Streptococci 

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
    • Urinalysis nitrite negative (other bacteria with negative nitrites is staph saprophyticus)
  • 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

Summary