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Promoter sequences necessary for high-level expression of the plasmid-associated ampC beta-lactamase gene blaMIR-1.

ABSTRACT: Little is known about mechanisms involved in high-level expression of plasmid-associated ampC genes. The sequence for bla(MIR-1) has been elucidated, and the gene is not inducible. Although the sequence for the promoter (prA) that drives expression of Enterobacter cloacae chromosomal ampC is present upstream of bla(MIR-1), high-level expression from bla(MIR-1) is directed from a hybrid promoter (prB) located further upstream of prA. The purpose of this study was to determine the influence of each promoter on bla(MIR-1) expression and beta-lactam resistance. RNA expression by deletion clones with both promoters was measured and compared to that by clones in which -35 and/or -10 elements of prA and/or prB were altered. Primer extension revealed two start sites for bla(MIR-1) transcription. Expression of bla(MIR-1) in clones with both promoters was 171-fold higher than that in clones carrying only prA. In addition, bla(MIR-1) expression from prA increased 11-fold in the presence of the prB -10 element compared to expression driven from prA alone. Ceftazidime and cefotaxime MICs increased 42- and 64-fold, respectively, for the clone expressing bla(MIR-1) from both promoters compared to expression from prA alone. The upstream promoter prB of bla(MIR-1) is solely responsible for high-level expression required for cefotaxime and ceftazidime resistance. These data suggest that resistance to extended-spectrum cephalosporins mediated by noninducible plasmid-associated ampC genes requires the formation of novel promoter elements that are capable of increasing ampC expression.

SUBMITTER: Reisbig MD

PROVIDER: S-EPMC525406 | biostudies-literature | 2004 Nov

REPOSITORIES: biostudies-literature

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Promoter sequences necessary for high-level expression of the plasmid-associated ampC beta-lactamase gene blaMIR-1.

Reisbig Mark D MD Hanson Nancy D ND

Antimicrobial agents and chemotherapy 20041101 11

Little is known about mechanisms involved in high-level expression of plasmid-associated ampC genes. The sequence for bla(MIR-1) has been elucidated, and the gene is not inducible. Although the sequence for the promoter (prA) that drives expression of Enterobacter cloacae chromosomal ampC is present upstream of bla(MIR-1), high-level expression from bla(MIR-1) is directed from a hybrid promoter (prB) located further upstream of prA. The purpose of this study was to determine the influence of eac ...[more]

PMID: 15504838

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Project description:Plasmid-mediated AmpC beta-lactamase-producing (pAmpC) Enterobacteriaceae are increasing worldwide, difficult to identify and often confounded with extended-spectrum beta-lactamase (ESBL) producers. The low prevalence precludes routine universal admission screening. Therefore, we evaluated potential risk factors for carriage of pAmpC-producing Enterobacteriaceae that would allow targeted screening to improve yield and reduce cost.We performed a case control study at a tertiary care center from 1/2006 to 12/2010. Cases were adult patients in whom pAmpC-producing Enterobacteriaceae were isolated; controls were chosen among carriers of ESBL-producing Enterobacteriaceae. Both infected and colonized patients were included.Over five years, we identified 40 pAmpC producers in 39 patients among 16,247 screened consecutive isolates of Enterobacteriaceae. The pAmpC prevalence was low (0.25%), but more than 30% of pAmpC carriers received incorrect empirical antibiotic treatment. When compared with 39 ESBL controls, pAmpC carriage was associated with clinically confirmed infections in 74% (versus 51%) (p=0.035), mainly of the urinary tract, previous antibiotic exposure in 63% (versus 36%) (p=0.035) and carriage of a nasogastric tube in 23% (versus 0%) (p=0.002). In the multivariate regression analysis only clinically confirmed infections remained significantly associated with pAmpC carriage (OR 1.44 (95%CI 1.15-2.57)). No other clinical and blood test-associated risk factor allowed discrimination of pAmpC-carrying patients from ESBL controls. The type of acquisition - nosocomial versus community-acquired - was also non-informative for resistance type, as 46% of pAmpC- and 44% of ESBL-producing Enterobacteriaceae were community-acquired.This study could not identify a clinical profile that would allow targeted screening for pAmpC-producing Enterobacteriaceae when compared to ESBL carriers. Because empiric antimicrobial therapy was inappropriate in more than 30%, rapid identification of pAmpC carriers is needed. New microbiological methods are therefore required to simplify rapid and reliable detection of pAmpC carriers.

Dataset Information

Promoter sequences necessary for high-level expression of the plasmid-associated ampC beta-lactamase gene blaMIR-1.

Publications

Promoter sequences necessary for high-level expression of the plasmid-associated ampC beta-lactamase gene blaMIR-1.

Similar Datasets

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