Journal
ANTIMICROBIAL AGENTS AND CHEMOTHERAPY
Volume 49, Issue 11, Pages 4567-4575Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/AAC.49.11.4567-4575.2005
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- NIGMS NIH HHS [S06 GM08205, S06 GM008205] Funding Source: Medline
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In members of the family Enterobacteriaceae, ampC, which encodes a P-lactamase, is regulated by an upstream, divergently transcribed gene, ampR. However, in Pseudomonas aeruginosa, the regulation of ampC is not understood. In this study, we compared the characteristics of a P. aeruginosa ampR mutant, PAOampR, with that of an isogenic ampR(+) parent. The ampR mutation greatly altered AmpC production. In the absence of antibiotic, PAOampR expressed increased basal beta-lactamase levels. However, this increase was not followed by a concomitant increase in the P-ampC, promoter activity. The discrepancy in protein and transcription analyses led us to discover the presence of another chromosomal AmpR-regulated beta-lactamase, PoxB. We found that the expression of P. aeruginosa ampR greatly altered the beta-lactamase production from ampC and poxB in Escherichia coli: it up-regulated AmpC but down-regulated PoxB activities. In addition, the constitutive P-ampR promoter activity in PAOampR indicated that AmpR did not autoregulate in the absence or presence of inducers. We further demonstrated that AmpR is a global regulator because the strain carrying the ampR mutation produced higher levels of pyocyanin and LasA protease and lower levels of LasB elastase than the wild-type strain. The increase in LasA levels was positively correlated with the P-lasA, P-lasl, and P-lasR expression. The reduction in the LasB activity was positively correlated with the P-rhlR expression. Thus, AmpR plays a dual role, positively regulating the ampC, lasB, and rhlR expression levels and negatively regulating the poxB, lasA, lasl, and lasR expression levels.
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