THE RESHAPING PROCESS OF KLEBSIELLA-PNEUMONIAE CELLS AFTER REMOVAL OFMECILLINAM, AN ANTIBIOTIC THAT CAUSES TRANSITION FROM ROD TO COCCAL SHAPE

The process of bacterial morphogenesis that leads to rod shape formati on was studied in synchronous cells during the reshaping process after removal of mecillinam, a beta-lactam antibiotic which, by specificall y inhibiting lateral wall formation of rods, cause rod-to-sphere trans ition in Gram-negative rods. The addition of mecillinam for 50 min of the cell cycle made the cells to skip a division, while the addition o f the antibiotic for 30 min (or less), allowed the cells to divide reg ularly. In order to study the interplay between lateral wall elongatio n and septum formation in reacquisition of rod shape, we evaluated the effect of re-adding mecillinam or adding piperacillin, a specific inh ibitor of septum formation, at various stages of the reshaping process . It was found that mecillinam was active only when added within the f irst 30 min of the reshaping process, while piperacillin was active on ly after 30 min when the cells were close to starting to divide again. These findings provide further support for our previous proposal that , in bacterial rods, elongation and septation are two alternating and competing events of the cell cycle, and are linked to each other in su ch a way as to force bacterial rods to grow to a given length.