Bacteria 1 The Streptococci MID 2029

Learning Objectives

  • Describe the medically pertinent anatomy of Streptococci:
        - Membrane
        - Cell wall
        - Gram-stain

  • List the streptococci by genus/species and by Lancefield group (if appropriate)

  • List any characteristic morphologies of the various streps:
        - Chains
        - Pairs
        - Lancet-shaped
        - Capsule

  • Be familiar with immunizations for any species of Streptococcus:
        - Indications
        - Targets

  • Organize the clinical diseases associated with each Strep species

  • Associate Streptococcus pyogenes (Lancefield group A) with its immunologic implications in heart, kidney, and systemic diseases.

  • Order the Strep species by antibiotic resistance, from least to most resistant.

Strep Vocabulary List

  • Gram-positive cocci

  • Blood agar

  • Hemolysis

  • Catalase negative

  • Peptidoglycan

  • Antibiotics:
        - Penicillin
        - Cephalosporin
        - Vancomycin

  • Streptococcus pyogenes:
        - Lancefield group A
        - Also known as flesh-eating strep
        - Associated diseases include cellulitis, pharyngitis, scarlet fever, erysipelas, pyoderma, impetigo, necrotizing fasciitis
        - Erythrogenic toxin

  • ASO (Antistreptolysin O) titers

  • M protein

  • Rheumatic fever

  • Post-streptococcal glomerulonephritis

  • Toxic shock syndrome and superantigens

  • Streptococcus agalactiae:
        - Lancefield group B
        - Causes pneumonia, sepsis, meningitis in neonates

  • Streptococcus pneumoniae:
        - Also known as pneumococcus, Strep pneumo
        - Immunizations available (polysaccharide capsule)
        - Morphology: lancet-shaped

  • Enterococcus:
        - Causes urinary tract infections, sepsis, subacute bacterial endocarditis (SBE)
        - VRE (vancomycin-resistant Enterococcus)

  • Viridans Strep:
        - Includes Streptococcus mutans and mitis
        - Also includes Streptococcus sanguinis.

The Why Question

  • Consider the prevalence of Strep throat:
        - Strep infections can lead to:
            - Rheumatic fever affecting the heart
            - Post-streptococcal glomerulonephritis which can cause renal failure

  • Streptococcus pneumoniae is a significant cause of pneumonia and meningitis.

  • Streptococcal toxic shock syndrome led to the death of Jim Henson, the creator of the Muppets.

Curiosity

  • Spend a few moments contemplating questions you might have about bacterial infections, Streptococcus, and immunology.

  • Write these questions down and seek the answers throughout this presentation.

  • Your curiosity is essential in becoming a life-long learner.

Resources for Further Learning

  • Murray Microbiology, especially the first couple of pages of each chapter

  • First Aid (2025 or 2026 edition)

  • Robbins chapter on Infectious Diseases (chapter 8)

  • Previous year’s notes from Dr. Gomez.

Streptococci Overview

  • General Characteristics:
        - Gram-positive cocci typically arranged in chains (with the exception of S. pneumoniae which is lance-shaped and diplococci)
        - Catalase-negative
        - Non-motile
        - Either facultative or obligate anaerobes

  • Lancefield Groupings:
        - Based on serology of cell wall C carbohydrate (total of 18 groups)

  • Virulence Factors:
        - M proteins in S. pyogenes resist phagocytosis
        - Lipoteichoic acids facilitate attachment to epithelial cells
        - S. pneumoniae, S. pyogenes, and S. agalactiae possess a capsule:
            - S. pyogenes has a hyaluronic acid capsule
        - Major toxins:
            - Streptolysins
            - NADase
            - Hyaluronidase
            - Streptokinase
            - DNAses
            - Erythrogenic exotoxin (causes rash in scarlet fever)
            - Toxic shock syndrome toxin
            - Pyrogenic exotoxin B (in erysipelas)

Group A Streptococcus (S. pyogenes)

  • Hemolysis and Classification:
        - β hemolysis: primary cause of bacterial pharyngitis, tonsillitis, sinusitis, otitis, arthritis, osteomyelitis, impetigo, cellulitis.
        - Can later cause rheumatic fever, rheumatic valvular disease, and post-streptococcal glomerulonephritis.
        - Can also cause scarlet fever (due to toxin) and pneumonia, bacteremia, necrotizing fasciitis, and toxic shock syndrome.

Group B Streptococcus (S. agalactiae)

  • Characteristics:
        - β hemolytic
        - Leading cause of neonatal septicemia, meningitis, and pneumonia

Group D Streptococcus

  • Includes S. bovis and S. equinus

  • ɑ or γ hemolytic

  • Associated with urinary tract infections and endocarditis

Streptococcus pneumoniae

  • Synonyms and Morphology:
        - Known as pneumococcus, Strep pneumo, or friend of the elderly
        - Gram-positive cocci in pairs (lancet-shaped diplococci)
        - ɑ hemolytic
        - Encapsulated with polysaccharide capsule, 94 types available for immunization.

  • Diseases Caused:
        - Primary causes respiratory infections including:
            - Lobar pneumonia: Symptoms include cough, rusty sputum, fever
            - Meningitis: Most common in adults.
            - Bacteremia in individuals without a spleen or with sickle cell disease.

Epidemiology of S. pneumoniae

  • Carried in the nasopharynx in 5-50% of individuals

  • Common in children: severe otitis media, pneumonia, and meningitis.

  • Common in adults: pneumonia and meningitis.

  • Drug resistance: up to 20% of S. pneumoniae are resistant to beta-lactams and macrolides.

  • Immunization:
        - Available for the capsule polysaccharide (PPS) or conjugate forms (PCV 15 or 20, PPSV 23).

More on Alpha Hemolytic Streptococcus

  • Viridans Strep:
        - Associated with dental health (S. mutans and S. mitis): Causes dental caries.
        - S. sanguinis: Associated with subacute bacterial endocarditis (SBE).

Beta Hemolytic Streptococcus

  • Characterized by type-specific antigens.

  • Lancefield Groups:
        - Group A = Strep pyogenes, commonly causes sore throat
        - Group B = Strep agalactiae
        - Other groups include C and D which are less common.

Streptococcus pyogenes (Group A strep)

  • Characteristics and Diseases:
        - Gram-positive cocci in chains
        - Causes strep throat (pharyngitis), which can be complicated by erythrogenic toxin leading to Scarlet Fever.
        - Skin infections include:
            - Erysipelas (superficial infection)
            - Pyoderma and impetigo (common in children, presents with a honey-like crust)
            - Cellulitis and necrotizing fasciitis (deeper infections).

Identification and Laboratory Testing for S. pyogenes

  • Rapid strep test: immunologic typing of Group A.

  • Culture: typically produces beta hemolytic colonies—subsequent typing (A or B); sensitive to Bacitracin.

  • ASO (Anti-Streptolysin O) titers may also be used for diagnosis.

  • Treatment:
        - Not highly resistant, so penicillin works well; alternatives include erythromycins/macrolides and vancomycin.

Virulence and Immunologic Implications of S. pyogenes

  • M proteins in the cell wall assist in avoiding phagocytes (PMNs).

  • Cross-reactivity with heart tissue:
        - Leads to rheumatic fever manifesting in the heart, valves, and joints.

  • Post-streptococcal glomerulonephritis results from immune complex deposition in the kidney.

  • Toxic shock syndrome toxin can be overwhelming, similar to staphylococcal toxic shock syndrome toxins known as superantigens.

Summary of Key Concepts

  • Characteristics of Gram-Positive Organisms:
        - Gram-positive organisms have a thick peptidoglycan layer in their cell wall which retains violet stain, making them appear blue-black under a microscope.
        - They typically have a single cell membrane.

Identification Guidelines

  • Strep species grow best on blood agar, a nutrient-rich medium that also serves as an indicator for hemolysis.

  • Distinguished from Staphylococci: Staphylococci produce catalase (catalase positive), whereas Streptococci are catalase negative.

  • Hemolysis Types:
        - Alpha: Partial hemolysis – greenish
        - Beta: Complete hemolysis – halo appearance
        - Gamma: No hemolysis

Enterococci

  • Characteristics:
        - Gram-positive diplococci or short chains (previously classified with group D streptococci)
        - Catalase negative, γ hemolytic (non-hemolytic)
        - Non-motile, facultative anaerobes

  • Diseases:
        - Can cause infections like urinary tract infections, bacteremia, bacterial endocarditis, diverticulitis, and meningitis.
        - E. faecalis and E. faecium are part of the normal intestinal flora.
        - These species show intrinsic resistance to beta-lactam antibiotics (penicillins, cephalosporins, carbapenems) and many aminoglycosides, leading to VRE (vancomycin-resistant Enterococcus).

Streptococcus bovis

  • An oddball gamma Streptococcus, lives in the colon but is associated with health complications, including endocarditis and sepsis frequently correlated with colorectal cancer (associated with subspecies gallolyticus).

Evaluations and Practice Questions

  • Utilize various presented scenarios to assess knowledge of Streptococcus, its pathogenesis, and treatment options.
        - Discuss clinical manifestations presented in cases of glomerulonephritis, pneumonia, and maternal-fetal transmission and the relevance to antibiotics and immunization strategies.