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Block III
Diseases due to Streptococci & Enterococci (33-34)
45
Biology
Graduate
05/02/2009

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Cards

Term

 

 

Streptococci & Enterococci

 

Definition
  • heterogenous group bacteria
  • classification: hemolytic characteristics
    • "strept throat"
    • cellultis
    • neonatal meningitis
    • brain abscess 
    • endocarditis
Term

 

 

Streptococci members

Definition
  • s. pyogenes "Group A"
  • s.pnemococcus
Term

 

 

beta hemolytic

Definition
  • Group A--streptococci pyogenes
  • Group B--streptococci agalactiae
Term

 

 

alpha hemolytic

Definition

 

  • streptococcus viridans
  • streptococcus pneumoniae
Term

 

 

Streptococus pyogenes

Definition
  • beta hemolytic
  • gram + cocci in chains
  • grows on blood agar
  • best in anaerobic conditions

 

Term

 

 

Group A Streptococcus

(GAS)

Definition
  • niche is pharynx
  • found on skin & nasopharynx of humans
  • carriers usually asymptomatic
  • may be colonized for months
  • P2P spread is helped by droplets or contact
Term

 

 

GAS entry

Definition
  • binds to mucous membranes of pharynx
  • uses lipoteichoic acid (adhesin)
  • LTA binds to fibronectin--coats cell of oropharynx
  • skin & soft tissue infection need deeper penetration into skin
Term

 

 

GAS spread & multiplication

Definition
  • remain localized to site of infection
  • increase in aggressive strains that invade deeper tissues--life threatening diseases
Term

 

 

GAS: Virulence & Pathogenesis (1)

Definition
  • virulence depends on proteins that represent toxins
  • M proteins that mimic host macromolecules
  • GAS must avoid phagocytosis for infection by these factors:
    • M protein
    • hyaluronic acid capsule
Term

 

 

M protein

Definition
  • important in streptococcal pathogenesis
  • prevents opsonization by complement
  • antibodies formed vs. M protein effectively opsonize organism--protective against infxn
  • > 100 M protein serotypes & protective immunity are specific
Term

 

 

How does M protein prevent opsonization by complement?

Definition
  • binds to fibrinogen & interferes w/alternative pathway of complement deposition by forming a dense layer on bacterial surface

                             (OR)

  • binds host complement control proteins & inhibit formation of opsonins by complement cascade
Term

 

 

GAS Damage

Definition
  • intense inflammatory response in tissues
  • secreted substances cause considerable damage to host tissues
  • digestive enzymes "hyaluronidase" enables spread to deep tissue
  • secretes toxins causing systemic effects
Term

 

 

GAS has 3 toxins

Definition
  • streptococcal pyogenic exotoxins:
    • A,B,C
  • A & C are superantigens that can nonspecifically activate T-cells
    • release of proinflammatory cytokines (IL-1 & TNF)
Term

 

 

GAS site of infxn (1)

Definition
  • pharynx: pharyngitis
  • toxin mediated
    • scarlet fever
    • toxic shock syndrome
  • non-suppurative complications:
    • acute rheumatic fever
    • glomerulonephritis
Term

 streptococcus pyogenes

 

Strept Throat (pharyngitis) Complications

Definition
  • tonsillar abscess
    • infxn of tonsils
  • cervical adenitis
    • spread & infxn of cervical lymph node forming abscess
Term

 

 

Pharyngitis RX

Definition
  • penicillin
    • benzathine PCN
    • PCN VK
  • amoxicillin
  • macrolide
    • azithromycin
    • clarithromycin
Term

Streptococcus Pyogenes:

 

Scarlet Fever

Definition
  • macular papular rash--feels live sandpaper
  • desquamation--usually hands & feet during 2nd week of illness
  • strawberry--raspberry tongue

 

Term

 

(streptococcus pyogenes)

sites of infxn (2)

Definition
  • skin: erysipelas, impetigo, cellulitis
  • soft tissue: fasciitis
  • muscle: myositis
  • endometrium
  • lung--pneumonia
  • bacteremia & septic shock
Term

 

 

Fasciitis RX

Definition
  • PENICILLIN G
  • severe pain, systemic toxicity, rapid spread, fever, skin necrosis w/bullae, tense edema, discoloration
Term

 

 

Streptococcal Toxic Shock Syndrome

 (STSS)

Definition
  • severe multiorgan system illness--abrupt onset requires findings:
    • Hypotension
    • multisystem involvement=renal, hematologic, hepatic, pulmonary, derm
Term

 

 

STSS RX

Definition
  • clindamycin + penicilllin G
    • inhibits toxin synthesis
  • supportive--albumin, massive IV fluids
Term

 

 

Streptococcus Agalactiae

(GBS)

Definition
  • beta hemolytic
  • Group B streptococci
  • gram + cocci in chains
  • aerobic
  • B antigen
  • capsulated
Term

 

 

GBS

Definition
  • vaginal & GI tracts
  • transmission from mother to baby (verticle)
  • diseases
    • neonatal
    • pnemonia
    • sepsis/meningitis
Term

 

 

GBS RX

Definition
  • ampicillin
  • all high risk moms should receive IV amp at onset of labor & throughout
Term

 

 

Streptococcus Pneumoniae

Definition
  • alpha hemolytic
  • gram + diplococcus
  • encapsulated bacteria
  • faculatative aerobic
Term

streptococcus pneumoniae (Spn):

 

Epidemiology & Encounter

Definition
  • nasopharyngeal colonization
  • disease caused by local spread or aspiration
  • smokers, alcoholics, & viral infxns
Term

 

 

Spn Pathogenesis

Definition
  • community acquired pnemonia
  • higher incidence in elderly, closed pop, males, american indians, AIDS
  • increased colonization w/young age, crowding, viral URI, fall/winter season
  • droplet spread--aspiration
Term

 

 

Spn Virulence Factors

Definition
  • IgA protease: mucosal colonization
  • Capsular polysaccharide
    • virulent type III serotype
  • Cell wall peptidoglycans, teichoic acid elicit inflammation
  • Pneumolysin
Term

 

 

Lung infxn

Definition
  • Pneumonia
    • cough, high fever, sputum, dyspnea
  • CNS meningitis
Term

 

 

Pneumonia RX

Definition

 

 

azithromycin + ceftriaxone/cefotaxime

Term

 

 

PCN resistance & sensitivity

Definition
  • PCN sensitive=MIC<1 (ceftri/cefota)
  •  

  • PCN resistannt= PCN MIC>1
  • use levofloxacin, vancomycin, or linezolid
  • Term

     

     

    Macrolide Resistance

    Definition
    • ribosomal methylation
    • mef E
      • efflux pump mechanism
      • MIC<32--low level resistance
    Term

     

     

    invasive pneumococcal infxn

    Definition
    • meningitis infxn due to streptococcus pneumonia bacteria
    Term

     

     

    Meningitis RX

    Definition
    • dexamethasone 10-20 min before antibiotic
    • vancomycin + ceftriaxone
      • vanco stops flow of organisms off--ceftriaxone kills across BBB
    • PCN sensitive (MIC<0.2)=ceftriaxone
    • PCN resistanct (MIC>0.2) or beta lactam hypersensitivity= vancomycin
    Term

     

     

    Spn sites of infxn

    Definition
    • sinuses
    • middle ear
    • bronchi
    Term

     

     

    Rx for Spn for respiratory

    Definition
    • sinusitis & otitis media
      • amoxicillin or amox/clav
    • acute exacerbations of chronic bronchitis
      • amoxicillin or doxycycline

     

    Term

     

     

    Pneumococcal Vaccine

    Definition
    • capsular polysaccharide from 23 serotypes
    • prevenar vaccine for kids<2yrs
    Term

     

     

    Questions to ask when designing vaccines

    Definition
    • Which immune system should be activated?
    • Is immunologic memory stimulated?
    Term

     

     

    Active Immunity

    Definition
    • protective immunity--immune memory
    • natural infxn or artificial
    • stimulates antigen reactive to T/B cells
    Term

     

     

    Viridans Streptococci

    Definition
    • Gram + in chains
    • alpha hemolytic
    • oropharynx/GI tract
    • cause of dental infxn
    • subacute bacterial endocarditis
    Term

     

     

    Subacute Bacterial Endocarditis

    Definition
    • sx: fever, malaise, chest/back pain, cough, dyspnea, myalgia, arthralgias, neurologic sx, wt loss, night sweats
    • RX: AMPICILLIN/SULBACTAM + GENTAMICIN
    Term

     

     

    Enterococci

    Definition
    • aerobic
    • gram + cocci short chains
    • part of normal colonic, vaginal flora
    Term

     

     

    Enterococci sites of infxn

    Definition
    • bactremia, endocarditis
    • polymicrobial intra-abdominal infxn--UTI minor

     

    Term

     

     

    Enterococci Risk Factors

    Definition
    • prolonged hospitalization
    • hemodialysis
    • ICU--vancomycin use
    Term

     

     

    Enterococci RX

    Definition
    • endocarditis: prolonged combo high doses of: AMINOGLYCOSIDES & AMPICILLIN or VANCOMYCIN
    • dalfopristin+quinupristin
    • linezolid
    • daptomycin
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