Lecture 5: Staphylococcus Aureus Bacteraemia

Question 1

is staph aureus gram positive or negative?

Answer 1

gram positive

Question 2

what are the most common sites of staph aureus colonisation?

Answer 2

• anterior nares most common
• skin (especially when damaged), vagina, axilla, perineum, and oropharynx may also be colonised.
• serve as a reservoir for future infections

Question 3

approx how many patients with S.aureus bacteraemia develop local complications or distant septic metastases?

Answer 3

1/3

Question 4

list the frequent sites of distant staph.aureus metastases

Answer 4

• bone and joint (especially when prosthetic materials are present)
• epidural space and intervertebral discs
• native and prosthetic cardiac valves, cardiac devices
• visceral abscesses in spleen, kidneys and lungs

Question 5

what are localised pyogenic staphylococcal infections called?

Answer 5

furuncles and carbuncles

Question 6

staph.aureus bacteraemia investigations

Answer 6

• microscopy and culture of specimens
• multiple blood cultures before commencing antibiotic therapy and 48-72hrs after.
• biopsy samples may be of value for bone infections.
• imaging: x-ray, CT, MRI, radionuclide imaging
• transthoracic echocardiography, TOE

Question 7

what is the basis of treatment for invasive staphylococcal infections?

Answer 7

• antibiotic therapy
• source identification and clearance
• and appropriate surgical intervention

Question 8

list the antibiotics used in the treatment of staph.aureus bacteraemia

Answer 8

• Flucloxacillin: min duration of treatment for uncomplicated S.aureus is 14 days.
• Vancomycin: far from ideal drug
• Teicoplanin: advantage of single daily dosing and could also be used 3 times weekly after appropriate loading
• Linezolid: bacteriostatic, synthetic oxazolidinone, good penetration into bone and excellent oral bioavailability.
• Daptomycin: cyclic lipopeptide with rapid bactericidal activity against S.aureus. Well tolerated. Once daily dosing advantage.

Question 9

which antibiotic would be given to a patient with S.aureus bacteraemia with a risk assessment = negative for MRSA?

Answer 9

• treat as MSSA: IV flucloxacillin 2g 4-6 hourly (assuming normal renal function)
• if penicillin allergy: use vancomycin

Question 10

which antibiotic would you prescribe to a patient with s.aureus bacteraemia and a positive risk assessment for MRSA?

Answer 10

• treat as MRSA: local vancomycin protocol