The phenomenon of bacterial resistance to the bactericidal activity of penicillins and cephalosporins, with only inhibition of growth, is known as which term?

• A. High-level resistance
• B. Intrinsic resistance
• C. Inducible resistance
• D. Tolerance

Answer: (D)

When bacteria are tolerant to a bactericidal antibiotic like penicillins or cephalosporins, exposure stops their growth without actually killing the cells. The drug may still prevent replication (the MIC may stay the same), but the rate of killing is markedly reduced, so the population survives the treatment. In practical terms, these organisms appear bacteriostatic during exposure, and once the drug is removed, they can resume growth. This is different from true resistance, where higher drug concentrations are needed to inhibit growth because the bacteria have acquired mechanisms (like enzymes that destroy the drug or altered targets) that raise the MIC. It’s also distinct from inducible or intrinsic resistance, which involve specific, sometimes inherent, mechanisms altering susceptibility. So the described phenomenon is best described as tolerance.