2 To CoverApologies Gram negative vs gram positive Bacteria Some common skin infections *Bonus time (basic antibiotics)
3 Sorry about the lack of sweets Reesha forgot the locker key, which is why we must all go hungry. If you want to blame somebody, then blame Reesha.
4 Explain the process of gram staining? (5) Stain bacteria with crystal violet and iodineWash out crystal violet with acetoneGram positive will remain blue/purpleIn gram negative, thin peptidoglycan wall allows stain to seep outCounterstain with red dye to see gram negative bacteria*Unlikely exam question, but useful to understand
5 Why do we care about gram staining? It informs the choice of antibiotic given:
6 An untrustworthy immunocompromised vagabond who is crap at chess and currently presenting hand anatomy in another room, Danny Waite, 80, enters your clinic. He has a red swollen right leg. What are some initial differentials? (2)-DVT -Compartment syndrome -Heart failure -CellulitisWhat other findings in clinic might point you towards a diagnosis of cellulitis? (2)- Entry point for infection (e.g. athletes foot, ulcers, skin wounds)- Systemic signs of infection (e.g. malaise, fever, fatigue)
7 Obligatory steps for infection Attachment +/-Evade natural protection and cleansing mechanismsEntry into bodyLocal or general spread Evade immediate local defencesMultiplicationEvasion of host defences Evade immune and other defences for growth in the host to be completedShedding from bodyLeave body at a site and on a scale that ensures spread to fresh host- transmission
8 What are the 2 most likely pathogenic causes of cellulitis? (2) Staphlococcus aureus Streptococcus pyogenes (Group A Strep)Strep (chains)How could gram staining differentiate between these 2 bacteria?Both bacteria would show gram positive (purple) cocciButStaph would appear as grapes, and Strep would appear as chainsStaph (grapes)*Memory tip: Grapes come from Staffordshire, and you go Strep by Strep by Strep to get there
9 What antibiotic would be used to treat cellulitis? AmoxicillinAztreonamGentamicinTrimethoprimFlucloxacillin
10 What part of the bacteria do penicillins attack? Cell wallWhat forms a core part of penicillin structure?Beta Lactam ringWhat enzyme might some bacteria have (e.g. staph aureus) that makes them resistant to some penicillins?Beta-lactamaseSome antibiotics are resistant to beta-lactamase. Either they have beta-lactamase inhibitor molecules (lactam or penam), or they have structures that cannot be bound by beta-lactamases (e.g. flucloxacillin)
11 Your niece Reesha (who forgot the sweets) comes home from school, and you see she has developed a couple of itchy, crusty sores around her face. Apparently her best mate Pogo has also been suffering from something similar. What is the likely diagnosis here?PsoriasisEczemaErysipelasImpetigoCellulitis*Impetigo is highly contagious, and presents with itchy, crusty lesions around the face. Common in children.
12 Impetigo is usually caused by which of the following? Abrasion of skin would be a risk factor (skin breaks/lesions are an entry point for bacteria)Abrasion of the skinGroup A streptococciNeisseria meningitidesStaphlococcus aureusEscherichia coliGroup A streptococcus is a less common cause of impetigo – watch out for this in lectures. Best to learn the main/common/”gold standard” answer first!Neisseria meningitides is notable for causing “meningococcal meningitis” – which features the petechial rash
13 Danny Waite (who is rubbish at FIFA) trips over a cat and lands on a hedgehog, skewering himself in the abdominal area. He patches up the wounds, but pain develops around the area over 3 days until it is “excruciating”. He goes to the hospital where antibiotics and fluids are administered, but after 6 hours these have no effect, and within a few more hours Danny’s skin becomes blackened and blistered. What is the appropriate action taken next?Abdominal trauma, pain out of proportion to appearance, failure to respond to antibiotics and skin changes (purple/black appearance, blistering/bullae) are all suggestive of necrotising fasciitis, which is a medical emergency – this is a RARE condition – therefore less likely to be examination materialChange the antibioticAbdominal CT scanSurgical exploration and debridementSEPSIS 6Tell Danny he is rubbish at FIFAYou would also do this
14 (P.S. sorry again that Reesha forgot the sweets) ThanksMatt and Tom(P.S. sorry again that Reesha forgot the sweets)
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