Interference with murein turnover has no effect on growth but reduces beta-lactamase induction in Escherichia coli

Physiological studies of a mutant of Escherichia coli lacking the three lyt ic transglycosylases Slt70, MltA, and MltB revealed that interference with murein turnover can prevent AmpC beta-lactamase induction. The triple mutan t, although growing normally, shows a dramatically reduced rate of murein t urnover. Despite the reduction in the formation of low-molecular-weight mur ein turnover products, neither the rate of murein synthesis nor the amount of murein per cell was increased. This might be explained by assuming that during growth in the absence of the major lytic transglycosylases native mu rein strands are excised by the action of endopeptidases and directly reuse d without further breakdown to muropeptides. The reduced rate of murein tur nover could be correlated with lowered cefoxitin-induced expression of beta -lactamase, present on a plasmid carrying the ampC and ampR genes from Ente robacter cloacae, Overproduction of MltB stimulated beta-lactamase inductio n, whereas specific inhibition of Slt70 by bulgecin repressed ampC expressi on. Thus, specific inhibitors of lytic transglycosylases can increase the p otency of penicillins and cephalosporins against bacteria inducing AmpC-lik e beta-lactamases.