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Microbiology & Infectious Diseases > 07: Streptococcus > Flashcards

07: Streptococcus Flashcards

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Biology 101 flashcards
1
Q

Give a general descripton of streptococci/enterococci.

A
  • Pyogenic (pus forming) pathogens
  • Nonmotile,non-spore forming, mostly facultatively anaerobic, catalase negative, GPC in chains
  • Enterococci established as separate species based on DNA homology studies
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2
Q

For s. pneumoniae:

  1. Sites of colonization
  2. Sites of infection
  3. Diseases
  4. Treatment
A
  1. Oropharynx, nose
  2. Lungs, sinuses, middle ear, meninges
  3. Pneumonia, otitis media, sinusitis, infant/adult meningitis
  4. PCN (3GC if resistant; vancomycin/levofloxacin if highly resistant)
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3
Q

For s. pyogenes (GAS):

  1. Sites of colonization
  2. Sites of infection
  3. Diseases
  4. Treatment
A
  1. Oropharynx, rectum
  2. Pharynx, skin, soft tissue
  3. Pharyngitis (strep throat), TSS, impetigo, rheumatic fever, pyoderma
  4. PCN/Amox; Macrolides/1GC if allergic
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4
Q

For enterococcal spp.:

  1. Sites of colonization
  2. Sites of infection
  3. Diseases
  4. Treatment
A
  1. GI tract
  2. Urinary and biliary tract, cardiac valves
  3. Acute bacterial prostatitis, endocarditis, neonatal meningitis
  4. PCN/Amp; if resistant, vanco; if endocarditis, aminoglycoside for synergy; if vanco resistant (VRE), linez/dapto/streptogramin
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5
Q

For s. agalactiae (GBS):

  1. Sites of colonization
  2. Sites of infection
  3. Diseases
  4. Treatment
A
  1. GU tract
  2. Neonatal infections involving blood, meninges, GU tract
  3. Neonatal miningitis, sepsis
  4. PCN/amox; macrolides/1GC if allergic
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6
Q

For viridans streptococci:

  1. Sites of colonization
  2. Sites of infection
  3. Diseases
  4. Treatment
A
  1. Oropharynx
  2. Cardiac valves, bloodstream
  3. Endocarditis
    4.
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7
Q

Describe the hemolysis patterns of strep.

A
  • S. pyogenes & agalactiae are beta (complete)
  • Viridans & pneumoniae are alpha (partial)
  • Enterococci are gamma (none)
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8
Q

Describe the disk patterns of strep.

A
  • S. pneumoniae is the only optochin susceptible species.
  • S. pyogenes (GAS) is the only bacitracin susceptible species.

Mnemonic: OVRPS & BBRAS

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9
Q

Describe the structural components of GAS.

A
  • Hyaluronic acid capsule: interferes with phagocytosis.
  • M protein: major virulence factor; interferes with phagocytosis (inhibits complement activation); implicated in pathogenesis of rheumatic fever.
  • Protein F & lipoteichoic acid: mediate binding to fibronecting
  • Protein G: binds Fc portion of immunoglobulin
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10
Q

Describe the secreted products of GAS.

A
  • Enzymes
    • Streptolysins O & S
    • DNase, hyaluronidase, streptokinase: tissue breakdown, pus formation.
  • Toxins
    • Pyrogenic exotoxins (SPE A, B, C): produce superantigen-mediated TSS; responsible for scarlet fever.
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11
Q

Describe the clinical features of GAS pharyngitis.

A
  • Epi: 5-15yo, winter/early spring
  • Most common of the streptococcal infections, but only account for a small number of pharyngitis cases
  • Sore throat, sudden onset, fever, pain with swallowing, headache, lymphadenitis, tonsillar exudates, soft palate petechiae
  • Non-suggestives: conjuctivitis, coryza (nasal discharge), cough, diarrhea
  • Sequelae: abscess, sepsis, dissemination
  • Diagnose using rapid strep kits (specific but not sensitive; treat if positive, confirm if negative), anti-streptolysin (ASO) test (reflects past, not present, infection)
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12
Q

Describe the nonsuppurative sequelae of pharyngitis.

A
  • Rheumatic fever: diagnose via Jones criteria:
    • Joints (polyarthitis)
    • Heart (carditis)
    • Nodules (subcutaneous)
    • Erythema marginatum (circular rash)
    • Sydenham’s chorea (jerking movements)
  • Glomerulonephritis: renal disease by strep antigens deposited in glomerular membrane.

Mnemonic: Pharyngitis can result in phever and glomerulonephritis.

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13
Q

Describe the clinical features of impetigo.

A
  • Rash on face
  • Small pustules that progress to thick honey-crusted lesions
  • Large primary lesion and several satellite lesions
  • Commonly results from GAS or S. aureus
  • Complications rare: lymphadenitis, immune-complex glomerulonephritis
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14
Q

Describe the clinical features of streptococcal toxic shock syndrome.

A
  • Pyrogenic exotoxins A-C implicated
  • Superantigen-mediated
  • Differs from S. aureus TSS because of frequent presence of infections
  • Necrotizing fascitis linked w/ specific M types
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15
Q

Describe the treatment/prevention of s. pyogenes infections.

A
  • Penicillin
  • Protein synthesis inhibitors (e.g., clindamycin) may improve outcome
  • Macrolide-resistance emerging
  • Vaccines under development (type-specific epitopes or highly conserved regions of M protein; target proteins mediating epithelial adherence)
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16
Q

Describe the microbiology and structure of streptococcus pneumoniae.

A
  • Lancet-shaped diplococci; optochin susceptible; alpha hemolytic; encapsulated (no virulence without)
  • Polysaccharide capsule inhibits phagocytosis and confers type-specific immunity
  • Cell wall (peptidoglycan) helps initiate inflammatory response (recruit PMNs, initiating coagulation, inducing cytokine production).
  • Competent: naturally transformable, can acquire DNA from environment, acquire genes conferring antimicrobial resistance
17
Q

Describe the epidemiology of pneumococcal disease.

A
  • Extremes of age: <2, >65
  • Colonize nasopharynx in 5-10% adults, 20-40% children
  • Disease increased in winter
  • Immunocompromised more likely to be infected
18
Q

What are the main diseases caused by S. pneumoniae?

A
  • Meningitis
  • Otitis media
  • Pneumonia
  • Sinusitis

(MOPS)

19
Q

Describe the pathogenesis of pneumococcal pneumonia.

A
  • Colonization: Strains w/ increased phosphoryl choline bind epithelial structures (platelet activating factor receptor (rPAF)).
  • Invasion: Respiratory via aspiration of nasopharyngeal secretions; increased capsule expression: IgA protease, reduced mucus entrapment, anti-phagocytic; pneumolysin lyses host cells, inhibits ciliary action, activates inflammation & CD4T recruitment
20
Q

Describe the clinical manifestations of pneumococcal disease.

A
  • Sudden onset of fever
  • Chills
  • Pleuritic chest pain
  • Cough associated with rusty-colored sputum
  • CXR: infiltrate (usually lobar)
  • 1/3rd of infx: bacteremia
  • Complications: meningitis, arthritis, endocarditis
21
Q

Describe the treatment and prevention of pneumococcal infections.

A
  • Penicillin unless resistance; 3GC; high resistance = vancomycin/levofloxacin
  • Poyvalent polysaccharide anticapsular vaccine (23 types) for adults; T cell independent (less immunogenic)
  • Polysaccharide protein conjugate vaccine (7 types) for infants 2yo or younger; T cell dependent

NB: Escape strains exist (e.g., 19a).

22
Q

Describe streptococcus agalactiae (GBS).

A
  • Narrow band of beta hemolysis; bacitracin resistant; able to hydrolyze hippurate
  • Commonly associated with infections in newborns (B for babies): pneumonia, meningits, sepsis
  • Colonizes vagina, therefore mothers tested at 35-37 weeks and chemoprophylaxed with penicillin as necessary.
23
Q

Describe viridans streptococci.

A
  • Heterogenous group of streptococci including 24 different species
    • Sanguis = subacute bacterial endocarditis at damaged valves
    • Mutans = dental caries
  • Alpha hemolytic, optochin resistant
  • Part of oropharyngeal flora, GI tract
24
Q

Describe enterococci.

A
  • Nonhemolytic (gamma)
  • Normal colonic flora (resistant to bile salts) that are penicillin G resistant and cause UTI, biliary tract infections, subacute endocarditis.
  • VRE are important cause of nosocomial infection.

Microbiology & Infectious Diseases (26 decks)

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