147 - Staphylococcal Infections

Question 1

Taxonomy of Staphylococcus
- Gram __ cocci, described as __
- Catalase __
- __ motile, aerobism: ___

Answer 1

• Gram positive, grape-like clusters
• Catalase positive (vs streptococcal negative)
• Non-motile, aerobic and facultative anaerobic

Question 2

Taxonomy of Staphylococcus Aureus
- Coagulase __, produces coagulase to convert __ to __
(Other staphylococci are coagulase negative (CONS))

• Ferments __, positive for __ and __
• Forms __ haemolytic colonies
  (Others form small white __ haemolytic colonies)

Answer 2

• Coagulase positive - converts fibrinogen to fibrin
• Ferments mannitol, positive for protein A and DNAse
• Forms beta-haemolytic colonies

Question 3

SA is both __ and __ pathogen, with approximately __ of healthy persons colonised with SA.
Colonisation is elevated among type 1 DM, HIV, haemodialysis, IVDU, skin diseases
Frequent sites of colonisation: __
Many individuals become infected by own commensal flora.

Mode of transmission:
1. Breaches of __ or __
2. __ of infected body site
3. Rarely __ or __ in heavily colonised individuals

Answer 3

Commensal and opportunistic pathogen, 20-40%

Sites of colonisation: anterior nares, oropharynx, skin, vagina, axilla, perineum

Mode of transmission:
1. Breaches in skin or mucosal membrane
2. Direct contact of infected body site
3. Aerosols or nasal secretions (rare)

Question 4

Risk factors for SA infection (6)

Answer 4

1. Diabetes
2. PMNs defect
   - Neutropenia, chemotherapy
   - Chronic granulomatous disease
   - Autosomal dominant hyperimmunoglobulin E (Job syndrome)
   - Chediak Higashi syndrome
3. ESRF
4. HIV infection
5. Skin abnormalities
6. Prosthetic devices

Question 5

What diseases do SA frequently cause?

Answer 5

1. Skin and soft tissue infection
2. Respiratory infection
3. Infective endocarditis
4. Toxic shock syndrome
5. Food poisoning

Question 6

Daptomycin in SA
- Formulation
- Action
- MOA
- Side effects
- Limitations

Answer 6

Daptomycin
- Intravenous
- Bactericidal
- MOA: disrupts cytoplasmic membrane
- Side effects: rhabdomyolysis, eosinophilic pneumonia
- Limitations: ineffective in respiratory infections

Question 7

Linezolid in SA
- Formulation
- Action
- MOA
- Side effects

Answer 7

Linezolid
- Intravenous or oral
- Bacteriosatic
- MOA
- Side effects: thrombocytopenia, neutropenia, lactic acidosis, peripheral neuropthy, optic neuropathy
(tends to occur after 2 weeks of treatment)

Question 8

Ceftaroline in SA - __ generation cephalosporin
- Action
- MOA

Answer 8

• Fifth generation cephalosporin
• Bactericidal
• ## MOA

Question 9

MRSA decolonisation can be achieved by topical __ and __

Answer 9

1. Mupirocin 2% ointment or octenisan nasal gel over anterior nares TDS for 5 days
2. Chlorhexidine 4% (Hibiscrub) or Octenisan solution 0.1% as body wash once a day for 5 days
   Leave solution on for at least 1 minute

Question 10

Vancomycin resistance in SA

Answer 10

1. Increased MIC
2. VISA (partial resistance due to thicker cell wall)
3. VRSA (full resistance derived from enterococci)

Question 11

MSSA can be treated with: (3)

Answer 11

1. Cloxacillin / nafcillin
2. First generation cephalosporin - cefazolin
3. Carbapenem

Question 12

Factors associated with higher SA infection complication rates

Answer 12

1. Persistent positive blood culture > 96 hours
2. Community acquired MRSA (CA-MRSA)
3. Failure to remove source of infection
4. Presence of significant infection

Question 13

SA toxin mediated infections (3)

Answer 13

1. Food poisoning (Enterotoxin)
2. TSS
3. SSSS

Question 14

Life-threatening CA-MRSA conditions

Answer 14

1. Necrotising pneumonia
2. Necrotising fasciitis
3. Sepsis with Waterhouse-Friderichsen syndrome