Dependence of induction of enterobacterial AmpC  -lactamase on cell-wall peptidoglycan, as demonstrated in Proteus mirabilis and its wall-less protoplast L-form

Abstract

~~The mobilizable plasmid pMDlOl (amp& ampC) was constructed by inserting cloned m p C , the structural gene for the chromosomal AmpC plactamase of Citrobacter freundii, and the closely linked ampR encoding the transcriptional regulator essential for enzyme induction, into the broad host-range plasmid pKT231. Plasmid pMDlO1 was transconjugated into Proteus mirabilis VI and its isogenic, cell-wall-less protoplast L-form LVI. AmpC &-lactamas? was expressed constitutively from cloned ampR and ampC in bacteria and in some L-form protoplasts. However, induction of the enzyme by @-lactam antibiotics occurred only in bacterial cells and not in the cell-wall-and peptidoglycan-deficient L-form. In agreement with current models, induction of AmpC lactamase is thought to be initiated by an induction signal arising from the metabolic disturbance of cell-wall peptidoglycan.

Cell-wall recycling and synthesis in Escherichia coli and Pseudomonas aeruginosa – their role in the development of resistance

“…The AmpRAmpC system has been investigated thoroughly in Enterobacteriaceae. In many members of the Enterobacteriaceae, the induction of ampC expression in response to b-lactam antibiotics is triggered through the activation of a transcriptional regulator AmpR by the cell-wall degradation products [191,[193][194][195][196]. The induction of ampC by AmpR also requires the products of ampG, ampD, ampDh2, ampDh3 and nagZ, all of which are involved in PG recycling, as described in previous sections.…”

A Common System Controls the Induction of Very Different Genes

“…Derivatives of the mobilizable pKT231 (Bagdasarian et al, 1981) were used for transconjugation in P. vulgaris. pMDl0l contains cloned ampR and ampC of C. freundii inserted into the EcoRI site of pKT321 (Tolg et al, 1993). pMD201 was constructed by inserting the cloned ampDE operon of E. coli in an 11-kbp EcoRI fragment from pNU413 (Lindquist et al, 1989b) into the EcoRI site of pKT231.…”

“…These interspecific activities may also reflect more general regulatory functions of genes ampG (cumG) and ampD (cumD) in an ubiquitous metabolic pathway of Gram-negative bacteria, and several lines of evidence point to an involvement of these genes in the metabolism of the cell wall peptidoglycan (Tuomanen et al, 1991 ;Lindquist et al, 1993;Tolg et al, 1993). …”

“…Expression of C. freundii AmpC a-lactamase was studied in P. vulgaris strain U7, whose own P-lactamase is only poorly inducible (Essig, 1984). C. freundii genes ampR and ampC on plasmid pMDlOl (Tolg et al, 1993) were introduced by transconjugation. The transconjugant U7/pMD101 contained an elevated amount of constitutively produced Plactamase, and the enzyme was induced 115-fold by cefotaxime, a good inducer in P vulgaris ( Table 2).…”

“…Moreover, we show that equivalents of the class-C P-lactamase signal transducer and negative modulator genes ampG and ampD are also present in l? vulgaris and can be interchangeably used for inducing expression of the class-C from the auxotrophic donor E. coli S17-1 into P. vulgaris was carried out as described by Tolg et al (1993).…”