Protein interactions with peptides generally have low thermodynamic and mechanical stability. Streptococcus pyogenes fibronectin-binding protein FbaB contains a domain with a spontaneous isopeptide bond between Lys and Asp. By splitting this domain and rational engineering of the fragments, we obtained a peptide (SpyTag) which formed an amide bond to its protein partner (SpyCatcher) in minutes. Reaction occurred in high yield simply upon mixing and amidst diverse conditions of pH, temperature, and buffer. SpyTag could be fused at either terminus or internally and reacted specifically at the mammalian cell surface. Peptide binding was not reversed by boiling or competing peptide. Single-molecule dynamic force spectroscopy showed that SpyTag did not separate from SpyCatcher until the force exceeded 1 nN, where covalent bonds snap. The robust reaction conditions and irreversible linkage of SpyTag shed light on spontaneous isopeptide bond formation and should provide a targetable lock in cells and a stable module for new protein architectures.

There is concern that group A streptococci, which have caused less serious infections in developed countries in recent decades, may be acquiring greater virulence. We describe 20 patients from the Rocky Mountain region who had group A streptococcal infections from 1986 to 1988 that were remarkable for the severity of local tissue destruction and life-threatening systemic toxicity. Among the 20 patients (median age, 36), necrotizing fasciitis with or without myositis was the most common soft-tissue infection (55 percent). Nineteen patients (95 percent) had shock, 16 (80 percent) had renal impairment, and 11 (55 percent) had acute respiratory distress syndrome. The mortality rate was 30 percent. All patients but 1 had positive tissue cultures for Streptococcus pyogenes; 12 had positive blood cultures. Most of the patients had no underlying disease; 2 used intravenous drugs. Strains of group A beta-hemolytic streptococci isolated from 10 patients were not of a single M or T type; however, 8 of the 10 strains produced pyrogenic exotoxin A (scarlet fever toxin A, a classic erythrogenic toxin), which has rarely been observed in recent years. From our study of this cluster of severe streptococcal infections with a toxic shock-like syndrome, we conclude that in our region, more virulent group A streptococci have reappeared that produce the pyrogenic toxin A associated with scarlet fever.

Macrolide-resistant Streptococcus pyogenes isolates from Finland, Australia, and the United Kingdom and, more recently, Streptococcus pneumoniae and S. pyogenes strains from the United States were shown to have an unusual resistance pattern to macrolides, lincosamides, and streptogramin B antibiotics. This pattern, referred to as M resistance, consists of susceptibility to clindamycin and streptogramin B antibiotics but resistance to 14- and 15-membered macrolides. An evaluation of the macrolide-lincosamide-streptogramin B resistance phenotypes among our streptococcal strains collected from 1993 to 1995 suggested that this unusual resistance pattern is not rare. Eighty-five percent (n = 66) of the S. pneumoniae and 75%(n = 28) of the S. pyogenes strains in our collection had an M phenotype. The mechanism of M resistance was not mediated by target modification, as isolated ribosomes from a pneumococcal strain bearing the M phenotype were fully sensitive to erythromycin. Further, the presence of an erm methylase was excluded with primers specific for an erm consensus sequence. However, results of studies that determined the uptake and incorporation of radiolabeled erythromycin into cells were consistent with the presence of a macrolide efflux determinant. The putative efflux determinant in streptococci seems to be distinct from the multicomponent macrolide efflux system in coagulase-negative staphylococci. The recognition of the prevalence of the M phenotype in streptococci has implications for sensitivity testing and may have an impact on the choice of antibiotic therapy in clinical practice.

Toxic-shock syndrome (TSS) is an acute onset, multiorgan illness which resembles severe scarlet fever. The illness is caused by Staphylococcus aureus strains that express TSS toxin-1 (TSST-1), enterotoxin B, or enterotoxin C. TSST-1 is associated with menstrual TSS and approximately one-half of nonmenstrual cases; the other two toxins cause nonmenstrual cases, 47% and 3%, respectively. The three toxins are expressed in culture media under similar environmental conditions. These conditions may explain the association of certain tampons with menstrual TSS. Biochemically, the toxins are all relatively low molecular weight and fairly heat and protease stable. Enterotoxins B and C, share nearly 50% sequence homology with streptococcal scarlet fever toxin A; they share no homology with TSST-1 despite sharing numerous biological properties. Numerous animal models for development of TSS have suggested mechanisms of toxin action, though the exact molecular action is not known. The toxins are all potent pyrogens, induce T lymphocyte proliferation, requiring interleukin 1 release from macrophages, suppress immunoglobulin production, enhance endotoxin shock, and enhance hypersensitivity skin reactions. The genetic control of the toxins has been studied and suggests the exotoxins are variable traits. Some additional properties of TSS S. aureus which facilitate disease causation have been clarified.

A new chemically defined medium for the growth of group A streptococci has been formulated. The advantages of this new medium over previously described defined media are:(i) rates of growth (i.e., doubling times) of 20 strains were comparable to the rates of growth in complex media;(ii) each strain grew to a higher culture density in the new defined medium than in complex media;(iii) transfer from complex media with small inocula was possible without any prior adaptation regimen; and (iv) the production of virulence factors (i.e., M protein and hyaluronic acid) and extracellular enzymes during growth in this new medium was comparable to that in complex media.

Kawasaki syndrome (KS), the main cause of acquired heart disease in children, is associated with the selective expansion of V beta 2+ T cells in peripheral blood. Our study suggests that KS may be caused by a superantigen--a staphylococcal or streptococcal toxin. Bacteria were cultured without knowledge of their origin, from the throat, rectum, axilla, and groin of 16 patients with untreated acute KS and 15 controls. Bacteria producing toxins were isolated from 13 of 16 KS patients but from only 1 of 15 controls (p < 0.0001). Toxic shock syndrome toxin (TSST) secreting Staphylococcus aureus was isolated from 11 of the 13 toxin-positive cultures, and streptococcal pyogenic exotoxin (SPE) B and C were found in the other 2. These toxins are known to stimulate V beta 2+ T cells. All TSST-producing KS isolates were tryptophan auxotrophs indicating they were clonally related. S aureus isolates from acute KS patients were unusual because they produced less lipase, haemolysin, and protease compared to other isolates (p < 0.01). S aureus colonies from KS patients were white, and could be easily mistaken for coagulase-negative staphylococci, whereas colonies of non-KS isolates were gold. These observations suggest that the expansion of V beta 2+ T cells in most patients with KS may be caused by a new clone of TSST-producing S aureus, and, in a minority of patients, SPEB-producing or SPEC-producing streptococci.

Since the 1980s there has been a marked increase in the recognition and reporting of highly invasive group A streptococcal infections with or without necrotizing fasciitis associated with shock and organ failure. Such dramatic cases have been defined as streptococcal toxic-shock syndrome. Strains of group A streptococci isolated from patients with invasive disease have been predominantly M types 1 and 3 that produce pyrogenic exotoxin A or B or both. In this paper, the clinical and demographic features of streptococcal bacteremia, myositis, and necrotizing fasciitis are presented and compared to those of streptococcal toxic-shock syndrome. Current concepts in the pathogenesis of invasive streptococcal infection are also presented, with emphasis on the interaction between group A Streptococcus virulence factors and host defense mechanisms. Finally, new concepts in the treatment of streptococcal toxic-shock syndrome are discussed.

A characteristic feature of infection by Staphylococcus aureus is bloodstream invasion and widespread metastatic abscess formation. The ability to extravasate, which entails crossing the vascular basement membrane, appears to be critical for the organism's pathogenicity. Extravasation by normal and neoplastic mammalian cells has been correlated with the presence of specific cell surface receptors for the basement membrane glycoprotein laminin. Similar laminin receptors were found in Staphylococcus aureus but not in Staphylococcus epidermidis, a noninvasive pathogen. There were about 100 binding sites per cell, with an apparent binding affinity of 2.9 nanomolar. The molecular weight of the receptor was 50,000 and pI was 4.2. Eukaryotic laminin receptors were visualized by means of the binding of S. aureus in the presence of laminin. Prokaryotic and eukaryotic invasive cells might utilize similar, if not identical, mechanisms for invasion.

The hyaluronic acid capsule of group A Streptococcus (GAS) is an important virulence factor, but little is known about mechanisms that regulate capsule expression. Transposon Tn916 mutagenesis of the poorly encapsulated M-type 3 GAS strain DLS003 produced a transconjugant that exhibited a mucoid colony morphology, reflecting increased hyaluronic acid capsule production. Analysis of chromosomal DNA sequence immediately downstream of the transposon insertion identified two open reading frames, designated csrR and csrS, which exhibited sequence similarity to bacterial two-component regulatory systems. We constructed an in-frame deletion mutation within csrR, which encodes the putative response component. Replacement of the native csrR gene in the DLS003 chromosome with the mutant allele resulted in a sixfold increase in capsule production and a corresponding increase in transcription of the has operon, which contains the essential genes for hyaluronic acid synthesis. Increased capsule production by the csrR mutant strain was associated with enhanced resistance to complement-mediated opsonophagocytic killing in vitro and with a 500-fold increase in virulence in mice. These results establish CsrR as a negative regulator of hyaluronic acid capsule synthesis and suggest that it is part of a two-component regulatory system that influences capsule expression and virulence.

Type III secretion for injection of effector proteins into host cells has not been described for Gram-positive bacteria despite their importance in disease. Here, we describe an injection pathway for the Gram-positive pathogen Streptococcus pyogenes that utilizes streptolysin O (SLO), a cholesterol-dependent cytolysin. The data support a model in which an effector is translocated through the SLO pore by a polarized process. The effector, SPN (S. pyogenes NAD-glycohydrolase), is capable of producing the potent second messenger cyclic ADP-ribose, and SLO and SPN act synergistically to trigger cytotoxicity. These data provide a novel paradigm for the function of the cholesterol-dependent cytolysin family and its wide distribution suggests that cytolysin-mediated translocation (CMT) may be the equivalent of type III secretion for Gram-positive pathogens.

Streptococcus pyogenes are important pathogenic bacteria which produce an extracellular cysteine proteinase contributing to their virulence and pathogenicity. S. pyogenes also express surface molecules, M proteins, that are major virulence determinants due to their antiphagocytic property. In the present work live S. pyogenes bacteria of the M1 serotype were incubated with purified cysteine proteinase. Several peptides were solubilized, and analysis of their protein-binding properties and amino acid sequences revealed two internal fibrinogen-binding fragments of M1 protein (17 and 21 kDa, respectively), and a 36-kDa IgG-binding NH2-terminal fragment of protein H, an IgGFc-binding surface molecule. M protein also plays a role in streptococcal adherence, and removal of this and other surface proteins could promote bacterial dissemination, whereas the generation of soluble complexes between immunoglobulins and immunoglobulin-binding streptococcal surface proteins could be an etiological factor in the development of glomerulonephritis and rheumatic fever. Thus, in these serious complications to S. pyogenes infections immune complexes are found in affected organs. The cysteine proteinase also solubilized a 116-kDa internal fragment of C5a peptidase, another streptococcal surface protein. Activation of the complement system generates C5a, a peptide stimulating leukocyte chemotaxis. C5a-mediated granulocyte migration was blocked by the 116-kDa fragment. This mechanism, by which phagocytes could be prevented from reaching the site of infection, may also contribute to the pathogenicity and virulence of S. pyogenes.