In which phase (lag, exponential or stationary) is a bacterium most sensitive to an antibiotic?

Answer 1

It is the exponential phase.
Many antibiotic such as the Streptogramin family work on the ribosome and indeed the DNA and RNA polymerases. These are most active when the bacteria are dividing and so it causes more harm as it were. Also in Mycobacterium, when dividing it does not have such a thick cell wall, and so it is easier for the antibiotics to penatrate.

Answer 2

Since most of the common antibiotics exert their effects on processes that are required for cell growth or division, the most sensitive time for any bacterium is during the exponential phase. In lag phase the bacteria are conditioning their environment more to their particular liking and in the stationary phase the number of nutrients starts to become limiting and the number of cells dividing is equaled by the number of cells dying, all of which leads to slower growth of those cells that are surviving.

Answer 3

Lag Phase Bacteria

Answer 4

The exponential phase - when they are busy forming new cells. Most antibiotics act by supressing or mimicing an essentail part of the microbe, thus rendering them dead or nonviable.

Answer 5

Whenever they're growing! Expo, of course.