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Methicillin Resistant Staphylococcus aureus

Methicillin Resistant Staphylococcus aureus. DAHS 1010 DAHS 2010 Beverley Gallacher. Learning Outcomes. Describe the epidemiology of MRSA infection Describe the mechanism of resistance for MRSA Discuss infection control strategies for MRSA infection. Description & Classification.

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Methicillin Resistant Staphylococcus aureus

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  1. Methicillin Resistant Staphylococcus aureus DAHS 1010 DAHS 2010 Beverley Gallacher

  2. Learning Outcomes • Describe the epidemiology of MRSA infection • Describe the mechanism of resistance for MRSA • Discuss infection control strategies for MRSA infection

  3. Description & Classification • Gram + - spherical, clusters • Aerobic • Most coagulase + (fibrinogen  fibrin) Sources nostrils, skin, groin, axilla • Staff • Patients Normal flora • Inanimate objects

  4. Hospital acquisition • 1950’s S aureus wound infections & outbreaks • mid 1950’s reports of penicillin resistance • Today Nosocomial Infection National Surveillance Scheme (2001) • 47% infection causing micro-organisms - Staphylococci, of which 82% S aureus. 62% of which are MRSA

  5. Infection control • Mode of spread - direct contact primarily - hands. Theatres & burns units - potentially airborne • Hospital equipment (indirect contact) - if not adequately decontaminated • Patients themselves sources • SOURCE ISOLATION?

  6. Search & Destroy Screen & treat carriers Began Holland 1989 Isolate or cohort nursing of all infected or colonised patients Costs of screening thought to be less than costs of outbreak Treat Infections Only Search & destroy does not work in UK Negative screens do not mean patient MRSA free. Transient carriage Screening costs outweigh outbreak costs Infection Control Policy

  7. Leeds Trust policy - risk assessment What is the risk of transferring the MRSA to another patient? Depends on site or specimen from which MRSA obtained Depends on environment patient being managed Depends on whether the patient is infected or colonised?

  8. High risk patients have • Leaking wounds, drains, exfoliating skin conditions. • Expectorating cough (sputum +ve) High risk environments High - ICU, HDU, Liver units Medium - surgical wards esp - vascular & orthopaedics. Renal, oncology, haemotology wards Low - medical & elderly wards. Out patients

  9. Do the Trust screen patients for carriage? • In specific areas • In patients admitted from a hospital outside the UK • Screening a nasal swab (one swab from both anterior nares) a groin swab a swab from each lesion or invasive device

  10. Treatment for carriage • See Trust Infection Control Policy folder: • Mupirocin 2% nasal ointment (Bactroban) 3 x daily for 5 days • Antiseptic body wash: Triclosan 2% (Aquasept) Aqueous povidone iodine 4% (Betadine) Chlorhexidine gluconate 4% (Hibiscrub) daily for 5 days

  11. Drug should not harm human cells, only those of the microorganism Therefore look for differences between the cells Cell wall Ribosomes Nucleic Acids Cell membrane Antibiotics work on the basis of selective toxicity

  12. Methicillin Resistant Staphylococcus Aureus • Selective toxicity - cell wall attacking • Weak wall susceptible to osmotic pressure - fluid enters cell which bursts “lysis” • Cell wall made of peptidoglycan • 2 sugar chains: n-acetylglucosamine N-acetylmuramic acid • Linked by peptide cross bridges

  13. “Link” = chemical bond • Formation of bond catalysed by ENZYMES • TRANSPEPTIDASES, sometimes called “penicillin binding proteins” • Penicillin binds to the transpeptidase enzyme and blocks its activity link between peptide bridge and sugar chains not made. • Weak bacterial cell wall - liable to rupture

  14. Resistance • Penicillin binds i.e. It’s shape is important • The “heart of the shape =  lactam ring • This type of antibiotic also known as  lactam antibiotics (see BNF) • Resistance can develop when the bacteria changes its transpeptidase/penicillin binding protein, so that penicillin no longer binds to it, thereby blocking its activity. • Protein changed by genetic mutation - genes “code“ for proteins

  15. How can bacteria “change” their proteins? • Can’t will it to happen - no brain! • Happens by chance • What in the bacterial cell carries the genetic blueprint that codes for proteins? • DNA • Chance mutation of bacterial DNA enables it to produce a new, different protein

  16. Non pathogenic Mutated bacteria

  17. Give antibiotic Susceptible Resistant

  18. Give antibiotic Susceptible Resistant

  19. Give antibiotic Susceptible Resistant

  20. Give antibiotic Susceptible Resistant

  21. Give antibiotic Susceptible Resistant

  22. References • Gould D & Chamberlaine A (1995) Staphylococcus aureus: a review of the literature. Journal of Clinical Nursing 4, 1, pg 5-12 • Ayliffe G.A. et al (1998) Revised guidelines for the control of MRSA in hospitals. Journal of Hospital Infection 39, 253 - 290 • Barrett S.P et al (1998) Trying to control MRSA causes more problems than it solves. Journal of Hospital Infection 39, 85 - 93 • Kelly J & Chivers G (1996) Built in Resistance. Nursing Times 92. 2. 50-54 • Duckworth G (1993) Diagnosis & management of MRSA infection. B.M.J. 307. 1049-52

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