Alpha, beta and gamma hemolytic strep Posted by Ahmad Azizov on July 15, 2020


These are gram-positive organisms that are catalase-negative and appear in chains. Strep bacteria are further divided into beta-hemolytic, alpha-hemolytic, and gamma-hemolytic

Diagram 1. All 3 classes of strep discussed below and how to identify them 

Alpha hemolytic strep 

  • Strep pneumonia 
    • Contained within a polysaccharide capsule 
    • Asplenic patients (and sickle cell anemia patients) at a higher risk 
    • Infections 
      • Lobar pneumonia 
      • Sinusitis 
      • Ear infections 
      • Meningitis 
  • Strep Viridians 
    • Multiple organisms of the normal mouth flora 
    • Can cause dental cavities and subacute endocarditis
    • Dental work can increase the risk with infection 

Beta-hemolytic streptococci 

  • Strep pyogenes = Group A Strep 
    • Contains PYR enzyme which can create beta-naphtyhylamide which is detected by a color-changing reagent = helps differentiate from other types of strep
    • Uses M protein virulence factor to avoid phagocytosis by host organisms 
    • Diseases
      • Infections
        • Strep throat 
          • In ~30% of the cases
          • Early diagnosis and treatment can prevent rheumatic fever 
          • Diagnosis 
            • Throat culture 
            • Rapid antigen test (sensitivity)
          • Treatment 
            • Penicillin, amoxicillin, and cephalosporin 
        • Cellulitis
          • Caused by staph and strep 
        • Impetigo 
          • Caused by staph and strep
      • Toxin mediated disease
        • Scarlet fever 
          • Rash after pharyngitis caused by strep 
          • Reaction to a bacterial toxin 
          • Symptoms 
            • Fever and pharyngitis symptoms + rash later (sandpaper skin) 
            • The rash starts from the head and goes down 
            • Strawberry tongue 
              • One of the 2 diseases described by "strawberry" tongue 
              • Another one is Kawasaki disease which is a type of vasculitis
            • The skin eventually comes off
            • Palms and soles are spared 
        • Necrotizing fasciitis 
          • Severe skin infection 
          • Muscular fascia infection 
          • Surgical debridement is the treatment
          • Types 
            • Type 1 - Polymicrobial 
              • Common in immunocompromised individuals 
            • Type 2 - Group A Strep = strep pyogenes caused 
              • Occurs in healthy people after skin injury 
              • The classic presentation is skin injury followed by redness and warmth 
                • Pain is more than cellulitis
                • Systemic symptoms such as fever and shock
        • TSS = toxic shock syndrome (mostly caused by staph, but strep can also cause this)
      • Immune 
        • Rheumatic fever
          • Occurs after group strep pharyngitis 
          • Type 2 autoimmune reaction 
          • Biochemical markers 
            • Aschoff bodies = type of granuloma 
            • Anitschkow's cells = macrophages 
            • ASO titer elevation 
          • Diagnosis 
            • Jones criteria 
          • Treatment 
            • Penicillin for treatment and for prevention 
        • Post-strep glomerulonephritis 
          • Nephritic syndrome after Group A strep
  • Strep Agalactiae = Group B strep 
    • Enhances hemolysis 
    • Can colonize the vagina and infect newborns 
    • Women are screened at 35-37 weeks 
    • Can cause pneumonia, sepsis in newborns 
    • Prophylaxis 
      • Penicillin, ampicillin or cefazolin in GBS+ women 

Gamma hemolytic strep

  • Enterococcus 
    • Part of the colon bacteria 
    • Group D strep 
    • Can cause endocarditis and UTIs
    • Resistant to penicillins and sometimes to Vancomycin (VRE) 
    • Treatment 
      • Usually a combination of antibiotics 
      • Vancomycin and gentamycin 
      • Ampicillin and gentamycin 
  • Strep Bovis
    • Lives in the colon normally 
    • Associated with colon cancer and spontaneous bacterial peritonitis



All information provided on this website is for educational purposes and does not constitute any medical advice. Please speak to you doctor before changing your diet, activity or medications. 

Written by
Ahmad Azizov
Writing since 2020 April

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