The latter complex issue has recently been reviewed by Renier
et al. . Figure 4 Effect of overproduction of PBP3 on the susceptibility of L. monocytogenes to β-lactams. (A) Susceptibility of L. monocytogenes pAKB (Lm pAKB) and L. monocytogenes pAKB-lmo1438 (Lm pAKB-lmo1438) to ampicillin measured using the E-test. The extent of the zone of partial autolysis of L. monocytogenes pAKB-lmo1438 is indicated by an arrow. (B) Survival of L. monocytogenes pAKB (○) and L. monocytogenes pAKB-lmo1438 (•) in the presence of a lethal dose of penicillin G (0.6 μg/ml). Following nisin induction, penicillin G was added (at the time indicated by an arrow) to the cultures in BHI broth and incubation at 37°C was continued. Survival was measured by performing viable cell counts. Error bars represent standard deviations from the means of three independent
experiments, each performed in triplicate. Conclusions CX-5461 solubility dmso The findings of RAD001 mouse the present study have helped to elucidate the somewhat conflicting results regarding the contribution of PBP3 to the β-lactam susceptibility of L. monocytogenes. Using the NICE expression system, it has been directly shown that PBP3 is encoded by the lmo1438 gene. Despite the excellent correlation between the MICs of different β-lactams and their affinity for PBP3 [4, 5], neither the absence  nor an excess of this protein affects the susceptibility of L. monocytogenes to β-lactams, and so it is not the primary lethal target of these antibiotics. An interesting
additional observation was that PBP3 overexpression SPTLC1 is accompanied by increased expression of PBP4. This finding indicates that the composition of the L. monocytogenes cell wall is subject to tight regulation, but it also makes it difficult to analyze the physiological role of PBP3 on the basis of overexpression studies, since the observed changes in growth rate and antibiotic sensitivity cannot be attributed to PBP3 overexpression alone. The overexpression of PBP3 induced the formation of short cells in the stationary phase of growth, which strongly suggests the involvement of PBP3 in cell division at this growth stage. It is possible that the changes in cell morphology produced by overexpression of PBP3 may be due to a putative FtsI activity, whereas the parallel increase in the expression of PBP4 (a cell wall synthetic enzyme not specific for cell division) could play an auxiliary role in this process. Finally, in the course of clarifying the contribution of PBP3 to the β-lactam susceptibility of L. monocytogenes, a new vector was constructed that is suitable for the overexpression of genes of interest in L. monocytogenes. The placement of components of the NICE system on a single plasmid provides an easy to use tool for expressing any protein of choice in L. monocytogenes. The construction of the plasmid pAKB and its successful application in L.