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Microbiology F2014 > Lecture 43 & 44: Skin, Blood, Muscle > Flashcards

Lecture 43 & 44: Skin, Blood, Muscle Flashcards

1
Q

Staph aureus infections

A
  • aerobic, beta-hemolytic, coagualase+, catalase+,
  • ferments mannitol -> yellow colonies
  • often found intracell in granulocytes
  • Protein A enables colonization of anterior nares
  • MRSA resistance via PBP
  • Grows on high salt (7.5%)

Toxins

  • alpha toxin causes necrosis, membrane leakage, RBC lysis
  • PVL is cytotoxic -> lyses neutrophils and releases enzymes that damage host cells
    • assoc w severe pneumonia, severe skin infections, MRSA
  • TSST: exotoxin & superantigen (tampon use)
  • Exfoliatin (SSSS)

Virulence factors: Staphylokinase AKA fibrinolysin -> Dissolves fibrin clots

Sx

  • Chronic Staph. disease assoc. w depressed immunity
    • CGD
    • Diabetes
  • Bullous impetigo: caused by strains of Staph producing exfoliatin
  • Abscesses
  • Post-viral URI pneumonia: patchy infiltrate on CXR -> high mortality
  • Septic arthritis
  • Tricuspid endocarditis (Rapid onset) in IV drug users
  • Osteomyelitis
  • Scalded skin syndrome
  • TSS
  • Gastroenteritis

Rx: Vancomycin

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2
Q

Staph. aureus: Toxic shock-like syndrome sx

A
  • diarrhea
  • rash
  • renal failure
  • hepatic damage
  • resp failure
  • vascular compromise
  • desquamation
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3
Q

Scalded skin syndrome

A
  • exfoliatin toxin (ET) produced at site of infection will eventually enter bloodstream, erythema & desquamation at distant site
  • Primary infection localized elsewhere -> No S. aureus at sites of desquamation
  • Cause intraepidermal splitting through the granular layer by cleavage a desmosomal protein that mediates cell-cell adhesion granular layer.
  • Minor pressure induces skin separation (Nikolsky’s sign).
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4
Q

Strep. pyogenes: Group A Toxin

A
  • pyrogenic toxin (SPE) from Strep. pyogenes (Group A)
  • stimulates cytokine production w multiple effects including Scarlett fever rash
  • Group A impetigo, ecthyma, erysipelas (spreading erythema and edema of upper dermis), cellulitis
  • Severe: streptococcus necrotizing fascitis
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5
Q

TSS

A
  • a life threatening S. aureus disease caused by TSST-1
  • Mechanism: absorption of toxin from local site
    • stimulates release of cytokines
    • direct toxic effects on endothelial cells
    • menstrual and non-mentstrual TSS caused by staph pyrogenic exotoxin.
  • characterized by: fever, vomitting, diarrhea, sore throat, muscle pain,
  • shock w/in 48 h
  • renal and liver failure
  • skin rash and strawberry tongue -> desquamation at deep level than Scalded Skin Syndrome
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6
Q

Scarlet fever sx

A
  • strawberry tongue
  • sandpaper rash on trunk, legs, arms
  • punctate hemorrhages on palate
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7
Q

Osteomyelitis: Direct extension and hematogenous

A
  • common agents: Staph. aureus (acute and chronic), mixed (diabetes), occassional agents (Gram neg. rods, Tb, syphillis, fungal infections,)
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8
Q

Staph. epidermidis & saprophyticus

A
  • Catalase+
  • Urease+
  • Coagualase-

Dx:

  • S. epidermidis: Novobiocin sensitive, nl skin flora
    • produces extracell slime or biofilm on indwelling cath tubes
    • artificial joints
    • artificial heart valves -> endocarditis
  • S. saprophyticus: Novobiocin resistant
    • UTI in young, sexually active females

Rx: Vancomycin

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9
Q

Strep pyogenes

A
  • Group A strep
  • Catalase -ve (no bubbles w H2O2)
  • Encapsulated -> Hyaluronic acid capsulse
  • Beta-hemolytic
  • Bacitracin-sensitive

Virulence factors

  • Streptokinase
  • Streptolysin
  • M-protein: antiphagocytic, M12 strains assoc w acute glomerulonephritis

Sx:

  • Impetigo: “honey-crusted” lesions
  • Strep throat aka pharyngitis
  • Cellulitis & erysipelas
  • Scarlett fever (erythogenic toxin)
    • sandpaper rash (palms and soles spared)
    • Strawberry tongue
    • circumoral pallor
  • TSSLS
  • Necrotizing fascitis (Exotoxin B)
  • Endocarditis: Mitral valve
  • Rheumatic fever (RF)
    • JONES criteria
    • Type II H
    • M protein
  • PSGN
    • Type III H
    • 2 wk post-strep infection

Dx: ASO titers

Rx: Penicillin

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10
Q

Mild Strep. pyogenes and Staph exotoxin sx

A
  • impetigo (stratum corneum)
  • ecthyma: deeper lesions
  • glomerulonephritis 2 to 4 wk after skininfection
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11
Q

GBS: streptococcus agalactiae

A
  • encapsulated
  • hydrolyzes sodium Hippurate+
  • cAMP test+ leading to enhanced hemolysis by Staph aureus
  • Beta-hemolytic
  • Bacitracin-resistant

Sx

  • Neonatal sx: lethargy, sepsis, meningitis, fever, pneumonia, respiratory distress
  • Older children & adults: postnatal fever
  • Intrapartum penicillin prophylaxis
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12
Q

Other pyogenic streptococci

A
  • beta strep, not group A or B
  • Groups C and G assoc w pharyngitis; no post infection sequelae
  • skin and soft tissue infections
    • infections of wounds
    • occasional bacteremias
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13
Q

Strep pneumonia

A
  • alpha-hemolytic caused by pneumolysin (also destroys resp epith)
  • encapsulated: Polysaccharide capsule
  • lancet shaped cocci
  • Optochin-sensitive
  • bile soluble
  • IgA protease -> major virulence factor
  • Sickle cell and asplenic Pt incr risk

Sx: MOPS

  • Meningitis
  • Otitis Media
  • Lobar pneumonia -> rusty sputum
  • Sinusitis

Dx:

  • Quellung for capsules (old-school)
  • Latex agglutination (current)

Rx:

  • Macroglide
  • Ceftriaxone

Vaccine

  • Polysacchride IgM for Adults
  • Conjugate vaccine in Children products IgG response
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14
Q

Strep. viridans spp.

A
  • alpha hemolytic
  • no capsules
  • Optochin-sensitive
  • Bile insoluble
  • S. milleri group: deep tissue abscesses
  • S. mutans: dental carries
  • S. mitis, S. salivarius
  • uses Dextrans to bind to platelets
  • Abiotrophia sp.: nutritionally deficient strep., will not grow on ordinary blood agar

Sx

  • refers to all alpha strep. once strep pneumoniae has been ruled out
  • Endocarditis subacute: previously damaged valves -> Mitral valve
  • dental caries
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15
Q

Enterococcus

A
  • comprised of 2 spp
    • E. faecalis:
    • E. faecium: less common, more pathogenic, resistant to ampicillin & vancomycin
  • Bile resistant
  • Vancomycin-resistant
  • resists 6.5% NaCl in culture
  • PYR +
  • Esculin agar -> turns black

Sx

  • UTI
  • Endocarditis
  • Biliary tree

Rx

  • Linezolid
  • Tigecyclin
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16
Q

Corynebacterium diphtheriae

A
  • Gram +ve rods, clubbed shape V or Y formation
  • transmission: respiratory droplets
  • metachromatic granules (red and blue)

Etiopath: toxin causes ADP ribosylation of E2F

Sx:

  • impetigo-like lesions in tropics; sometimes in American Indians
  • pseudomembranes on throat and tonsils
  • bull’s neck pharyngitis
  • demyelination starting with posterior oropharynx
  • cardiotoxic effects: myocarditis, heart block, arrhythmias

Dx:

  • Tellurite medium
  • Loeffler’s medium
  • Elek’s test to differentiate bw clostridia spp.

Vaccination: inactivated pertusis toxoid vaccine

17
Q

Rickettsial rashes

A
  • Etiopath:
    • infects vascular endothelium
    • RBC leak out of damaged endothelium
18
Q

Lice-Borne Typhus Fever

A
  • caused by R. prowazeki in wars and refugees
  • vector: lice
  • Etiopath: vascular injury
  • sx: rash seen 10 d after illness
  • Dx: PCR
19
Q

1o classic lyme disease

A
  • Initial tick bite -> Borrelia burgdoferi (spirochete) enters skin -> 3 to 30 d later at site of bite
    • Erythema chronicum migrans (ECM)
    • slowly expanding red ring
    • biopsy of leading edge show organism
    • resolves within wks
  • Constititutional sx for months
    • fever, muscle, and joint pains
    • meningeal irritation
  • Dx: culture stains not productive
    • ELISA or Western blot
    • PCR or synovial fluid rarely used
20
Q

Erysipelothrix rhusiopathiae

Disease: Eryspeloid

A
  • Gram +ve diphtheroid-like rod
  • found in animals, meat, and sea food -> fishermen, butcher, vets
  • painful slowly spreading skin infection
  • Rx: penicllin or erythromycin
21
Q

Clostridium infections

A
  • 2 forms
  • marked gas formation & toxicity of gas gangrene is absent
    • less pain and swelling
  • C. perfrigens and gas gangrene (see fig.)
    • Gram +ve spore forming rod but no spores are seen in stains of tissues
    • Fast growing fermenter -> generates a lot of H2 & CO2
    • encapsulated & non-motile
    • found in colon and soil
    • culture characteristics
      • double zone of hemolysis on blood agar
      • litmus milk stormy fermentation
22
Q

Bacteroides fragilis

A
  • most common Gram -ve rods causing anaerobic infections
  • capsule w antiphagocytic fx
  • 10 spp. penicillin resistant
23
Q

Other anaerobic rods

A
  • fusobacterium
  • actinomyces
  • propionobacterium: P. acnes & shoulder surgery
  • mobiluncus: may cause vaginitis
  • lactobaccilus
  • eubacterium
  • rothia
24
Q

Actinomyces

A
  • Anaerobic, branching, non-spore forming
  • A. israeli likes to colonize teeth (exam q)
  • serious chronic infection: uterus, pneumonia, abscesses in neck or head (“lumpy jaw”)
  • pus w sulfur granules
  • colonies resemble molar
25
Q
A

Propionibacterium acnes

  • P. acnes & shoulder surgery
  • anaerobic “coryneform”
26
Q

C. perfringens

A
  • Fermentation of muscle carbohydrates -> produces crepitation on palpation (palpable gas)
  • Anaerobic: “stormy fermentation” in milk media
  • Double zone of hemolysis
  • ID by Nagler rxn: egg yolk agar plate; one side with anti-alpha-toxin; lecinthinase activity detect on side w no antitoxin
  • Degradative enzymes: collagenase, hyaluronidase, DNAase, protease
  • Gas gangrene: occurs in severe traumatic wounds
    • contamination w dirt, feces such as in gunshot wounds, gall bladder surgery
    • rapidly lie threatening
      • can’t wait for lab cultures
      • clinical dx required: detect gas in infected tissue

Toxins

  • alpha toxin: main pathogenic factor; diffuses thru cells causing cell necrosis
  • theta toxin: toxic for heart muscle & capillaries; similar to streptolysin
  • enterotoxin: causes food poisoning
27
Q

Corynebacterium

A
  • pleomorphic shapes, coccobacilli, irregular rods,
  • pathogens: C diphtheriae
  • opportunistic: C. ulcerans (skin infections), C. jeikeium (nosocomial bloodstram and wound infections)

Microbiology F2014 (36 decks)

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