Strep

• BETA HEMOLYTIC STREPTOCOCCUS

  Group A: Streptococcus pyogenes (GAS), Major Virulence Factors, Enzymes and Toxins, Pathogenesis and Clinical Manifestations, Post-Streptococcal Diseases, Diagnostic Laboratory Tests
• GROUP B: Streptococcus agalactiae (GBS)


  Pathogenesis and Clinical Manifestation, ADULT STREPTOCOCCAL INFECTION, CAMP TEST, SODIUM HIPPURATE HYDROLYSIS
• Enteroccocus was previously identified under the genus Streptococcus, Current genus is now Enterococcus and not Streptococcus but they still belong to that group of organisms
• Divided into 3 genera: (Bergey's Manual of Determinative Bacteriology)


  • Streptococcus
  • Enterococcus
  • Lactococcus

  
• Streptococci: General Characteristics


  • Gram Positive Cocci (spherical organisms)
  • Can be seen in pairs or chains (long or short)
  • Catalase Negative - sets them apart from the other gram-positive cocci Staphylococcus
  • Mostly Fastidious organisms
  • Colonies: Small, pinpoint, and translucent
  • Large part of this group are able to create zones of hemolysis
  • Facultative anaerobes
  • Needs 5-10% CO2 for proper growth
  • Non-motile & non-spore forming

  
• Streptococci: Classification


  • Patterns of Hemolysis
  • Physiologic Requirement
  • Lancefield Antigen Grouping: Antigenic character in the polysaccharide cell wall
• Alpha hemolytic


  Those that incompletely or partially hemolyse RBC, Produces green discoloration on the zones of hemolysis due to the remnants of incomplete or partial hemolysis
• Beta hemolytic


  Those that can completely hemolyse RBC creating clear or colorless zone of hemolysis surrounding bacterial colonies
• Gamma hemolytic


  Includes non-hemolytic organisms, Produce no zones of hemolysis whether complete or incomplete, no hemolysis of RBC
• Physiologic Division

  • Pyogenic division
  • Viridans division
  • Enterococcus division
  • Lactic division
• Lancefield Grouping


  Discovered by Rebecca Lancefield (1933), Divides the Streptococci into serologic groups based on antigenic properties of carbohydrate group antigens in their cell wall, A,B,C,D,E (first 5), Currently: almost 20 groups = (A-H) & (K-T), They can be successfully differentiated by performing Serological Testing, Amongst the almost 20 groups of Lancefield classification, Lancefield groups A, B, C, D, E, and G are clinically significant (associated with human infections)
• BETA HEMOLYTIC STREPTOCOCCUS


  Lancefield group A (Represented by S. pyogenes), Lancefield group B (Represented by S. agalactiae), Lancefield group C & G (Representative species: S. dysgalactiae; S. equi), Lancefield group A, C, F & G (S. anginosus, Several strains of S. anginosus have different types of carbohydrate antigens found in cell wall)
• Group A: Streptococcus pyogenes (GAS)


  Not a normal flora, Most virulent Streptococcal species or organism for humans, Causes Bacterial pharyngitis, Skin infections, Invasive diseases, Complications: Rheumatic Heart Disease, Rheumatic Fever, Acute Glomerulonephritis, Transmission: Direct contact, Inhalation of contaminated aerosol droplets
• Major Virulence Factors

  • Cell Surface Antigens: Hyaluronic acid Capsule, M protein, Group-specific cell wall antigen, IgG & IgA-binding proteins, C5a protease, F protein, Lipoteichoic acid
  • Enzymes and Toxins: Streptokinase, Streptodornase, Hyaluronidase, Diphosphopyridine Nucleotidase, Pyrogenic Exotoxins/Erythrogenic Toxins (A, B, A), Streptolysin O, Streptolysin S
• Pathogenesis and Clinical Manifestations

  PYOGENIC DISEASES: Erypsipelas, Cellulitis, Impetigo
• Erysipelas: Spreading of rashes across the face or on extremities (legs), Infected area is itchy and feels hotter compared to the other parts of the body, May not have pus production, Exotoxin A production
• Cellulitis: Inflammation or infection of deep tissues including the skin, Common in middle-aged, not common in children
• Impetigo: Begins as fluid-filled blisters; will pop up or erupt creating weeping lesions, Lesions release pus
• Streptococcus pyogenes


  • Able to create antibodies against it, so its presence cannot be detected
  • Antiphagocytic
  • Toxic to various human cell types
• Most common disease type caused by S. pyogenes are pyogenic in nature, associated with pus production
• Common skin infections caused by S. pyogenes

  • Erysipelas
  • Cellulitis
  • Impetigo
• Agents of Streptococcal Pharyngitis include pus production
• Erysipelas


  Spreading of rashes across the face or on extremities (legs), also known as Saint Anthony's Fire, infected area is itchy and feels hotter compared to the other parts of the body, may not have pus production, caused by exotoxin A production
• Cellulitis


  Inflammation or infection of deep tissues including the skin, common in middle-aged, not common in children
• Impetigo


  Begins as fluid-filled blisters, will pop up or erupt creating weeping lesions, lesions release fluid and will eventually cross over, usually seen around nose or mouth area, common in young children
• Strep Throat


  Characterized by red, swollen tonsils and pus formation, lasts from 3-5 days, treated: lasts 3 days (shortest), some may go longer than 5 days, infection is dependent on the individual and treatment
• Toxigenic diseases are brought about by the elaboration of the toxins the organism can release
• Toxigenic infections caused by S. pyogenes


  • Necrotizing fasciitis
  • Scarlet fever
  • Streptococcal toxic Shock Syndrome
• How toxigenic infection occurs


  1. S. pyogenes enters the infected wound

  2. Bacteria enter the blood stream and secrete Exotoxin A

  3. Exotoxin A can cause fever, rash, shock, bacteremia, respiratory failure (50 % death rate)
• Scarlet Fever


  May occur after Streptococcal pharyngitis or other infections, presence of pyrogenic exotoxin results to fever, rashes, and strawberry tongue, rashes usually starts from the neck to the chest, arms and legs
• Streptococcal Toxic Shock Syndrome


  Similar to Staphylococcal Toxic Shock Syndrome, toxin mediated, there's a hypotension, multi-organ failure, fever, erythema, swelling, tachycardia, acute respiratory distress, renal impairment, and shock, can be observed in men and women, milder compared to staphylococcal toxic shock syndrome
• Necrotizing Fasciitis


  Which has earned Streptococcus pyogenes, the name of flesh-eating bacteria, necrotizing "rotting", fasciitis "fascia is infected", muscles are wrapped or contained to create that shape using the fascia which wraps the muscles, if fascia is infected, infection goes around the tissue, difficult because it covers wide area of cells and tissues, presence of necrosis where cells die and turn black, cells appear charred that is usually debrided so infections won't spread, spreads from one point to another, acquired by a puncture of a structure like a plant thorn or abrasion by bushes
• The active component in Necrotizing Fasciitis is Exotoxin A, which acts as a superantigen and causes overprodution of cytokines and tissue destruction at a rate of two inches per hour
• Streptococcal infections must be treated otherwise complications may occur later on such as Rheumatic heart disease, Acute rheumatic fever, and Acute glomerulonephritis
• Rheumatic Heart disease


  Cardiac inflammation and scarring, usually triggered by an autoimmune reaction to infection with Group A Streptococci (GAS), in the acute stage, the condition may consist of pancarditis where the entire layers of the heart may be infected or inflamed
• Acute Rheumatic Fever


  Systemic disease that affects the connective tissue around the arterioles, can occur after an untreated strep throat, especially if it's due to GAS, individuals who suffer from strep throat 2-3 times a year must have their throat examined
• Acute Glomerulonephritis


  Comprises a specific set of renal diseases with an immunologic mechanism, triggers inflammation, proliferation of glomerular tissue that can result to damage of the basement membrane, antigen-antibody complexes involved where exotoxin A can create excess release of cytokines which may trigger immune cells to produce antibodies, the extra antibodies may attach to antigens or structures that may appear like the antigen, several antigen-antibody complexes are produced which can travel and get deposited into the glomerulus, kidney is destroyed in the long run
• Diagnostic Laboratory Tests for Streptococcus pyogenes

  • Microscopic: Gram staining (Gram(+)cocci in pairs or chains)
  • Culture: 18-24 hours at 37°C with 5-10% CO2, BAP - White to gray pinpoint colonies, translucent, opalescent, wide zone of ß-hemolysis, contaminated samples inoculated with BAP and trimethoprim sulfamethoxazole or SXT, mucoid colonies indicate M-CHON (+) strains
  • Biochemical: Catalase (-), BAP with SXT = (R ), Taxo A/Bacitracin Disk test (positive: any zone of inhibition), PYR Test (positive: dark pink color indicates hydrolysis of L-pyrrolidonyl-2-napththylamide)
  • Serological Tests: ASO (Anti-streptolysin O), Sero typing of specific M CHON

  
• Scarlet Fever Susceptibility Tests

  • Dick Test (positive: area of induration >1cm, redness spreads away from the marked area)
  • Schultz-Charlton Test (positive: fading of rashes after 6 to 8 hours, proves rashes are caused by Scarlet fever)
• Streptococcus agalactiae (GBS)


  • Normal flora of the GIT & Vaginal tract, Gram positive cocci in chains, Beta hemolytic in BAP (not as wide as GAS), Polysaccharide capsule with sialic acid which is anti-phagocytic, inhibits Complement activation, able to mimic host molecules, enhancing pathogenicity by diminishing immune recognition