Method for the serological typing of the capsular polysaccharides of Staphylococcus aureus

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.

capB2 Expression Is Associated with Staphylococcus aureus Pathogenicity

CapB2 is recognized as a tyrosine kinase and is likely a vital factor in extracellular polysaccharide synthesis in Staphylococcus aureus, but its pathogenicity function and regulatory mechanism remain obscure. Here, we demonstrate that CapB2 enhances bacterial virulence in a murine model. Mice infected with the wild type SA75 strain exhibited significantly larger (P < 0.05) skin lesions from days 4 to 7 of infection than those challenged with the capB2 mutant strain. The effect on virulence was reverted by restoring the capB2 mutation to the wild type. The related components of the wild type SA75 cell wall in the capB2 mutant strain (SA75ΔcapB2) were thinner than wild type SA75 strain and the capB2 mutant complemented strain (SA75ΔcapB2-C), which was determined by the transmission electron microscopy. The survival percentages of the wild type strain SA75 and SA75ΔcapB2-C were significantly higher relative to SA75ΔcapB2. The results of qRT-PCR studies also indicated that mutations in regulatory gene sarA led to a drastic increase in capB2 gene transcription, with a 326-fold increase of growth at 6 h compared with the wild type strain, suggesting that sarA is a major negative regulator of capB2 expression. Taken together, these results demonstrate that the expression of CapB2 promotes S. aureus virulence in a mouse model of skin infection, and that capB2 gene transcription is regulated negatively by SarA.

Epidemiologic and Clinical Utility of Typing Systems for Differentiating Among Strains of Methicillin-Resistant Staphylococcus aureus

Typing systems for differentiating among strains of methicillin-resistant Staphylococcus aureus (MRSA) can be valuable tools for the epidemiologist and the clinician. Specific criteria for evaluating such systems are typeability, reproducibility, and discriminatory power. An ideal typing system also would be rapid, inexpensive, technically simple, and readily available. Systems based on the detection of phenotypic variations include antimicrobial susceptibility testing, bacteriophage typing, multilocus enzyme electrophoresis, and electrophoretic methods such as protein eletrophoresis and immunoblotting. Systems that directly detect genotypic variations include plasmid profile analysis, restriction enzyme analysis of plasmid DNA, restriction enzyme analysis of chromosomal DNA, Southern blot analysis of specific restriction fragment length polymorphisms, and pulse field gel electrophoresis. in general, the more widely available typing systems based on phenotypic assays and plasmid analysis have limitations in typeability and/or discriminatory power.The chromosomal DNA-based techniques, although promising, are unproven approaches still under active investigation.

Preparation and characterization of a Staphylococcus aureus capsular polysaccharide-protein conjugate prepared by a low cost technique: a proof-of-concept study

Staphylococcus aureus is a worldwide distributed pathogen that produces several diseases in many species and is the major cause of mastitis in dairy cows. S. aureus capsular polysaccharide 5 (CP5) has been widely proposed as a vaccine candidate since it is expressed in a high proportion of isolates from intramammary infections and is able to induce opsonophagocytic antibodies. However, to reach immunological properties, polysaccharides need to be coupled to carrier proteins. The aim of this study was to evaluate a conjugation method employing p-benzoquinone (PBQ), which was not previously reported for the development of vaccine components. Purified S. aureus CP5 was coupled to human serum albumin (HSA) with high efficiency, reaching a rate PS/protein of 0.5. Mice groups were immunized at days 0, 14, 28, and 42, with the conjugate (CP5-HSAPBQ), free CP5, or PBS, formulated with incomplete Freund adjuvant, and after 3 months, they were challenged with free CP5 to evaluate the memory response. IgG and IgM isotypes were measured on serum samples all along the experiment, and IgG subclasses were determined to analyze the humoral profile. In contrast to the response obtained with free CP5, CP5-HSAPBQ induced IgG titers of 1/238,900 after three doses and a memory response was observed after the challenge. Results indicate that immunization with CP5-HSAPBQ effectively induce a T-dependent immune response against CP5. Moreover, besides IgG2a was the main subtype obtained, the joint production of specific IgG1, IgG2b, and IgG3 types indicated a balanced humoral response. As p-benzoquinone conjugation of CPs to proteins is far less expensive and straightforward than other methods commonly used in vaccine preparations, the robust humoral response obtained using this method points out that this can be an interesting alternative to prepare S. aureus CP5 conjugate vaccines.

Antibodies to Staphylococcus aureus serotype 8 capsular polysaccharide react with and protect against serotype 5 and 8 isolates

Most Staphylococcus aureus isolates produce either a serotype 5 (CP5) or 8 (CP8) capsular polysaccharide, and the CP antigens are targets for vaccine development. Since CP5 and CP8 have similar trisaccharide repeating units, it is important to identify an epitope shared by both CP5 and CP8. To characterize cross-reactivity between CP5 and CP8, the immunogenicity of CP5 and CP8 conjugate vaccines in mice and rabbits was evaluated by serological assays. Immune sera were also tested for functional activity by in vitro opsonophagocytic-killing assays and a murine bacteremia model. Antibodies to the CP5-cross-reactive material 197 (CRM197) conjugate vaccine bound only to purified CP5. In contrast, antibodies to the CP8-CRM conjugate vaccine reacted with CP8 and (to a lesser extent) CP5. De-O-acetylation of CP5 increased its reactivity with CP8 antibodies. Moreover, CP8 antibodies bound to Pseudomonas aeruginosa O11 lipopolysaccharide, which has a trisaccharide repeating unit similar to that of the S. aureus CPs. CP8-CRM antibodies mediated in vitro opsonophagocytic killing of S. aureus expressing CP5 or CP8, whereas CP5-CRM antibodies were serotype specific. Passive immunization with antiserum to CP5-CRM or CP8-CRM protected mice against bacteremia induced by a serotype 5 S. aureus isolate, suggesting that CP8-CRM elicits antibodies cross-reactive to CP5. The identification of epitopes shared by CP5 and CP8 may inform the rational design of a vaccine to protect against infections caused by CP5- or CP8-producing strains of S. aureus.

Models matter: the search for an effective Staphylococcus aureus vaccine

Staphylococcus aureus is a highly successful bacterial pathogen owing to its abundance of cell surface and secreted virulence factors. It is estimated that 30% of the population is colonized with S. aureus, usually on mucosal surfaces, and methicillin-resistant S. aureus is a major public health concern. There have been multiple attempts to develop an S. aureus vaccine using one or more cell surface virulence factors as antigens; all of these vaccine trials have failed. In this Opinion article, we suggest that an over-reliance on rodent models and a focus on targeting cell surface components have been major contributing factors to this failure.

The capsular polysaccharide of Staphylococcus aureus is attached to peptidoglycan by the LytR-CpsA-Psr (LCP) family of enzymes

Envelope biogenesis in bacteria involves synthesis of intermediates that are tethered to the lipid carrier undecaprenol-phosphate. LytR-CpsA-Psr (LCP) enzymes have been proposed to catalyze the transfer of undecaprenol-linked intermediates onto the C6-hydroxyl of MurNAc in peptidoglycan, thereby promoting attachment of wall teichoic acid (WTA) in bacilli and staphylococci and capsular polysaccharides (CPS) in streptococci. S. aureus encodes three lcp enzymes, and a variant lacking all three genes (Δlcp) releases WTA from the bacterial envelope and displays a growth defect. Here, we report that the type 5 capsular polysaccharide (CP5) of Staphylococcus aureus Newman is covalently attached to the glycan strands of peptidoglycan. Cell wall attachment of CP5 is abrogated in the Δlcp variant, a defect that is best complemented via expression of lcpC in trans. CP5 synthesis and peptidoglycan attachment are not impaired in the tagO mutant, suggesting that CP5 synthesis does not involve the GlcNAc-ManNAc linkage unit of WTA and may instead utilize another Wzy-type ligase to assemble undecaprenyl-phosphate intermediates. Thus, LCP enzymes of S. aureus are promiscuous enzymes that attach secondary cell wall polymers with discrete linkage units to peptidoglycan.

Rapid and reliable identification of Staphylococcus aureus capsular serotypes by means of artificial neural network-assisted Fourier transform infrared spectroscopy

Staphylococcus aureus capsular polysaccharides (CP) are important virulence factors and represent putative targets for vaccine development. Therefore, the purpose of this study was to develop a high-throughput method to identify and discriminate the clinically important S. aureus capsular serotypes 5, 8, and NT (nontypeable). A comprehensive set of clinical isolates derived from different origins and control strains, representative for each serotype, were used to establish a CP typing system based on Fourier transform infrared (FTIR) spectroscopy and chemometric techniques. By combining FTIR spectroscopy with artificial neuronal network (ANN) analysis, a system was successfully established, allowing a rapid identification and discrimination of all three serotypes. The overall accuracy of the ANN-assisted FTIR spectroscopy CP typing system was 96.7% for the internal validation and 98.2% for the external validation. One isolate in the internal validation and one isolate in the external validation failed in the classification procedure, but none of the isolates was incorrectly classified. The present study demonstrates that ANN-assisted FTIR spectroscopy allows a rapid and reliable discrimination of S. aureus capsular serotypes. It is suitable for diagnostic as well as large-scale epidemiologic surveillance of S. aureus capsule expression and provides useful information with respect to chronicity of infection.

Genotypic and phenotypic detection of capsular polysaccharides in Staphylococcus aureus isolated from bovine intramammary infections in Argentina

Staphylococcus aureus (n=157) isolated from intramammary infections in Argentine dairy areas were evaluated for presence of cap5 and cap8 loci. Isolates carrying cap5 and cap8 were serotyped using specific antisera. Sixty four percent of the isolates were genotyped as cap5 or cap8 and 50% of them expressed CP5 or 8.

An evaluation of the emerging vaccines and immunotherapy against staphylococcal pneumonia in children

Background

Staphylococcus aureus is a commensal of human skin and nares. It is also one of the leading nosocomial pathogens in both developed and developing countries and is responsible for a wide range of life threatening infections, especially in patients who are immunocompromised, post-surgery, undergoing haemodialysis and those who are treated with catheters and ventilators. Over the past two decades, the incidence of nosocomial staphylococcal infections has increased dramatically. Currently there are at least seven vaccine and immunotherapy candidates against S. aureus in the developmental phase targeting both active and passive immunization.

Methods

We used a modified CHNRI methodology for setting priorities in health research investments. This was done in two stages. In Stage I, we systematically reviewed the literature related to emerging vaccines against Staphylococcus aureus relevant to several criteria of interest: answerability; cost of development, production and implementation; efficacy and effectiveness; deliverability, affordability and sustainability; maximum potential impact on disease burden reduction; acceptability to the end users and health workers; and effect on equity. In Stage II, we conducted an expert opinion exercise by inviting 20 experts (leading basic scientists, international public health researchers, international policy makers and representatives of pharmaceutical companies) to participate. The policy makers and industry representatives accepted our invitation on the condition of anonymity, due to sensitive nature of their involvement in such exercises. They answered questions from CHNRI framework and their “collective optimism” towards each criterion was documented on a scale from 0 to 100%.

Results

The panel of experts expressed low levels of optimism (score around or below 50%) on the criteria of answerability, efficacy, maximum disease burden reduction potential, low cost of production, low cost of implementation and affordability; moderate levels of optimism (scores around 60 to 80%) that these vaccines could be developed at a low cost, and thus on the deliverability, sustainability and impact on equity; and high levels of optimism (scores above 80%) regarding acceptable of such a product to both the end-users and health workers. While assessing the candidates for passive immunization against S.aureus, the experts were poorly optimistic regarding low production cost, low implementation cost, efficacy, deliverability, sustainability, affordability and equity; moderately optimistic regarding answerability and acceptability to health workers and end-users. They were of the opinion that these interventions would have only a modest impact (3 to 5%) on the burden of childhood pneumonia. .

Conclusion

In order to provide an effective vaccine against S. aureus, a number of unresolved issues in vaccine development relating to optimal antigenic target identification, criteria for acceptable efficacy, identification of target population, commercial development limitations, optimal timing of immunization strategy, storage, cold chain requirements and cost need to be addressed properly. There is still a great deal unknown about the complex interaction between S. aureus and the human host. However, given the nature of S. aureus and the lessons learned from the recent failure of two emerging vaccines, it is clear that a multi-component vaccine is essential. Combating only one virulence factor is not sufficient in the human host but finding the right combination of factors will be very challenging.

Salicylic acid diminishes Staphylococcus aureus capsular polysaccharide type 5 expression

Capsular polysaccharides (CP) of serotypes 5 (CP5) and 8 (CP8) are major Staphylococcus aureus virulence factors. Previous studies have shown that salicylic acid (SAL), the main aspirin metabolite, affects the expression of certain bacterial virulence factors. In the present study, we found that S. aureus strain Reynolds (CP5) cultured with SAL was internalized by MAC-T cells in larger numbers than strain Reynolds organisms not exposed to SAL. Furthermore, the internalization of the isogenic nonencapsulated Reynolds strain into MAC-T cells was not significantly affected by preexposure to SAL. Pretreatment of S. aureus strain Newman with SAL also enhanced internalization into MAC-T cells compared with that of untreated control strains. Using strain Newman organisms, we evaluated the activity of the major cap5 promoter, which was significantly decreased upon preexposure to SAL. Diminished transcription of mgrA and upregulation of the saeRS transcript, both global regulators of CP expression, were found in S. aureus cultured in the presence of SAL, as ascertained by real-time PCR analysis. In addition, CP5 production by S. aureus Newman was also decreased by treatment with SAL. Collectively, our data demonstrate that exposure of encapsulated S. aureus strains to low concentrations of SAL reduced CP production, thus unmasking surface adhesins and leading to an increased capacity of staphylococci to invade epithelial cells. The high capacity of internalization of the encapsulated S. aureus strains induced by SAL pretreatment may contribute to the persistence of bacteria in certain hosts.

Protection from Staphylococcus aureus mastitis associated with poly-N-acetyl beta-1,6 glucosamine specific antibody production using biofilm-embedded bacteria

Staphylococcus aureus vaccines based on bacterins surrounded by slime, surface polysaccharides coupled to protein carriers and polysaccharides embedded in liposomes administered together with non-biofilm bacterins confer protection against mastitis. However, it remains unknown whether protective antibodies are directed to slime-associated known exopolysaccharides and could be produced in the absence of bacterin immunizations. Here, a sheep mastitis vaccination study was carried out using bacterins, crude bacterial extracts or a purified exopolysaccharide from biofilm bacteria delivered in different vehicles. This polysaccharide reacted specifically with antibodies to poly-N-acetyl-beta-1,6-glucosamine (PNAG) and not with antibodies to other capsular antigens or bacterial components. Following intra-mammary challenge with biofilm-producing bacteria, antibody production against the polysaccharide, milk bacterial counts and mastitis lesions were determined. Bacterins from strong biofilm-producing bacteria triggered the highest production of antibodies to PNAG and conferred the highest protection against infection and mastitis, compared with weak biofilm-producing bacteria and non-cellular inocula. Thus, bacterins from strong biofilm bacteria, rather than purified polysaccharide, are proposed as a cost-efficient vaccination against S. aureus ruminant mastitis.

Molecular diagnostics of clinically important staphylococci

Bacterial species of the genus Staphylococcus known as important human and animal pathogens are the cause of a number of severe infectious diseases. Apart from the major pathogen Staphylococcus aureus, other species until recently considered to be nonpathogenic may also be involved in serious infections. Rapid and accurate identification of the disease-causing agent is therefore prerequisite for disease control and epidemiological surveillance. Modern methods for identification and typing of bacterial species are based on genome analysis and have many advantages compared to phenotypic methods. The genotypic methods currently used in molecular diagnostics of staphylococcal species, particularly of S. aureus, are reviewed. Attention is also paid to new molecular methods with the highest discriminatory power. Efforts made to achieve interlaboratory reproducibility of diagnostic methods are presented.

Serotyping of Dutch Staphylococcus aureus strains from carriage and infection

International epidemiological studies have shown that clinical isolates of Staphylococcus aureus are usually capsulated with either type 5 or 8 capsular polysaccharides (CPs). Because all noncapsulated strains were found to be cross-reactive with polysaccharide 336 (336PS) antibodies, the noncapsulated strains were denoted as type 336PS. The capsular types of 162 Dutch methicillin-susceptible S. aureus strains derived from individuals living in the Rotterdam area were determined. The serotype distribution was 28.4% serotype 5, 53.7% type 8, and 17.9% type 336PS. Serotyping was in agreement with genotyping by amplified fragment length polymorphism (AFLP) and multi locus sequence typing (MLST). Among 49 nasal carriage isolates from healthy children 24.5% belonged to serotype 5, 67.3% were type 8 and 8.2% were type 336PS. For 28 adult patients on chronic ambulatory peritoneal dialysis (CAPD) the serotype incidences among carriage isolates obtained from the nose, catheter exit-site, and abdominal skin were 45.1%, 41.2% and 13.7%, respectively. Among S. aureus strains deriving from blood cultures, the serotype incidences were 17.7% serotype 5, 53.2% type 8, and 29.0% type 336PS. Apparently, type 336PS strains are more prevalent (P=0.017) among bacteraemia isolates as compared with the nasal carriage isolates obtained from healthy children and CAPD patients. In conclusion, all Dutch S. aureus isolates belonged to types 5, 8, or 336PS, which is in agreement with data from other countries. Thus, addition of the 336PS conjugate to a type 5- and type 8-CP protein conjugate vaccine would significantly extend the vaccine coverage.

Distribution of capsular and surface polysaccharide serotypes of Staphylococcus aureus

Because of its ability to cause serious and fatal infections, Staphylococcus aureus remains one of the most feared microorganisms. Methicillin-resistant S. aureus (MRSA) has long been a common pathogen in healthcare facilities, but within the past decade, it has emerged as a problematic pathogen in the community setting as well. The severe consequences of infection heighten the importance of prevention. To analyze the potential applicability of a putative S. aureus polysaccharide conjugate vaccine, we tested 714 German methicillin-susceptible S. aureus (MSSA) and MRSA strains for their capsular and surface polysaccharide serotype by slide agglutination with specific antibodies (anti-T5-DT, anti-T8-DT, anti-336-rEPA). The strain serotypes were confirmed by immunodiffusion using lysostaphin-digested cell lysates. Regarding MRSA strains representing 86 unique spa types and thus covering >90% of MRSA spa types registered, 39 (45.3%) were type 5, 36 (41.9%) were type 8, and 11 (12.8%) were type 336. Of particular interest, type 336 was the second most common serotype among MRSA isolates collected from 10 different laboratories (40 isolates per site) covering university hospitals, general hospitals, and clinics throughout Germany. Type 8-positive strains were more prevalent among isolates recovered from anterior nares of patients who did not subsequently develop S. aureus bacteremia compared with those who became bacteremic with this pathogen. In conclusion, the addition of the newly described type 336 to a capsular polysaccharide-protein conjugate vaccine could extend the coverage substantially and would include virtually all MSSA and MRSA strains currently circulating in Germany.

Identification of the capsular polysaccharides in Staphylococcus aureus clinical isolates by PCR and agglutination tests

Staphylococcus aureus is a major cause of nosocomial and community-acquired infections. The predominance of two capsular polysaccharides, types 5 and 8, on the surface of clinical isolates led to the development of a conjugate vaccine (StaphVAX) based on capsular polysaccharides types 5 and 8 conjugated to a carrier protein. We have studied the capsular phenotypes and genotypes of 195 isolates representative of all clinical syndromes that encompassed both hospital and community-acquired infections. These isolates were mainly detected in France between January 2001 and December 2004. In this population, most of clinical isolates (87%) expressed either capsular polysaccharide type 5 (42%) or 8 (45%), whereas 13% were nontypeable by the serotyping method with antibodies specific to capsular polysaccharide type 5 or 8. These 26 nontypeable strains were further serotyped and were demonstrated to express the cell wall surface antigen 336, a polyribitol phosphate N-acetylglucosamine, which resembles cell wall teichoic acid. Among methicillin-resistant Staphylococcus aureus (MRSA) strains, we found a predominance of serotype 5 for 64% of strains, whereas MSSA isolates were predominantly capsular serotype 8 (60%). All S. aureus clinical isolates included in the present study have been investigated by PCR method, demonstrating that all isolates carried either the cap5 or the cap8 locus.

Future vaccine development at NICHD

Using published data and the results of our studies, we hypothesized that a critical level of serum IgG antibodies to the surface structures of invasive pathogens (capsular polysaccharides of Haemophilus influenzae type b, pneumococcus, meningococcus, Salmonella typhi, Escherichia coli, and Staphylococcus aureus, the O-specific polysaccharide LPS domain of the LPS of Shigella, non-typhoidal Salmonella, and E. coli, and the capsular polypeptide of Bacillus anthraces) confer immunity to these pathogens. Covalent attachment to a protein increases their immunogenicity and bestows T-cell properties to these antigens. We have also shown that a critical level of serum IgG antibodies to pertussis toxin alone induces immunity on both an individual and on a community basis (herd immunity) to Bordetella pertussis. It is likely that all the above conjugates and pertussis toxoid will be incorporated into vaccines for routine infant immunization.

Bacillus anthracis CapD, belonging to the γ-glutamyltranspeptidase family, is required for the covalent anchoring of capsule to peptidoglycan

Several examples of bacterial surface-structure anchoring have been described, but they do not include polyglutamate capsule. Bacillus anthracis capsule, which is composed only of poly-gamma- d-glutamate, is one of the two major virulence factors of the bacterium. We analysed its anchoring. We report that the polyglutamate is anchored directly to the peptidoglycan and that the bond is covalent. We constructed a capD mutant strain, capD being the fourth gene of the capsule biosynthetic operon. The mutant bacilli are surrounded by polyglutamate material that is not covalently anchored. Thus, CapD is required for the covalent anchoring of polyglutamate to the peptidoglycan. Sequence similarities suggest that CapD is a gamma-glutamyltranspeptidase. Furthermore, CapD is cleaved at the gamma-glutamyltranspeptidase consensus cleavage site, and the two subunits remain associated, as necessary for gamma-glutamyltranspeptidase activity. Other Gram-positive gamma-glutamyltranspeptidases are secreted, but CapD is located at the Bacillus surface, associated both with the membrane and the peptidoglycan. Polyglutamate is hydrolysed by CapD indicating that it is a CapD substrate. We suggest that CapD catalyses the capsule anchoring reaction. Interestingly, the CapD(-) strain is far less virulent than the parental strain.

Chemical structure, conjugation, and cross-reactivity of Bacillus pumilus Sh18 cell wall polysaccharide

Bacillus pumilus strain Sh18 cell wall polysaccharide (CWP), cross-reactive with the capsular polysaccharide of Haemophilus influenzae type b, was purified and its chemical structure was elucidated using fast atom bombardment mass spectrometry, nuclear magnetic resonance techniques, and sugar-specific degradation procedures. Two major structures, 1,5-poly(ribitol phosphate) and 1,3-poly(glycerol phosphate), with the latter partially substituted by 2-acetamido-2-deoxy-alpha-galactopyranose (13%) and 2-acetamido-2-deoxy-alpha-glucopyranose (6%) on position O-2, were found. A minor component was established to be a polymer of -->3-O-(2-acetamido-2-deoxy-beta-glucopyranosyl)-1-->4-ribitol-1-OPO3-->. The ratios of the three components were 56, 34, and 10 mol%, respectively. The Sh18 CWP was covalently bound to carrier proteins, and the immunogenicity of the resulting conjugates was evaluated in mice. Two methods of conjugation were compared: (i) binding of 1-cyano-4-dimethylaminopyridinium tetrafluoroborate-activated hydroxyl groups of the CWP to adipic acid dihydrazide (ADH)-derivatized protein, and (ii) binding of the carbodiimide-activated terminal phosphate group of the CWP to ADH-derivatized protein. The conjugate-induced antibodies reacted in an enzyme-linked immunosorbent assay with the homologous polysaccharide and with a number of other bacterial polysaccharides containing ribitol and glycerol phosphates, including H. influenzae types a and b and strains of Staphylococcus aureus and Staphylococcus epidermidis.

Staphylococcus aureus types 5 and 8 capsular polysaccharide-protein conjugate vaccines

BACKGROUND

Staphylococcus aureus, the first or second most common pathogen isolated from patients, is capsulated; there are at least 12 capsular types, and types 5 and 8 comprise approximately 85% of blood. Types 5 and 8, composed of a trisaccharide repeat unit including a mannose uronic acid and 2 fucoses, are non-immunogenic. As protein conjugates, they induce opsonophagocytic antibodies that confer type-specific active and passive protection in mice.

METHODS

A phase II study of patients with end-stage renal disease showed that these conjugates induced approximately one third of the immunoglobulin G antibody of healthy individuals. Increasing the dose to 100 microg of polysaccharide induced levels similar to that in healthy individuals injected with 25 microg.

RESULTS

In a double-blinded randomized and controlled study of patients undergoing renal dialysis, the conjugates induced statistically significant protection against bacteremia for as long as 10 months after immunization. The estimated protective level was 80 microg Ab/mL. At re-injection approximately 2 years later, 83 of 83 recipients responded with protective levels.

CONCLUSIONS

Conjugate vaccine-induced antibodies to the types 5 and 8 capsular polysaccharide antibodies of S aureus prevent bacteremia caused by this pathogen. The extent and duration of conjugate-induced immunity can be extended by re-immunization approximately 1 year later. Studies of patients undergoing cardiovascular surgery who would be immunized with the staphylococcus conjugates when they are immunologically intact are planned.

Evaluation of Serotypes of Staphylococcus aureus Strains Used in the Production of a Bovine Mastitis Bacterin

The five Staphylococcus aureus strains used in the manufacture of a commercially available bacterin were examined for capsular and surface polysaccharide serotypes. Double immunodiffusion assays of antigenic extracts of test and reference strains with monospecific typing sera to capsular serotypes 1, 2, 5, and 8 and to surface polysaccharide serotype 336 were performed to detect the specific reactivities and antigenic relationships of test samples. Antigenic extracts of two S. aureus strains reacted with antibodies to serotype 8, but not with antibodies to serotype 5, by producing specific precipitin lines. A third strain reacted with monospecific antibodies to serotype 5 and not with the antibodies to serotype 8. The extracts of two other strains failed to exhibit any detectable reaction with antiserum to serotypes 1, 2, 5, or 8. Antibodies to serotype 336, however, precipitated an identical, specific 336 antigen from the antigenic extracts of these two nontypeable strains. Thus, S. aureus bacterin includes one serotype 5, two serotype 8, and two serotype 336 strains, the three predominant serotypes responsible for bovine mastitis.

The role of molecular biology and nucleic Acid technology in the study of human infection and epidemiology

OBJECTIVE

In this review, we will focus on recent molecular typing methods that can be applied to different pathogens and assess their values and limitations.

BACKGROUND

Resistant subgroups within a species of pathogenic organisms often emerge as dominant strains under the selective pressures of antibiotics, vaccinations, and new health care practices. The emergence of resistant organisms has added to the burden and cost of health care-related infections. Pathogens derived from a common ancestry are often difficult to distinguish by conventional methods, and the practice of clinical microbiology and infectious disease epidemiology must adapt to this problem.

DISCUSSION

Conventional strain typing methods provide a limited means of distinguishing epidemic from endemic or sporadic isolates of pathogens. Nucleic acid-based methods complement conventional and serologic methods of organism isolation and typing. Often, these genomic methods offer more discrimination and details than the phenotype-based conventional methods.

RESULTS AND CONCLUSIONS

Highly sensitive molecular techniques are capable of detecting single base pair substitutions and resolving the mechanism of underlying complex variation.

Discrimination of Staphylococcus aureus biotypes by pulsed-field gel electrophoresis of DNA macro-restriction fragments

AIMS

To examine whether pulsed-field gel electrophoresis (PFGE) of DNA macro-restriction fragments could provide better discrimination among the different biotypes previously described within the species Staphylococcus aureus than the traditional biochemical approach.

METHODS AND RESULTS

Seventy three Staph. aureus strains from various sources (human, animal or food origin) and belonging to eight biotypes, including the poultry-like biotype, tentatively designated as an 'abattoir' biotype, were genotyped by PFGE after SmaI digestion of DNA. The PFGE patterns were compared using the average linkage matching method (UPGMA) with the Dice coefficient. A total of 61 PFGE patterns were observed, showing between 31 and 100% similarity. In most cases, strains with the same biotype were grouped specifically into one, two or three separate sub-clusters. Strains from the 'abattoir' biotype were clustered in one separate sub-cluster.

CONCLUSIONS

The PFGE typing is useful to distinguish the traditional biotypes of Staph. aureus and has a more discriminatory power than the biochemical typing.

SIGNIFICANCE AND IMPACT OF THE STUDY

The PFGE typing confirms the 'abattoir' biotype as a separate group on a genetic level and is well suited to investigate modes of staphylococcal contamination of food.

Therapeutic approaches to superantigen-based diseases: a review

Superantigens secreted by the bacterial pathogen Staphyloccocus aureus are extremely potent toxins that overstimulate the host immune system by binding to the MHC class II and T cell receptors and activating a large population of T cells. Superantigen infection has been shown to be the causative agents in acute diseases, food poisoning and toxic shock syndrome, and in more chronic conditions such as inflammatory skin diseases. In addition to the toll on public health, S. aureus superantigens also represent a potential biothreat to our national security. To address these risks, a number of different therapeutic strategies have been developed that target different aspects of the pathogenic mechanism of S. aureus and superantigen infection. These therapies, which encompass strategies as diverse as production of neutralizing antibodies, inhibitory peptide/receptor design and blockage of superantigen gene transcription, are being tested for treatment of established S. aureus infections in pre- and post-exposure scenarios. In this review, we will describe these different strategies and their efficacies in inhibition of superantigen-induced effects in the host, and present the future outlook for successfully producing therapies for superantigen-based disease.

Use of a Staphylococcus aureus conjugate vaccine in patients receiving hemodialysis

BACKGROUND

In patients with decreased resistance to infection, Staphylococcus aureus is a major cause of bacteremia and its complications. The capsular polysaccharides are essential for the pathogenesis of and immunity to S. aureus infection and are targets for vaccines.

METHODS

In a double-blind trial involving patients with end-stage renal disease who were receiving hemodialysis, we evaluated the safety, immunogenicity, and efficacy of a vaccine with S. aureus type 5 and 8 capsular polysaccharides conjugated to nontoxic recombinant Pseudomonas aeruginosa exotoxin A. Between April 1998 and August 1999, 1804 adult patients at 73 hemodialysis centers were randomly assigned to receive a single intramuscular injection of either vaccine or saline. IgG antibodies to S. aureus type 5 and 8 capsular polysaccharides were measured for up to two years, and episodes of S. aureus bacteremia were recorded. Efficacy was estimated by comparing the incidence of S. aureus bacteremia in the patients who received the vaccine with the incidence in the control patients.

RESULTS

Reactions to the vaccine were generally mild to moderate, and most resolved within two days. The capsular polysaccharides elicited an antibody response of at least 80 microg per milliliter (the estimated minimal level conferring protection) in 80 percent of patients for type 5 and in 75 percent of patients for type 8. The efficacy during weeks 3 to 54 was only 26 percent (P=0.23). However, between weeks 3 and 40 after vaccination, S. aureus bacteremia developed in 11 of 892 patients in the vaccine group who could be evaluated for bacteremia, as compared with 26 of 906 patients in the control group (estimate of efficacy, 57 percent; 95 percent confidence interval, 10 to 81 percent; nominal P=0.02).

CONCLUSIONS

In patients receiving hemodialysis, a conjugate vaccine can confer partial immunity against S. aureus bacteremia for approximately 40 weeks, after which protection wanes as antibody levels decrease.

A Shared noncapsular antigen is responsible for false-positive reactions by Staphylococcus epidermidis in commercial agglutination tests for Staphylococcus aureus

Many of the commercial slide agglutination tests for Staphylococcus aureus incorporate antibodies against cell surface antigens associated with methicillin resistance, including capsular polysaccharides and an uncharacterized antigen, serotype 18. These tests are more sensitive than the first-generation agglutination procedures that detected only bound coagulase and protein A, but they suffer from false-positive reactions with some coagulase-negative staphylococci. The aim of this study was to elucidate the mechanism for false-positive agglutination by S. epidermidis in these tests. A group of methicillin-resistant S. aureus (MRSA) isolates, including a serotype 18 strain, that were not detectable in the first-generation tests were found to be of capsular polysaccharide type 8. All of these isolates were deficient in bound coagulase and/or protein A, and they possessed a heat-stable, proteinaceous antigen that was absent from a prototype capsule type 8 strain. Enzyme-linked immunosorbent assay and agarose gel immunodiffusion experiments demonstrated that this proteinaceous antigen was also present on both methicillin-sensitive and methicillin-resistant S. epidermidis clinical isolates. S. epidermidis strains that gave false-positive agglutination test results had a considerably higher level of this antigen than strains that gave the correct negative result. These findings reveal the importance of the careful selection of MRSA strains for raising anti-capsular type 8 antibodies for use in agglutination tests. Strains devoid of the antigen shared with S. epidermidis should be used to eliminate potential cross-reactions with this coagulase-negative coccus.

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.

Vaccine potential of poly-1-6 beta-D-N-succinylglucosamine, an immunoprotective surface polysaccharide of Staphylococcus aureus and Staphylococcus epidermidis

Staphylococcus aureus and S. epidermidis are among the most common causes of nosocomial infection, and S. aureus is also of major concern to human health due to its occurrence in community-acquired infections. These staphylococcal species are also major pathogens for domesticated animals. We have previously identified poly-N-succinyl beta-1-6 glucosamine (PNSG) as the chemical form of the S. epidermidis capsular polysaccharide/adhesin (PS/A) which mediates adherence of coagulase-negative staphylococci (CoNS) to biomaterials, serves as the capsule for strains of CoNS that express PS/A, and is a target for protective antibodies. We have recently found that PNSG is made by S. aureus as well, where it is an environmentally regulated, in vivo-expressed surface polysaccharide and similarly serves as a target for protective immunity. Only a minority of fresh human clinical isolates of S. aureus elaborate PNSG in vitro but most could be induced to do so under specific in vitro growth conditions. However, by immunofluorescence microscopy, S. aureus cells in infected human sputa and lung elaborated PNSG. The ica genes, previously shown to encode proteins in CoNS that synthesize PNSG, were found by PCR in all S. aureus strains examined, and immunogenic and protective PNSG could be isolated from S. aureus. Active and passive immunization of mice with PNSG protected them against metastatic kidney infections after intravenous inoculation with eight phenotypically PNSG-negative S. aureus. Isolates recovered from kidneys expressed PNSG, but expression was lost with in vitro culture. Strong antibody responses to PNSG were elicited in S. aureus infected mice, and a PNSG-capsule was observed by electron microscopy on isolates directly plated from infected kidneys. PNSG represents a previously unidentified surface polysaccharide of S. aureus that is elaborated during human and animal infection and is a prominent target for protective antibodies.

Location of Staphylococcus aureus within the experimentally infected bovine udder and the expression of capsular polysaccharide type 5 in situ

The objective of this study was to locate Staphylococcus aureus in the bovine udder and to investigate the expression of capsular polysaccharide type 5 (CP5) in situ in both the early and chronic stages of experimental intramammary S. aureus infections. Bovine udder tissue was obtained in early and chronic stages of intramammary infection; i.e., 24 to 96 h and 122 d after experimental intramammary infection with S. aureus Newbould 305. The presence and location of S. aureus was investigated by Gram staining of tissue sections. The expression of CP5 by S. aureus in situ was investigated by immunochemical staining of tissue sections with specific antibodies against CP5. Both in the early and chronic stages of infection, S. aureus was located within the lumen of alveoli or lactiferous ducts, in association with the epithelium, and within phagocytic cells. The staphylococci were mainly observed in clusters and often in the presence of polymorphonuclear neutrophils. Expression of CP5 by S. aureus was observed both in the early and chronic stages of infection. In general, CP5-positive S. aureus were located in alveoli and in association with the mammary epithelium. In the chronic infection, CP5-positive S. aureus were also located deep in the interstitial tissue. These results indicate that--both in early and chronic stages of experimental S. aureus mastitis--colonization of the mammary epithelia and invasion into the interstitial tissue occurs and that CP5 is expressed by S. aureus Newbould 305 in situ. The invasion of S. aureus in the interstitial tissue and the expression of CP5 probably help the bacteria to withstand the host defense mechanisms.

Genetic and serologic evaluation of capsule production by bovine mammary isolates of Staphylococcus aureus and other Staphylococcus spp. from Europe and the United States

Bovine mastitis caused by Staphylococcus aureus is responsible for major economic losses to the dairy industry, and more-effective therapeutic or preventive approaches are sorely needed. The predominance of staphylococcal capsular polysaccharide types 5 and 8 among human isolates from many sources is well documented, but there seems to be a greater variation in the distribution of capsular serotypes among isolates from cows. A total of 636 isolates of S. aureus from cases of bovine mastitis in Sweden, Denmark, Finland, Iceland, Ireland, and the United States were investigated for production of capsular polysaccharide types 5 and 8. Approximately half of all the European isolates tested were of serotype 8, although variation among countries and among isolates of clinical and subclinical origin was observed. Sweden had the highest frequency (87%) of serotypeable isolates, and Finland had the lowest (48%). Capsule types 5 and 8 accounted for only 42% of the U.S. isolates tested. A few isolates showed weak reactivity with CP5 antiserum in a colony blot assay, and an enzyme-linked immunosorbent assay inhibition method confirmed that the levels of capsule produced by these strains were <10% of those produced by control strains. Fifty isolates that failed to react with capsular antisera all possessed the genes for production of capsular polysaccharide type 5 or 8. These results underscore the variability in capsule production by bovine isolates of S. aureus from different geographic regions. This information is important for the rational design of a capsule-based vaccine to prevent S. aureus bovine mastitis.

Characterization of the linkage between the type III capsular polysaccharide and the bacterial cell wall of group B Streptococcus

The capsular polysaccharide of group B Streptococcus is a key virulence factor and an important target for protective immune responses. Until now, the nature of the attachment between the capsular polysaccharide and the bacterial cell has been poorly defined. We isolated insoluble cell wall fragments from lysates of type III group B Streptococcus and showed that the complexes contained both capsular polysaccharide and group B carbohydrate covalently bound to peptidoglycan. Treatment with the endo-N-acetylmuramidase mutanolysin released soluble complexes of capsular polysaccharide linked to group B carbohydrate by peptidoglycan fragments. Capsular polysaccharide could be enzymatically cleaved from group B carbohydrate by treatment of the soluble complexes with beta-N-acetylglucosaminidase, which catalyzes hydrolysis of the beta-D-GlcNAc(1-->4)beta-D-MurNAc subunit produced by mutanolysin digestion of peptidoglycan. Evidence from gas chromatography/mass spectrometry and (31)P NMR analysis of the separated polysaccharides supports a model of the group B Streptococcus cell surface in which the group B carbohydrate and the capsular polysaccharide are independently linked to the glycan backbone of cell wall peptidoglycan; group B carbohydrate is linked to N-acetylmuramic acid, and capsular polysaccharide is linked via a phosphodiester bond and an oligosaccharide linker to N-acetylglucosamine.

Broadly protective vaccine for Staphylococcus aureus based on an in vivo-expressed antigen

Vaccines based on preferential expression of bacterial antigens during human infection have not been described. Staphylococcus aureus synthesized poly-N-succinyl beta-1-6 glucosamine (PNSG) as a surface polysaccharide during human and animal infection, but few strains expressed PNSG in vitro. All S. aureus strains examined carried genes for PNSG synthesis. Immunization protected mice against kidney infections and death from strains that produced little PNSG in vitro. Nonimmune infected animals made antibody to PNSG, but serial in vitro cultures of kidney isolates yielded mostly cells that did not produce PNSG. PNSG is a candidate for use in a vaccine to protect against S. aureus infection.

Promoter analysis of the cap8 operon, involved in type 8 capsular polysaccharide production in Staphylococcus aureus

The production of type 8 capsular polysaccharide (CP8) in Staphylococcus aureus is regulated in response to a variety of environmental factors. The cap8 genes required for the CP8 production in strain Becker are transcribed as a single large transcript by a primary promoter located within a 0.45-kb region upstream of the first gene of the cap8 gene cluster. In this study, we analyzed the primary cap8 promoter region in detail. We determined the transcription initiation site of the primary transcript by primer extension and identified the potential promoter sequences. We found several inverted and direct repeats upstream of the promoter. Deletion analysis and site-directed mutagenesis showed that a 10-bp inverted repeat of one of the repeats was required for promoter activity. We showed that the distance but not the specific sequences between the inverted repeat and the promoter was critical to the promoter activity. However, insertion of a DNA sequence with two or four helix turns in this intervening region had a slight effect on promoter activity. To demonstrate the biological significance of the 10-bp inverted repeat, we constructed a strain with a mutation in the repeat in the S. aureus Becker chromosome and showed that the repeat affected CP8 production mostly at the transcriptional level. By gel mobility shift assay, we demonstrated that strain Becker produced at least one protein capable of specific binding to the 10-bp inverted repeat, indicating that the repeat serves as a positive regulatory protein binding site. In addition, reporter gene fusion analysis showed that the cap8 promoter activity was influenced by various growth media and affected most by yeast extract. Our results suggest that yeast extract may exert its profound inhibitory effect on cap8 gene expression through the 10-bp inverted repeat element.

Genetic analysis of the cap5 locus of Staphylococcus aureus

Staphylococcus aureus expresses at least eight distinct serotypes of capsular polysaccharide (CP). Gene clusters involved in the expression of serotypes 1, 5 and 8 have been cloned and sequenced. In this report we describe the isolation and analysis of serotype 5 capsular polysaccharide-defective mutants. A naturally occurring cap mutation in the laboratory strains 8325-4 and RN4220 was mapped to the cap5E gene by genetic complementation. The cap5H-K genes were shown to be responsible for CP5 serotype specificity by transduction and complementation.

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.

Detection of human serum antibody to encapsulated strains of Staphylococcus aureus by enzyme-linked immunosorbent assay inhibition test

A specific and rapid enzyme-linked immunosorbent assay (ELISA) inhibition test was employed for detection of immunoglobulins to Staphylococcus aureus (S. aureus) capsular polysaccharide in human serum. Cap-sular polysaccharide antigens obtained from Smith diffuse (capsular type 2), Reynolds (capsular type 5), or Becker (capsular type 8) strains of S. aureus were added to microplates coated with these strains. Seventy-four patients with open fractures (31 serum samples from those with staphylococcal infections, 10 serum samples from those with non-staphylococcal infections, and 33 serum samples from the non-infected group) and 28 serum samples from healthy controls were then added. The plates were incubated at 37 degreesC for 2 h and the ELISA was performed. The ELISA inhibition assay showed remarkable inhibition with the capsular type 2, 5, and 8 polysaccharides in the 33 serum samples from the non-infected group and in the 28 serum samples from the healthy controls, but low inhibition was observed with the 31 sera with staphylococcal infections. Positive immunoglobulin (Ig)G and IgM titers showed marked inhibition with this assay, but IgA titer were not seen in any samples. These results indicate that the quantitation of human serum antibody against S. aureus capsular polysaccharide by the ELISA inhibition assay is useful for the demonstration of protective activities against S. aureus.

Factors affecting the collagen binding capacity of Staphylococcus aureus

To determine whether the ability of Staphylococcus aureus to bind collagen involves an adhesin other than the collagen adhesin encoded by cna, we examined the collagen binding capacity (CBC) of 32 strains of S. aureus. With only two exceptions, a high CBC corresponded with the presence of cna. Both exceptions involved cna-positive strains with a low CBC. The first was a single strain (ACH5) that encoded but did not express cna. The second were the mucoid strains Smith diffuse and M, both of which encoded and expressed cna but bound only minimal amounts of collagen. Analysis of capsule mutants suggests that the reduced CBC observed in the mucoid strains was due to masking of the collagen adhesin on the cell surface and that this masking effect is restricted to heavily encapsulated strains. Differences in the CBC of the remaining cna-positive strains were correlated to variations in the level of cna transcription and were independent of the number of B domain repeats in the cna gene. In all cna-positive strains other than ACH5, cna transcription was temporally regulated, with cna mRNA levels being highest in cells taken from exponentially growing cultures and falling to almost undetectable levels as cultures entered the post-exponential growth phase. The CBC was also highest with cells taken from exponentially growing cultures. Mutation of agr resulted in a slight increase in cna transcription and a corresponding increase in CBC during the exponential growth phase but did not affect the temporal pattern of cna transcription. Mutation of sar resulted in a more dramatic increase in CBC and a delay in the post-exponential-phase repression of cna transcription. Mutation of both sar and agr had an additive effect on both CBC and cna transcription. We conclude that (i) cna encodes the primary collagen-binding adhesin in S. aureus, (ii) sar is the primary regulatory element controlling expression of cna, and (iii) the regulatory effects of sar and agr on cna transcription are independent of the interaction between sar and agr.

Phenotypic and genotypic characterization of nosocomial Staphylococcus aureus isolates from trauma patients

Staphylococcus aureus is a major cause of nosocomial infections. During the period from March 1992 to March 1994, the patients admitted to the intensive care unit of the University of Maryland Shock Trauma Center were monitored for the development of S. aureus infections. Among the 776 patients eligible for the study, 60 (7.7%) patients developed 65 incidents of nosocomial S. aureus infections. Of the clinical isolates, 43.1% possessed a polysaccharide type 5 capsule, 44.6% possessed a type 8 capsule, and the remaining 12.3% had capsules that were not typed by the type 5 or type 8 antibodies. Six antibiogram types were noted among the infection-related isolates, with the majority of the types being resistant only to penicillin and ampicillin. It was noted that the majority of cases of pneumonia were caused by relatively susceptible strains, while resistant strains were isolated from patients with bacteremia and other infections. Only 16 (6.3%) of the isolates were found to be methicillin-resistant S. aureus (MRSA). DNA fingerprinting by pulsed-field gel electrophoresis showed 36 different patterns, with characteristic patterns being found for MRSA strains and the strains with different capsular types. Clonal relationships were established, and the origins of the infection-related isolates in each patient were determined. We conclude that (i) nosocomial infection-related isolates from the shock trauma patients did not belong to a single clone, although the predominance of a methicillin-resistant genotype was noted, (ii) most infection-related S. aureus isolates were relatively susceptible to antibiotics, but a MRSA strain was endemic, and (iii) for practical purposes, the combination of the results of capsular and antibiogram typing can be used as a useful epidemiological marker.

Prevalence of capsular serotypes among Staphylococcus aureus isolates from cows with mastitis in the United States

Development of an appropriate Staphylococcus aureus vaccine for bovine mastitis has eluded researchers for decades. The ability of S. aureus to form a protective exopolysaccharide capsule has posed a major obstacle because of the multiple serotypes and the poor immune response elicited by exopolysaccharides. This study characterized S. aureus serotypes isolated from cases of bovine mastitis obtained from veterinary diagnostic laboratories that service 44% of the dairy cattle in the United States. Major milk producing areas of the northeast, north central, Pacific coast and southwest were proportionately represented. Sub-samples of mastitic milk that contained S. aureus were frozen and sent to our laboratory for strain serotyping. The only other regional serotyping of S. aureus from bovine mastitis to date was done in France. The primary serotypes found were types 5 (51%) and 8 (18%) and 31% were non-typeable. In the current study, serotype 5 accounted for 18% of the isolates and serotype 8 for 23%. More importantly 59% of the isolates were not typeable with either type 5 or 8 antisera. These data indicate that S. aureus vaccines employing serotypes 5 and 8 would only be marginally effective in the United States. These data also suggest that development of a S. aureus vaccine for bovine mastitis should take into account regional variation in S. aureus serotypes.

The role of staphylococcal polysaccharide microcapsule expression in septicemia and septic arthritis

Staphylococcus aureus arthritis is a rapidly progressive and highly erosive disease of the joints in which both host and bacterial factors are of pathogenic importance. One potential bacterial virulence factor is the ability to express a polysaccharide capsule (CP). Among 11 reported capsular serotypes, CP type 5 (CP5) and CP8 comprise 80 to 85% of all clinical blood isolates. The aim of this study was to assess the role of CP5 as a virulence factor in staphylococcal septicemia and septic arthritis with a recently established murine model of hematogenously spread S. aureus arthritis. NMRI mice were inoculated intravenously with S. aureus strains isogenic for expression of CP5, and clinical, bacteriological, serological, and histopathological progression of disease was studied. Inoculation of 7 x 10(6) CFU of S. aureus per mouse induced 55% mortality in the group inoculated with the CP-expressing bacteria, compared to 18% in the group inoculated with CP- mutants. A lower dose of inoculum (3 x 10[6] per mouse) did not give rise to mortality in mice inoculated with CP mutant strains, whereas 18% of the mice inoculated with the CP5-expressing S. aureus died. Importantly, mice inoculated with S. aureus expressing CP5 had a significantly higher frequency of arthritis and a more severe form of the disease. In vitro assays suggested that macrophages were not able to phagocytize CP5+ staphylococci as efficiently as they were CP5- strains. In addition, once phagocytized, CP5+ bacteria were less efficiently killed than CP- mutants. In summary, CP5 leads to a higher frequency of arthritis and a more severe course of the disease. This seems to be related to the effects of the downregulatory properties of CP on the ingestion and intracellular killing capacity of phagocytes. Our results clearly indicate that the expression of CP5 is a determinant of the virulence of S. aureus in arthritis and septicemia.

The Staphylococcus aureus allelic genetic loci for serotype 5 and 8 capsule expression contain the type-specific genes flanked by common genes

The nucleotide sequences of two gene clusters, cap5 and cap8, involved in the synthesis of Staphylococcus aureus type 5 and type 8 capsular polysaccharides (CPs), respectively were determined. Each gene cluster contained 16 ORFs, which were named cap5A through cap5P for type 5 CP and cap8A through cap8P for type 8 CP. The cap5 and cap8 loci were allelic and were mapped to the SmaI-G fragment in the standard SmaI map of Staph. aureus strain NCTC 8325. The predicted gene products of cap5A through cap5G and cap5L through cap5P are essentially identical to those of cap8A through cap8G and cap8L through cap8P, respectively, with very few amino acid substitutions. Four ORFs located in the central region of each locus are type-specific. A comparison of the predicted amino acid sequences of cap5 and cap8 with sequences found in the databases allowed tentative assignment of functions to 15 of the 16 ORFs. The majority of the capsule genes are likely to be involved in amino sugar synthesis; the remainder are likely to be involved in sugar transfer, capsule chain-length regulation, polymerization and transport.

Heterogeneity of cell-associated CP5 expression on Staphylococcus aureus strains demonstrated by flow cytometry

It was reported previously that two capsular polysaccharides, types 5 and 8 (CP5 and CP8), account for 70 to 80% of Staphylococcus aureus strains isolated from human and animal sources. The capsular material has been shown to play a part in virulence and in resistance to phagocytosis. With a view to investigating the role that CP plays in pathogenicity or protection, relative measurement of cell-associated CP is desirable. Flow cytometry, which permits the analysis of individual bacteria, was used to that end. Thirty isolates expressing CP5, of human (n = 7) and animal (cow, n = 11; goat, n = 3; swine, n = 3; hen, n = 3; and rabbit, n = 3) origin, were cultivated on either brain heart infusion agar (BHI) or modified medium 110 (mod 110) agar. Staphylococci were incubated with a mouse anti-CP5 monoclonal antibody (an immunoglobulin M, which does not react with staphylococcal protein A) and then stained with a fluorescein-labeled anti-murine antibody. The bacteria were washed, sonicated, and analyzed by flow cytometry. Except for three isolates, the expression of cell-bound CP5 was higher when bacteria were cultivated on mod 110 than when they were cultivated on BHI. We found a wide intraisolate phenotypic heterogeneity in surface-exposed CP5 in many strains, which appeared as mixtures of stained and unstained bacteria. Four main patterns could be distinguished on the basis of the distribution of the fluorescence of individual bacteria within the strain population as a function of growth medium. Great variations in both percentages of stained bacteria and fluorescence intensity were recorded among strains regardless of their origin. Flow cytometry analysis provided information on both the relative amounts and the distribution patterns of the surface expression of CP. This information is potentially useful for the evaluation of the part played by the capsule in the interaction of bacteria with host cells or for the study of the activities of antibodies to this target antigen, such as opsonization or prevention of adherence.

Staphylococcus aureus vaccination for dialysis patients--an update

Staphylococcus aureus infections are a major cause in both hemodialysis and peritoneal dialysis patients. The availability of a safe and effective protective vaccine would be of great benefit to these patients, but attempts at using vaccines consisting of inactivated whole cells have been unsuccessful. This article discusses an alternate approach to S. aureus vaccine design using a capsular polysaccharide conjugate and preliminary results in hemodialysis and peritoneal patients.

Respiratory activity is essential for post-exponential-phase production of type 5 capsular polysaccharide by Staphylococcus aureus

Capsule formation is believed to have a significant role in bacterial virulence. To examine the possible involvement of capsular polysaccharide (CP) from Staphylococcus aureus in the pathological mechanisms associated with staphylococcal infections, we investigated the influence of respiratory activity on type 5 CP production by S. aureus grown in the presence of various concentrations of dissolved oxygen or nitrate. The effects of several metabolic inhibitors (arsenite, cyanide, azide, trimethylamine N-oxide, 2-heptyl-4-hydroxyquinoline N-oxide, and 2,4-dinitrophenol) were also tested. The metabolism of the bacteria was estimated by measuring their reductive capacity and by monitoring the pH and concentrations of fermentation products. Type 5 CP was always produced by S. aureus during the exponential phase of growth under all culture conditions tested. In contrast, post-exponential-phase CP production appeared to be strictly dependent on the respiratory activity. Since post-exponential-phase CP production contributes at least two-thirds of the total CP obtained, the influence of S. aureus respiration on CP production might be of some importance in the process of infection.

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.

Staphylococcal vaccines: a realistic dream

Staphylococcus aureus, especially multidrug resistant strains, continues to be a leading cause of serious nosocomial infections. In spite of the debate among investigators in the field, the discovery of serologically distinct capsular polysaccharides on the surface of clinical isolates has renewed the prospects for development of vaccines and passive protective immunity against S. aureus infections. Capsular polysaccharide conjugate vaccines have now been produced and proven to be safe and immunogenic in both healthy and in a significant percentage of immunocompromised patients. Antibodies generated in humans against these vaccines have been shown to mediate type-specific opsonophagocytosis, and to protect animals against lethal challenge with the appropriate S. aureus isolate.