The D test is used to detect which resistance mechanism?

The D test is used to detect which resistance mechanism?

• A. Inducible clindamycin resistance
• B. Innate clindamycin resistance
• C. Innate erythromycin resistance
• D. Constitutive clindamycin resistance

Answer: (A)

The D test reveals inducible clindamycin resistance caused by an inducible MLSB (macrolide-lincosamide-streptogramin B) phenotype. Some bacteria carry erm genes that encode an enzyme modifying the 23S rRNA, which can be expressed in response to exposure to macrolides like erythromycin. In the lab, placing an erythromycin disk near a clindamycin disk on an agar plate will show how the bacteria respond. If the resistance to clindamycin is inducible, erythromycin induces the resistance mechanism and the clindamycin zone is blunted on the side facing the erythromycin disk, creating a distinctive D-shaped zone. This pattern confirms inducible clindamycin resistance. If resistance were constitutive, the bacteria would resist both drugs regardless of proximity; if resistance were innate, the pattern would not produce the characteristic D shape. Thus the test specifically detects inducible clindamycin resistance.

The D test reveals inducible clindamycin resistance caused by an inducible MLSB (macrolide-lincosamide-streptogramin B) phenotype. Some bacteria carry erm genes that encode an enzyme modifying the 23S rRNA, which can be expressed in response to exposure to macrolides like erythromycin. In the lab, placing an erythromycin disk near a clindamycin disk on an agar plate will show how the bacteria respond. If the resistance to clindamycin is inducible, erythromycin induces the resistance mechanism and the clindamycin zone is blunted on the side facing the erythromycin disk, creating a distinctive D-shaped zone. This pattern confirms inducible clindamycin resistance. If resistance were constitutive, the bacteria would resist both drugs regardless of proximity; if resistance were innate, the pattern would not produce the characteristic D shape. Thus the test specifically detects inducible clindamycin resistance.