Influence of penicillin and nalidixic acid on growth and cell division of Escherichia coli K-12.

Ultrastructure of E. coli K-12 cells and the synthesis of DNA in bacteria treated with low concentration of nalidixic acid and penicillin was investigated. In E. coli both drugs caused inhibition of cell division in period D of the life cycle although nalidixic acid inhibits division at an earlier stage of septum formation. The ability of cells to form filaments in the presence of nalidixic acid depends on their age, i.e. time at which cells are taken from synchronous culture.