Group A Streptococcus produce pilus-like structures containing protective antigens and Lancefield T antigens Marirosa Mora*†, Giuliano Bensi*†, Sabrina Capo*, Fabiana Falugi*, Chiara Zingaretti*, Andrea G. O. Manetti*, Tiziana Maggi*, Anna Rita Taddei‡, Guido Grandi*, and John L. Telford*§ *Chiron Vaccines, Via Fiorentina 1, 53100 Siena, Italy; and ‡Centro Interdipartimentale di Microscopia Elettronica, University of Tuscia, 01100 Viterbo, Italy Communicated by Rino Rappuoli, Chiron Corporation, Siena, Italy, September 8, 2005 (received for review July 29, 2005) Although pili have long been recognized in Gram-negative patho- extensively characterized and despite five decades of study, there gens as important virulence factors involved in adhesion and is still very little known about the structure and variability of T invasion, very little is known about extended surface organelles in antigens, although a gene of unknown function has been shown Gram-positive pathogens. Here we report that Group A Strepto- to code for the antigen recognized by T6 sera (9). Here we show coccus (GAS), a Gram-positive human-specific pathogen that that four of the 20 T antigens correspond to trypsin-resistant pili causes pharyngitis, impetigo, invasive disease, necrotizing fasciitis, composed of putative adhesion proteins and that recombinant and autoimmune sequelae has long, surface-exposed, pilus-like pilus proteins confer protection against lethal GAS challenge in structures composed of members of a family of extracellular a mouse model of infection and invasive disease. matrix-binding proteins. We describe four variant pili and show that each is recognized by a specific serum of the Lancefield Materials and Methods T-typing system, which has been used for over five decades to Bacterial Strains, Media, and Growth Conditions. GAS strains used characterize GAS isolates. Furthermore, we show that immuniza- are listed in Table 2, which is published as supporting informa- tion of mice with a combination of recombinant pilus proteins tion on the PNAS web site. Wild-type and mutant strains were confers protection against mucosal challenge with virulent GAS grown at 37°C or 30°C in Todd–Hewitt medium supplemented bacteria. The data indicate that induction of a protective immune with 0.5% yeast extract (THY) (Difco), or THY agars supple- response against these structures may be a useful strategy for mented with 5% defibrinated sheep blood. development of a vaccine against disease caused by GAS infection. Cell-Wall Fraction Preparation. GAS strains were grown in THY to ϭ fibronectin-binding ͉ Gram-positive OD600 0.4 at 37°C. Cells were washed once in PBS, suspended in 1 ml of ice-cold protoplasting buffer [40% sucrose͞0.1 M KPO ,pH6.2͞10 mM MgCl ͞Complete EDTA-free protease any Gram-negative bacterial pathogens use long pili that 4 2 inhibitors (Roche)͞2 mg/ml lysozime͞400 units of mutanolysin extend from the bacterial surface in adhesion and invasion M (Sigma)] and incubated at 37°C for 3 h. After centrifuging at of host tissues (reviewed in ref. 1). Immunization designed to 13,000 ϫ g for 15 min, the supernatants (cell-wall fractions) were target these important functions offer attractive strategies for frozen at Ϫ20°C. vaccine development. Although pilus biogenesis and function in Gram-negative pathogens are well understood, little is known Recombinant Proteins and Antisera. Genes coding for surface- about surface organelles in Gram-positive pathogens (2). Pilus- expressed proteins were cloned by PCR from genomic DNA into like structures have been identified in Gram-positive Coryne- Escherichia coli plasmid vectors to produce ether 6Xhistidine or bacterium diphtheriae, and their structure and assembly have GST as described by Maione et al. (5). Recombinant fusion been elucidated, but little is known of their function (2, 3). More proteins were purified by affinity chromatography as in Monti- recently, similar structures have been reported in the human giani et al. (10). Mouse antisera specific for the recombinant pathogen Group B Streptococcus (GBS, Streptococcus agalac- proteins were produced by immunizing groups of four CD1 mice tiae), and the component proteins were shown to be effective with the purified recombinant proteins. protective antigens against lethal GBS challenge in a mouse Primers used to clone and sequence major pilus genes are model of infection and disease (4, 5). listed in Table 3, which is published as supporting information on Here, we report the presence of pili on the surface of Group the PNAS web site. A Streptococcus (GAS, Streptococcus pyogenes), a Gram-positive bacteria that colonizes the pharynx and skin of humans and is the Immunoblotting. Cell-wall preparations were separated by 3–8% most common cause of bacterial pharyngitis in children. Al- gradient gels (NuPAGE Tris-acetate gels, Invitrogen) and trans- though bacterial pharyngitis is usually a self-limiting infection ferred to nitrocellulose membranes (Bio-Rad) for immunoblot with little long-term pathology, autoimmune sequelae may result analysis with mouse polyclonal antisera (1:500) and ECL en- in severe cardiac pathology and glomerulonephritis. In addition, hanced chemiluminescence detection (SuperSignal West Pico GAS causes severe invasive disease, which may result in strep- tococcal toxic shock syndrome or necrotizing fasciitis (6). MICROBIOLOGY More than 50 years ago, Lancefield and colleagues (7, 8) Conflict of interest statement: Member Rino Rappuoli is employed by Chiron Corporation. classified GAS isolates into serotypes on the basis of serum Freely available online through the PNAS open access option. recognition of a variable trypsin-sensitive surface protein, the M Abbreviations: GAS, Group A Streptococcus; GBS, Group B Streptococcus; ECM, extracel- protein (7), and a variable trypsin-resistant antigen, the T lular matrix; FCT, fibronectin-binding collagen-binding T antigen. antigen (8). To date, Ͼ100 M serotypes and Ϸ20 T serotypes Data deposition: The sequences reported in this paper have been deposited in the GenBank have been identified. Epidemiologic studies based on M and T database (accession nos. DQ106872–DQ106882). serological typing have been central to our understanding of the †M.M. and G.B. contributed equally to the work. biological diversity and disease-causing potential of GAS. §To whom correspondence should be addressed. E-mail: john࿝[email protected]. Whereas the M protein and its inherent variability have been © 2005 by The National Academy of Sciences of the USA www.pnas.org͞cgi͞doi͞10.1073͞pnas.0507808102 PNAS ͉ October 25, 2005 ͉ vol. 102 ͉ no. 43 ͉ 15641–15646 Downloaded by guest on October 1, 2021 chemiluminescent substrate, Pierce). The secondary antibody (ECL, horseradish-peroxidase-linked anti-mouse IgG, GE Healthcare) was used at a 1:5,000 dilution. In the experiment with recombinant proteins, commercially available standard anti-T-typing sera (11) were obtained from Sevapharma (Prague) and used at a 1:500 dilution and the secondary antibody (horseradish peroxidase-linked anti-rabbit IgG, Bio-Rad) was used at a 1:10,000 dilution. Flow Cytometry. Bacteria were grown in THY to OD600 ϭ 0.4, washed twice with PBS, suspended in newborn calf serum (Sigma), incubated for 20 min at room temperature, and dis- pensed in a 96-well plate (20 ␮l per well). Eighty microliters of preimmune or immune mouse sera diluted in PBS͞0.1% BSA was added to the bacterial suspension to a final dilution of 1:200. Incubation was performed on ice for 30 min. The bacteria were washed, incubated on ice for 30 min in 10 ␮l of goat anti-mouse Fig. 1. Schematic representation of the FCT region from seven GAS strains. IgG, and conjugated with F(abЈ) fragment-specific R- Genes coding for LPXTG-containing proteins are represented with orange 2 arrows, whereas transcriptional regulators (rofA, nra, and msmRL) are in phycoerythrin (Jackson Immunoresearch Laboratories) in PBS͞ ͞ green and conserved flanking genes (Spy0123 and Spy0136) are in gray. At 0.1% BSA 20% newborn calf serum to a final dilution of 1:100. least one sortase is present in every FCT region (black arrows), and a signal The stained bacteria were analyzed with a FACSCalibur cytom- peptidase, lepA, is present in three of four regions (white arrows). In the FCT eter (Becton Dickinson) and CELLQUEST software (Becton Dick- region of the M1 strains, two transposable elements are also present (blue inson). In experiments in which trypsin treatment was required arrows). and before antibody reaction, bacteria were suspended in 20 ␮l of 40% PBS plus 2, 20, or 200 ␮g of trypsin. After 30 min of incubation at 37°C, 80 ␮l of PBS and 2 ␮l of PMSF were added recombinant forms of the major pilin proteins confer protection to the samples (toa2mMfinal concentration), which were then in a mouse model of GBS disease (5). To date, these covalently incubated at room temperature for 10 min and washed with PBS. linked pili have been identified in C. diphtheriae (2) and GBS (4). In both organisms the pili are formed by the sortase enzyme- Construction of In-Frame Deletion and Complementation Mutants. catalyzed covalent linkage of surface proteins containing the Mutations were constructed by using splicing-by-overlap- cell-wall-sorting signal LPXTG and conserved pilin motifs in- extension PCR as described in ref. 12. Primers used for the volved in the linkage reaction (2, 3). These data prompted us to construction and screening of deletion alleles are listed in Table search available GAS genomes for genes coding for similar pili 4, which is published as supporting information on the PNAS to test the hypothesis that pilin components may represent web site. Restriction sites that were used in cloning are shown in protective antigens also against GAS disease. Because we failed boldface type in Table 4. The PCR deletion construct was ligated to identify pilus genes in GAS by gene or protein similarity with to the temperature-sensitive allelic exchange vector pJRS233 the pilin genes of GBS, our strategy involved a search in the five (13), and transformation and allelic exchanges were performed complete genomes (GenBank accession nos.