Effect of overproduction of PBP3 on growth and morphology of L. monocytogenes. (A) Growth of L. monocytogenes pAKB (○) and L. monocytogenes pAKB-lmo1438 (•) incubated in BHI broth at 37°C following nisin induction, determined by serial dilution of the cultures and enumeration of viable cells on BHI agar. Error bars represent standard deviation from the means of three independent experiments, each performed in triplicate. (B) SEM images of L. monocytogenes pAKB (Lm pAKB) and L. monocytogenes pAKB-lmo1438 (Lm pAKB-lmo1438) cells grown overnight in BHI broth at 37°C following nisin induction. The mean cell lengths (± SD), determined by measuring 100 cells of each strain, are shown in parentheses. Bar = 2 μm.