Online Textbook Bacteriology is continuously updated and includes information on Staphylococcus, MRSA, Streptococcus, E. coli, anthrax, cholera, tuberculosis, Lyme disease and other bacterial diseases of humans.
Kenneth Todar is the author of the Online Textbook of Bacteriology and an emeritus lecturer at the University of Wisconsin-Madison.WearaMask.org encourages people to wear a FDA approved face mask during the Swine Flu pandemic.
The Online Textbook of Bacteriology is a general and medical microbiology text and includes discussion of staph, MRSA, strep, Anthrax, E. coli, cholera, tuberculosis, Lyme Disease and other bacterial pathogens.
Kenneth Todar, PhDKenneth Todar's Online Textbook of Bacteriology Home PageOnline Textbook of Bacteriology Table of ContentsInformation about materials for teaching bacteriology.Contact Kenneth Todar.



Looking for the most current news, updates, and articles relating to microbiology, go to The American Society for Microbiology educational website Microbe World.






Web Review of Todar's Online Textbook of Bacteriology. "The Good, the Bad, and the Deadly".

Tag words: Streptococcus, Streptococcus pyogenes, S pyogenes, strep, Group A strep, GAS, strep throat, streptococcal streptococci, Gram-positive cocci, cocci, wound infection, acute rheumatic fever, acute glomerulonephritis, scarlet fever, pharyngitis, impetigo, tonsillitis, pharyngeal cellulitis, pharyngeal abscess, otitis media, sinusitis, necrotizing fasciitis, streptococcal bacteremia, meningitis, brain abscess, gangrene

Streptococcus pyogenes

Kingdom: Bacteria
Phylum: Firmicutes
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus
Species: S. pyogenes


Common References: Streptococcus, Streptococcus pyogenes, S pyogenes, strep, Group A strep, GAS, strep throat, Streptococcus pyogenes







Kenneth Todar currently teaches Microbiology 100 at the University of Wisconsin-Madison.  His main teaching interest include general microbiology, bacterial diversity, microbial ecology and pathogenic bacteriology.

Staphylococcus bacteriaPrint this Page

To search the entire book, enter a term or phrase in the form below

Custom Search


Streptococcus pyogenes and Streptococcal Disease (page 1)

(This chapter has 4 pages)

© Kenneth Todar, PhD

Introduction

Streptococcus pyogenes (Group A streptococcus) is a Gram-positive, nonmotile, nonsporeforming coccus that occurs in chains or in pairs of cells. Individual cells are round-to-ovoid cocci, 0.6-1.0 micrometer in diameter (Figure 1). Streptococci divide in one plane and thus occur in pairs or (especially in liquid media or clinical material) in chains of varying lengths. The metabolism of S. pyogenes is fermentative; the organism is a catalase-negative aerotolerant anaerobe (facultative anaerobe), and requires enriched medium containing blood in order to grow. Group A streptococci typically have a capsule composed of hyaluronic acid and exhibit beta (clear) hemolysis on blood agar.
 



Figure 1. Streptococcus pyogenes. Left. Gram stain of Streptococcus pyogenes in a clinical specimen. Right. Colonies of Streptococcus pyogenes on blood agar exhibiting beta (clear) hemolysis.

Streptococcus pyogenes is one of the most frequent pathogens of humans. It is estimated that between 5-15% of normal individuals harbor the bacterium, usually in the respiratory tract, without signs of disease. As normal flora, S. pyogenes can infect when defenses are compromised or when the organisms are able to penetrate the constitutive defenses. When the bacteria are introduced or transmitted to vulnerable tissues, a variety of types of suppurative infections can occur.

In the last century, infections by S. pyogenes claimed many lives especially since the organism was the most important cause of puerperal fever (sepsis after childbirth). Scarlet fever was formerly a severe complication of streptococcal infection, but now, because of antibiotic therapy, it is little more than streptococcal pharyngitis accompanied by rash. Similarly, erysipelas (a form of cellulitis accompanied by fever and systemic toxicity) is less common today. However, there has been a recent increase in variety, severity and sequelae of Streptococcus pyogenes infections, and a resurgence of severe invasive infections, prompting descriptions of "flesh eating bacteria" in the news media. A complete explanation for the decline and resurgence is not known. Today, the pathogen is of major concern because of the occasional cases of rapidly progressive disease and because of the small risk of serious sequelae in untreated infections. These diseases remain a major worldwide health concern, and effort is being directed toward clarifying the risk and mechanisms of these sequelae and identifying rheumatogenic and nephritogenic strains of streptococci.

Acute Streptococcus pyogenes infections may present as pharyngitis (strep throat), scarlet fever (rash), impetigo (infection of the superficial layers of the skin) or cellulitis (infection of the deep layers of the skin). Invasive, toxigenic infections can result in necrotizing fasciitis, myositis and streptococcal toxic shock syndrome. Patients may also develop immune-mediated post-streptococcal sequelae, such as acute rheumatic fever and acute glomerulonephritis, following acute infections caused by Streptococcus pyogenes.

Streptococcus pyogenes produces a wide array of virulence factors and a very large number of diseases. Virulence factors of Group A streptococci include: (1) M protein, fibronectin-binding protein (Protein F) and lipoteichoic acid for adherence; (2) hyaluronic acid capsule as an immunological disguise and to inhibit phagocytosis; M-protein to inhibit phagocytosis (3) invasins such as streptokinase, streptodornase (DNase B), hyaluronidase, and streptolysins; (4) exotoxins, such as pyrogenic (erythrogenic) toxin which causes the rash of scarlet fever and systemic toxic shock syndrome.

Classification of Streptococci

Hemolysis on blood agar

The type of hemolytic reaction displayed on blood agar has long been used to classify the streptococci. Beta -hemolysis is associated with complete lysis of red cells surrounding the colony, whereas alpha-hemolysis is a partial or "green" hemolysis associated with reduction of red cell hemoglobin. Nonhemolytic colonies have been termed gamma-hemolytic. Hemolysis is affected by the species and age of red cells, as well as by other properties of the base medium. Group A streptococci are nearly always beta-hemolytic; related Group B can manifest alpha, beta or gamma hemolysis. Most strains of S. pneumoniae are alpha-hemolytic but can cause ß-hemolysis during anaerobic incubation. Most of the oral streptococci and enterococci are non hemolytic. The property of hemolysis is not very reliable for the absolute identification of streptococci, but it is widely used in rapid screens for identification of S. pyogenes and S. pneumoniae.

Antigenic types

The cell surface structure of Group A streptococci is among the most studied of any bacteria (Figure 2). The cell wall is composed of repeating units of N-acetylglucosamine and N-acetylmuramic acid, the standard peptidoglycan. Historically, the definitive identification of streptococci has rested on the serologic reactivity of "cell wall" polysaccharide antigens as originally described by Rebecca Lancefield. Eighteen group-specific antigens (Lancefield groups) were established. The Group A polysaccharide is a polymer of N-acetylglucosamine and rhamnose. Some group antigens are shared by more than one species. This polysaccharide is also called the C substance or group carbohydrate antigen.





chapter continued

Next Page

© Kenneth Todar, Ph.D. All rights reserved. - www.textbookofbacteriology.net



Kenneth Todar, PhD | Home | Table of Contents | Lecture Aids | Contact | Donate

Kenneth Todar has taught microbiology to undergraduate students at The University of Texas, University of Alaska and University of Wisconsin since 1969.

© 2008-2012 Kenneth Todar, PhD - Madison, Wisconsin