Lecture 43 & 44: Skin, Blood, Muscle

Question 1

Staph aureus infections

Answer 1

• 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

Question 2

Staph. aureus: Toxic shock-like syndrome sx

Answer 2

• diarrhea
• rash
• renal failure
• hepatic damage
• resp failure
• vascular compromise
• desquamation

Question 3

Scalded skin syndrome

Answer 3

• 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).

Question 4

Strep. pyogenes: Group A Toxin

Answer 4

• 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

Question 5

TSS

Answer 5

• 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

Question 6

Scarlet fever sx

Answer 6

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

Question 7

Osteomyelitis: Direct extension and hematogenous

Answer 7

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

Question 8

Staph. epidermidis & saprophyticus

Answer 8

• 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

Question 9

Strep pyogenes

Answer 9

• 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

Question 10

Mild Strep. pyogenes and Staph exotoxin sx

Answer 10

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

Question 11

GBS: streptococcus agalactiae

Answer 11

• 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

Question 12

Other pyogenic streptococci

Answer 12

• 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

Question 13

Strep pneumonia

Answer 13

• 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

Question 14

Strep. viridans spp.

Answer 14

• 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

Question 15

Enterococcus

Answer 15

• 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

Question 16

Corynebacterium diphtheriae

Answer 16

• 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

Question 17

Rickettsial rashes

Answer 17

• Etiopath:
  
  • infects vascular endothelium
  • RBC leak out of damaged endothelium

Question 18

Lice-Borne Typhus Fever

Answer 18

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

Question 19

1o classic lyme disease

Answer 19

• 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

Question 20

Erysipelothrix rhusiopathiae

Disease: Eryspeloid

Answer 20

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

Question 21

Clostridium infections

Answer 21

• 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

Question 22

Bacteroides fragilis

Answer 22

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

Question 23

Other anaerobic rods

Answer 23

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

Question 24

Actinomyces

Answer 24

• 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

Question 25

Answer 25

Propionibacterium acnes * P. acnes & shoulder surgery * anaerobic "coryneform"

Question 26

C. perfringens

Answer 26

* 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

Question 27

Corynebacterium

Answer 27

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