Abstract
Expression of the chromosomal beta-lactamase from the ampC gene in inducible in both Enterobacter cloacae and Citrobacter freundii. Cloning of ampC as well as its regulatory gene, ampR, from E. cloacae P99 revealed a gene organization indentical to that of C. freundii in the corresponding region. Although almost no similarities could be found between the restriction maps of ampC and ampR in the two species, the genes cross-hybridize. Also, both ampR gene products have a size of about 31,000. The regulatory features of E. cloacae beta-lactamase induction are very similar to those in C. freundii, i.e., beta-lactamase synthesis is repressed by AmpR in the absence, and stimulated in the presence, of inducer. The AmpR function can be transcomplemented between the two species, but there are quantitative regulatory aberrations in such hybrids, in contrast to the total complementation obtained within each system. These results suggest that the mechanism of beta-lactamase induction is the same in E. cloacae, C. freundii, and other gram-negative bacteria with inducible chromosomal beta-lactamase expression.
Highlights
Expression of the chromosomal j8-lactamase from the ampC gene is inducible in both Enterobacter cloacae and Citrobacterfreundii
These results suggest that the mechanism of I8-lactamase induction is the same in E. cloacae, C. freundii, and other gram-negative bacteria with inducible chromosomal
The sequence for the 20 amino-terminal residues of the p-lactamase produced from this recombinant plasmid was identical to that published for the E. cloacae P99 enzyme [16]
Summary
Expression of the chromosomal j8-lactamase from the ampC gene is inducible in both Enterobacter cloacae and Citrobacterfreundii. The AmpR function can be transcomplemented between the two species, but there are quantitative regulatory aberrations in such hybrids, in contrast to the total complementation obtained within each system These results suggest that the mechanism of I8-lactamase induction is the same in E. cloacae, C. freundii, and other gram-negative bacteria with inducible chromosomal. A regulatory gene, ampR, which decreases expression in the absence of inducer and increases it in the presence of inducer has been identified in C. freundii [21] This gene is not present in E. coli. A similar mutation which leads to ampR-dependent overproduction of the C. freundii P-lactamase from the cloned ampC gene has been described in E. coli [21].
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