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Pharmacology · single question

What is the PRIMARY mechanism by which bacteria within biofilms resist antibiotics?

  1. Rapid mutation of antibiotic-binding sites
  2. Extracellular matrix barrier + reduced metabolic activity + shared resistance genes
  3. Production of exotoxins that neutralize antibiotics
  4. Capsule formation preventing antibiotic entry
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Correct answer: B. Extracellular matrix barrier + reduced metabolic activity + shared resistance genes

Biofilm resistance to antibiotics is multifactorial: (1) Extracellular polysaccharide matrix — physical barrier limiting antibiotic penetration, (2) Reduced metabolic activity of deeper cells — many antibiotics target actively dividing bacteria, (3) Horizontal gene transfer of resistance genes within the biofilm community. Biofilm bacteria can be 100–1000× more resistant than planktonic bacteria.
  • A. ❌ Rapid mutation occurs but is not the PRIMARY mechanism within established biofilms.
  • B. ✅ Extracellular matrix barrier + reduced metabolism + gene sharing — the three main mechanisms of biofilm antibiotic resistance.
  • C. ❌ Exotoxin production contributes to virulence but does not neutralize antibiotics.
  • D. ❌ Capsule provides immune evasion — biofilm matrix is more relevant to antibiotic resistance.

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