Adhesive proteins of haemagglutinating Staphylococcus aureus isolated from bovine mastitis

Factors involved in the early pathogenesis of bovine Staphylococcus aureus mastitis with emphasis on bacterial adhesion and invasion. A review

Staphylococcus aureus is the most important and prevalent contagious mammary pathogen; it causes clinical and subclinical intramammary infection with serious economic loss and herd management problems in dairy cows. In vitro studies have shown that Staphylococcus aureus adheres to mammary epithelial cells and extracellular matrix components and invades into mammary epithelial as well as other mammary cells. Staphylococcus aureus strains from intramammary infection produce several cell surface-associated and extracellular secretory products. The exact pathogenic roles of most of the products and their effects on adhesion and invasion are not well evaluated. It is also known that mammary epithelial cell-associated molecules and extracellular matrix components interact with S. aureus during the pathogenesis of mastitis, but their roles on adhesion and invasion have not been characterized. The adhesion of S. aureus to epithelial cells may involve non-specific physicochemical interactions and/or specific interactions between bacterial cell-associated ligands and host cell surface receptors. In vitro adhesion depends on the S. aureus strain, the growth phase of the bacteria, the growth medium and the origin of the epithelial cells. Adhesion is hypothesized to be a prerequisite and crucial early step for mammary gland infection. Staphylococcus aureus invades mammary epithelial cells. It also invades other cells such as endothelial cells and fibroblasts. Bacteria are found enclosed in membrane bound vacuoles in the cytoplasm of mammary epithelial cells. Recent observations indicate that S. aureus escapes from the phagosome into the cytoplasm and induces apoptosis. The invasion into mammary epithelial cells may occur through an endocytic process that requires involvement of elements of the cytoskeleton or by direct binding of bacteria to epithelial cells through a process mediated by specific receptors that needs de novo protein synthesis by both cells. Thus, the recurrent subclinical infection may result from this intracellular existence of bacteria that are protected from host defenses and effects of antibiotics. This review emphasizes on recent findings on S. aureus adhesion to mammary epithelial cells and extracellular matrix components and invasion into mammary epithelial cells.

Attachment of Staphylococcus aureus to eukaryotic cells and experimental pitfalls in staphylococcal adherence assays: a critical appraisal

Staphylococcus aureus is a bacterial species with pathogenic potential to both humans and animals. The primary natural niche is said to be the human vestibulum nasi from where bacterial cells may spread to the environment or additional anatomical sites such as the perineum or the hands, where residence is usually transient. Apparently, S. aureus is capable of a precise and balanced interaction with specific types of eukaryotic nasal cells. Although a wide variety of important bacterial ligands and possible eukaryote receptors have been described, the precise mechanisms leading to persistent bacterial colonization and, even more importantly, associated infection have not yet been elucidated in detail. This may be a consequence of the fact that most of the adherence factors have been studied individually in simplified in vitro systems, not taking the complexity of multi-factorial in vivo cell-cell interactions into account. An overall scheme of the initial and sequential interactions leading to S. aureus colonization of eukaryotic cell surfaces has not yet emerged. This review concisely describes the current state of affairs in the multi-disciplinary field of staphylococcal adherence research. Specific emphasis is placed upon the pros and cons of the various artificial, mostly in vitro models employed to study the interaction between bacterial and human or animal cells.

Binding of a surface protein of Staphylococcus aureus to cultured ovine mammary gland epithelial cells

Staphylococcus aureus is the most persistent pathogen causing ovine mastitis. This study investigated S. aureus binding to cultured epithelial cells obtained from the mammary gland. A staphylococcal 145kDa cell wall adhesin, originally isolated from a bovine mastitis strain, was detected in lysostaphin-solubilized ovine mastitis strains and in the encapsulated strain A. This adhesin was able to bind to cultured ovine mammary gland epithelial cells (MGEC) and to a rat intestinal epithelial cell line (RIE-1), exhibiting different electrophoretic mobilities that could be attributable to protein polymorphism. Inhibition assays using antibodies against 145kDa adhesin and against whole bacteria showed the specificity of the binding to cells. The role of this protein in adherence was assessed by adherence inhibition tests carried out in vitro with radiolabeled bacteria and cultured epithelial cells. Preincubation of bacteria with antibodies against adhesin 145kDa or against strain c195 resulted in a statistically significant decrease of adherence. These experiments suggest that adherence of S. aureus to MGEC may be critical for colonization.

Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks

Staphylococcus aureus has long been recognized as an important pathogen in human disease. Due to an increasing number of infections caused by methicillin-resistant S. aureus (MRSA) strains, therapy has become problematic. Therefore, prevention of staphylococcal infections has become more important. Carriage of S. aureus appears to play a key role in the epidemiology and pathogenesis of infection. The ecological niches of S. aureus are the anterior nares. In healthy subjects, over time, three patterns of carriage can be distinguished: about 20% of people are persistent carriers, 60% are intermittent carriers, and approximately 20% almost never carry S. aureus. The molecular basis of the carrier state remains to be elucidated. In patients who repeatedly puncture the skin (e.g., hemodialysis or continuous ambulatory peritoneal dialysis [CAPD] patients and intravenous drug addicts) and patients with human immunodeficiency virus (HIV) infection, increased carriage rates are found. Carriage has been identified as an important risk factor for infection in patients undergoing surgery, those on hemodialysis or CAPD, those with HIV infection and AIDS, those with intravascular devices, and those colonized with MRSA. Elimination of carriage has been found to reduce the infection rates in surgical patients and those on hemodialysis and CAPD. Elimination of carriage appears to be an attractive preventive strategy in patients at risk. Further studies are needed to optimize this strategy and to define the groups at risk.

Influence of age of the donor sheep on the phagocytosis of Staphylococcus aureus subspecies anaerobius and S aureus by neutrophils

The age of the sheep donating neutrophils had a marked influence in vitro on their phagocytic ability with respect to Staphylococcus aureus and S aureus subspecies anaerobius. Neutrophils from lambs five to eight weeks old phagocytosed these organisms significantly less efficiently (P < 0.001) than neutrophils from adults two to four years old. However, neutrophils from the young animals phagocytosed S aureus significantly (P < 0.001) better than S aureus subspecies anaerobius (61.5 v 53.8 per cent), whereas there was no significant difference in the ability of the neutrophils from adult sheep to phagocytose S aureus and S aureus subspecies anaerobius (68.2 v 68.2 per cent).

Genotyping by PCR, of Staphylococcus aureus strains, isolated from mammary glands of cows

A total of 71 Staphylococcus aureus strains isolated from bovine mammary glands were identified and subtyped. The methods used to differentiate between the S. aureus isolates were the DNA polymorphism pattern after amplification with a Polymerase Chain Reaction using several primer combinations and phage typing. The DNA fingerprinting technique using RAPD, ERIC1R and ERIC primers proved to be useful in differentiating isolates of S. aureus. Differentiation of isolates using phage typing gave no additional information compared to the DNA technique. The outbreak of S. aureus in the herd studied was mainly caused by one S. aureus strain. Other strains were only found on three occasions, twice in subclinical infections and once from a case of clinical mastitis. In the latter case the dominant strain was isolated from a different quarter of the same cow. Four of the ten cows studied suffered from clinical mastitis. From those four cows, three remained infected with the same S. aureus strain despite antibiotic treatment.

Inflammation in the bovine teat cistern induced by Staphylococcus aureus

The inflammatory response, characterized by the accumulation of leukocytes, bovine serum albumin and the lysosomal enzyme N-acetyl-beta-D-glucosaminidase, was studied after inoculation of either 5 x 10(5) colony-forming units (CFU) or 2 x 10(2) CFU of the Staphylococcus aureus strain SA 14391 into teat cisterns of dry cows after surgical closure of the passage between the teat and udder cisterns. Teat cistern samples were taken before, and twice daily for 7 days after, inoculation of the bacteria. Infusion of sterile saline constituted a control. Persistent infections occurred in all teats inoculated with the higher dose (5 x 10(5) CFU) of bacteria, and a prominent inflammatory response was elicited. Marked differences were observed in leukocyte migration patterns between different cows, and a cyclic influx of leukocytes was evident. Inoculation of the lower dose (2 x 10(2) CFU) of bacteria did not result in a persistent infection, and only a slight inflammatory response was observed. The results indicate that the bovine teat tissues are capable of mounting a strong local inflammatory response to S. aureus infection. A large number of leukocytes invaded the teat, but, despite their numbers, they were unable to subdue the infection, except when the bacterial count was low.

Hemagglutination by Staphylococcus aureus strains responsible for human bacteremia or bovine mastitis

Although hemagglutination by Staphylococcus aureus has been associated with the pathogenesis of bovine mastitis, this trait has not been characterized with regard to human disease. In this study, the prevalence of hemagglutination in 100 strains of S. aureus responsible for bovine mastitis or human bacteremia, was characterized. Under optimum conditions hemagglutination was noted in 23% of the bovine strains, but only 13% of human strains, leading us to conclude that this trait is not a significant virulence determinant in human systemic infection. Additional studies indicate the hemagglutinin of S. aureus strains responsible for human bacteremia is proteinaceous in character.

Effect of alpha-toxin and capsular exopolysaccharide on the adherence of Staphylococcus aureus to cultured teat, ductal and secretory mammary epithelial cells

Cultures of teat, ductal and secretory epithelial cells were used to study the role of alpha-toxin and the capsular exopolysaccharide on the adherence of Staphylococcus aureus to mammary epithelium. The adherence of S aureus to the cells and their susceptibility to damage by alpha-toxin increased from teat to ductal to secretory cells. Alpha-toxin increased the susceptibility of epithelial cell monolayers to adherence by S aureus, and the extent of the adherence increased with the time of exposure to alpha-toxin. The exopolysaccharide capsule deterred the adherence of S aureus to mammary epithelial cells and to collagen. Organisms with a rigid capsule adhered to a smaller extent than those with a flaccid capsule. Both encapsulated and unencapsulated S aureus adhered more readily to collagen than to either healthy monolayers of epithelial cells or monolayers of cells damaged by alpha-toxin.

Staphylococcus aureus capsule and slime as virulence factors in ruminant mastitis. A review

Staphylococcus aureus is one of the most prevalent causes of ruminant mastitis. The interaction of this microorganism with the host is strongly dependent on its cell surface properties, specially concerning the presence of the exopolysaccharide-containing outer layers (glycocalyx), which appear to play an important role in virulence. In this article, the definition and recognition of the types of exopolysaccharide layers are described, together with their likely role in the pathogenesis of mastitis.

Adherence of Staphylococcus aureus to cultured bovine mammary epithelial cells

Bovine mammary secretory cells, isolated at necropsy, were cultured in vitro and used as a model to study the mode of adherence of Staphylococcus aureus to mammary epithelium. Cultured cells were characterized by their morphology and physiology as secretory epithelial cells. Cells showed characteristic growth patterns when grown on polystyrene, fibronectin, laminin, collagen, and reconstituted basement membrane from the Engelbreth-Holm-Swarm murine sarcoma. Cells cultured on collagen formed confluent monolayers and were the most suitable for bacterial adherence studies. Cultured cells stained intensely for cytokeratin and for specific milk proteins, i.e., alpha-casein, beta-casein, alpha-lactalbumin, beta-lactoglobulin, and lactoferrin. The effect of frozen storage for 10 mo on cell viability or presence of milk proteins was minimal. Staphylococcus aureus showed large affinity for extracellular matrix components, i.e., fibronectin, laminin, and collagen. Adherence to confluent cell monolayers was minimal. In preconfluent cell monolayers, most S. aureus adhered more readily to the exposed matrix than to the epithelial cells. Overnight exposure to staphylococcal alpha-toxin greatly increased adherence of S. aureus to confluent monolayers. However, whether bacteria adhered to alpha-toxin damaged cells or to exposed matrix is not clear. Unencapsulated S. aureus adhered in larger numbers than did encapsulated S. aureus.

Adherence of ruminant mastitis Staphylococcus aureus strains to epithelial cells from ovine mammary gland primary cultures and from a rat intestinal cell line

Staphylococcus aureus isolated from mastitis (14 bovine and 11 ovine strains) exhibited an ability to adhere to epithelial primary cultures from ovine mammary gland and to a rat epithelial cell line, RIE-1. Strain differences in the degree of adherence were observed in both cases. These differences were maintained when comparing different epithelial sources (rat vs. ovine). RIE-1 cells can thus be used as a model for studying staphylococcal adherence to epithelial cells. Changes in bacterial adherence were observed according to the bacterial growth phase. The magnitude of these changes differed among strains. Bacterial cell surface hydrophobicity was not related to the degree of adherence to mammalian epithelial cells.

Staphylococcus saprophyticus hemagglutinin is a 160-kilodalton surface polypeptide

Many strains of Staphylococcus saprophyticus cause direct hemagglutination of sheep erythrocytes. For a high proportion of clinical isolates, a surface protein (Ssp) that is apparently not involved in this property has been described. In this study, S. saprophyticus CCM883, a hemagglutinating but Ssp-negative strain, was used for the identification, purification, and characterization of a 160-kDa surface polypeptide that appears to be the major component of the hemagglutinin. Expression of the protein required the addition to the growth medium of EDTA in micromolar quantities, suggesting an inhibitory role for some unidentified metal ion. The protein was purified by means of Sephacryl S-300 chromatography, and antisera were raised in rabbits. Antibody against this protein inhibited the hemagglutination of two other, unrelated strains and was used to demonstrate, by electron microscopy, the presence of the protein on the surface of the cells. In a confirmatory experiment, the purified antigen was incubated with erythrocytes and binding was detected by the Western immunoblot technique with the antibody to the 160-kDa polypeptide. These experiments indicate that this surface protein is the hemagglutinin of S. saprophyticus.

Potential for vaccination against infections caused by Staphylococcus aureus

Surface polysaccharides and proteins from S. aureus which could serve as components of a future subunit vaccine against staphylococcal disease in man and animals have recently been characterized. The majority of bovine mastitis and human clinical isolates of S. aureus produce a thin polysaccharide capsule which probably impairs phagocytosis. Protective immunity to S. aureus infections in laboratory animals has been induced by immunization with polysaccharide, and immune serum promotes phagocytosis of bacteria in vitro. S. aureus expresses several surface-exposed proteins that bind host plasma proteins to the bacterial cell or promote adherence of bacteria to host cells or to tissues. These activities may help bacteria avoid host defences and stimulate adherence and colonization to form foci of infection. In this article the properties of S. aureus surface polysaccharides and proteins are reviewed. Their contribution to virulence and the possibility that they could be used as components of new vaccine to combat mastitis in ruminants and nosocomial infections is discussed.