Episode 32 - Resistance is Futile! Managing MRS in Practice
Chapter 1: Meet the Microbes
(02:41) John opens the episode, introducing Dr Vanessa Schmidt and inviting her to share her background. Vanessa explains her role at the University of Liverpool, her PhD in antimicrobial resistance in staphylococci, and her leadership in infection control and antimicrobial stewardship.
(03:38) John asks whether staph infections in pets are usually caught or part of their natural skin flora. Vanessa replies that most infections come from an animal's own commensal microbiota, which coexist harmlessly but can cause disease when the immune system or skin barrier is compromised.
(05:07) Sue asks whether humans and animals share the same commensals. Vanessa explains that while many organisms are shared across species, each host also harbours unique flora. Cross-species transfer is possible but not common.
(06:16) Sue asks whether different body sites have different staph species. Vanessa says this is well-mapped in humans, while in pets we know carriage is common in the nose, mouth, and perineum, but site-specific species need more study.
(07:28) John asks about coagulase-positive vs coagulase-negative staph. Vanessa explains that coagulase-positive staph are generally more virulent, while coagulase-negative species can still be important, especially in immunocompromised hosts or in association with implants.
(09:37) Sue asks how to interpret a coagulase-negative result on a lab report. Vanessa advises considering clinical context, immune status, culture growth level, and cytology to judge significance.
(12:34) Sue emphasises the value of cytology. Vanessa agrees, explaining it's routine in dermatology and helps identify intracellular bacteria and neutrophilic inflammation.
Chapter 2: Resistance Training
(14:30) John transitions to methicillin resistance. Vanessa explains MRSP carries the mecA gene, conferring resistance to beta-lactam antibiotics. It spreads clonally and is more stable than resistance in Gram-negatives.
(17:40) Sue asks whether antibiotic use can switch the resistance gene on or off. Vanessa says it's about selection pressure - resistant strains survive when antibiotics are overused.
(19:03) Sue shares her “rucksack” analogy. Vanessa agrees, adding that over time resistant strains adapt, carrying resistance genes more efficiently.
(20:15) John asks about zoonotic risk. Vanessa confirms bacteria like MRSP can pass between pets and owners, though actual infections are rare.
Chapter 3: Less is More: Treating MRS the Smarter Way
(22:33) Sue asks about managing MRSP pyoderma in practice. Vanessa outlines a tiered approach: treat the underlying disease, apply barrier nursing, and use topical therapy like chlorhexidine, aiming to avoid systemic antibiotics.
(27:00) Sue raises chlorhexidine use and guideline updates. Vanessa recommends 2% or above concentrations of chlorhexidine and warns that dilution reduces effectiveness and may lead to treatment failure.
(30:05) Sue mentions suspected resistance. Vanessa confirms resistance is reported and linked to bacterial efflux pumps. She uses hypochlorous acid or bleach as follow-up options in certain MRSP cases.
(33:15) John asks what Vanessa avoids. She avoids systemic antibiotics in superficial MRSP unless absolutely needed, and tailors treatment to the underlying disease. Immunosuppressives are avoided if the infection arose due to immune compromise.
(35:00) Sue asks about treating MRSP otitis. Vanessa explains that lower chlorhexidine concentrations are potentiated by TRIS-EDTA, so she still uses them as first-line ear cleaners.
(36:40) John asks about long-term carriage. Vanessa explains MRSP can persist for months or even years. Decolonisation before high-risk surgery is common, but long-term clearance is difficult and evidence is limited.
(39:42) Sue summarises the discussion: in MRSP, less is more - fewer antibiotics and more topicals. New guidelines offer hope for better resistance control.
ISCAID guidelines
Protect Me guidance from BSAVA
https://www.bsava.com/Resources/Veterinary-resources/PROTECT-ME/