Staphylococci Flashcards Preview

Unit 1 ID+LC > Staphylococci > Flashcards

Flashcards in Staphylococci Deck (35):
1

#1 cause of bacteremia

Staph

2

Staph grows in pairs, groups or chains?

Pairs + Groups
- strep is chains

3

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

4

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)

5

How to identify Staphylococci? (start with GPC ID)

1. GPC aerobic
2. Blood +, Chocolate +, MacConkey -
3. Catalase Positive

*MacConkey suppress gram + growth

6

S. aureus is coagulase _____ (+/-?)

coagulase positive
- golden

(staphylococci 31+ species are coag - and white)

7

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)

8

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)

9

lipotechoic acid - adhesin

Staph techoic acids bind to epithelial cells via cell attachment to fibronectin

10

2 types of cytolytic proteins that staph contains that cause tissue damage.

1. Hemolysins (a, b, gamma)
- Red cell lysis
- tissue damage

2. Panton-Valentine Leucocidin
- white cell lysis
- protection from phagocytosis
- invasive skin disease

11

Exfoliatin A + B effects

two immunologically distinct toxins with identical effects
- bind to GM4 glycolipids (infants)

Causes separation at granular-cell layer (desmosomes)

12

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

13

Most common cause of food poisoning

Enterotoxins due to s. aureus

14

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

15

Where are they found in nl flora?
1. S. aureus
2. Coag neg staph

1. S. aureus
- nose, throat, vagina

2. Coag neg staph
- skin, throat

16

MRSA

carry mecA gene
Codes for altered PBP: PB2A
- decreases beta lactam binding and cell wall inhibition

17

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

18

Alternatives you can use if bug is VISA or VRSA

trimethoprim/sulfa
linezolid
Synercid
daptomycin

19

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

20

Which is a localizing presentation, staph or strep?

Staph = localizing disease
(ie: furuncles/boils, lymphadenitis)

21

How can staph cause bacteremia?

1. Respiratory colonization --> otitis, sinusitis pneumonia --> bacteremia

2. Cutaneous injury/defect --> cellulitis/boils --> bacteremia

bacteremia can result in either disseminated septicemia or deep focal infection (osteomyelitis, arthritis, pericarditis, endocarditis)

22

Osteomyelitis

hematogenous spread
local bone absecess

staph most common cause

23

Most common cause of osteomyelitis

staph

24

Sinusitis

staph is uncommon cause of local respiratory spread:
- otitis, sinusitis, pneumonia (CF)

25

Disseminated staph septicemia does not localized, but what is it often associated with?

endocarditis or thrombophlebitis

Protease + strains

26

Phagocytosis is the major host defense, how does staph impede this?

1. protein A
2. Panton-valentine leukocidin
3. Localizing factors (clumping factor, coagulase)

27

Chronic granulomatous disease

Sex linked recessive neutrophil defect

Most common neutrophil defect

Impaired H2O2 mediated intracellular killing

28

Job's syndrome (214)

Hyper IgE

Cold (noninflammed) staph abscess

Poor neutrophil chemotaxis to site of infxn

29

Do you see strawberry tongue in staph scarlet fever?

no

*scarlet fever is caused by exfoliatin
seen in strep scarlet fever

30

Toxic shock syndrome
- Virulence factor
- signs

TSST-1
Enterotoxins

1. Acute fever
2. Erythroderma (desquamation usually late)
3. Hypotension
4. Multi-organ system involvement

31

Scalded skin
- Virulence factor
- Clinical findings

Exfoliatins

1. Painful Erythroderma
2. + Nikolsly sign
3. Bullous Impetigo

32

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)

33

Exfolatins from S. aureus can cause what?

Scalded skin syndrome

Staphylococcal scarlet fever
(diff from strep)

34

Tx for S. aureus
Tx for MRSA
Tx for Coag - Staph

S. aureus:
1. Methicillin
2. Cephalosporins
3. Vancomycin

MRSA:
1. Vancomycin
2. Bactrim

Coag - Staph
1. Vancomycin
2. Rifamin (alwaysuse with primary drug)

35

Tx regimens

1. Draining critical for focal infxn

2. Antibiotic duration
- Mild infxn: 7-10 days
- Severe infxn: 3-6 weeks

3. Add clindamycin in TSS to shut off toxin production