Isolation of type 5 capsular polysaccharide from Staphylococcus aureus

Pathogenicity and virulence of Staphylococcus aureus

Staphylococcus aureus is one of the most frequent worldwide causes of morbidity and mortality due to an infectious agent. This pathogen can cause a wide variety of diseases, ranging from moderately severe skin infections to fatal pneumonia and sepsis. Treatment of S. aureus infections is complicated by antibiotic resistance and a working vaccine is not available. There has been ongoing and increasing interest in the extraordinarily high number of toxins and other virulence determinants that S. aureus produces and how they impact disease. In this review, we will give an overview of how S. aureus initiates and maintains infection and discuss the main determinants involved. A more in-depth understanding of the function and contribution of S. aureus virulence determinants to S. aureus infection will enable us to develop anti-virulence strategies to counteract the lack of an anti-S. aureus vaccine and the ever-increasing shortage of working antibiotics against this important pathogen.

Staphylococcus aureuscapsular polysaccharides: a structural and synthetic perspective

This review surveys known structures of staphylococcal polysaccharides and summarizes all synthetic efforts to obtain these sequences.

Absence of Protein A Expression Is Associated With Higher Capsule Production in Staphylococcal Isolates

Staphylococcus aureus is a major human pathogen, and a leading cause of soft tissue and blood stream infections. One of the causes of its success as a pathogen is the peculiar array of immune evasion factors through which the bacterium avoids host defenses, where the staphylococcal protein A (SpA) plays a major role thanks to its IgG binding activities. Moreover, SpA has recently been proposed as a promising vaccine antigen. In this study, we evaluated the expression of SpA in a collection of staphylococcal strains, about 7% of which did not express SpA (SpA^- strains), despite the presence of the gene. By a comparative genomic analysis, we identified that a mutation in the spa 5′ UTR sequence affecting the RBS is responsible for the loss of SpA in a subset of SpA^- strains. Using a high-throughput qRT-PCR approach on a selected panel of virulence-related genes, we identified that the SpA^- phenotype is associated with lower spa transcript levels and increased expression and production of capsule as well as other changes in the transcription of several key virulence factors. Our data suggest that the SpA^- phenotype has occurred in geographically distinct strains through different molecular mechanisms including both mutation, leading likely to translation alterations, and transcriptional deregulation. Furthermore, we provide evidence that SpA^- strains are highly susceptible to phagocytic uptake mediated by anti-capsule antibodies. These data suggest that S. aureus may alter its virulence factor expression pattern as an adaptation to the host or environment. Vaccination strategies targeting both SpA and capsule could therefore result in broader coverage against staphylococcal isolates than SpA alone.

Immune response of heifers against a Staphylococcus aureus CP5 whole cell vaccine formulated with ISCOMATRIX™ adjuvant

The shortcomings of Staphylococcus aureus vaccines to control bovine mastitis have been attributed to insufficient capacity of the vaccines to induce opsonizing antibodies and to stimulate cellular immune responses. Types of antigen, administration route and adjuvant used in a vaccine formulation have been identified as critical factors for the development of opsonic antibodies. Current commercially available vaccines for Staph. aureus bovine mastitis control are formulated with Al(OH)3 and oil-based adjuvants. The aim of this study was to evaluate the immune response of heifers immunized with a Staph. aureus CP5 whole cell vaccine formulated either with Al(OH)3 or ISCOMATRIX™. Twenty primigravid Holstein dairy heifers in the last trimester of gestation were immunized either with a vaccine formulated with ISCOMATRIX™ (n = 6), Al(OH)3 (n = 7), or saline solution (placebo) (n = 7). Immunization was carried out 38 and 10 d before calving. Heifers vaccinated with Staph. aureus adjuvanted with ISCOMATRIX™ responded with significantly higher levels of anti-bacterin and anti-CP5 IgG and IgG2 in sera than animals in the Al(OH)3 or control groups. Animals in the ISCOMATRIX™ group responded with significantly higher anti-bacterin specific IgG in whey than animals in the Al(OH)3 and control groups, detected from the first week post calving until 60 d of lactation. Sera from animals inoculated with Staph. aureus in ISCOMATRIX™, obtained 7 d post partum, significantly increased both the number of neutrophils ingesting bacteria and the number of bacteria being ingested by the neutrophils, compared with sera obtained from heifers vaccinated with Al(OH)3 or non-vaccinated controls. These features coupled to safety of the ISCOMATRIX™ formulation, warrant additional studies.

Campylobacter jejuni cocultured with epithelial cells reduces surface capsular polysaccharide expression

The host cell environment can alter bacterial pathogenicity. We employed a combination of cellular and molecular techniques to study the expression of Campylobacter jejuni polysaccharides cocultured with HCT-8 epithelial cells. After two passages, the amount of membrane-bound high-molecular-weight polysaccharide was considerably reduced. Microarray profiling confirmed significant downregulation of capsular polysaccharide (CPS) locus genes. Experiments using conditioned media showed that sugar depletion occurred only when the bacterial and epithelial cells were cocultured. CPS depletion occurred when C. jejuni organisms were exposed to conditioned media from a different C. jejuni strain but not when exposed to conditioned media from other bacterial species. Proteinase K or heat treatment of conditioned media under coculture conditions abrogated the effect on the sugars, as did formaldehyde fixation and cycloheximide treatment of host cells or chloramphenicol treatment of the bacteria. However, sugar depletion was not affected in flagellar export (fliQ) and quorum-sensing (luxS) gene mutants. Passaged C. jejuni showed reduced invasiveness and increased serum sensitivity in vitro. C. jejuni alters its surface polysaccharides when cocultured with epithelial cells, suggesting the existence of a cross talk mechanism that modulates CPS expression during infection.

Development of StaphVAX™, a polysaccharide conjugate vaccine against S. aureus infection: from the lab bench to phase III clinical trials

Staphylococcus aureus is the most common nosocomial pathogen and is responsible for approximately one-third of hospital-acquired bacteremias. The emergence of strains with multidrug resistance, including resistance to vancomycin, the antibiotic of last resort, presents the medical community with a major public health problem. Alternative therapies, including immunotherapy, have been in development for several decades. The discovery of S. aureus capsular polysaccharides from clinical isolates, and their importance to pathogenicity via antiphagocytic activity, opened a new window of opportunity for development of vaccines and immunotherapy against this pathogen. A conjugate vaccine, StaphVAX that includes the two most prevalent capsular polysaccharides, types 5 and 8, coupled to a carrier protein efficient in promoting a Th2 response, was developed. In a recent phase III clinical study in hemodialysis patients, StaphVAX was shown to prevent S. aureus bacteremia for up to 10 months following a single immunization. The history, epidemiology, serology, and development of StaphVAX, including preclinical and clinical studies demonstrating efficacy are described in this review.

Staphylococcus aureus capsular polysaccharides

Serotype 5 and 8 capsular polysaccharides predominate among clinical isolates of Staphylococcus aureus. The results of experiments in animal models of infection have revealed that staphylococcal capsules are important in the pathogenesis of S. aureus infections. The capsule enhances staphylococcal virulence by impeding phagocytosis, resulting in bacterial persistence in the bloodstream of infected hosts. S. aureus capsules also promote abscess formation in rats. Although the capsule has been shown to modulate S. aureus adherence to endothelial surfaces in vitro, animal studies suggest that it also promotes bacterial colonization and persistence on mucosal surfaces. S. aureus capsular antigens are surface associated, limited in antigenic specificity, and highly conserved among clinical isolates. With the emergence of vancomycin-resistant S. aureus in the United States in 2002, new strategies are needed to combat staphylococcal infections. Purified serotype 5 and 8 capsular polysaccharides offer promise as target antigens for a vaccine to prevent staphylococcal infections, although the inclusion of other antigens is likely to be essential in the development of an effective S. aureus vaccine. The genetics and mechanisms of capsule biosynthesis are complex, and much work remains to enhance our understanding of capsule biosynthesis and its regulation.

Evaluation of seven different enzyme-linked immunosorbent assays for serodiagnosis of Staphylococcus aureus bacteremia

OBJECTIVE

Serologic assays for Staphylococcus aureus antibodies were evaluated regarding their ability to differentiate between uncomplicated and complicated S. aureus bacteremia, between S. aureus and non-S. aureus bacteremia, and between S. aureus and non-S. aureus endocarditis.

METHODS

Enzyme-linked immunosorbent assays (ELISAs) were performed to measure Ig G antibodies against seven S. aureus antigens (peptidoglycan, teichoic acid, S. aureus ultrasonicate, whole S. aureus cells, alpha-toxin, lipase and capsular polysaccharide) in 129 patients with S. aureus bacteremia (including 51 with endocarditis), 78 patients with non-S. aureus bacteremia (including 27 with endocarditis) and 100 febrile non-bacteremic controls.

RESULTS

Whole-cell ELISA was the most sensitive assay. The specificity of all assays was low. Two different combinations of ELISAs for whole cells, teichoic acid,alpha-toxin, lipase and capsular polysaccharide did distinguish between S. aureus and non-S. aureus endocarditis, but not between uncomplicated and complicated S. aureus bacteremia.

Staphylococcus aureus capsular polysaccharide type 5 conjugate and whole cell vaccines stimulate antibody responses in cattle

Dairy heifers were immunized subcutaneously with one of four different vaccines which contained preparations of Staphylococcus aureus capsular polysaccharide type 5 (CP5) and a mineral oil adjuvant, or received a placebo containing saline and adjuvant. The vaccine containing a CP5-human serum albumin conjugate (CP5-HSA) and the vaccine with formaldehyde inactivated whole cells expressing CP5, both elicited strong anti-CP5 antibody responses. After two injections three weeks apart and a third injection 10 months later, the mean level and duration of the anti-CP5 antibody response was significantly higher in the whole cell group. No differences were found between the two groups with regard to the relative proportion of IgG subclasses, and the antibody responses to the polysaccharide were composed of both the IgG1 and IgG2. Vaccines containing only free CP5 or CP5 mixed with HSA produced weak and transient humoral immune responses. Only animals vaccinated with the whole cell vaccine or the conjugate vaccine showed responses to CP5 in a lymphocyte proliferation assay conducted one year after the third vaccination. This study indicates that CP5 expressed on the surface of formaldehyde inactivated whole cells, emulsified in an oil adjuvant, gives a strong and long lasting immune response in cattle. The use of conjugation technology, although effective, might not be necessary in order to achieve an immune response against S. aureus CP5 in cattle.

Immunopotentiation of Staphylococcus aureus type 5 capsular polysaccharide co-entrapped in liposomes with alpha-toxin

Immunopotentiation of Staphylococcus aureus type 5 capsular polysaccharide (CP5) by use of liposomes as an alternative to protein-polysaccharide conjugates was investigated. Mice were immunized twice with cationic liposomes containing CP5 alone or CP5 co-entrapped with alpha-toxin or heat-detoxified alpha-toxin. Immunogenicity of these different antigens was compared with CP5-alpha-toxin conjugates. Antibodies against CP5 were elicited in mice immunized with conjugates or liposomes containing co-entrapped CP5 and alpha-toxin. Liposomes containing CP5 alone or co-entrapped CP5 and alpha-toxoid failed to induce antibodies against CP5. All the preparations entailed an antibody response against alpha-toxin and highest antibody and neutralizing activity titers were obtained with liposomes. These results show that liposomes can be used to immunopotentiate CP5, however, a co-incorporated protein able to insert lipids bilayers is probably required.

Effect of slime on adherence of Staphylococcus aureus isolated from bovine and ovine mastitis

The interactions between slime, Staphylococcus aureus and ovine mammary gland epithelial cells (MGEC) were studied in vitro. Suspensions of radiolabelled bacteria incubated with slime significantly increased the ability of S. aureus strains to adhere to a filter. When suspensions of radiolabelled bacteria were incubated with MGEC treated with trypsin, the ability of slime to improve S. aureus adherence was also shown, indicating that it was not dependent on cell membrane proteins. The interaction of radiolabelled bacteria with slime prior to the adherence test with MGEC demonstrated that the adherence process requires the interaction between slime and bacteria. This interaction is inhibited by anti-slime antibodies. This study provides evidence that a specific interaction between bacteria coated with slime and MGEC could be a critical part of mammary gland infection.

Antigenic determinants of Staphylococcus aureus type 5 and type 8 capsular polysaccharide vaccines

Bacterial capsular polysaccharides (CP) are carbohydrate polymers comprised of repeating saccharide units. Several of these CP have side chains attached to their backbone structures. The side chains may include O-acetyl, phosphate, sialic acid, and other moieties. Those moieties represent the immunodominant epitopes and the most functional ones. The clinically significant Staphylococcus aureus type 5 CP (CP 5) and type 8 CP (CP 8) are comprised of a trisaccharide repeat unit with one O-acetyl group attached to each repeat unit. The immunogenicity of these CP and the functionality of antibodies to the backbone and the O-acetyl moieties were investigated. Immunization with the native CP conjugates (CP with 75% O-acetylation) elicited a high proportion of antibodies directed against the O-acetyl moiety. Nonetheless, all of the vaccinees produced antibodies to the backbone moieties as well. Conjugate vaccines made of de-O-acetylated CP elicited backbone antibodies only. Antibodies to both backbone and O-acetyl groups were found to be opsonic against S. aureus strains which varied in their O-acetyl content. Absorption studies with O-acetylated and de-O-acetylated CP showed that (i) native CP conjugates generated antibodies to both backbone and O-acetyl groups and (ii) O-acetylated isolates were opsonized by both populations of antibodies while the non-O-acetylated strains were predominantly opsonized by the backbone antibodies. These results suggest that S. aureus CP conjugate vaccines elicit multiple populations of antibodies with diverse specificities. Moreover, the antibodies of different specificities (backbone or O-acetyl) are all functional and efficient against the variations in bacterial CP that may occur among clinically significant S. aureus pathogenic isolates.

Identification of a gene essential for O-acetylation of the Staphylococcus aureus type 5 capsular polysaccharide

The Staphylococcus aureus serotype 5 capsular polysaccharide (CP5) has a trisaccharide repeating unit of (-->4)-3-O-Ac-beta-D-ManNAcAp-(1-->4)-alpha-L-FucNAcp-(1-->3 )-beta-D-FucNAcp-(1-->). Tn918 mutagenesis of strain Reynolds yielded a mutant that produced wild-type levels of O-deacetylated CP5. The site and orientation of the single transposon insertion in mutant JL232 were determined by analysis of Southern blots and amplification of DNA flanking the transposon. DNA sequencing revealed that Tn918 was inserted within an open reading frame of 627 bp. The predicted amino acid sequence encodes a protein of approximately 26 kDa with homology to members of the NodL-LacA-CysE family of bacterial acetyltransferases. Southern blot analysis showed that genes similar to cap5H were present only in strains of S. aureus belonging to capsular serotypes 2, 4 and 5. In an in vitro assay, the parental strain was more resistant to opsonophagocytic killing than the mutant strain. In a mouse model of staphylococcal infection, the parental strain was able to seed the bloodstream from the peritoneal cavity and colonize the kidneys more efficiently than the O-deacetylated mutant. When cap5H was provided to the mutant in trans, it fully restored CP5 O-acetylation. The virulence of the complemented mutant strain closely approximated that of the parental strain.

A Staphylococcus aureus capsular polysaccharide (CP) vaccine and CP-specific antibodies protect mice against bacterial challenge

The efficacy of capsular polysaccharide (CP)-specific antibodies elicited by active immunization with vaccines composed of Staphylococcus aureus types 5 and 8 CP linked to Pseudomonas aeruginosa exoprotein A or with immune immunoglobulin G (I-IgG) obtained from vaccinated plasma donors was tested in lethal and sublethal bacterial mouse challenge models. A dose of 2 x 10(5) CFU of S. aureus type 5 CP per mouse administered intraperitoneally (i.p.) with 5% hog mucin was found to cause 80 to 100% mortality in BALB/c mice within 2 to 5 days. Mice passively immunized i.p. 24 h earlier or subcutaneously 48 h earlier with 0.5 ml of I-IgG showed significantly higher average survival rates than animals receiving standard IgG or saline (P < 0.01) following the bacterial challenge. Animals actively immunized with the monovalent type 5 CP-P. aeruginosa exoprotein A conjugate showed a survival rate of 73% compared with 13% in phosphate-buffered saline-immunized animals. The prechallenge geometric mean titer of type 5 CP antibodies in animals that died was significantly (P < 0.05) lower than that of animals which survived the challenge (95.7 versus 223.6 micrograms/ml, respectively). The IgG was further evaluated in mice challenged i.p. with a sublethal dose of 5 x 10(4) CFU per mouse. Serial blood counts were performed on surviving animals at 6, 12, 24, and 48 h. Surviving animals were sacrificed at 72 h, and bacterial counts were performed on their kidneys, livers, and peritoneal lavage fluids. Animals receiving I-IgG had lower bacterial counts in blood samples and lower bacterial densities in kidneys, livers, and peritoneal lavage samples than mice immunized with standard IgG (P < 0.05). These data suggest that S. aureus type 5 CP antibodies induced by active immunization or administered by passive immunization confer protection against S. aureus infections.

Effects of culture conditions on production of type 5 capsular polysaccharide by human and bovine Staphylococcus aureus strains

Two Staphylococcus aureus strains, the prototype human Reynolds strain and a bovine isolate, were grown in different complex media and in a synthetic medium (D. Taylor and K. T. Holland, J. Appl. Bacteriol. 66:319-329, 1989) and compared for their ability to produce type 5 capsular polysaccharide. Cell-bound and cell-free type 5 capsular polysaccharide were measured by a new one-step competition enzyme-linked immunosorbent assay. The total production and the proportion of cell-bound type 5 capsular polysaccharide were dependent on the nature of the medium, the duration of the culture, and the strain. Both strains produced more type 5 capsular polysaccharide when cultivated in the synthetic medium than when cultivated in complex media. The best yield of type 5 capsular polysaccharide, about 300 micrograms/ml of medium, was obtained with strain Reynolds grown for 48 h with shaking in the synthetic broth containing glucose as a carbon source.

The capsular turnover product of Staphylococcus aureus strain Smith

The capsular polysaccharide released from the bacterial surface by cell wall turnover during growth exhibited less size heterogeneity and a higher average molecular mass than the polysaccharide extracted from the cell by treatment with lysostaphin or low pH. Treatment of turnover polysaccharide, radiolabelled by growth of the bacteria in the presence of N-acetyl-[3H]-glucosamine, with muramidase B from Chalaropsis released a low molecular weight product chromatographically identical to the peptidoglycan degradation products released from the peptidoglycan-teichoic acid complex by the same treatment. It is concluded that some or all of the capsular polysaccharide released into the culture fluid during growth is derived from peptidoglycan-linked capsular material, solubilised by cell wall turnover.

Immunogenicity in cows of Staphylococcus aureus type 5 capsular polysaccharide-ovalbumin conjugate

Six dairy cows were immunized subcutaneously with purified type 5 capsular polysaccharide (CP5) of Staphylococcus aureus or CP5-ovalbumin conjugate in Freund's incomplete adjuvant. The CP5 antibodies elicited were measured in sera and analysed with regard to isotypes by enzyme-linked immunosorbent assay. At the doses tested, the purified CP5 did not induce a humoral response in the cows. Immunization of two cows with the CP5-ovalbumin conjugate elicited a CP5 antibody response mainly of the IgG2 isotype, which culminated 4 weeks later. A second injection of conjugate, 3 months after the first one, resulted in a rapid and durable anti-CP5 response without exceeding the first antibody peak value. Intramammary infusion of purified CP5 failed to provoke an inflammatory response in the milk of the immunized cows. In contrast, a marked recruitment of cells was recorded in the milk of the sensitized cows after intramammary infusion of ovalbumin. These results demonstrate that injection of CP5-protein carrier conjugate in cows entails both antibody response against CP5 and carrier-specific recruitment of cells in milk of immunized animals.

Use of liposome-immunopotentiated exopolysaccharide as a component of an ovine mastitis staphylococcal vaccine

Experiments on the development of a vaccine against staphylococcal mastitis were carried out in ewes. The vaccine (Spanish patent no. 9200223) has the following components: (i) inactivated (formalinized) bacteria (Staphylococcus aureus and a coagulase-negative staphylococcal species. Staphylococcus simulans) and S. aureus toxoid in presence of an adjuvant (dextran sulfate, Mw 500,000); and (ii) S. aureus exopolysaccharide included within liposomes. High serum antibody titres were obtained against whole cells from Staphylococcus aureus, Staphylococcus simulans, Staphylococcus hyicus and Staphylococcus epidermidis strains. However, there was no response to cells from Staphylococcus warneri and Staphylococcus chromogenes strains. An immune response (serum IgG) against the inoculated exopolysaccharide was obtained when > or = 20 micrograms of exopolysaccharide were included in liposomes and when > or = 20 mg of exopolysaccharide were adjuvanted with dextran sulfate instead of liposomes. For experimental infection assays, ewes were vaccinated during pregnancy and challenged either with a low virulence S. simulans strain or with a highly virulent S. aureus strain. In these assays, the incidence of S. simulans subclinical mastitis and of S. aureus acute mastitis was significantly lower in vaccinated animals than in unvaccinated controls. Specifically, on challenge with S. simulans, two out of 14 glands became infected among the vaccinated animals and nine out of ten glands in the unvaccinated group (p < 0.001). On challenge with S. aureus, no protection was detected when component (ii) was omitted from the vaccine; nine out of ten animals developed mastitis (two mild, two moderate and five severe).(ABSTRACT TRUNCATED AT 250 WORDS)

Phase variation of slime production in Staphylococcus aureus: implications in colonization and virulence

Two methods commonly used for slime detection in coagulase-negative staphylococci (tube biofilm formation and colony morphology in Congo red agar) were used to study 144 ruminant mastitis Staphylococcus aureus strains. Slime production was detected in 21 strains. A majority of cells (85%) in slime-producing (SP) strains and a minority of cells (5%) in non-slime-producing (NSP) strains showed a condensed exopolysaccharide matrix (slime) surrounding the bacterial cell wall, as revealed by electron microscopy and immunofluorescence. In vivo slime production was also detected immunohistochemically after experimental infection of the mammary gland in sheep. Upon repeated subcultures in Congo red agar, NSP variants were obtained from four ovine and four bovine SP strains at a frequency ranging from 0.5 x 10(-4) to 10(-4). Because SP variants could not be obtained from NSP strains within this range or at a higher frequency, they were obtained by the tube biofilm formation (requiring repeated subculturing of NSP strains in tryptic soy broth containing 2% glucose for subsequent recovery of colonies adherent to the walls of the culture tubes). In experimental challenge, the SP variant showed a significantly higher colonization capacity than did the NSP variant of the same strain used (P < 0.001). However, the NSP variant had a higher virulence than did the SP variant (P < 0.001). These results may help to explain the different roles of S. aureus slime production cell types (SP and NSP) coexisting in disease.

Effects of in vitro and in vivo growth conditions on expression of type 8 capsular polysaccharide by Staphylococcus aureus

Type 8 capsular polysaccharide (CP8) is widely prevalent among clinical isolates of Staphylococcus aureus, but the role that the capsule plays in the pathogenesis of staphylococcal infections is unclear. This study was performed to identify growth conditions that would optimize the production of CP8 and to determine whether enhanced CP8 expression would influence staphylococcal virulence. S. aureus Becker grown in a chemically defined broth medium with < 1 microM ferric nitrate produced up to eightfold more CP8 per milligram of biomass than did bacteria cultivated in the same medium containing 20 microM ferric nitrate. The bacteria produced > 350-fold more cell-associated CP8 per milligram of biomass when grown on the surface of Columbia agar than when grown in Columbia broth. Most of the CP8 produced by broth-grown cells was secreted into the culture medium. S. aureus cultivated on the surface of nitrocellulose membranes floating on Columbia broth produced levels of CP8 similar to those produced by cells grown on Columbia agar. Similarly, bacteria harvested from endocardial vegetations of rabbits infected with S. aureus produced high levels of CP8. These results indicate that staphylococci grown on surfaces, both in vitro and in vivo, produce larger quantities of cell-associated CP8 than those grown in liquid cultures. However, no differences were observed in the 50% lethal dose for mice of strain Becker grown on solid medium (high levels of capsule expression) or in liquid medium (low levels of capsule expression).

Typing of Staphylococcus aureus by pulsed-field gel electrophoresis, zymotyping, capsular typing, and phage typing: resolution of clonal relationships

Sixty-nine Staphylococcus aureus isolates from two epidemiologically unrelated sources were typed by pulsed-field gel electrophoresis after SmaI digestion of chromosomal DNA (genome typing), and the results were compared with those obtained by other typing methods: phage typing with the international set of phages, capsular serotyping with monoclonal antibodies against capsular polysaccharides type 5 and 8, and zymotyping by polyacrylamide agarose electrophoresis for esterase polymorphism. A good correlation of S. aureus types was found by these four typing methods. Differentiation increased in the order capsular typing < zymotyping < phage typing < genome typing, yielding 2, 10, 20, and 26 different S. aureus types, respectively. Five of the 26 genome types were further divided into several subtypes revealing clonal relationships. When 36 French S. aureus isolates were compared with 33 German S. aureus isolates, 3 strains representing clonal populations were identical in both groups. S. aureus isolates from patients with cystic fibrosis were also typed at the beginning and the end of a 4-week summer camp for these patients. The results suggested a possible strain transmission during the summer camp. We conclude that genome typing by pulsed-field gel electrophoresis is a powerful tool not only for strain identification but also for the resolution of the clonal relationships of S. aureus strains.

Type 5 and 8 capsular polysaccharides are expressed by Staphylococcus aureus isolates from rabbits, poultry, pigs, and horses

A total of 103 Staphylococcus aureus isolates from rabbits (n = 37), poultry (n = 33), pigs (n = 27), and horses (n = 6) and 14 Staphylococcus intermedius isolates from wild animals were serotyped for capsular polysaccharide types 5 and 8 by an enzyme-linked immunosorbent assay using polyclonal rabbit antibodies. About 98% of the S. aureus isolates were typeable. Type 5 was predominant in the poultry (75.8%) and pig (66.7%) isolates, whereas type 8 was more frequent among the isolates from rabbits (59.5%) and horses (83.3%). By contrast, none of the 14 S. intermedius isolates was typeable.

Cloning of genes affecting capsule expression in Staphylococcus aureus strain M

Staphylococcus aureus strain M produces large amounts of capsular polysaccharide. It produces a non-encapsulated variant at a frequency of 0.01% at 37 degrees C. At high temperature (43 degrees C), the frequency of capsule loss was shown to be 1-38%. A 19 kb plasmid and a prophage were found to be carried by the M strain, but curing of these elements did not affect capsular production. To clone the capsular (cap) genes, a plasmid library of S. aureus M was constructed directly in S. aureus RN4200. The library was then infected with phage 80 alpha. After transduction of the phage lysates to a Cap- mutant derived from M strain, a recombinant plasmid was obtained which complemented the mutant to a Cap+ phenotype. Chromosomal walking experiments were used to clone additional nearby cap genes. Complementation tests using a collection of Cap- mutants showed that most of the mutants were complemented by a 19.4 kb DNA fragment, suggesting that the majority of the cap genes affecting capsule production are clustered together.

Comparison between lactoferrin and subepithelial matrix protein binding in Staphylococcus aureus associated with bovine mastitis

Staphylococcus aureus strains (n = 100) isolated from bovine mastitis were classified according to the presence of capsular polysaccharide serotype 5 (n = 46), type 8 (n = 26), and non-5/8 (n = 28). Strains from each type were tested for protein interaction in a 125I-labeled ligand binding assay. A majority of type 5 and type 8 strains showed a higher degree of binding to lactoferrin, fibronectin, and IgG than the non-5/8 strains. Fibrinogen binding was low in all serotypes. Most of the type 5 and non-5/8 strains bound less than 10% laminin, whereas type 8 strains bound laminin in the 11 to 20% range. Non-5/8 strains significantly differed from type 5 in lactoferrin, fibronectin, fibrinogen, and IgG and also from type 8 in fibrinogen and IgG binding. The differences in protein binding between type 5 and type 8 were nonsignificant. The degree of lactoferrin binding in all types positively correlated with laminin binding. Lactoferrin and fibrinogen bindings were correlated in type 5 and type 8 strains. Lactoferrin and fibronectin bindings were correlated only in type 5 strains. These data suggest that bovine lactoferrin binding is common and associated with subepithelial matrix protein interactions in certain serotypes of S. aureus.

Virulence of Staphylococcus aureus mutants altered in type 5 capsule production

Most clinical isolates of Staphylococcus aureus produce microcapsules (uronic acid-containing extracellular polysaccharides) that are detectable by serologic methods but are not visible by negative staining. Among the 11 reported serotypes, capsule types 5 and 8 comprise approximately 75% of all isolates. Transposon mutagenesis was performed on S. aureus to create mutants altered in capsule expression. Tn918 was introduced into the capsule type 5 strain Reynolds by filter mating, and a capsule-deficient transconjugate, JL236, was isolated. The wild-type strain was transformed with JL236 chromosomal DNA to confirm that transfer of the appropriate-size chromosomal fragment containing Tn918 generated a capsule-deficient transformant. Strain Reynolds was mutagenized with ethyl methanesulfonate to obtain a capsule-negative mutant (strain JL240). Capsular phenotypes were determined by colony immunoblots, antibody adsorption experiments, and transmission electron microscopy. The virulences of the parental and mutant strains in mice were compared. The 50% lethal doses for strains Reynolds, JL236, and JL240 were similar (10(8.59), 10(8.98), and 10(8.93) CFU, respectively). Animals injected intraperitoneally with either wild-type or mutant strains had comparable levels of bacteremia at 3 and 24 h after challenge. Quantitative cultures of blood and kidneys from animals challenged intravenously with sublethal doses of the S. aureus strains also showed no differences in bacterial clearance or renal abscess formation. These studies indicate that the type 5 S. aureus microcapsule does not promote bacterial virulence in the animal models tested.

Staphylococcus aureus growth and type 5 capsular polysaccharide production in synthetic media

The production of type 5 capsular polysaccharide by Staphylococcus aureus in synthetic media was investigated. The influence of medium components on capsular polysaccharide synthesis appeared to relate to the presence or absence of the component rather than to concentration gradient. The production of type 5 capsular polysaccharide was linked to energy availability and energy source, but not to carbohydrate concentration or carbon/nitrogen ratio. Regulation of capsular polysaccharide production by S. aureus in response to medium changes would appear to differ from that typically displayed in other organisms that produce polysaccharides.

Phagocytosis of mastitis isolates of Staphylococcus aureus and expression of type 5 capsular polysaccharide are influenced by growth in the presence of milk

Phagocytosis by bovine polymorphonuclear granulocytes of seven capsular polysaccharide type 5 Staphylococcus aureus strains isolated from mastitis [corrected] was investigated by means of luminol-dependent chemiluminescence. Bacteria were grown on four different agar media (brain heart infusion, Columbia broth, modified staphylococcus medium 110, and skim milk) and were opsonized by normal bovine serum. When compared to growth on brain heart infusion agar, Columbia agar, and modified staphylococcus medium 110 agar, growth on skim milk agar rendered five of the strains more resistant to opsonization. The other two strains were resistant in all culture media used. Short periods of incubation in milk after growth on brain heart infusion agar did not augment resistance to phagocytosis, indicating that mere adsorption of milk components on bacteria was not responsible. The variability of the chemiluminescence response of polymorphonuclear leukocytes was pronounced among strains with each growth medium except milk. Growth on modified staphylococcus medium 110 and on milk agar favored the masking of teichoic acid, as shown by inagglutinability with rabbit antiserum. Interestingly, agglutination by a monoclonal antibody to capsular polysaccharide type 5 was optimal when bacteria were grown on skim milk agar. This suggests that capsular polysaccharide participated in the masking effect. These findings indicate that masking of the bacterial target of most of the naturally acquired opsonins present in normal bovine serum occurred when bacteria grew in the presence of milk, resulting in an increased resistance to phagocytosis by polymorphonuclear leukocytes.

Synthesis and immunologic properties in mice of vaccines composed of Staphylococcus aureus type 5 and type 8 capsular polysaccharides conjugated to Pseudomonas aeruginosa exotoxin A

Epidemiological, serological and in vitro phagocytosis experiments provide evidence that the newly discovered type 5 and type 8 capsular polysaccharides (CPs) are both virulence factors and protective antigens for bacteremia caused by Staphylococcus aureus. Neither type 5 nor type 8 CP elicited serum antibodies when injected into mice. These two CPs were bound to Pseudomonas aeruginosa exotoxin A (ETA) to form conjugates by using the synthetic scheme devised for the CP (Vi) of Salmonella typhi and of pneumococcus type 12F (A. Fattom, W. F. Vann, S. C. Szu, A. Sutton, X. Li, D. Bryla, G. Schiffman, J. B. Robbins, and R. Schneerson, Infect. Immun. 56:2292-2298, 1988; S. C. Szu, A. L. Stone, J. D. Robbins, R. Schneerson, and J. B. Robbins, J. Exp. Med. 166:1510-1524, 1987). Both S. aureus CP-ETA conjugates elicited a rise in CP antibodies. As components of conjugates, both S. aureus CPs acquired T-cell-dependent properties, as shown by their ability to respond to carrier priming and to stimulate booster responses. The conjugate-induced antibodies facilitated type-specific opsonization of S. aureus by human polymorphonuclear leukocytes. The conjugates also induced ETA antibodies which neutralized the native toxin in vitro. Clinical studies of these two conjugates for active or passive immunization of patients at risk for S. aureus bacteremia are planned.

Structure of the type 5 capsular polysaccharide of Staphylococcus aureus

The Staphylococcus aureus type 5 capsular polysaccharide is composed of 2-acetamido-2-deoxy-L-fucose (1 part), 2-acetamido-2-deoxy-D-fucose (1 part), and 2-acetamido-2-deoxy-D-mannuronic acid (1 part). On the basis of methylation analysis, optical rotation, high-field one- and two-dimensional 1H- and 13C-n.m.r. experiments, and selective cleavage with 70% aqueous hydrogen fluoride, the polysaccharide was found to be a partially O-acetylated (50%) polymer of the repeating trisaccharide unit, [----4)-3-O-Ac-beta-D-ManpNAcA-(1----4)-a-L-FucpNAc-(1----3) -beta-D-FucpNAc-(1----]n.

Epidemiological markers for epidemic strain and carrier isolates in an outbreak of nosocomial oxacillin-resistant Staphylococcus aureus

An outbreak of nosocomial infections occurring in a postoperative intensive care unit was caused by a single strain of oxacillin-resistant Staphylococcus aureus. Six patients were infected, or colonized, by this strain, which was traced by using the following four epidemiological markers: antibiogram, bacteriophage type, capsular polysaccharide type, and esterase electrophoretic type. This strain was compared with S. aureus isolates obtained from the noses of 13 carriers from a group of 42 staff members. A good correlation in terms of phenotypic markers was found between the epidemic strain and a strain isolated from one carrier. Both exhibited the same pattern of multiple resistance as well as the same phage type, 77, capsular polysaccharide type, 5, and esterase electrophoretic type, 6. In contrast, an oxacillin-resistant strain, isolated from another carrier, differed from the epidemic strain by susceptibility to rifampin and by susceptibility to four additional bacteriophages. The other 11 strains isolated from carriers were susceptible to oxacillin and exhibited widely different phenotypes. These results confirm the interest of using several epidemiological markers to trace the spread of epidemic S. aureus strains and to delineate the carrier strains.

Reactivity of coagulase-negative staphylococci isolated from cow and goat milk with monoclonal antibodies to Staphylococcus aureus capsular polysaccharide types 5 and 8

Monoclonal antibodies to Staphylococcus aureus capsular polysaccharide types 5 and 8 were used in an enzyme-linked immunosorbent assay to serotype 74 and 42 coagulase-negative isolates from cow and goat milk, respectively. Eighteen (15.5%) isolates were typable: 13 Staphylococcus haemolyticus, 1 S. hyicus, 1 S. simulans, and 1 S. warneri from bovine origin and 2 S. lentus from caprine origin. Type 5 was predominant, accounting for about 89% of typable isolates. Reactivity with monoclonal antibodies varied considerably according to isolates. The significance and the potential importance of these findings are discussed.

Direct testing of blood culture for detection of the serotype 5 and 8 capsular polysaccharides of Staphylococcus aureus

Monoclonal antibodies (MAbs) reactive with serotype 5 and 8 capsular polysaccharides of Staphylococcus aureus have been used to test, by enzyme-linked immunosorbent assay (ELISA), blood culture fluids for the presence of S. aureus. A total of 748 blood cultures from 665 patients yielding 706 bacterial isolates belonging to more than 26 bacterial species were studied. All blood cultures containing bacterial strains belonging to species other than S. aureus were negative in ELISA. All 23 blood cultures containing serotype 5 S. aureus were positive in ELISA with the corresponding MAb. Out of 20 blood cultures containing serotype 8 S. aureus, 19 were positive with the corresponding MAb. All 5 blood cultures containing nontypeable S. aureus were negative in ELISA with both MAbs. This method provides reliable identification of serotype 5 or serotype 8 S. aureus by direct testing of blood culture fluids with ELISA.

Staphylococcus aureus capsular types and antibody response to lung infection in patients with cystic fibrosis

Chronic respiratory tract infections caused by Staphylococcus aureus are common in patients with cystic fibrosis (CF). Recently, it was shown in a few CF patients that S. aureus isolates produce capsular polysaccharides (CPs). However, it is not known whether this is a common feature and whether an immune response to CPs in CF is detectable. Therefore, we examined 170 S. aureus isolates from CF patients and healthy individuals for production of CP types 5 and 8 by using monoclonal antibodies. We found that CP-producing staphylococcal isolates were randomly distributed among CF patients and healthy carriers. Eighty-five percent of all isolates produced CPs, 77% of which were type 8. Examination of one sputum sample by an immunofluorescence technique suggested that production of CPs is not an in vitro phenomenon. S. aureus isolates from various sites of a single person often yielded more than one CP type. A random distribution of S. aureus strains with CP type 5 or 8 from the skin and respiratory tracts of patients and from the skin of healthy individuals was found. Antibody response to CP types 5 and 8, measured by enzyme-linked immunosorbent assay, was not elevated in CF patients with chronic S. aureus lung infection in comparison with healthy carriers. On the contrary, in CF patients the ratios of antibodies to CP 8 were significantly lower (P less than 0.005; alpha = 0.025). The ratios of antibodies to CP types did not change when monitored longitudinally over several months. This study suggests that the production of CPs is a universal property of S. aureus and that infected CF patients do not have elevated ratios of antibodies to these antigens.