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Research Article

ampG is essential for high-level expression of AmpC beta-lactamase in Enterobacter cloacae.

G Korfmann, C C Sanders
G Korfmann
Department of Medical Microbiology, Creighton University School of Medicine, Omaha, Nebraska 68178.
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C C Sanders
Department of Medical Microbiology, Creighton University School of Medicine, Omaha, Nebraska 68178.
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DOI: 10.1128/AAC.33.11.1946
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ABSTRACT

Mutants of Enterobacter cloacae 55 were studied to delineate more completely the genetics of inducible expression of AmpC beta-lactamase. E. cloacae 55M-L, derived by mutagenesis from a mutant with high-level cefotaxime resistance (MIC, greater than 64 micrograms/ml), E. cloacae 55M, demonstrated a novel phenotype by producing only low levels of AmpC constitutively. Neither the parental phenotype of E. cloacae 55M nor the wild-type phenotype of E. cloacae 55 could be restored in E. cloacae 55M-L by the introduction of functional ampR, ampC, or ampD genes. Cloning each of these genes from E. cloacae 55M-L confirmed the same genotype for this mutant as for its parental strain. Mutation of E. cloacae 55M-L to the E. cloacae 55M phenotype was found to occur spontaneously at a frequency of 10(-8). All such revertants demonstrated an inducible wild-type phenotype after introduction of a functional ampD. These results suggested that the E. cloacae 55M-L phenotype was due to a mutation in an as yet unrecognized gene, designated ampG. Verification of this gene was obtained by the restoration of the E. cloacae 55M phenotype in E. cloacae 55M-L by introduction of a cloned 2.9-kilobase BamHI fragment from the E. cloacae 55 chromosome. Transformation of both ampG and ampD into E. cloacae 55M-L reconstituted the inducible wild-type phenotype. These results indicate that ampG is required for the activation of ampC by AmpR. Without ampG, neither induction nor high-level expression of AmpC is possible. It is likely that the ampG gene product and AmpD together modulate the ability of AmpR to activate ampC expression.

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ampG is essential for high-level expression of AmpC beta-lactamase in Enterobacter cloacae.
G Korfmann, C C Sanders
Antimicrobial Agents and Chemotherapy Nov 1989, 33 (11) 1946-1951; DOI: 10.1128/AAC.33.11.1946

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ampG is essential for high-level expression of AmpC beta-lactamase in Enterobacter cloacae.
G Korfmann, C C Sanders
Antimicrobial Agents and Chemotherapy Nov 1989, 33 (11) 1946-1951; DOI: 10.1128/AAC.33.11.1946
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