Makindo Medical Notes

🦠 Organisms and Antibiotic Sensitivities: A Comprehensive Guide

Choosing the right antibiotic requires balancing efficacy, resistance risk, patient safety, and stewardship. Resistance rates vary widely by geography, hospital, and community setting. Always confirm with local microbiology guidance and susceptibility testing (e.g. EUCAST/UKMIC, BNF, NICE).

🌍 Why Sensitivities Matter

• Antibiotic resistance is a global health emergency — predicted to cause 10 million deaths per year by 2050 if unchecked.
• Empiric antibiotics should cover the likely pathogen but be de-escalated once sensitivities are known.
• Broad-spectrum use (e.g. carbapenems, fluoroquinolones) accelerates resistance → use sparingly and document indication.
• Local antibiograms (hospital-specific data) guide the best empiric choice.

Gram-positive organisms

These bacteria often cause skin, soft-tissue, bloodstream, and respiratory infections. Resistance to beta-lactams is a major concern (e.g. MRSA, VRE).

💡 Clinical pearl: Always treat MRSA bacteraemia in consultation with microbiology. Duration is typically ≥2 weeks IV therapy.

Gram-negative organisms

Gram-negatives often cause urinary tract, intra-abdominal, and hospital-acquired infections. Resistance is rapidly emerging, especially ESBLs and carbapenemase-producers.

💡 Clinical pearl: Avoid fluoroquinolones in uncomplicated UTIs unless local resistance rates <10%.

Strict Anaerobes

Important in intra-abdominal infections, abscesses, and dental sepsis. Always cover anaerobes when treating perforations.

Other Notable Pathogens

Resistance Mechanisms (Exam / Clinical Notes)

• Beta-lactamases (ESBLs, AmpC, carbapenemases) → break down penicillins & cephalosporins.
• Target modification: MRSA alters penicillin-binding proteins (PBP2a).
• Efflux pumps: Pseudomonas, Neisseria resist quinolones and macrolides.
• Biofilm production: Coagulase-negative staphylococci, Pseudomonas.

💡 Clinical Stewardship Pearls

• Always narrow therapy once culture results are back.
• Avoid unnecessary dual cover unless directed by microbiology.
• Monitor renal/hepatic function for dose adjustment.
• Never use Rifampicin or Fluoroquinolones as monotherapy for serious infections.
• Document indication, duration, and review date for every antibiotic prescription.

📚 References

• BNF – British National Formulary
• NICE Guidelines
• EUCAST – European Committee on Antimicrobial Susceptibility Testing
• WHO AWaRe Antibiotic Classification (2023 update)