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

Phenotypic characterization of epidemic versus sporadic strains of methicillin-resistant Staphylococcus aureus

Forty strains of methicillin-resistant Staphylococcus aureus (MRSA) were divided on the basis of their epidemiologic behavior into two subgroups, sporadic MRSA (SMRSA) and epidemic MRSA (EMRSA) strains. The strains were examined for binding of 125I-labelled fibronectin, vitronectin, collagen, Fc fragments of immunoglobulin G, and fibrinogen. A significant difference between EMRSA and SMRSA strains was found for binding of 125I-labelled fibrinogen and for Fc fragments of immunoglobulin G, (P < 0.05). No significant difference in the binding of 125I-labelled fibronectin and collagen was found between EMRSA and SMRSA strains. The binding of 125I-labelled vitronectin to MRSA strains was found to be aspecific. Capsular serotypes of the strains were determined with monoclonal antibodies against capsular types 5 and 8. Strains could be divided into the following four groups: types 5, 8, and 5/8 and nontypeable. More nontypeable strains were found in the EMRSA group (66.6%). Significantly more EMRSA strains (79%) than SMRSA strains (44%) produced alpha-toxin (P < 0.025). Logistic regression analysis using a combination of the parameters 125I-labelled immunoglobulin G binding, capsular type, and alpha-toxin production predicted the epidemic character with a sensitivity of 83% and a specificity of 75%.

Evaluation of new agglutination test for identification of oxacillin-susceptible and oxacillin-resistant Staphylococcus aureus

A new agglutination test (Monostaph +; Bionor, Skien, Norway) has been developed. This new agglutination test has been compared with two other agglutination tests for the identification of 128 isolates of Staphylococcus aureus and 82 coagulase-negative staphylococci. The sensitivities of both Monostaph + and Pastorex Staph-Plus were excellent (98.7 and 97.4%, respectively) in detection of oxacillin-resistant Staphylococcus aureus. The specificity was 96.4% (two Staphylococcus epidermidis isolates and one Staphylococcus hominis isolate were false positive).

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.

Antibodies to capsular polysaccharides are not protective against experimental Staphylococcus aureus endocarditis

The protective efficacy of antibodies to the Staphylococcus aureus capsular polysaccharide was examined in a rat model of catheter-induced endocarditis. Capsular antibodies were induced either by active immunization with killed S. aureus or by passive immunization with hyperimmune rabbit antiserum to S. aureus. Control rats were injected with phosphate-buffered saline or passively immunized with normal rabbit serum or rabbit antiserum to a nonencapsulated strain. Animals with indwelling catheters were challenged intravenously with 5 x 10(4) to 4 x 10(6) CFU of the homologous S. aureus strain (capsular serotype 5 strain Reynolds or serotype 1 strain SA1 mucoid). Both immunized and control rats developed S. aureus endocarditis. The numbers of S. aureus cells recovered from the blood and aortic valve vegetations of immunized rats were similar to those of control rats, indicating that capsule-specific antibodies were not protective. To determine whether the presence of an indwelling catheter interfered with antibody-mediated protection against S. aureus endocarditis, catheters were removed 2 h after insertion in additional groups of rats. An inoculum of 10(8) CFU of strain Reynolds was needed to provoke endocarditis in rats catheterized for 2 h, compared with 5 x 10(4) CFU for rats with indwelling catheters. Passively transferred capsular antibodies were not protective since both immunized and nonimmunized animals developed endocarditis, and quantitative cultures of blood and valvular vegetations revealed no differences between immunized and control animals. The findings of this study indicate that antibodies to the capsular polysaccharide are not protective in the rat model of experimental S. aureus endocarditis.

Sequence analysis and molecular characterization of genes required for the biosynthesis of type 1 capsular polysaccharide in Staphylococcus aureus

We previously cloned a 19.4-kb DNA region containing a cluster of genes affecting type 1 capsule production from Staphylococcus aureus M. Subcloning experiments showed that these capsule (cap) genes are localized in a 14.6-kb region. Sequencing analysis of the 14.6-kb fragment revealed 13 open reading frames (ORFs). Using complementation tests, we have mapped a collection of Cap- mutations in 10 of the 13 ORFs, indicating that these 10 genes are involved in capsule biosynthesis. The requirement for the remaining three ORFs in the synthesis of the capsule was demonstrated by constructing site-specific mutations corresponding to each of the three ORFs. Using an Escherichia coli S30 in vitro transcription-translation system, we clearly identified 7 of the 13 proteins predicted from the ORFs. Homology search between the predicted proteins and those in the data bank showed very high homology (52.3% identity) between capL and vipA, moderate homology (29% identity) between capI and vipB, and limited homology (21.8% identity) between capM and vipC. The vipA, vipB, and vipC genes have been shown to be involved in the biosynthesis of Salmonella typhi Vi antigen, a homopolymer polysaccharide consisting of N-acetylgalactosamino uronic acid, which is also one of the components of the staphylococcal type 1 capsule. The homology between these sets of genes therefore suggests that capL, capI, and capM may be involved in the biosynthesis of amino sugar, N-acetylgalactosamino uronic acid. In addition, the search showed that CapG aligned well with the consensus sequence of a family of acetyltransferases from various prokaryotic organisms, suggesting that CapG may be an acetyltransferase. Using the isogenic Cap- and Cap+ strains constructed in this study, we have confirmed that type 1 capsule is an important virulence factor in a mouse lethality test.

Epidemiology of Staphylococcus aureus in patients with cystic fibrosis

Seven hundred and thirty-four isolates of Staphylococcus aureus, recovered from the sputum of 238 cystic fibrosis patients in six French hospitals, were characterized by esterase electrophoretic typing, capsular polysaccharide serotyping and phage typing and tested against 14 antibiotics for sensitivity. Thirty-four esterase electrophoretic types were found with a genotypic diversity coefficient of 0.91. Five hundred and forty-eight (78.7%) isolates produced capsular polysaccharide and 350 (50.3%) were type 8. Four hundred and sixty isolates (66.6%) were phage typable and 202 (28.2%) were lysed by group III bacteriophages. No esterase electrophoretic type, capsular type or phage type was specific to cystic fibrosis. Isolates belonged to a wide range of types, similar to strains acquired outside hospitals. Eighty-five patients had three or more consecutive isolates over at least 6 months. The ability of S. aureus to persist for long periods of time has been demonstrated in 73% of them. Methicillin-resistance was encountered among 73 strains (9.8%) which were also multiresistant. Two hundred and eighty-nine (39.9%) strains were sensitive to all antibiotics tested except to penicillin. Pristinamycin and co-trimoxazole were the most effective antibiotics. These results could contribute to the elaboration of a rational approach to the prophylaxis and therapy of respiratory staphylococcal infections in cystic fibrosis patients.

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

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

Outbreak of methicillin-resistant Staphylococcus aureus in a teaching hospital--epidemiological and microbiological surveillance

An outbreak of methicillin-resistant S. aureus (MRSA) in a large university teaching hospital occurred between December 1991 and May 1992, involving 7 different wards and more than 30 patients. Epidemiological typing was performed to control the epidemic and to identify the MRSA carriers. By a combination of various classical methods (antimicrobial susceptibility, phage typing) and molecular typing procedures (SDS-PAGE of extracellular proteins, plasmid DNA profile, restriction enzyme fragment pattern of chromosomal DNA), three different clones of MRSA could be discriminated. The epidemic clone A was recovered from 30 patients and from 3 staff members. By strict microbiological monitoring together with hygienic measures, the epidemic could be successfully controlled. It is concluded that a combination of phenotypic markers and DNA-based epidemiological markers is extremely useful in the microbiological surveillance of MRSA outbreaks.

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.

New latex reagent using monoclonal antibodies to capsular polysaccharide for reliable identification of both oxacillin-susceptible and oxacillin-resistant Staphylococcus aureus

A new latex agglutination test (Pastorex Staph-Plus, Sanofi Diagnostics Pasteur), consisting of a mixture of latex particles coated with fibrinogen and immunoglobulin G for the detection of clumping factor and protein A and latex particles sensitized with monoclonal antibodies directed to Staphylococcus aureus serotype 5 and 8 capsular polysaccharides, was compared with three commercially available rapid agglutination methods for the identification of 220 isolates of S. aureus (61 oxacillin resistant) and 128 isolates of coagulase-negative staphylococci. The sensitivity for identification of S. aureus was high with the Pastorex Staph-Plus test (98.6%) compared with those of the other tests, which ranged from 91.8 to 84.5%. Test sensitivities for the identification of oxacillin-resistant S. aureus were as follows: Pastorex Staph-Plus, 95.1%; Pastorex Staph, 73.8%; Staphyslide, 72.1%; and StaphAurex, 49.2%.

Laboratory and clinical evaluation of conjugate vaccines composed of Staphylococcus aureus type 5 and type 8 capsular polysaccharides bound to Pseudomonas aeruginosa recombinant exoprotein A

The synthesis, standardization, and immunogenicity in young outbred mice and clinical evaluation in adult volunteers of investigational vaccines designed to induce serum antibodies to the type 5 and type 8 capsular polysaccharides (CPs) of Staphylococcus aureus are described. Conjugates composed of the type 5 CP and a sonicated preparation of a high-molecular-weight type 8 CP bound to a nontoxic recombinant protein derived from Pseudomonas aeruginosa exotoxin A (rEPA) were synthesized. The conjugates were nontoxic and elicited serum CP antibodies after two subcutaneous injections into young outbred mice; a third injection elicited a booster response. The lower-molecular-weight type 8 CP was not immunogenic in the mice, and the high-molecular-weight type 8 CP elicited low levels of antibodies without a booster effect. In the volunteers, neither the conjugates nor the type 8 CP alone caused significant local reactions or fever. The conjugates elicited type-specific antibodies of both the immunoglobulin M (IgM) and IgG classes after the first injection; a second injection 6 weeks later did not stimulate a booster effect. The high-molecular-weight type 8 CP alone, injected once only, elicited levels of IgG and IgM type-specific antibodies similar to those of the conjugate. The vaccine-induced CP antibodies were mostly of the IgG1 and IgG2 subclasses and had opsonophagocytic activity. The conjugates elicited IgG antibodies to the native exotoxin A with neutralizing activity. In summary, the type 5 and type 8 conjugates were safe and elicited biologically active antibodies to both the CP and rEPA components.

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.

The role of capsular antigens in Staphylococcus aureus immunity

Most clinical blood isolates of Staphylococcus aureus have been shown to be encapsulated. Techniques are now available for the preparation of type-specific capsular antisera and to provide reliable serologic methods for the identification of clinical isolates of Staphylococcus aureus. Epidemiologic studies in the U.S.A. and Europe indicated the prevalence of capsular types 5 and 8 among clinical isolates from human, bovine, and poultry. Encapsulated types 5 and 8 resisted in vitro phagocytosis and specific anti-capsular serum facilitated type-specific opsonization of S. aureus by polymorphonuclear leukocytes (PMN). The structure of the prevalent types 5 and 8 capsular polysaccharides (CP) have been elucidated. Vaccines of CP conjugated to exotoxin A of Pseudomonas aeruginosa have been prepared and have been injected into animals and human volunteers. Antibodies elicated by these conjugates facilitated opsonization of specific S. aureus types by human PMN.

Capsular polysaccharide serotyping scheme for Staphylococcus epidermidis

A scheme for the capsular typing of Staphylococcus epidermidis that is based on direct slide agglutination between proteinase-treated bacterial cells and specific antisera is described. Antisera were prepared from serum from rabbits immunized with two selected strains of encapsulated S. epidermidis isolated from bacteremic patients. Antisera were shown to be type specific and designated type 1 and type 2. Blood isolates of S. epidermidis from hospitals in different locations within the United States and Europe were serotyped, and it was found that over 90% of all strains were of type 1 or type 2. Type-specific antibodies mediated type-specific opsonophagocytosis and killing of S. epidermidis. The specificity was shown to be due to two distinct capsular polysaccharides. The data presented in this report may open a new window on the pathogenesis of S. epidermidis which could lead to the development of new vaccines and therapies.

Staphylococcus aureus susceptibility to thrombin-induced platelet microbicidal protein is independent of platelet adherence and aggregation in vitro

Bacterium-platelet interactions at the cardiac valve surface represent an important initial step in the induction of infective endocarditis (IE). This cell-cell interaction may play either a protagonistic role in the induction of IE via bacterial adherence to and aggregation of platelets or an antagonistic role via secretion of platelet-derived microbicidal molecules. We examined the spectrum and interrelationship of three aspects of the interaction of 20 clinical Staphylococcus aureus isolates with rabbit platelets in vitro: (i) S. aureus adherence to platelets; (ii) S. aureus-induced platelet aggregation; and (iii) S. aureus resistance to the action of thrombin-induced platelet microbicidal protein (PMP; low-molecular-weight cationic peptides contained in alpha granules). Among the 20 S. aureus isolates (11 bacteremia, 9 endocarditis), there was a heterogeneous distribution profile for each of the bacterium-platelet interaction parameters studied. For S. aureus-platelet adherence and S. aureus-induced platelet aggregation, 3 of 20 and 7 of 20 isolates tested were considered highly active for each respective parameter; 5 of 20 staphylococcal strains were deemed resistant to the bactericidal action of PMP. In addition, more endocarditis isolates (45%) were PMP resistant than strains from patients without endocarditis (19%). When analyzed concomitantly, there was a significant, positive correlation between S. aureus-platelet adherence and S. aureus-induced platelet aggregation among isolates (P = 0.003; r = 0.78). In contrast, there were no statistically significant relationships between either platelet adherence or aggregation and PMP resistance among these 20 S. aureus isolates. These data suggest that platelet adherence and aggregation are related abilities of S. aureus, while resistance to thrombin-induced PMP is an independent phenotypic characteristic and potential virulence factor.

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.

Comparative immunogenicity of conjugates composed of the Staphylococcus aureus type 8 capsular polysaccharide bound to carrier proteins by adipic acid dihydrazide or N-succinimidyl-3-(2-pyridyldithio)propionate

Staphylococcus aureus type 8 capsular polysaccharide (CP) was conjugated either to diphtheria toxoid or to Pseudomonas aeruginosa recombinant exoprotein A by using adipic acid dihydrazide (ADH) or N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP) as the joining reagent. The polysaccharide/protein ratios of these two pairs of conjugates were similar. The two synthetic schemes bound the linker to the carboxyls of the type 8 CP by carbodiimide-mediated condensation. ADH was bound to the carboxyls of the protein, whereas SPDP reacted with the amino groups of the protein. Intermolecular linking of the carrier protein, caused by the carbodiimide during the conjugation reaction with the type 8 CP derivative, probably accounts for the larger size of the conjugates formed with ADH compared with those formed with SPDP. Both conjugates synthesized with ADH elicited higher levels of CP antibodies, especially after the first immunization, than did those prepared with SPDP. Similar levels of exoprotein A antibodies were elicited by both conjugates. Higher levels of diphtheria toxoid antibodies were elicited by the conjugate prepared with SPDP than by the one prepared with ADH. The basis for the differences in the immunogenicities of these two pairs of S. aureus type 8 CP conjugates is discussed.

A periodate-sensitive anti-phagocytic surface structure, induced by growth in milk whey, on Staphylococcus aureus isolated from bovine mastitis

The phagocytic and chemiluminescent activity of purified bovine neutrophils in response to two Staphylococcus aureus strains isolated from mastitic bovine milk and grown in milk whey was studied. The activity was significantly reduced compared with the response elicited by the same strains grown in tryptic soy broth (TSB). A mild periodate treatment of the milk whey-grown strains resulted in a significant increase of both chemiluminescence and phagocytosis, whereas trypsin, subtilisin or papain treatment had no effect. The decreased binding of complement factor C3 to milk-whey-grown bacteria was restored to the level of TSB-grown homologous organisms by periodate treatment. Moreover, this treatment, but not treatment with trypsin, increased the surface hydrophobicity of milk-whey-grown bacteria. The chemiluminescent activity was as high towards heat-killed as towards live bacteria. Also, incubation of heat-killed TSB-grown bacteria in milk whey did not alter the chemiluminescent response, indicating that the reduced neutrophil activity towards milk-whey-grown bacteria was not due to binding of milk components to the microorganisms. These results strongly suggest that bovine mastitis S. aureus strains grown in milk whey produce an anti-phagocytic surface structure. This structure is heat- and protease-resistant and renders the bacterial surface hydrophilic. The anti-phagocytic material is altered or, more likely, released from the bacterial surface on periodate treatment and is probably of carbohydrate nature.

Potential for vaccination against infections caused by Staphylococcus aureus

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

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.

Thrombospondin binds to Staphylococcus aureus and promotes staphylococcal adherence to surfaces

Bacterial adherence to surfaces is the determining first step in staphylococcal infections. Activated platelets mediate adherence of staphylococci to tissues during inflammation or infection; however, the molecular mechanisms of this interaction are not clearly understood. Thrombospondin, a large multifunctional glycoprotein, is the principal platelet-stored glycoprotein. It is secreted upon platelet activation and either bound to receptors on the platelet surface or released and incorporated into blood clots and extracellular matrices. To characterize thrombospondin binding to staphylococci, we incubated [125I]thrombospondin with Staphylococcus aureus Cowan 1 in the presence of albumin and separated bound and free thrombospondin by centrifugation. We found that binding was (i) specific, since it was up to 76% inhibitable and up to 60% reversible in the presence of a 100-fold excess of unlabeled thrombospondin, (ii) saturable, with an apparent dissociation constant (Kd) of 5.6 x 10(-9) M and a maximal number of 2,600 binding sites per microorganism, and (iii) Ca2+ dependent, since omission of this ion from the medium decreased significantly the binding capacity. The binding reaction was insensitive to previous trypsin treatment of bacteria, but it was strongly inhibited in the presence of heparin. Protein A-negative and -positive strains had similar binding characteristics. To determine the promotion of staphylococcal adherence to surfaces by solid-phase thrombospondin, we incubated 3H-labeled S. aureus Cowan 1 and 26 pathogenic staphylococcal isolates with thrombospondin-coated polymethylmethacrylate disks and found that adherence was significantly promoted as a function of adsorbed thrombospondin. These results indicate a role for thrombospondin as an important mediator of staphylococcal adherence to activated platelets, to blood clots, or to extracellular matrices in pyogenic infections.

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 electrophoresis 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.

Expression of type 8 capsular polysaccharide and production of toxic shock syndrome toxin 1 are associated among vaginal isolates of Staphylococcus aureus

A colony immunoblot method was developed for serotyping the capsular polysaccharides expressed by Staphylococcus aureus isolates. The method was rapid and specific and was performed with either polyclonal or monoclonal antibodies specific for each of the capsule types. S. aureus isolates were obtained from patients with toxic shock syndrome (TSS) or other staphylococcal infections and from asymptomatic women with vaginal colonization. Among the vaginal isolates of S. aureus, expression of the type 8 capsule was significantly (P less than 0.001) more frequent among strains that produced TSS toxin 1 (TSST-1) than it was among TSST-1-negative strains. In contrast, the frequency of type 8 capsule expression was similar among both TSST-1-positive and -negative strains of S. aureus from patients with nonvaginal TSS. When all vaginal and nonvaginal isolates were compared, TSST-1-negative S. aureus strains were equally distributed among the type 5 and 8 and nontypeable capsule groups, whereas TSST-1-positive strains were predominantly capsule type 8.

A model of Staphylococcus aureus bacteremia, septic arthritis, and osteomyelitis in chickens

We studied the occurrence, magnitude, and kinetics of bacteremia and the resultant osteomyelitis and septic arthritis in an avian model of Staphylococcus aureus infection. Thirty-day-old male broiler chicks were inoculated i.v. with 10(5), 10(6), or 10(7) cfu of strain Duntravis, a beta-hemolytic, coagulase-producing, capsular type 8 isolate from the synovial fluid of a 2-year-old black boy. Bacteremia occurred in 80%, 90%, and 100% of animals inoculated with 10(5), 10(6), or 10(7) cfu, respectively. The magnitude of bacteremia in surviving, bacteremic animals increased for 96 hours after inoculation and then decreased after a plateau phase. Osteomyelitis and septic arthritis occurred only in chicks that were continuously bacteremic. The occurrence of osteomyelitis was uniform among continuously bacteremic animals and developed 1 to 23 hours after inoculation. Chickens are susceptible to systemic infections with S. aureus. Bacteremia, osteomyelitis, and septic arthritis may be induced in healthy chickens without prior manipulations that depress their resistance.

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.

Covalent linkage between the capsular polysaccharide and the cell wall peptidoglycan of Streptococcus pneumoniae revealed by immunochemical methods

The attachment of capsular polysaccharide to Streptococcus pneumoniae was examined using monoclonal and polyclonal antibodies. Among the strains examined, the capsular polysaccharide of types 2, 4, 6A, 6B, 7F, 8, 14, 19F and 23F was bound to the pneumococci whereas that of a type 3 strain was not. Sequential treatment with 2% SDS at 100 degrees C, pronase, and EDTA did not dissociate the capsular polysaccharide from the pneumococci. Treatment of the cells with mutanolysin, a muramidase that degrades the cell wall peptidoglycan of pneumococci and other streptococci, released both the capsular and the cell wall C-polysaccharide (C-Ps). Type 6A capsular polysaccharide released from cell walls by mutanolysin treatment, was fractionated by high performance liquid chromatography and examined by immunoelectrophoresis. It was found to be bound to both the C-Ps and the peptidoglycan. The bond between the capsular polysaccharide and the peptidoglycan has not yet been identified but is probably covalent, as the two components could not be dissociated after boiling in SDS. Based on our studies with type 6A, we propose that capsular polysaccharide and C-Ps of the pneumococcus are linked to the peptidoglycan at different sites and, thereby, indirectly to each other. Studies in mice showed that the peptidoglycan enhanced the serum antibody response to C-Ps but not to type 6A polysaccharide.

Encapsulation of Staphylococcus aureus isolates from mastitic milk: relationship between capsular polysaccharide types 5 and 8 and colony morphology in serum-soft agar, clumping factor, teichoic acid, and protein A

A total of 193 Staphylococcus aureus isolates from bovine, caprine, and ovine mastitis producing type 5 or 8 capsular polysaccharides were investigated for colony morphology in serum-soft agar and agglutinability by an anti-teichoic acid serum, after cultivation in modified staphylococcus medium no. 110. Also, 40 of these strains were cultivated in brain heart infusion and submitted to clumping factor and protein A detection tests. Considering capsular serotyping as a reference method, diffuse growth in serum-soft agar and inagglutinability by anti-teichoic acid serum identified, respectively, 57.5 and 45% of encapsulated strains cultivated in brain heart infusion and 85.5 and 77.2% of those cultivated in modified staphylococcus medium 110. Consequently, these indirect techniques underestimated encapsulation and were greatly influenced by culture conditions. Whatever the medium used, diffuse colony morphology in serum-soft agar was generally characterized by a masking of teichoic acid and protein A. By contrast, these surface antigens were detected in association with compact morphology; the presence of a thin or discontinuous capsular material could explain this result. Moreover, the masking of teichoic acid and the removal of capsular polysaccharide by washing in saline suggest that type 8 capsular polysaccharide is more abundant and labile than type 5.

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.

Correlation between esterase electrophoretic types and capsular polysaccharide types 5 and 8 among methicillin-susceptible and methicillin-resistant strains of Staphylococcus aureus

The relationship between capsular polysaccharide types 5 and 8 and esterase electrophoretic types (zymotypes) in 160 French clinical isolates of Staphylococcus aureus was studied. Methicillin-susceptible strains of capsular types 5 and 8 were represented by 11 zymotypes, indicating a high polymorphism. Methicillin-resistant strains were mainly distributed in only two distinct populations. The predominant population was represented by strains of zymotype 6 and capsular type 5, and the second population was represented by strains of zymotype 14 and capsular type 8.

Staphylococcus aureus exopolysaccharide in vivo demonstrated by immunomagnetic separation and electron microscopy

Staphylococcus aureus strains were separated from mastitis milk samples without cultivation by using monodisperse magnetic polymer particles coated with polyclonal antiserum against an encapsulated S. aureus strain. Exopolysaccharide was verified by transmission electron microscopy and the serum soft-agar culture technique. Capsular polysaccharide was found on virtually all clinical isolates. Surface protein A and S. aureus-specific cell wall components were masked when the strains were cultured on an exopolysaccharide-promoting medium. Masking of surface determinants was dependent on their concentration on the bacterial surface as well as on exopolysaccharide abundance. The polysaccharide layer on in vivo bacteria was reduced markedly after just one transfer from milk to blood agar plates but was reexpressed after culturing was done on a capsule-generating medium.

Staphylococcus aureus strains which are not identified by rapid agglutination methods are of capsular serotype 5

A total of 183 recent Staphylococcus aureus clinical isolates were tested with three commercially available rapid agglutination methods. The capsular polysaccharide type and resistance to oxacillin of these isolates were also determined. Seven isolates were not identified correctly by agglutination methods. All isolates not identified by the rapid methods were of capsular serotype 5, and of these isolates, six were resistant to oxacillin. The results suggest that these agglutination kits can be improved by the use of antibodies reactive with S. aureus capsular polysaccharide.

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.

Cross protection between an encapsulated strain of Staphylococcus hyicus and encapsulated strains of Staphylococcus aureus

Strain ST67P of Staphylococcus hyicus grew diffusely in regular serum-soft agar. With the addition of rabbit antisera prepared with Staph. aureus strains, Smith, NS58D or NS41D, capsular type A, B or C, respectively, the organisms converted to compact type growth. Mice immunized with heat-killed vaccine of strain ST67P showed significant resistance against either homologous or heterologous strains, Smith, NS58D and NS41D. Passive protective activities in rabbit antisera prepared with strains Smith, NS58D and NS41D were absorbed out with either homologous cell surface polysaccharide fraction or cell surface polysaccharide fraction extracted from strain ST67P. Well-defined large capsules were observed in ultra-thin sections treated with rabbit antiserum prepared with homologous strain conjugated with ferritin. Also, the capsule surrounded by ferritin granules was shown in ultra-thin sections treated with ferritin conjugated with antisera prepared with those heterologous strains although the capsular size was significantly smaller than those observed by homologous antiserum.

Comparison of compact colony-forming activity and paracoagulation activity of strains of Staphylococcus aureus in serum and plasmas of various animals

Using 20 strains of Staphylococcus aureus isolated from clinical specimens, the compact colony-forming activity (CCFA) in serum-soft agar (SSA) in sera from various animals and the paracoagulation (PC) activity of the compact colony-forming active substance (CCFAS) extracted from these strains were investigated. The results of this comparative study revealed that the CCFA and PC of S. aureus for sera from various animals in SSA were different, not only among different strains but also in the same strains. In addition, the effect of galactose and calcium ions on the PC activity of these strains in experiments employing human fibrinogen permitted the recognition of these groups of S. aureus strains. In one group, PC activity was decreased by galactose but unaffected by calcium ions, in the second group PC activity was unaffected by galactose but increased by calcium ions, while in the third group it was unaffected by both. These results suggest the possibility of heterogeneity of CCFA among different strains of S. aureus.

Capsular antibodies induce type-specific phagocytosis of capsulated Staphylococcus aureus by human polymorphonuclear leukocytes

Capsular types 5 and 8, which account for about 70% of Staphylococcus aureus strains isolated from the blood of patients, resisted in vitro phagocytosis by human polymorphonuclear leukocytes (PMN). Antisera and monoclonal antibody to type 5 and 8 capsular polysaccharides (CPS) induced type-specific in vitro phagocytosis of capsulated organisms by PMN. Antibodies directed against the O-acetyl moiety of the type 8 CPS were more effective in inducing phagocytosis of type 8 organisms by PMN. Either type-specific antiserum or monoclonal antibody reactive with the native O-acetylated type 8 CPS was most effective in inducing in vitro phagocytosis of type 8 organisms by PMN. These results provide further evidence that CPS of S. aureus are associated with host immunity to this organism.

Prevalence of capsular polysaccharide types 5 and 8 among Staphylococcus aureus isolates from cow, goat, and ewe milk

Monoclonal antibodies to Staphylococcus aureus capsular polysaccharide types 5 and 8 were used to serotype by enzyme-linked immunosorbent assay 212, 54, and 33 isolates from cow, goat, and ewe milk, respectively. Capsular types 5 and 8 accounted for 69.4% of bovine isolates and 71.5 and 78.8% of goat and ewe isolates, respectively. Type 5 was predominant in strains from bovine sources (51.4%), whereas type 8 was prevalent in strains from caprine (68.5%) and ovine (75.8%) sources.

Predominance of capsular polysaccharide type 5 among oxacillin-resistant Staphylococcus aureus

The relationship between capsular polysaccharide types 5 and 8 and resistance of Staphylococcus aureus to oxacillin was studied with a collection of 406 clinical isolates from six French hospitals. Of 175 type 5 isolates, 84 (48%) were resistant to oxacillin. In contrast, only 8 of 160 type 8 isolates (5%) and 5 of 71 nontypeable isolates (7%) were resistant to oxacillin. Therefore, capsular typing of clinical isolates of S. aureus may facilitate the choice of first-line antibiotic therapy.

Isolation of type 5 capsular polysaccharide from Staphylococcus aureus

Clinical surveys have indicated the predominance of type 5 and type 8 capsular polysaccharides among clinical isolates of Staphylococcus aureus. The type 5 capsular polysaccharide was extracted from three clinical isolates of S. aureus grown on solid media, and purified by ion exchange chromatography and gel filtration. Chemical analysis showed that the type 5 capsular polysaccharide is composed of N-acetylfucosamine and N-acetylhexosaminuronic acid. Immunodiffusion and 13C nuclear magnetic resonance experiments showed that the type 5 capsular polysaccharide is both immunologically and chemically distinct from the type 8 capsular polysaccharide and the teichoic acid of S. aureus.

Induction of resistance in mice by the capsular polysaccharide antigens of Staphylococcus aureus

Mice actively immunized with capsular polysaccharides extracted from capsular type strains A, B, C, and D, determined by the serum-soft agar technique, were protected against lethal infection by homologous strains, but no animals survived infection by heterologous substance immunization even with at high doses. Passive protective antibody in rabbit antisera prepared using these strains was absorbed out only by homologous capsular polysaccharide in mice. These results indicated that resistance was specific for capsular polysaccharide. The substance contained mainly neutral sugar, small amounts of hexosamine, methyl-pentose, and phosphate although these amounts varied depending on the capsular types strains.

Serotyping and electron microscopy studies of Staphylococcus aureus clinical isolates with monoclonal antibodies to capsular polysaccharide types 5 and 8

Monoclonal antibodies to Staphylococcus aureus capsular polysaccharide types 5 and 8 were prepared and used to serotype 821 clinical isolates of S. aureus from four countries. The capsular polysaccharide-binding sites on the bacterial membrane were examined by transmission and scanning electron microscopy.