Staphylococci Flashcards
1 cause of bacteremia
Staph
Staph grows in pairs, groups or chains?
Pairs + Groups
- strep is chains
Staph toxin actions:
Enterotoxin A-1
Exfoliatin A-B
TSST-1
Enterotoxin A-1
- vagal stimulator
Exfoliatin A-B
- Granular cell layer cleavage
TSST-1
- TNF, IL-1 stimulator
Exotoxins vs Endotoxins (123)
Exotoxins source:
secreted from certain Gram +/- species
- Polypeptide
Endotoxins source:
outer cm of most Gram -
(not secreted)
- Lipopolysaccaride (released when lysed)
How to identify Staphylococci? (start with GPC ID)
- GPC aerobic
- Blood +, Chocolate +, MacConkey -
- Catalase Positive
*MacConkey suppress gram + growth
S. aureus is coagulase _____ (+/-?)
coagulase positive
- golden
(staphylococci 31+ species are coag - and white)
how is S. aureus clumping factor positive?
due to its cell wall protein
- similar binding proteins to fibronectin and collagen
It binds to fibrinogen and converts it to fibrin causing clumping and protection from phagocytosis (very virulent to hu)
Significance of S. aureus being Protein A positive?
S. aureus produces Protein A
Protein A binds to Fc receptor of IgG, which prevents antibody mediated phagocytosis
(nl foreign bact bind at FAV site –> phago)
lipotechoic acid - adhesin
Staph techoic acids bind to epithelial cells via cell attachment to fibronectin
2 types of cytolytic proteins that staph contains that cause tissue damage.
- Hemolysins (a, b, gamma)
- Red cell lysis
- tissue damage - Panton-Valentine Leucocidin
- white cell lysis
- protection from phagocytosis
- invasive skin disease
Exfoliatin A + B effects
two immunologically distinct toxins with identical effects
- bind to GM4 glycolipids (infants)
Causes separation at granular-cell layer (desmosomes)
Enterotoxins of s. aureus
heat and acid stable proteins
8 serotypes
30-40% of s. aureus strains
preformed toxin in contaminated food causes vomiting and diarrhea when ingested
Most common cause of food poisoning
Enterotoxins due to s. aureus
TSST-1 toxin mediated disease
toxic shock syndrome
Exposure to TSST-1 S. aureus strain –>
growth of organism that promote toxin production –>
No pre-existing antibody to toxins –>
superantigen stimulates cytokines –> causes endothelial leakage
Where are they found in nl flora?
- S. aureus
- Coag neg staph
- S. aureus
- nose, throat, vagina - Coag neg staph
- skin, throat
MRSA
carry mecA gene
Codes for altered PBP: PB2A
- decreases beta lactam binding and cell wall inhibition
Vancomycine intermediate s. aureus (VISA) and VRSA (vanco resistance)
Vancomycin inhibits D-ala D-ala cross polymerization in peptidoglycan layer
VISA have increase # peptidoglycan layer
VRSA have vanA gene from enterococcus
Alternatives you can use if bug is VISA or VRSA
trimethoprim/sulfa
linezolid
Synercid
daptomycin
D test
erythromycin-induced clindamycine resistance in Clindamycin-susceptible, Erythromycin-resistant S. aureus
S. aureus can harbor inducible erm methylase system or macrolide efflux pump system.
- First one can cause resistance to clindamycin due to mutation and constitutive expression of erm. Need to differentiate –> use D test.
- be wary of using clindamycin or macrolides bc of mutation occurs
Which is a localizing presentation, staph or strep?
Staph = localizing disease
ie: furuncles/boils, lymphadenitis
How can staph cause bacteremia?
- Respiratory colonization –> otitis, sinusitis pneumonia –> bacteremia
- Cutaneous injury/defect –> cellulitis/boils –> bacteremia
bacteremia can result in either disseminated septicemia or deep focal infection (osteomyelitis, arthritis, pericarditis, endocarditis)
Osteomyelitis
hematogenous spread
local bone absecess
staph most common cause
Most common cause of osteomyelitis
staph
Sinusitis
staph is uncommon cause of local respiratory spread:
- otitis, sinusitis, pneumonia (CF)
Disseminated staph septicemia does not localized, but what is it often associated with?
endocarditis or thrombophlebitis
Protease + strains
Phagocytosis is the major host defense, how does staph impede this?
- protein A
- Panton-valentine leukocidin
- Localizing factors (clumping factor, coagulase)
Chronic granulomatous disease
Sex linked recessive neutrophil defect
Most common neutrophil defect
Impaired H2O2 mediated intracellular killing
Job’s syndrome (214)
Hyper IgE
Cold (noninflammed) staph abscess
Poor neutrophil chemotaxis to site of infxn
Do you see strawberry tongue in staph scarlet fever?
no
*scarlet fever is caused by exfoliatin
seen in strep scarlet fever
Toxic shock syndrome
- Virulence factor
- signs
TSST-1
Enterotoxins
- Acute fever
- Erythroderma (desquamation usually late)
- Hypotension
- Multi-organ system involvement
Scalded skin
- Virulence factor
- Clinical findings
Exfoliatins
- Painful Erythroderma
- Nikolsly sign
- Bullous Impetigo
Which staph virulence factors causes vomiting and diarrhea?
Preformed Enterotoxins (in food)
- it is heat stable and is not destroyed by cooking
- an exotoxin (not endotoxin)
Exfolatins from S. aureus can cause what?
Scalded skin syndrome
Staphylococcal scarlet fever
diff from strep
Tx for S. aureus
Tx for MRSA
Tx for Coag - Staph
S. aureus:
- Methicillin
- Cephalosporins
- Vancomycin
MRSA:
- Vancomycin
- Bactrim
Coag - Staph
- Vancomycin
- Rifamin (alwaysuse with primary drug)
Tx regimens
- Draining critical for focal infxn
- Antibiotic duration
- Mild infxn: 7-10 days
- Severe infxn: 3-6 weeks - Add clindamycin in TSS to shut off toxin production
