Evaluation and Standardization of an Agglutination Test for Human Listeriosis

Human sera from patients with culturally confirmed listeriosis were tested for immunoglobulin M (IgM) and immunoglobulin G (IgG) agglutinating antibodies with trypsinized antigens of Listeria monocytogenes, Streptococcus faecalis, and Staphylococcus aureus. The response of humans to listeria infections is mainly IgM rather than IgG as found in animals. The antigens prepared from L. monocytogenes serotypes 1a, 1b, 2, 4b, and 4d were evaluated for specificity with normal sera, sera from patients with various other diseases, and sera from patients with listeriosis. The trypsinized antigens appeared to be specific for listeria antibodies with a cross-reaction rate of from 5.4 to 6%. Cross-reaction with S. aureus can be eliminated by absorption of the serum with S. aureus. This agglutination technique appears to be applicable for diagnostic testing, but, as with all serological procedures, both acute and convalescent sera should be tested.     

Staphylococcus aureus strains isolated from bovine mastitis: virulence,antibody production and protection from challenge in a mouse model

Septic arthritis in mice was used as a model to evaluate the virulence of Staphylococcus aureus and coagulase-negative staphylococci (CNS) isolated from cases of bovine mastitis. In addition, the model was used to evaluate the cross protection elicited by heterologous antibodies. Mice were intramuscularly inoculated with serial bacterial doses of different strains of S. aureus or CNS, for virulence determination; they were monitored for arthritis, gangrene or death up to 20 days. Antibody response, cross reactivity and resistance to challenge were tested by subcutaneous inoculation with a low dose of one of the S. aureus or CNS strains followed by challenge with two S. aureus strains. S. aureus alpha-hemolysin isolate was the most virulent, followed by alpha+beta-hemolysin and beta-hemolysin isolates. The least virulent isolates were the non-hemolytic S. aureus strains but even they were more virulent than the CNS strains tested. Antibodies against three different S. aureus antigens were detected by the ELISA in all mice that were inoculated with the S. aureus strains but not in any of those with the CNS strains. Immunoblot test against various S. aureus strains as antigens showed high cross-reactivity among the S. aureus strains but only a slight similarity, restricted to the bands above 36 kDa, with the CNS sera. Low-dose inoculation of alpha or alpha+beta strains before challenge with homologous and heterologous strains protected the mice, whereas the two beta strains provided only partial protection. The inoculations of non-hemolytic S. aureus or the CNS strains did not elicit any protection. Our findings demonstrate that pre-exposure of mice to a low dose of certain S. aureus strains could provide protection and that the antibodies produced could have an important protective role.     

Immunoblotting of a Staphylococcus aureus DNA library as a tool for isolating potential antigenic proteins

Abstract A Staphylococcus aureus DNA library was created in the lambda vector EMBL4 and expressed in Escherichia coli strain Y1090. Plaques were screened using serum from a S. aureus -infected patient. A number of positive clones that expressed proteins recognised by serum antibodies were further analysed using Western blots of total lysates from cultures infected with the lambda clones. Differences were found between patient and control sera in both the specificity and tite of anti- S. aureus antibodies. Expressed staphylococcal proteins appeared to be stable and were easily distinnguishable from E. coli proteins in the Western blot. This method may have applications in specifically selecting clones encoding antigens associated with infection and may be of potential use clinically.     

Synthesis and Evaluation of a Conjugate Vaccine Composed of Staphylococcus aureus Poly-N-Acetyl-Glucosamine and Clumping Factor A

The increasing frequency, severity and antimicrobial resistance of Staphylococcus aureus infections has made the development of immunotherapies against this pathogen more urgent than ever. Previous immunization attempts using monovalent antigens resulted in at best partial levels of protection against S. aureus infection. We therefore reasoned that synthesizing a bivalent conjugate vaccine composed of two widely expressed antigens of S. aureus would result in additive/synergetic activities by antibodies to each vaccine component and/or in increased strain coverage. For this we used reductive amination, to covalently link the S. aureus antigens clumping factor A (ClfA) and deacetylated poly-N-β-(1-6)-acetyl-glucosamine (dPNAG). Mice immunized with 1, 5 or 10 μg of the dPNAG-ClfA conjugate responded in a dose-dependent manner with IgG to dPNAG and ClfA, whereas mice immunized with a mixture of ClfA and dPNAG developed significantly lower antibody titers to ClfA and no antibodies to PNAG. The dPNAG-ClfA vaccine was also highly immunogenic in rabbits, rhesus monkeys and a goat. Moreover, affinity-purified, antibodies to ClfA from dPNAG-ClfA immune serum blocked the binding of three S. aureus strains to immobilized fibrinogen. In an opsonophagocytic assay (OPKA) goat antibodies to dPNAG-ClfA vaccine, in the presence of complement and polymorphonuclear cells, killed S. aureus Newman and, to a lower extent, S. aureus Newman ΔclfA. A PNAG-negative isogenic mutant was not killed. Moreover, PNAG antigen fully inhibited the killing of S. aureus Newman by antisera to dPNAG-ClfA vaccine. Finally, mice passively vaccinated with goat antisera to dPNAG-ClfA or dPNAG-diphtheria toxoid conjugate had comparable levels of reductions of bacteria in the blood 2 h after infection with three different S. aureus strains as compared to mice given normal goat serum. In conclusion, ClfA is an immunogenic carrier protein that elicited anti-adhesive antibodies that fail to augment the OPK and protective activities of antibodies to the PNAG cell surface polysaccharide.     

The adhesion of protein A-bearing Staphylococcus aureus organisms to soluble-staphylococcal-antigens-coated HeLa cells mediated by specific antibodies

The adhesion of staphylococcal protein A (SpA)-bearing Staphylococcus aureus Cowan I organisms to HeLa cells was enhanced by pretreatment of HeLa cells with staphylococcal extracellular antigens and antibodies to them. The adhesion of HLj, an SpA-poor mutant derived from Cowan I, to HeLa cells was not enhanced by the same pretreatment of HeLa cells. Furthermore, the enhanced staphylococcal adhesion was inhibited by soluble SpA. The antigen(s) responsible for the enhanced staphylococcal adhesion was(were) heat stable. Pretreatment of HeLa cells with the mixture of staphylococcal extracellular antigens and antibodies to them also enhanced the adhesion of Cowan I. Similarly the adhesion of Cowan I was enhanced by pretreatment of HeLa cells with extracellular antigens of Pseudomonas aeruginosa and antibodies to them. These results indicated that cell-bound SpA mediated the binding of S. aureus to immune complexes composed of extracellular bacterial products and antibodies to them bound to the surface of HeLa cells, and suggested another role of cell-bound SpA as a co-adhesin with other factors in infections due to S. aureus.     

Immunoblotting of a Staphylococcus aureus DNA library as a tool for isolating potential antigenic proteins

A Staphylococcus aureus DNA library was created in the lambda vector EMBL4 and expressed in Escherichia coli strain Y1090. Plaques were screened using serum from a S. aureus-infected patient. A number of positive clones that expressed proteins recognised by serum antibodies were further analysed using Western blots of total lysates from cultures infected with the lambda clones. Differences were found between patient and control sera in both the specificity and titre of anti-S. aureus antibodies. Expressed staphylococcal proteins appeared to be stable and were easily distinguishable from E. coli proteins in the Western blot. This method may have applications in specifically selecting clones encoding antigens associated with infection and may be of potential use clinically.     

IgY antibodies of chicken do not bind staphylococcal binder of immunoglobulin (Sbi) from Staphylococcus aureus

The immunoglobulin (Ig) binding proteins of Staphylococcus aureus namely staphylococcal protein A (SpA) and staphylococcal binder of immunoglobulin (Sbi) are responsible for false positives during immunoassays. Avian IgY antibodies were reported to have no affinity to SpA and thus are safe for use in immunoassays. However, the behaviour of Sbi with IgY was not reported. The purpose of the present study is to evaluate the interactions between IgY antibodies and Sbi protein from different S. aureus strains. Initially, heterologous cloning and expression of complete sbi gene in Escherichia coli was undertaken. Recombinant Sbi protein was utilized to generate polyclonal anti-Sbi IgY and anti-Sbi antibodies in chicken and BALB/c mice respectively. Indirect ELISA and Western blotting were performed to evaluate the reactivity of anti-Sbi antibodies. Non-reducing PAGE followed by Western blotting and double-antibody sandwich dot-ELISA were performed to analyze the reactivity of IgY antibodies with recombinant Sbi and native Sbi from S. aureus strains. To avoid the possible interference of enzyme-conjugated secondary antibodies from mammalian sources, mouse anti-Sbi revealing antibodies were labeled with biotin so that streptavidin-HRP was used as developing reagent for chromogenic reaction. Sbi was highly immunogenic in chicken and mouse with antibody titers of 1:128,000 and 1:64,000 dilutions respectively. We observed that unimmunized IgY antibodies showed no affinity to either recombinant Sbi or native Sbi from S. aureus strains in Western blotting and double antibody sandwich ELISA. In view of these observations, we recommend that IgY antibodies are safe and free from false positives due to SpA and Sbi in immunoassays involving detection of S. aureus antigens/exotoxins.     

Evidence for a Multiplicity of Capsular Types Among Staphylococcus aureus Strains

The Smith diffuse variant and the wound mucoid strain of Staphylococcus aureus were shown to exhibit serologically distinct capsules. The Welwood and K-6 strains of S. aureus were tested to determine their capsular types. Both Welwood and K-6 were found to be representative of the Smith capsular type. An additional 13 isolates of S. aureus from mice were tested. Gel double-diffusion tests and immunoelectrophoresis of staphylococcal antigens disclosed the possible existence of at least two additional capsular types. Passive hemagglutination tests carried out with cells sensitized with 1 mg of antigen per ml showed a multiplicity of cross-reacting antigens. However, cells sensitized either with 0.1 or 0.05 mg of antigen per ml and reacted with antisera absorbed with 10 or 1 mug/ml showed the presence of a specific antigen in each strain of S. aureus. Corroborative evidence for a multiplicity of capsular types was obtained by the specific capsular reaction. At least four capsular types of S. aureus were found. The prototypic strains for these antigens are the RLM or wound strain, the Smith diffuse strain, and mouse strains designated 36T and 43R. We propose to designate these types 1, 2, 3, and 4, respectively.     

An Agar Diffusion Method for the Determination Of Antibodies Against Staphylococcus Aureus Deoxyribonuclease

On the addition of small concentrations of deoxyribonuclease, produced by Staphylococcus aureus, to Toluidine Blue DNA agar, a medium is produced on which antibodies against S. aureus deoxyribonuclease may be detected. When samples of milk, or blood serum, containing antibodies against S. aureus are applied into wells in the agar, the deoxyribonuclease activity is inhibited by the antibodies diffusing into the agar. As a result of this inhibition, blue zones are produced around the wells in the otherwise bluish-red agar. The diameters of the zones correspond to the concentrations of antibodies, and the method may consequently be used for qualitative and quantitative examinations of antibodies against S. aureus deoxyribonuclease in milk and serum. The procedure and certain limitations of the method are described.     

Antibody response to Staphylococcus aureus whole cell, lipase and staphylolysin in patients with S. aureus infections

Abstract Three assays to measure antibodies against Staphylococcus aureus whole cells, lipase and staphylolysin were used to try to discriminate between complicated and uncomplicated S. aureus septicaemia. Sera were examined from 8 patients with S. aureus endocarditis, 23 patients with complicated S. aureus septicaemia, 12 patients with uncomplicated S. aureus septicaemia and 93 febrile non-septicaemic controls. No single assay could distinguish between complicated and uncomplicated S. aureus septicaemia. If the criterion for a positive result is defined as positive antibody level in the anti-lipase ELISA as well as in at least 1 of the other 2 assays, 10/31 patients with S. aureus endocarditis or complicated septicaemia were positive compared to 0/93 non-septicaemic patients and 0/12 patients with uncomplicated S. aureus septicaemia. Therefore, the combined use of serological assays in the diagnosis of complicated S. aureus septicaemia, one of which is the anti-lipase ELISA, is recommended.     

Heterogenetic antigens of gram-positive bacteria

Chorpenning, Frank W. (The Ohio State University, Columbus), and Matthew C. Dodd. Heterogenetic antigens of gram-positive bacteria. J. Bacteriol. 91:1440-1445. 1966.-Soluble antigens obtained by various methods from gram-positive bacteria were used to modify erythrocytes whose hemagglutinating reactions with immune rabbit sera and normal human sera were then studied. Antigens from all gram-positive organisms studied except corynbacteria altered red cells, causing them to react with specific bacterial antisera and with normal human sera; however, cross-absorption and inhibition tests indicated that at least three different specificites were involved. One of these antigens seemed to be similar to Rantz's streptococcal NSS, which is shared with Staphylococcus aureus and Bacillus spp., and is therefore heterogenetic. Another was found in streptococci but was apparently not present in S. aureus and Bacillus spp. A third antigen, also heterogenetic, appeared to be shared by several species of Bacillus and by S. aureus, but not by streptococci or any gram-negative bacteria. The third antigen was heat-stable at pH 8.0, and appeared to be essentially polysaccharide in nature. Normal human sera varied in their content of antibodies which reacted with erythrocytes modified by extracts from gram-positive bacteria. Whereas some sera reacted very broadly with red cells modified by extracts of practically any gram-positive organism, other sera agglutinated only cells which had been modified by streptococcal antigen.     

Rapid, automated separation of specific bacteria from lake water and sewage by flow cytometry and cell sorting.

The use of fluorescence-activated flow cytometric cell sorting to obtain highly enriched populations of viable target bacteria was investigated. Preliminary studies employed mixtures of Staphylococcus aureus and Escherichia coli. Cells of S. aureus, when mixed in different proportions with E. coli, could be selectively recovered at a purity in excess of 90%. This was possible even when S. aureus composed only approximately 0.4% of the total cells. Cell sorting was also tested for the ability to recover E. coli from natural lake water populations and sewage. The environmental samples were challenged with fluorescently labelled antibodies specific for E. coli prior to cell sorting. Final sample purities of greater than 70% were routinely achieved, as determined by CFU. Populations of E. coli released into environmental samples were recovered at greater than 90% purity. The use of flow cytometry and cell sorting to detect and recover viable target bacteria present at levels of less than 1% within an indigenous microflora was also demonstrated.     

Antibody response to the extracellular adherence protein (Eap) of Staphylococcus aureus in healthy and infected individuals

The extracellular adherence protein (Eap) from Staphylococcus aureus has been suggested as a vaccine candidate and for therapeutic use due to its immunomodulating and antiangiogenic properties; however, little is known about anti-Eap antibodies in humans. We determined anti-Eap antibody titers by enzyme-linked immunosorbent assay and Western blot and measured serum samples from 92 patients with proven S. aureus infections and 93 healthy controls. The functionality of antibodies was assessed by a phagocytosis assay using Eap-coated fluorescent microspheres. Antibodies were detected in all human samples, but not in mice. Patients showed significantly higher titers than controls [immunoglobulin M (IgM), P=0.007; IgG, P<0.0001]. Patients with deep or severe infections showed higher titers than those with superficial or mild disease. Eap alone was sufficient to promote phagocytosis by peripheral blood mononuclear cell and granulocytes that was moderately enhanced in the presence of human serum, but no correlation was found with the levels of anti-Eap antibodies. Anti-Eap antibodies are prevalent in all tested humans and correlate with the severity of S. aureus infection; however, they do not seem to provide protection against invasive infections. Before considering Eap for therapy or as a vaccine candidate, further studies are warranted to assess the impact of the interference between Eap and its specific antibodies.     

The protective effect of breast feeding in relation to sudden infant death syndrome (SIDS): I. The effect of human milk and infant formula preparations on binding of toxigenic Staphylococcus aureus to epithelial cells

Epidemiological studies indicate that breast-fed infants are at a decreased risk of sudden infant death syndrome (SIDS) compared to formula-fed infants. Increasing evidence suggests that infectious agents might be involved in some of these deaths, in particular bacteria which colonise mucosal surfaces and produce superantigenic toxins. One species implicated in recent studies of SIDS infants is Staphylococcus aureus. We tested the hypothesis that in comparison to infant formula, human milk might be a better inhibitor of binding of S. aureus to epithelial cells. In this study, two protocols were used for the binding assays which were assessed by flow cytometry: the in vitro method in which bacteria were treated with milk or formula, washed and added to epithelial cells; and a method more closely reflecting the competitive interactions in vivo in which cells, bacteria, and milk or infant formula were added at the same time. With the in vivo method, breast milk caused enhancement of bacterial binding to cells whilst infant formula caused inhibition; however, for the in vitro method, both human milk and infant formula caused consistent enhancement of binding. Flow cytometry and light microscopy studies indicated that the enhancement was due to the formation of bacterial aggregates. Human milk and infant formula preparations were also compared for components (antibodies or oligosaccharides) that could inhibit binding of S. aureus using the in vitro method. Human milk contained both IgA and IgG. Neither human milk nor infant formula contained oligosaccharides reactive with the Ulex europaeus lectin but both contained components that bound monoclonal antibodies to Lewis(a) and Lewis(b) antigens which can act as receptors for S. aureus. With both methods, synthetic Lewis(a) and Lewis(b) inhibited S. aureus binding in a dose-dependent manner. With human milk, however, the only component which showed a significant correlation with inhibition of binding was the IgA specific for the staphylococcal surface component that binds Lewis(a). Both human milk and infant formula contain components which could potentially inhibit bacterial binding but only breast milk contains the IgA specific for the bacterial adhesin that binds Lewis(a). Studies using the in vivo method suggest that protection associated with breast feeding in relation to SIDS could be due mainly to the formation of bacterial aggregates. The studies have implications for further research into constituents of infant formula.     

Targeting tumor cells

Several recent scientific and technical developments have made it possible to postulate the use of the 'magic bullet' concept; that is, the identification of specific antigens present on tumor cells that can be targeted either by therapeutic antibodies or by small molecules. The use of monoclonal antibodies in cancer, in particular, has moved beyond the proof-of-concept stage, and many such antibodies are presently being tested in the clinic. Several antibodies have been successfully developed and are now in use against various cancers, and we can expect many more to become available in the next few years. The use and development of these new therapeutics represent significant opportunities but also new challenges.     

Internalizing Cancer Antibodies from Phage Libraries Selected on Tumor Cells and Yeast-Displayed Tumor Antigens

A number of approaches have been utilized to generate antibodies to cancer cell surface receptors that can be used as potential therapeutics. A number of these therapeutic approaches, including antibody-drug conjugates, immunotoxins, and targeted nucleic acid delivery, require antibodies that not only bind receptor but also undergo internalization into the cell upon binding. We previously reported on the ability to generate cancer cell binding and internalizing antibodies directly from human phage antibody libraries selected for internalization into cancer cell lines. While a number of useful antibodies have been generated using this approach, limitations include the inability to direct the selections to specific antigens and to identify the antigen bound by the antibodies. Here we show that these limitations can be overcome by using yeast-displayed antigens known to be associated with a cell type to select the phage antibody output after several rounds of selection on a mammalian cell line. We used this approach to generate several human phage antibodies to yeast-displayed EphA2 and CD44. The antibodies bound both yeast-displayed and mammalian cell surface antigens, and were endocytosed upon binding to mammalian cells. This approach is generalizable to many mammalian cell surface proteins, results in the generation of functional internalizing antibodies, and does not require antigen expression and purification for antibody generation.     

Inhibition of Staphylococcus aureus pathogenesis in vitro and in vivo by RAP-binding peptides

Staphylococcus aureus cause many diseases by producing toxins, whose synthesis is regulated by quorum-sensing mechanisms. S. aureus secretes a protein termed RNAIII activating protein (RAP) which autoinduces toxin production via the phosphorylation of is target protein TRAP. Mice vaccinated with RAP were protected from S. aureus infection, suggesting that RAP is an useful target for selecting potential therapeutic molecules to inhibit S. aureus pathogenesis. We show here that RAP (native and recombinant) was used to select RAP-binding peptides (RBPs) from a random 12-mer phage-displayed peptide library. Two RBPs were shown to inhibit RNAIII production in vitro (used a marker for pathogenesis). The peptide WPFAHWPWQYPR, which had the strongest inhibitory activity, was chemically synthesized and also expressed in Escherichia coli as a GST-fusion. Both synthetic peptide and GST-fusion peptide decreased RNAIII levels in a dose-dependent manner. The GST-fusion peptide was also shown to protect mice from a S. aureus infection in vivo (tested in a murine cutaneous S. aureus infection model). Our results suggest the potential use of RAP-binding proteins in treating clinical S. aureus infections.     

The protective effect of breast feeding in relation to sudden infant death syndrome (SIDS): III. Detection of IgA antibodies in human milk that bind to bacterial toxins implicated in SIDS

Two toxin-producing bacteria implicated in sudden infant death syndrome (SIDS) are Staphylococcus aureus and Clostridium perfringens. Epidemiological studies have shown that breast feeding reduces an infant's risk of SIDS. This protective effect could be due partly to IgA antibodies to these toxins in human milk. The aim of this work was to use a quantitative ELISA to determine levels of IgA antibodies that bound to toxic shock syndrome toxin (TSST-1), staphylococcal enterotoxin C (SEC) and C. perfringens enterotoxin A (CEA) in individual samples of human milk. All samples of milk tested contained IgA antibodies that bound to the bacterial toxins. For individual samples, IgA bound to TSST-1, SEC and CEA were in the range of 900-3100 ng ml(-1), 1000-3600 ng ml(-1) and 1000-4300 ng ml(-1) respectively. Isolation of S. aureus from mothers donating breast milk samples was used to determine if the presence of bacteria affected IgA levels which bound TSST-1 and SEC. For 3/5 samples with levels above the upper limit of the standard deviation (2375 ng ml(-1)) for IgA bound to TSST-1, S. aureus was isolated from the mother whilst 4/5 samples found to contain levels above the upper limit of the standard deviation (2627 ng ml(-1)) for IgA bound to SEC, had S. aureus isolated from the mother. In conclusion, if bacterial toxins do play a role in precipitating a SIDS death, the presence of IgA antibodies to toxins in breast milk, but not in infant formula, might contribute to the protective effect of breast feeding in relation to SIDS.     

Non-specific immunoprecipitation of rotavirus Vp6 protein with Staphylococcus aureus

The specificity of Staphylococcus aureus and protein A-Sepharose (PA-S) were compared in the radioimmunoprecipitation assay for the characterization of monoclonal antibodies (mAbs) against rotavirus proteins. Five mAbs directed against bovine rotavirus Q17 proteins Vp6 and Vp7 and one mAb directed against human rotavirus protein Vp4 were used in this study. mAbs directed against other viruses, NS-1 culture supernatant and ascitic fluid, were used as control reagents. A non-specific immunoprecipitation of the viral protein Vp6 was always found with S. aureus, but not with PA-S. mAb 74 reacted with rotavirus antigens in ELISA and in indirect immunofluorescence assay but did not immunoprecipitate a viral protein with PA-S. This mAb immunoprecipitated the viral protein Vp6 when S. aureus reagent was used. This false positive reaction was always present and could lead to confusing results in the analysis and characterization of mAbs against rotavirus.     

Failure to Detect Cell-Associated Enterotoxin B in Staphylococcus aureus by Immunofluorescence

Enterotoxin B-producing and -nonproducing Staphylococcus aureus strains showed cell fluorescence when tested with fluoresceinisothiocyanate-labeled rabbit anti-enterotoxin B globulin, probably as a result of a protein A-immunoglobulin G (Ig G) interaction. No cell-bound enterotoxin B could be detected by immunofluorescence using F(ab(1))(2)-fragments of anti-enterotoxin B globulin. However, soluble enterotoxin B could be estimated by immunofluorescence. Approximately 1,000-fold more enterotoxin B was detected by immunodiffusion as an extracellular product in the media than could be detected in the cell fraction. The results show that intact Ig G is not suitable for the detection of antigens other than protein A on the cell surface of S. aureus in conventional immunofluorescence. For such purposes, the use of F(ab(1))(2)-fragments of Ig G is recommended.