Engineering a soluble high-affinity receptor domain that neutralizes staphylococcal enterotoxin C in rabbit models of disease

Superantigens (SAgs) are a class of immunostimulatory exotoxins that activate large numbers of T cells, leading to overproduction of cytokines and subsequent inflammatory reactions and systemic toxicity. Staphylococcal enterotoxin C (SEC), a SAg secreted by Staphylococcus aureus, has been implicated in various illnesses including non-menstrual toxic shock syndrome (TSS) and necrotizing pneumonia. SEC has been shown to cause TSS illness in rabbits and the toxin contributes to lethality associated with methicillin-resistant S.aureus (MRSA) in a rabbit model of pneumonia. With the goal of reducing morbidity and mortality associated with SEC, a high-affinity variant of the extracellular variable domain of the T-cell receptor beta-chain for SEC (~14 kDa) was generated by directed evolution using yeast display. This protein was characterized biochemically and shown to cross-react with the homologous (65% identical) SAg staphylococcal enterotoxin B (SEB). The soluble, high-affinity T-cell receptor protein neutralized SEC and SEB in vitro and also significantly reduced the bacterial burden of an SEC-positive strain of MRSA (USA400 MW2) in an infective endocarditis model. The neutralizing agent also prevented lethality due to MW2 in a necrotizing pneumonia rabbit model. These studies characterize a soluble high-affinity neutralizing agent against SEC, which is cross-reactive with SEB, and that has potential to be used intravenously with antibiotics to manage staphylococcal diseases that involve these SAgs.

Pathogenicity and resistance islands of staphylococci

Variable genetic elements including plasmids, transposons and prophages are involved in pathogenesis and antibiotic resistance, and are an important component of the staphylococcal genome. This review covers a set of newly described variable chromosomal elements, pathogenicity and resistance islands, carrying superantigen and resistance genes, especially toxic shock and methicillin resistance, respectively.

Heat shock proteins and experimental autoimmune encephalomyelitis (EAE): I. Immunization with a peptide of the myelin protein 2',3' cyclic nucleotide 3' phosphodiesterase that is cross-reactive with a heat shock protein alters the course of EAE

We describe sequence similarity and immunologic cross-reactivity between a peptide of the mycobacterial hsp, HSP65, and the myelin protein 2',3' cyclic nucleotide 3' phosphodiesterase (CNP). We demonstrate that immunization with the homologous cross-reactive CNP peptide (hsp-CNP peptide) has significant biological consequences. Rats immunized with hsp-CNP peptide in either complete Freund's adjuvant (CFA) or incomplete Freund's adjuvant (IFA) produce large amounts of peptide-specific antibody. Isotypes of antibodies in animals immunized with peptide in CFA are IgG1 and IgG2a. Isotypes of antibodies in rats immunized with peptide in IFA are predominantly IgG1, with low titers of IgG2a. T cell proliferative responses to HSP65 are present in rats immunized with peptide in CFA. T cell responses to HSP65 initially are absent in rats immunized with peptide in IFA but develop over time. T cell proliferative responses to hsp-CNP peptide were not detected. None of the groups of rats developed clinical or histologic evidence of experimental autoimmune encephalomyelitis (EAE). To induce EAE, rats preimmunized with hsp-CNP peptide were challenged with guinea pig spinal cord (GPSC) emulsified in CFA. Rats preimmunized with peptide in CFA developed severe EAE. Rats preimmunized with hsp-CNP peptide in IFA were protected from EAE, with both a lower incidence and severity of disease. Injecting the murine monoclonal antibody recognizing the shared HSP65 and CNP epitope did not protect against EAE. Our data suggest that a Th2 pattern of immune response to a CNP peptide that itself is non-encephalitogenic protects against EAE. Immune responses to either hsp or myelin proteins cross-reactive with hsp may play an important role in the development of EAE.

Apparent lower rates of streptococcal toxic shock syndrome and lower mortality in children with invasive group A streptococcal infections compared with adults

Since 1985 there have been worldwide reports of increases in severe invasive Group A streptococcal (IGAS) infections. We reviewed the charts of all children with IGAS infections (defined as isolation of Group A streptococcus from a normally sterile site) presenting to our institution over a 7-year period (January, 1985, to December, 1991) and the literature. Streptococcal toxic shock syndrome required hypotension and multisystem organ involvement. Twenty-four patients (mean age, 4.96 +/- 4.4 years) were identified with IGAS infection. One patient (presenting in 1989) met the criteria for probable streptococcal toxic shock syndrome and none died. Eight of 19 Group A streptococcal isolates tested were streptococcal pyrogenic exotoxin (SPE) A producers, most (90%) had the speC gene and all had the speB gene and produced the toxin. No M or T type predominated. The low rates of streptococcal toxic shock syndrome and fatalities among children with IGAS infection are consistent with other pediatric but not with adult series. The apparent differences in outcome of IGAS between children and adults were not explained by the virulence factors we examined and may warrant further investigation.

Transmission of 'toxic strep' syndrome from an infected child to a firefighter during CPR

Several cases of a toxic shocklike syndrome have been reported in the United States during the past five years in association with Streptococcus pyogenes infection. We report a case of a firefighter exposed during attempted CPR to the secretions of an S pyogenes-infected child. The firefighter developed an infection of the hand and subsequent febrile illness with hypotension, erythematous rash, renal failure, and hypocalcemia. Bacterial isolates of blood and cerebrospinal fluid from the deceased child were identical in type and exotoxin production with isolates grown from the hand wound of the firefighter. This is the first reported case of documented transmission of S pyogenes, causing a toxic shocklike syndrome in an emergency medical technician.

Cloning, characterization, and sequencing of an accessory gene regulator (agr) in Staphylococcus aureus

We have previously identified a gene in Staphylococcus aureus, agr, whose activity is required for high-level post-exponential-phase expression of a series of secreted proteins. In this paper, we describe the cloning of this gene in Escherichia coli by using an inserted transposon (Tn551) as a cloning probe. The cloned gene, consisting of a 241-codon open reading frame containing the site of the transposon insertion, was recloned to an S. aureus vector, pSK265, and shown to be functional in S. aureus. Activity was evaluated by determinations of alpha-hemolysin, beta-hemolysin, and toxic shock syndrome toxin-1 production in early-stationary-phase cultures. The cloned gene showed considerable variation with respect to different exoproteins and different host strains compared with the chromosomal agr determinant; this variation could not be attributed to the higher copy number of the cloned gene and probably reflects inapparent subtleties of the regulatory system.

Regulation of exoprotein gene expression in Staphylococcus aureus by agar

Insertion of the erythromycin-resistance transposon Tn551 into the Staphylococcus aureus chromosome at a site which maps between the purB and ilv loci has a pleiotrophic effect on the production of a number of extracellular proteins. Production of alpha, beta and delta hemolysin, toxic shock syndrome toxin (TSST-1) and staphylokinase was depressed about fifty-fold while protein A production was elevated twenty-fold. Hybridization analysis showed that the defect in expression of TSST-1 and alpha hemolysin was at the transcriptional level. Inability of the mutant strain to express either a cloned TSST-1 gene or the chromosomal gene indicates that the transposon has inactivated a trans-active positive control element. This element has been designated agr for accessory gene regulator.

The round window membrane following application of staphylococcal exotoxin: an electron microscopic study

The round window membrane has been considered as a pathway for the passage of toxic substances from the middle ear cavity to the vestibular labyrinth in cases of otitis media. To determine the role of the round window membrane in this passage, chinchillas were given intrabullar inoculations with staphylococcal exotoxin and the round window membranes were examined electron microscopically. We observed cytoplasmic vacuolization, intercellular edema, cellular and nuclear swelling of the surface epithelia and polymorphonuclear leukocyte (PMN) infiltration of the fibrous layer. Light microscopic observation of the labyrinth revealed PMN infiltration of the most basal portion of the scala tympani. These findings demonstrate a chemotactic effect of the toxin for PMNs and support the concept of the round window membrane as an important avenue of entry.

Bacterial growth inhibition by amniotic fluid. VII. The effect of zinc supplementation on bacterial inhibitory activity of amniotic fluids from gestation of 20 weeks

Twenty human amniotic fluids obtained from gestations of 20 weeks' duration supported bacterial growth. Nine of the 20 fluids could be made inhibitory by adjusting the phosphate to zinc ratios of the fluids to less than 200 mug per milliliter. These fluids contained the phosphate-sensitive bacterial inhibitor previously, but the fluids contained sufficient phosphate to inactivate the antibacterial system. The remaining 11 amniotic fluids did not contain the peptide component of the phosphate-sensitive bacterial inhibitor and could not be made inhibitory by adjusting the phosphate to zinc ratio to less than 200 mug per milliliter. The data obtained suggested synthesis of the peptide component may occur at a gestational age of approximately 20 weeks. The peptide may indirectly be detected in fluids by determining whether antibacterial activity is obtained when the phosphate to zinc ratio of the fluids is adjusted to less than 200 mug per milliliter.

Amniotic fluid antibacterial mechanisms: newer concepts

In this review the factors present in human amniotic fluid that may function to inhibit bacterial growth have been examined. It appears that several potential antibacterial systems are present. Lysozyme and B-lysin may significantly contribute to the killing of gram-positive bacteria. Whether or not the remaining antibacterial systems function to inhibit gram-positive organisms remains to be determined. The phosphate-sensitive bacterial inhibitor recently described in our laboratory may represent the primary defense mechanism against gram-negative bacteria in amniotic fluid. Studies are warranted to ascertain whether this antibacterial system also inhibits gram-positive bacteria. The phosphate-sensitive bacterial inhibitor is quite different from other bacterial inhibitors in at least three respects. The system is very sensitive to the ubiquitous phosphate anion. The reason for this sensitivity is unknown and is difficult to explain phylogenetically, since phosphates are present virtually everywhere. To our knowledge this is the first antibacterial system of human origin which has been shown to require a metal cation as an integral part of the bactericidal effect. The peptide component of the phosphate-sensitive bacterial inhibitor is also unique in that it is of the molecular size of antibiotics or hormones. Additionally, the peptide does not appear to contain any unusual amino acids to explain its antibacterial activity. The mechanism of bacterial destruction of the phosphate-sensitive bacterial inhibitor, and its relation to the other antibacterial systems in amniotic fluid, remain to be elucidated.

Isolation of a low-molecular-weight antibacterial system from human amniotic fluid

A low-molecular-weight antibacterial system has been isolated from human amniotic fluid. The bacterial inhibitor requires the metal cation zinc and a peptide with a molecular weight of 630. The peptide component was purified using ultrafiltration, gel filtration, and ion-exchange chromatography. It can be inactivated by digestion with carboxypeptidase. The amino acid composition of the peptide is: 3 glutamine-glutamic acid, 2 glycine, and 1 lysine. Removal of zinc from the peptide has been shown to remove bacterial inhibitory activity.

Bacterial growth inhibition by amniotic fluid. V. Phosphate-to-zinc ratio as a predictor of bacterial growth-inhibitory activity

Human amniotic fluid has been shown to contain an inorganic bacterial growth-inhibitory component, zinc. The average zinc concentration in amniotic fluid was 0.44 mug per milliliter. The phosphate concentration of amniotic fluid appears to determine the expression of zinc inhibitory activity. The average phosphate concentration was 92 mug per milliliter. For 22 fluid samples tested, a phosphate-to-zinc ratio of 100 or less predicted a bactericidal fluid. A ratio between 100 and 200 predicted a bacteriostatic fluid. A ratio of greater than 200 predicted a noninhibitory fluid. The possible clinical significance of the ratio is discussed.

Bacterial growth inhibition by amniotic fluid. IV. Studies on the nature of bacterial inhibition with the use of plate-count determinations

Bacterial growth inhibition in amniotic fluid is associated with a compound or class of compounds which resembles antibacterial cationic peptides. The inhibitor studied in amniotic fluid is sensitive to treatment with monobasic and dibasic potassium phosphate, and the inhibitory activity of amniotic fluid is lost following adsorption onto bentomite. The inhibitory component in amniotic fluid interacts with bacterial cells by adsorption or is internalized by viable cells only. The inhibitory quality of amniotic fluid is not destroyed by heating to 100 degrees C. for 15 minutes, and this heat-stable inhibitory activity is associated with the compound or compounds which are phosphate sensitive. A possible mode of antibacterial action which is consistent with the data presented is discussed.

Bacterial growth inhibition by amniotic fluid. III. Demonstration of the variability of bacterial growth inhibition by amniotic fluid with a new plate-count technique

The ability of 50 human amniotic fluid samples to inhibit the growth of Escherichia coli was measured with a new semimicro plate-count technique. A range from bacterial growth-sustaining fluid to bactericidal fluid was observed. When the inhibitory capacities of the fluid samples were correlated with gestational age, a progressive increase was obtained with maximum inhibitory capacity at 36 to 40 weeks. All fluid samples obtained before 20 weeks' gestation were capable of supporting bacterial growth. Fluid samples of 36 to 40 weeks' gestation were all bactericidal or bacteriostatic. More variability in inhibitory capacity was seen after 40 weeks, with an over-all loss of inhibition observed.