primary bovine mammary epithelial cell culture and a bovine mammary epithelial cell line were pretreated with inhibitors of nucleic acid and protein synthesis. In addition, mammary epithelial cells were pretreated with inhibitors of receptor-mediated endocytosis and oxidative phosphorylation. Protein and nucleic acid synthesis in prokaryotic and eukaryotic cells and eukaryotic oxidative phosphorylation were required for invasion of S. aureus into mammary epithelial cells. Inhibition of receptor-mediated endocytosis caused a significant reduction in the number of invading S. aureus. These results suggest that invasion of S. aureus into bovine mammary epithelial cells occurs through a receptor-mediated endocytosis process. Furthermore, eukaryotic oxidative metabolism, protein synthesis and nucleic acid synthesis as well as bacterial protein synthesis are required for bacterial invasion.

Influence of Streptococcus dysgalactiae surface hydrophobicity on adherence to mammary epithelial cells and phagocytosis by mammary macrophages

Bacterial surface hydrophobicity (SH) plays a role in adhesion of bacteria to host surfaces and ingestion by phagocytic cells. Streptococcus dysgalactiae (n = 60) isolated from bovine intramammary infections were examined for expression of SH after growth in Todd-Hewitt broth (THB) and THB supplemented with skim milk, whey, lactose, and casein. Strains were significantly more hydrophobic after growth in THB and THB plus whey and more hydrophilic after growth in THB plus skim milk. Both trypsin and proteinase K abolished SH in three strains tested. Mild pepsin treatment had little effect on SH, while heat treatment at 70 degrees or 80 degrees C abolished SH in two strains tested. A hydrophilic strain of S. dysgalactiae did not adhere as well to bovine mammary epithelial cells as a hydrophobic strain. Trypsin treatment significantly reduced adherence of a hydrophobic strain of S. dysgalactiae to epithelial cells while adherence of a hydrophilic strain remained unaltered. A hydrophilic strain of S. dysgalactiae was significantly more resistant to phagocytosis by bovine mammary gland macrophages than a hydrophobic strain. Differences in expression of SH may play an important role in determining the ability of S. dysgalactiae to establish successfully within the mammary gland.

Staphylococcus aureus invasion of bovine mammary epithelial cells

Staphylococcus aureus is a frequent cause of mastitis in dairy cows. However, pathogenesis of the infection has not been completely defined. We report the invasion of two strains of S. aureus into a bovine mammary epithelial cell line and a bovine mammary epithelial cell primary culture. Invasion of S. aureus into bovine mammary cells was time-dependent. Transmission electron microscopy of bovine mammary cells invaded by S. aureus showed intracellular replication of the bacterium within membrane-bound vacuoles. Invasion was reduced significantly when bovine mammary epithelial cells were treated with inhibitors of F-actin microfilament polymerization but not when these cells were treated with inhibitors of microtubule formation. Results indicated that S. aureus is capable of invading and replicating inside bovine mammary epithelial cells. Data also suggested that S. aureus invasion of bovine mammary epithelial cells requires active participation of specific components of the cytoskeleton of the epithelial cell.