BMI10 - Streptococcus Pyogenes

What is Streptococcus pyogenes classified as?

Streptococcus pyogenes is classified as Group A Streptococcus (GAS).

What are the major diseases caused by Streptococcus pyogenes?

Major diseases caused by Streptococcus pyogenes include streptococcal pharyngitis (strep throat), scarlet fever, acute rheumatic fever, acute glomerulonephritis, streptococcal pyoderma (impetigo), erysipelas, cellulitis, and necrotizing fasciitis.

What is streptococcal pharyngitis?

Streptococcal pharyngitis, also called strep throat, is an infection of the throat caused by Streptococcus pyogenes.

What is scarlet fever?

Scarlet fever is a disease caused by Streptococcus pyogenes characterized by pharyngitis and a diffuse rash caused by streptococcal toxin production.

What are nonsuppurative complications of Streptococcus pyogenes infections?

Nonsuppurative complications are inflammatory complications without pus formation and include acute rheumatic fever (ARF) and acute glomerulonephritis (AGN).

What does ARF stand for in streptococcal disease?

ARF stands for acute rheumatic fever.

What does AGN stand for in streptococcal disease?

AGN stands for acute glomerulonephritis.

What is streptococcal pyoderma?

Streptococcal pyoderma is a surface skin infection caused by Streptococcus pyogenes, also called impetigo.

What invasive infections can Streptococcus pyogenes cause?

Streptococcus pyogenes can cause erysipelas, cellulitis, and necrotizing fasciitis.

What is erysipelas?

Erysipelas is a superficial skin infection involving the upper dermis and lymphatics caused by Streptococcus pyogenes.

What is cellulitis?

Cellulitis is a deeper invasive infection of the subcutaneous tissues caused by Streptococcus pyogenes.

What is necrotizing fasciitis?

Necrotizing fasciitis is a rapidly spreading, life-threatening infection involving the fascia, muscle, fat, and deeper subcutaneous tissues caused by Streptococcus pyogenes.

Why is necrotizing fasciitis called flesh-eating disease?

Necrotizing fasciitis is called flesh-eating disease because it causes extensive and rapidly spreading necrosis of skin and underlying tissues.

Approximately how many cases of noninvasive Group A Streptococcal disease occur annually according to the CDC?

The CDC estimates approximately 10 million cases of noninvasive Group A Streptococcal disease annually.

What are the most common noninvasive Group A Streptococcal diseases?

The most common noninvasive Group A Streptococcal diseases are pharyngitis and pyoderma.

What is the composition of the Streptococcus pyogenes capsule?

The Streptococcus pyogenes capsule is composed of hyaluronic acid.

Why is the Streptococcus pyogenes capsule considered nonimmunogenic?

The hyaluronic acid capsule is nonimmunogenic because it resembles host connective tissue components and is poorly recognized by the immune system.

How does the capsule of Streptococcus pyogenes help the bacterium evade the immune system?

The capsule is antiphagocytic and helps prevent engulfment and destruction by phagocytic cells.

What is the function of M protein in Streptococcus pyogenes?

M protein is an antiphagocytic virulence factor that interferes with complement activity and facilitates degradation of C3b.

How does M protein interfere with complement?

M protein prevents effective interaction with complement by facilitating degradation of C3b.

Why is M protein important for Streptococcus pyogenes virulence?

M protein is important because it helps the bacterium avoid phagocytosis and survive in host tissues.

How many M protein types exist in Streptococcus pyogenes?

There are more than 80 different M protein types in Streptococcus pyogenes.

What is the function of F protein in Streptococcus pyogenes?

F protein binds fibronectin and functions as a major adhesin for bacterial attachment and entry into epithelial cells.

What host molecule does F protein bind?

F protein binds fibronectin.

Why is fibronectin binding important for Streptococcus pyogenes?

Fibronectin binding allows bacterial attachment to epithelial cells and facilitates colonization and invasion.

What are the hemolysins produced by Streptococcus pyogenes?

The hemolysins produced by Streptococcus pyogenes are streptolysin S and streptolysin O.

What do streptolysin S and streptolysin O do?

Streptolysin S and streptolysin O lyse white blood cells, red blood cells, and platelets.

How do hemolysins contribute to tissue damage in Streptococcus pyogenes infections?

Hemolysins stimulate the release of lysosomal enzymes from damaged cells, increasing tissue destruction.

What cells are lysed by streptococcal hemolysins?

Streptococcal hemolysins lyse white blood cells, red blood cells, and platelets.

What are streptokinases?

Streptokinases are fibrinolytic enzymes produced by Streptococcus pyogenes that dissolve blood clots.

How do streptokinases facilitate bacterial spread?

Streptokinases dissolve fibrin clots, allowing bacteria to spread more easily through tissues.

Why are streptokinases considered tissue dissemination factors?

Streptokinases promote bacterial movement through tissues by breaking down blood clots that would otherwise contain infection.

What is hyaluronidase?

Hyaluronidase is an enzyme produced by Streptococcus pyogenes that degrades hyaluronic acid in the extracellular matrix.

Why is hyaluronidase called a spreading factor?

Hyaluronidase is called a spreading factor because it breaks down extracellular matrix components, facilitating spread of bacteria through tissues.

What extracellular matrix component is degraded by hyaluronidase?

Hyaluronidase degrades hyaluronic acid in the extracellular matrix.

Which Streptococcus pyogenes virulence factors are primarily involved in immune evasion?

The capsule and M protein are primarily involved in immune evasion.

Which Streptococcus pyogenes virulence factor is primarily involved in adhesion?

F protein is primarily involved in adhesion to host epithelial cells.

Which Streptococcus pyogenes virulence factors are involved in tissue dissemination?

Streptokinase and hyaluronidase are involved in tissue dissemination.

What is streptococcal impetigo also called?

Streptococcal impetigo is also called pyoderma.

What type of infection is streptococcal impetigo?

Streptococcal impetigo is a confined purulent infection of the skin.

What does “pyoderma” mean?

“Pyo” refers to pus and “derma” refers to skin, so pyoderma means a pus-forming skin infection.

How does streptococcal impetigo usually begin?

Streptococcal impetigo begins when skin is colonized with Streptococcus pyogenes after direct contact with an infected person or contaminated fomites.

How is Streptococcus pyogenes introduced into the skin during impetigo?

The organism enters through breaks in the skin and reaches subcutaneous tissue.

How is streptococcal impetigo transmitted?

Streptococcal impetigo is transmitted by direct contact with infected individuals or contaminated fomites.

What age group is most commonly affected by streptococcal impetigo?

Streptococcal impetigo most commonly affects children 2–5 years of age.

In what climates is streptococcal impetigo more common?

Streptococcal impetigo is more common in tropical and subtropical climates.

During what season is streptococcal impetigo more common in northern climates?

In northern climates, streptococcal impetigo is more common during summer months.

How do skin strains of Streptococcus pyogenes differ from throat strains?

Skin strains and throat strains differ in their M protein types.

What is the initial lesion seen in streptococcal impetigo?

The initial lesion is a vesicle surrounded by erythema.

How do impetigo lesions progress over time?

Vesicles progress to pustules that enlarge, rupture, and crust over over 4–6 days.

How long does it typically take impetigo lesions to crust over?

Impetigo lesions usually crust over within 4–6 days.

What happens after impetigo lesions heal?

Lesions heal slowly and may leave depigmented areas.

Are impetigo lesions usually localized or widespread?

Impetigo lesions are usually localized but are often multiple.

How do impetigo lesions spread on the body?

Impetigo lesions commonly spread through scratching.

What other bacterial species may be involved in impetigo infections?

Staphylococcus aureus may also be present in impetigo infections.

Why is penicillin no longer recommended as sole treatment for streptococcal pyoderma?

Penicillin is no longer recommended because impetigo is frequently a combined infection with beta-lactamase-producing Staphylococcus aureus.

What oral antibiotics are effective for streptococcal pyoderma?

Effective oral antibiotics include cloxacillin, cephalexin, cefadroxil, and cefaclor.

Why is cloxacillin useful in treating impetigo?

Cloxacillin is resistant to beta-lactamases commonly produced by Staphylococcus aureus.

How long is treatment for streptococcal pyoderma typically given?

Treatment is typically given for 10 days.

What topical antibiotic may be used to treat streptococcal pyoderma?

Mupirocin ointment may be used to treat streptococcal pyoderma.

How often is mupirocin ointment applied for streptococcal pyoderma?

Mupirocin ointment is applied three times per day.

How effective is mupirocin compared with oral therapy for impetigo?

Mupirocin has a cure rate equivalent to oral therapy.

What is a disadvantage of mupirocin therapy?

Mupirocin therapy is expensive.

What is the mechanism of action of mupirocin?

Mupirocin inhibits bacterial tRNA synthetase.

What tissues are affected in erysipelas?

Erysipelas affects the upper dermis and lymphatic vessels.

What are the clinical features of erysipelas?

Erysipelas presents as a painful, bright red, swollen, warm, raised lesion with systemic signs.

What shape is classically associated with erysipelas lesions?

Erysipelas lesions are classically butterfly-shaped.

Why can facial erysipelas be difficult to diagnose?

Facial erysipelas is rare and may be confused with facial cellulitis from dental infections.

How does cellulitis differ from erysipelas?

Cellulitis is more invasive and involves deeper subcutaneous tissues, while erysipelas is more superficial.

What tissues are involved in cellulitis?

Cellulitis involves the subcutaneous tissues.

What tissues are affected in necrotizing fasciitis?

Necrotizing fasciitis affects deeper subcutaneous tissues, fascia, muscle, and fat layers.

Why is necrotizing fasciitis considered life threatening?

Necrotizing fasciitis spreads rapidly, causes extensive tissue necrosis, and has a high mortality rate even with treatment.

How does necrotizing fasciitis usually begin?

Necrotizing fasciitis usually begins at the site of minor or inapparent trauma.

What toxin-mediated syndrome may accompany necrotizing fasciitis?

Necrotizing fasciitis may be associated with streptococcal toxic shock syndrome.

Why is early recognition of necrotizing fasciitis critical?

Early recognition is critical because mortality rates are high even with treatment and tissue destruction progresses rapidly.

What antibiotics are used to treat necrotizing fasciitis caused by Streptococcus pyogenes?

High-dose penicillin and clindamycin are used to treat necrotizing fasciitis.

Why is clindamycin added to penicillin therapy in necrotizing fasciitis?

Clindamycin suppresses exotoxin and M-protein production by inhibiting protein synthesis.

What is the mechanism of clindamycin in Streptococcus pyogenes infections?

Clindamycin inhibits protein synthesis, reducing exotoxin and M-protein production.

What surgical treatment is required for necrotizing fasciitis?

Extensive surgical debridement is required and may include amputation.

What symptoms may precede severe necrotizing fasciitis?

Patients may initially experience malaise, diffuse myalgia, low-grade fever, and rapidly worsening localized pain.

Why can pain in necrotizing fasciitis become severe quickly?

Rapid tissue necrosis and deep tissue invasion cause excruciating pain over a short period of time.