Which antibiotic can induce clindamycin resistance in vitro?

Which antibiotic can induce clindamycin resistance in vitro?

• A. Gentamicin
• B. Penicillin
• C. Ampicillin
• D. Erythromycin

Answer: (D)

Inducible resistance to clindamycin arises when bacteria carry erm genes that encode an rRNA methylase. This enzyme can be produced in response to exposure to macrolide antibiotics, such as erythromycin. Once expressed, the methylase modifies the 23S rRNA of the 50S ribosomal subunit, reducing binding of macrolides, lincosamides (like clindamycin), and streptogramin B. In vitro, exposing the organism to erythromycin can trigger this methylase production, causing clindamycin resistance to emerge even if initial tests show susceptibility. That’s why erythromycin can induce clindamycin resistance in vitro. Other antibiotics listed—gentamicin, penicillin, and ampicillin—do not induce this methylase-mediated resistance, so they don’t reveal inducible clindamycin resistance via this mechanism.

Inducible resistance to clindamycin arises when bacteria carry erm genes that encode an rRNA methylase. This enzyme can be produced in response to exposure to macrolide antibiotics, such as erythromycin. Once expressed, the methylase modifies the 23S rRNA of the 50S ribosomal subunit, reducing binding of macrolides, lincosamides (like clindamycin), and streptogramin B. In vitro, exposing the organism to erythromycin can trigger this methylase production, causing clindamycin resistance to emerge even if initial tests show susceptibility. That’s why erythromycin can induce clindamycin resistance in vitro. Other antibiotics listed—gentamicin, penicillin, and ampicillin—do not induce this methylase-mediated resistance, so they don’t reveal inducible clindamycin resistance via this mechanism.