Enterococcus - Microbiology - Lecture Slides, Slides of Microbiology

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STREPTOCOCCUS

Enterococcus

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REVIEW

Bacterial Cell Morphology

• Gram Stain
• Cytoplasmic (plasma) membrane
• Cell wall structure
• Bacterial cell shapes

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Genus Streptococcus

Physiology & Metabolism

Facultative Anaerobes

Fastidious Growth Requirements

Fermentative Metabolism of Carbohydrates: Lactic acid, ethanol, acetate endproducts produced; No gas

Catalase Negative (2H 2 O 2 ---> O 2 + 2H 2 O) Separation of streptococci from staphylococci Oxidase Negative (oxidoreductase oxidizes substrate w/ O 2 ) Beta, Alpha, or Gamma Hemolysis on blood agar

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Genus Streptococcus

Rebecca Lancefield

Developed useful serogrouping system Classification of beta-hemolytic streptococci by group-specific cell wall carbohydrate (CHO) antigen As of 1992, Serogroups A to H and K to V Groups A, B, C, D, and G are most comonly associated with human disease Viridans streptococci and Streptococcus pneumoniae have no group-specific antigen

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Antigenic Structure

Streptococcus pyogenes (Group A)

Lancefield Group-specific antigen (C polysaccharide)

Complex polysaccharide in cell wall

Proteins: Two major classes, M & T antigens

Two minor classes, R & F

M-Protein: Type-specific antigen

Fimbriae-like, hairy extensions Resistant to heat and acid Trypsin Sensitive Specific adherence by lipoteichoic acid and M-protein (LTA-M) complexes

T Antigens (not virulence factor)

Resistant to trypsin, heat and acid; Adjunct to M-typing; Routine surveillance

Others Docsity.com

Antigenic Structure (cont.)

Streptococcus pyogenes (Group A)

Capsular Polysaccharide:

Hyaluronic acid

Not present in all strains Same as host hyaluronic acid (cartilage,skin etc) Nonimmunogenic Antiphagocytic Hyaluronidase (cell wall division) during late growth

Lipoteichoic Acid

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Lancefield Serogroup Classification of

Beta-Hemolytic Streptococci Important in

Human Disease (cont.)

Group B Streptococci:

Streptococcus agalactiae

• Neonatal disease & obstetric complications
• Systemic, Cutaneous, UTI's

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Lancefield Classification of Beta- Hemolytic Streptococci (cont.)

Group C Streptococci: Pharyngitis

Group G Streptococci:

S.anginosus-milleri grp; Streptococcus spp. Pharyngitis

Non-Lancefield Group Streptococci

Viridans Streptococci

Dental Caries: Streptococcus mutans Streptococcus sanguis ; Streptococcus salivarius; Streptococcus mitis

Streptococcus pneumoniae

Enterococcus & Group D Streptococci

Genitourinary Tract Infections (UTIs) Endocarditis

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Major Human Diseases of Beta-Hemolytic Streptococci (cont.)

Group A Streptococcus (S. pyogenes)

Suppurative Streptococcal Diseases

Cutaneous & Soft Tissue Infxns (cont.)

Cellulitis: Involvement of deeper subcutaneous

tissues; Deeper invasion with systemic symptoms

Necrotizing fasciitis: (a.k.a., “flesh-eating

bacteria”): Infection deep in subcutaneous tissues that spreads along fascial planes, destroying muscle and fat; Initially cellulitis followed by bullae (fluid filled blisters; bulla is singular), gangrene, systemic toxicity, multiorgan failure and mortality in more than 50% of patients

Wound Infections

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Suppurative Streptococcal Diseases

Group A Streptococcus (cont.)

Other Suppurative Diseases

Puerperal & neonatal sepsis

Lymphangitis: Inflammation of lymphatic vessel(s)

Pneumonia

Systemic Disease

Streptococcal Toxic Shock

Syndrome (TSS): Multisystem toxicity following

soft tissue infection progressing to shock and organ

failure (not to be confused with Staphylococcal

Toxic Shock Syndrome where hyperabsorbent

tampons have been identified as an important risk factor)

Bacteremia Docsity.com

Epidemiology of Acute Streptococcal Infection

• Predilection for upper respiratory tract or skin
• Group A commonly colonize oropharynx of healthy children
• M-types of strains colonizing throat differ from those on skin
• Rapidly killed after phagocytosis, but cell walls not digested and may lead to chronic inflammatory lesions

Pharyngitis transmitted by droplets from respiratory secretions

• Crowding increases risk (e.g., classrooms, day care facilities)

Pyoderma transmitted by direct contact with infectious lesions

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Nonsuppurative Sequelae of Acute Group A Streptococcal Infection

Acute Rheumatic Fever (ARF)

Inflammatory reaction characterized by arthritis, carditis, chorea (disorder of CNS with involuntary spastic movements), erythema marginatum (skin redness with defined margin), or subcutaneous nodules Within 2-3 weeks following pharyngitis

• Epidemic pharyngitis: ARF in as many as 3%
• Sporadic pharyngitis: ARF in 1 per 1000

Morbidity & mortality linked to subsequent disease of heart valve (Rheumatic Heart Disease)

Poorly understood pathogenesis with several proposed theories including cross-reactivity of heart tissues & strep AGNs

• ?? (Type ?? II hypersensitivity, exotoxins, direct invasion)Docsity.com

Determinants of Pathogenicity

Cellular Virulence Factors

Capsule

Antiphagocytic; Nonspecific adherence Hyaluronic acid (polysaccharide) mimics animal tissue

Lipoteichoic Acid

Cytotoxic for wide variety of cells Adherence: Complexes with M protein (LTA-M) and binds to fibronectin on epithelial cells

M-Protein

LTA-M protein is adhesin Antiphagocytic Inhibits alternate C’ pathway and opsonization

M-like Proteins: bind IgM and IgG

F Protein: mediates adherence Docsity.com

Extracellular Virulence Factors

Exotoxins:

Streptolysin O (SLO):

Hemolytic and Cytolytic Prototype of oxygen-labile and thiol-activated cytolytic exotoxins (e.g., Streptococcus, Bacillus, Clostridium, Listeria ) Lytic for variety of cells: bind to cholesterol- containing membranes and form arc- or ring- shaped oligomers that make cell leaky (RBC's, WBC’s, PMN's, platelets, etc.) Causes sub-surface hemolysis on BAP Stimulate release of lysosomal enzymes SLO titer indicates recent infection (300-500 in pediatric populations) Docsity.com