- Describe how Staphylococcus aureus is identified in the lab : a discussion of methods should include:
- Gram stain appearance
- Colony morphology on blood agar – may be haemolytic- colour etc
- Coagulase detection – bound coagulase and tube coagulase – NB these are not equivalent procedures. Tube coagulase is the most reliable of the two methods
- Other phenotypic characters – utilises mannitol , DNASe production, presence of protein A on surface (usually detected in a combined latex particle agglutination reaction that also includes bound coagulase), MALDITOF – commonest now in Australia – look it up!
- Molecular – presence of nuclease gene by PCR is a common way
In general for important specimens – e.g. blood, the identification should be by at least two phenotypic methods – eg Mannitol positive and tube coagulase positive.
2. What antibiotics are useful for treating S. aureus skin/soft tissue infections (boils, infected exzema or scabies)
- For Methicillin -susceptible S. aureus (MSSA): fluclox IV for infection with sepsis or positive blood culture. Oral diclox or flucloxacillin, cephalexin or amoxycillin+clavulanate. Some strains are betalactamase negative and susceptible to penicillin.
- For MRSA: vancomycin IV for severe infection with sepsis or positive blood isolate. Depending on tested susceptibility, cotrimoxazole, doxycycline or a macrolide – erythromycin or lincosamide- clindamycin.
For either: dependent on the local antibiogram, cotrimoxazile or doxycycline may be suitable.
- Miller et al Clindamycin versus Trimethoprim–Sulfamethoxazole
for Uncomplicated Skin Infections NEJM 2015
- Talan et al. A Randomized Trial of Clindamycin Versus Trimethoprim-sulfamethoxazole for Uncomplicated Wound Infection . Clin Inf Diseases 2016
- Medicine Today Preventive strategies for recurrent staphylococcal skin infection. Ferguson, 2012; 13(9): 65-70.
Distinguish the approach to impetigo: important trial –
- Bowen-A, Short-course oral co-trimoxazole versus intramuscular benzathine benzylpenicillin for impetigo in a highly endemic region: an open-label, randomised, controlled, non-inferiority trial . Lancet 2014.
3. What is the current pattern of susceptibility for these antibiotics at PMGH in 2016 ?
4. Describe the pyogenic (direct infection consequences) and non-pyogenic complications of group A strep (Streptococcus pyogenes) infection
Important text book reading and understanding about pathogenesis in general!
5. Read through the Tropical Microbiology presentation from Prof. Baird (NT) – describe some of the Gram negative pathogens associated with skin and soft tissue disease in the tropics. Australian-tropical-skin-bacteriology-rbaird. Vibrio, Shewenella, Aeromonas, Melioidosis.