Final answer:
The non-desirable characteristic of an ideal antimicrobial agent is that it only arrests growth of vegetative cells, whereas an ideal agent should be broad-spectrum and be able to target a variety of microbes. Additionally, the new broad-spectrum antimicrobial developed by the scientist is classified as semisynthetic.
Step-by-step explanation:
The characteristic that is NOT a desirable feature of an ideal antimicrobial agent according to the options provided is A) it only arrests growth of vegetative cells. An ideal antimicrobial agent should not only arrest the growth of vegetative cells, but it should also be capable of killing or inhibiting a wide range of microbes, including endospores if possible, to be effective in a variety of scenarios. The desirable characteristics of an antimicrobial agent would be that it is inexpensive (B), acts quickly (C), is stable during storage (D), and is harmless to humans (E).
In response to the additional information provided, the new antimicrobial drug with broad-spectrum activity is considered to be B. semisynthetic. This is because the scientist started with a natural compound and chemically altered it, hence it is not completely synthetic or natural. The broad-spectrum activity of the drug that now works against both gram-positive and gram-negative bacteria shows an improvement in the range of the drug's efficacy.