Characteristics and Classification of Streptococci

Questions and Answers

What is the characteristic arrangement of gram-positive cocci in Streptococci?

In clusters

In pairs or chains (correct)

In single cells

In irregular patterns

What is the primary basis for serologic grouping of streptococci?

Fatty acid composition

Nucleic acid sequence

Protein structure

Carbohydrate (correct)

What is the function of M protein in Streptococci?

Increases virulence

Decreases acid resistance

Inhibits phagocytosis (correct)

Enhances phagocytosis

Which of the following is NOT a characteristic of Streptococci?

Catalase-positive Signup and view all the answers

What is the name of the disease caused by Streptococcus pyogenes?

All of the above Signup and view all the answers

What is the effect of 10% carbon dioxide on the growth of Streptococci?

Enhances growth Signup and view all the answers

What is the type of hemolysis caused by Streptococcus pyogenes?

β -hemolysis Signup and view all the answers

What is the name of the component of Streptococci that provides type-specific immunity?

M protein Signup and view all the answers

What is the primary function of the polysaccharide capsule in Streptococcus pyogenes?

To retard phagocytosis Signup and view all the answers

What is the main difference between group A streptococci and group B streptococci in response to the bacitracin test?

Group A streptococci produce a wider zone of inhibition Signup and view all the answers

Which of the following enzymes is NOT produced by Streptococcus pyogenes?

Lipase Signup and view all the answers

What is the primary site of colonization for Streptococcus agalactiae?

Vagina and colon Signup and view all the answers

What is the mechanism by which Streptococcus pyogenes adheres to pharyngeal epithelium?

Via M protein and lipoteichoic acid Signup and view all the answers

What is the result of the growth of Streptococcus pyogenes on agar plates in the laboratory when exposed to bacitracin?

Zone of inhibition Signup and view all the answers

How do group A streptococci cause disease?

Through pyogenic inflammation, exotoxin production, and immunologic response Signup and view all the answers

What is the role of M protein in group A streptococci?

To confer rheumatogenicity Signup and view all the answers

What is the main predisposing factor for neonatal sepsis, pneumonia, and meningitis caused by Group B streptococci?

Prolonged rupture of the membranes in women who lack antibody to Group B streptococci IgGs Signup and view all the answers

What is a characteristic of Group B streptococci?

They hydrolyze hippurate Signup and view all the answers

What is a complication of Group B streptococcal infections in adults?

Endocarditis Signup and view all the answers

What is the primary site of colonization for Group B streptococci?

Genital tract Signup and view all the answers

What is a major criterion in the diagnosis of rheumatic fever?

Erythema marginatum Signup and view all the answers

What is the main predisposing factor for adult Group B streptococcal infections?

Diabetes Signup and view all the answers

What is the function of hyaluronidase in Skin infections?

It degrades hyaluronic acid and facilitates the rapid spread of Str.pyogenes Signup and view all the answers

What is the mechanism of action of erythrogenic toxin?

It acts as a superantigen, similar to TSST of Sta.aureus Signup and view all the answers

What is the function of streptolysin O?

It is a hemolysin that causes β-hemolysis when colonies grow under the surface of a blood agar plate Signup and view all the answers

What is the function of streptolysin S?

It causes β-hemolysis when colonies grow on the surface of a blood agar plate Signup and view all the answers

What is the function of pyogenic exotoxin A?

It is a superantigen that causes the release of large amounts of cytokines from helper T cells and macrophages Signup and view all the answers

What is the function of exotoxin B?

It is a protease that rapidly destroys tissue Signup and view all the answers

What is the significance of the Dick test?

It is a skin test used to determine if a person has antitoxin against erythrogenic toxin Signup and view all the answers

What is the significance of the titer of ASO antibody?

It is important in the diagnosis of rheumatic fever Signup and view all the answers

Study Notes

Characteristics of Streptococci

Spherical or oval gram-positive cocci arranged in chains or pairs
Facultative anaerobes
Grow well on ordinary solid media enriched with blood, serum, or glucose as discoid colonies
Capsular streptococcal strains give rise to mucoid colonies
Aerobic bacteria in which growth is enhanced with 10% carbon dioxide
Catalase-negative
Heterogeneous group of bacteria

Classification of Streptococci

Based on:
- Colony morphology and hemolysis in blood agar
- Serologic specificity of the cell wall group-specific substances or capsular antigens
- Biochemical reactions and resistance to physical and chemical factors
- Molecular genetics

α and β-Hemolysis

α-Hemolysis: partial lysis of red blood cells
β-Hemolysis: complete lysis of red blood cells
α-Hemolytic colony: probably a viridans group streptococcus
β-Hemolytic colony: probably Streptococcus pyogenes

Diseases Caused by Streptococcus pyogenes

Pharyngitis
Cellulitis
Impetigo
Necrotizing fasciitis
Streptococcal toxic shock syndrome
Rheumatic fever
Acute glomerulonephritis

Antigenic Structure of Streptococcus pyogenes

Group-specific cell wall antigen (carbohydrate)
M protein (most important virulence factor)
- Found in hair-like projections on the outer surface of the streptococcal cell
- Antiphagocytic
- Acid and heat resistant
- Provides type-specific immunity
Polysaccharide capsule (plays a role in retarding phagocytosis)
Protein F (fibronectin-binding proteins)

Transmission of Streptococcus pyogenes

Part of the normal flora of the human throat, skin, and intestines
Produce disease when they gain access to tissues or blood
Found on the skin and in the oropharynx in small numbers

Streptococcus pyogenes - Pathogenesis

Cause disease by three mechanisms:
- Pyogenic inflammation
- Exotoxin production
- Immunologic
Produce three important inflammation-related enzymes:
- Hyaluronidase (degrades hyaluronic acid, facilitates rapid spread of Str.pyogenes in skin infections)
- Streptokinase (activates plasminogen to form plasmin, which dissolves fibrin in clots, thrombi, and emboli)
Produce five important toxins and hemolysins:
- Erythrogenic toxin (causes the rash of scarlet fever, acts as a superantigen)
- Streptolysin O (hemolysin, inactivated by oxidation, causes β-hemolysis only when colonies grow under the surface of a blood agar plate)
- Streptolysin S (hemolysin, not inactivated by oxygen, responsible for β-hemolysis when colonies grow on the surface of a blood agar plate)
- Pyogenic exotoxin A (toxin responsible for most cases of streptococcal toxic shock syndrome, acts as a superantigen)
- Exotoxin B (protease, rapidly destroys tissue, produced in large amounts by "flesh-eating" streptococci that cause necrotizing fasciitis)

Group B Streptococci (Streptococcus agalactiae)

Colonize the genital tract of some women
Bacitracin-resistant
Hydrolyze hippurate
Clinical features:
- Neonatal sepsis, pneumonia, and meningitis
- Predisposing factor: prolonged rupture of the membranes in women who are colonized with the organism and lack antibody to group B streptococci IgGs
- Meningitis during the first month of life
- Pneumonia, endocarditis, arthritis, and osteomyelitis in adults
- Postpartum endometritis
- Diabetes is the main predisposing factor for adult group B streptococcal infections

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Description

Learn about the properties and classification of Streptococci, including their arrangement, metabolism, growth conditions, and differentiation based on colony morphology and hemolysis.