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
2
Q
Staph. aureus: Toxic shock-like syndrome sx
A
- diarrhea
- rash
- renal failure
- hepatic damage
- resp failure
- vascular compromise
- desquamation
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).
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
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
6
Q
Scarlet fever sx
A
- strawberry tongue
- sandpaper rash on trunk, legs, arms
- punctate hemorrhages on palate
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,)
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
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
10
Q
Mild Strep. pyogenes and Staph exotoxin sx
A
- impetigo (stratum corneum)
- ecthyma: deeper lesions
- glomerulonephritis 2 to 4 wk after skininfection
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
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
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
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
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
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
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
25
Q
A
Propionibacterium acnes
- P. acnes & shoulder surgery
- anaerobic “coryneform”
27
Q
Corynebacterium
A
- pleomorphic shapes, coccobacilli, irregular rods,
- pathogens: C diphtheriae
- opportunistic: C. ulcerans (skin infections), C. jeikeium (nosocomial bloodstram and wound infections)
