Why are Mycoplasma resistant to penicillin?

Mycoplasma species are unique among bacteria in that they lack a cell wall. This absence is a defining characteristic and is significant because the mode of action of penicillin and other beta-lactam antibiotics relies on the presence of a bacterial cell wall composed of peptidoglycan. Penicillin targets the enzymes involved in cell wall synthesis, preventing bacteria from forming a stable cell wall, which ultimately leads to cell lysis and death.

In the case of Mycoplasma, since they do not possess a cell wall, penicillin has no target to act upon, rendering it ineffective. This fundamental difference in structure is the key reason for their resistance to penicillin. The lack of a cell wall not only allows Mycoplasma to evade the action of penicillin, but it also contributes to their distinctive morphology and the ability to survive in various environments. Other options, while related to antibiotic resistance or cellular structure, do not accurately describe the specific reason for Mycoplasma's resistance to penicillin.