A single emm gene-specific oligonucleotide probe does not recognise all members of the Streptococcus pyogenes M type 1

Vaccine Approaches To Protect against Group A Streptococcal Pharyngitis

Streptococcal pharyngitis (or strep throat) is a common childhood disease affecting millions of children each year, but it is one of the only childhood diseases for which a vaccine does not exist. While for decades the development of a vaccine has been the center of attention in many laboratories worldwide, with some successes, no corporate development has yet to be initiated. The reason for this probably lies in our inability to conclusively identify the streptococcal molecule or molecules responsible for the heart cross-reactive antibodies observed in the serum of rheumatic fever patients. Without this specific knowledge, any streptococcal vaccine antigen is suspect and thus not the target for a billion-dollar investment, despite the fact that the exact role of cross-reactive antibodies in rheumatic fever is still questionable. This article will describe the development of several approaches to protect against Streptococcus pyogenes infections over the past several decades.

Streptococcal M proteins and their role as virulence determinants

Group A streptococci (GAS, Streptococcus pyogenes) are exclusive human pathogens that have been extensively studied for many decades. The spectrum of diseases caused by these bacteria ranges from uncomplicated and superficial to severe and invasive infections. In order to give rise to these complications, GAS have evolved a number of surface-bound and secreted virulence factors, of which the M proteins are probably the best characterized. Evidence has emerged that M proteins are multifunctional pathogenic determinants, and over the years many interactions between M proteins and the human host have been reported. The present review article aims to present a state-of-the-art overview of the most important virulence mechanisms employed by M proteins to trigger disease.

Temporal Changes in Streptococcal M Protein Types and the Near-Disappearance of Acute Rheumatic Fever in the United States

BACKGROUND

The explanation for the very substantial decrease in the incidence of acute rheumatic fever in the United States, particularly over the past 50 years, is unclear. It has been proposed that certain M types of group A streptococci (GAS) include strains that are particularly rheumatogenic and that others are nonrheumatogenic.

METHODS

We compared the M type distribution of GAS recovered from children from Chicago, Illinois, with acute pharyngitis during 1961-1968 to that of GAS recovered from Chicago children and children from across the United States in 2000-2004, with attention to changes in M types that previously were associated with rheumatogenic strains.

RESULTS

The rheumatogenic types 3, 5, 6, 14, 18, 19, and 29 comprised 49.7% of 468 pharyngeal isolates during 1961-1968 but only 10.6% of 450 Chicago isolates during 2000-2004 (P < .001) and 17.9% of 3969 isolates nationwide during 2000-2004 (P < .001). Significant decreases in types 3, 5, and 6 and virtual disappearance of types 14, 18, 19, and 29 occurred between the 2 study periods. No change in the proportion of type 1 isolates, a highly heterogeneous group that includes some rheumatogenic strains, was observed. The nonrheumatogenic GAS types 2, 4, 22, and 28 increased from 4.9% to approximately 28% of pharyngeal isolates in Chicago and nationwide between the 2 study periods (P < .001).

CONCLUSIONS

These data support the concept of rheumatogenic strains of GAS and indicate that the marked decrease in the incidence of acute rheumatic fever in the United States over the past 4 decades is correlated with the replacement of rheumatogenic types by nonrheumatogenic types in cases of acute streptococcal pharyngitis in children. The reasons underlying the observed change in distribution of M types remain to be elucidated.

M protein typing of Thai group A streptococcal isolates by PCR-Restriction fragment length polymorphism analysis

BACKGROUND

Group A streptococcal (GAS) infections can lead to the development of severe post-infectious sequelae, such as rheumatic fever (RF) and rheumatic heart disease (RHD). RF and RHD are a major health concern in developing countries, and in indigenous populations of developed nations. The majority of GAS isolates are M protein-nontypeable (MNT) by standard serotyping. However, GAS typing is a necessary tool in the epidemiologically analysis of GAS and provides useful information for vaccine development. Although DNA sequencing is the most conclusive method for M protein typing, this is not a feasible approach especially in developing countries. To overcome this problem, we have developed a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-based assay for molecular typing the M protein gene (emm) of GAS.

RESULTS

Using one pair of primers, 13 known GAS M types showed one to four bands of PCR products and after digestion with Alu I, they gave different RFLP patterns. Of 106 GAS isolates examined from the normal Thai population and from patients with GAS-associated complications including RHD, 95 isolates gave RFLP patterns that corresponded to the 13 known M types. Only 11 isolates gave RFLP patterns that differed from the 13 known M types. These were then analyzed by DNA sequencing and six additional M types were identified. In addition, we found that M93 GAS was the most common M type in the population studied, and is consistent with a previous study of Thai GAS isolates.

CONCLUSION

PCR-RFLP analysis has the potential for the rapid screening of different GAS M types and is therefore considerably advantageous as an alternative M typing approach in developing countries in which GAS is endemic.

The Protein Expression of Streptococcus pyogenes Is Significantly Influenced by Human Plasma

During the course of infection, the common human pathogen Streptococcus pyogenes encounters plasma. We show that plasma causes S. pyogenes to rapidly remodel its cellular metabolism and virulence pathways. We also identified a variant of the major virulence factor, M1 protein, lacking 13 amino acids at the NH(2)-terminus in bacteria grown with plasma. The pronounced effect of plasma on protein expression, suggests this is an important adaptive mechanism with implications for S. pyogenes pathogenicity.

Molecular basis of group A streptococcal virulence

The group A streptococcus (GAS) (Streptococcus pyogenes) is among the most common and versatile of human pathogens. It is responsible for a wide spectrum of human diseases, ranging from trivial to lethal. The advent of modern techniques of molecular biology has taught much about the organism's virulence, and the genomes of several GAS types have now been deciphered. Surface structures of GAS including a family of M proteins, the hyaluronic acid capsule, and fibronectin-binding proteins, allow the organism to adhere to, colonise, and invade human skin and mucus membranes under varying environmental conditions. M protein binds to complement control factors and other host proteins to prevent activation of the alternate complement pathway and thus evade phagocytosis and killing by polymorphonuclear leucocytes. Extracellular toxins, including superantigenic streptococcal pyrogenic exotoxins, contribute to tissue invasion and initiate the cytokine storm felt responsible for illnesses such as necrotising fasciitis and the highly lethal streptococcal toxic shock syndrome. Progress has been made in understanding the molecular epidemiology of acute rheumatic fever but less is understood about its basic pathogenesis. The improved understanding of GAS genetic regulation, structure, and function has opened exciting possibilities for developing safe and effective GAS vaccines. Studies directed towards achieving this long-sought goal are being aggressively pursued.

Surface proteins of gram-positive bacteria and mechanisms of their targeting to the cell wall envelope

The cell wall envelope of gram-positive bacteria is a macromolecular, exoskeletal organelle that is assembled and turned over at designated sites. The cell wall also functions as a surface organelle that allows gram-positive pathogens to interact with their environment, in particular the tissues of the infected host. All of these functions require that surface proteins and enzymes be properly targeted to the cell wall envelope. Two basic mechanisms, cell wall sorting and targeting, have been identified. Cell well sorting is the covalent attachment of surface proteins to the peptidoglycan via a C-terminal sorting signal that contains a consensus LPXTG sequence. More than 100 proteins that possess cell wall-sorting signals, including the M proteins of Streptococcus pyogenes, protein A of Staphylococcus aureus, and several internalins of Listeria monocytogenes, have been identified. Cell wall targeting involves the noncovalent attachment of proteins to the cell surface via specialized binding domains. Several of these wall-binding domains appear to interact with secondary wall polymers that are associated with the peptidoglycan, for example teichoic acids and polysaccharides. Proteins that are targeted to the cell surface include muralytic enzymes such as autolysins, lysostaphin, and phage lytic enzymes. Other examples for targeted proteins are the surface S-layer proteins of bacilli and clostridia, as well as virulence factors required for the pathogenesis of L. monocytogenes (internalin B) and Streptococcus pneumoniae (PspA) infections. In this review we describe the mechanisms for both sorting and targeting of proteins to the envelope of gram-positive bacteria and review the functions of known surface proteins.

PCR-enzyme-linked immunosorbent assay and sequencing as an alternative to serology for M-antigen typing of Streptococcus pyogenes

A rapid PCR-enzyme-linked immunosorbent assay for identification of 10 important emm gene types of Streptococcus pyogenes was developed. The emm genotypes of a coded panel of strains of known M serotype were determined, and in 144 of 149 cases (97%) the results were congruous. Strains of types that were not included in the panel of capture probes were emm genotyped by sequencing.

Sequencing emm-specific PCR products for routine and accurate typing of group A streptococci

Rapid sequence analysis of specific PCR products was used to accurately deduce emm types corresponding to the majority of the known group A streptococcal (GAS) M serotypes. The study involved 95 M type reference GAS strains and a survey of 74 recent clinical isolates. A high percentage of agreement between M type serology and the previously published 5' sequences of the emm genes of M type reference strains was noted. The 5' sequences for six established M protein genes--the emm-32, emm-34, emm-38, emm-40, emm-42, and emm-71 genes--were determined to supplement the existing emm sequence database. Rapid sequence analysis differentiated serologically M-nontypeable strains and was used to establish the probable.