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Detection of amp C in Enterobacter cloacae in China

Y L Zhang1, J T Li, M W Zhao

  • 1Institute of Clinical Pharmacology, Peking University First Hospital, Beijing 100083, People's Republic of China. zhengyl@163bj.com

International Journal of Antimicrobial Agents
|November 3, 2001
PubMed

Insights

Most Enterobacter cloacae strains possess the ampC gene. Imipenem effectively induces ampC gene expression, and the AmpC beta-lactamase enzyme is inhibited by R0481220, with most strains susceptible to cefepime.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Pharmacology

Background:

  • Enterobacter cloacae is an opportunistic pathogen frequently associated with hospital-acquired infections.
  • The ampC gene encodes for a clinically significant beta-lactamase enzyme, conferring resistance to various beta-lactam antibiotics.
  • Understanding the prevalence and regulation of ampC gene expression is crucial for guiding antimicrobial therapy.

Purpose of the Study:

  • To investigate the presence and characteristics of the ampC structural gene in Enterobacter cloacae strains.
  • To evaluate the induction of ampC gene expression and beta-lactamase activity by imipenem.
  • To assess the efficacy of a novel beta-lactamase inhibitor (R0481220) and cefepime against AmpC-producing Enterobacter cloacae.

Main Methods:

  • Polymerase chain reaction (PCR) amplification and DNA sequencing were used to identify the ampC gene in 55 Enterobacter cloacae isolates.
  • Southern blotting confirmed the presence of the ampC gene.
  • Restriction enzyme digestion (Kpn1) analyzed PCR products.
  • Messenger RNA (mRNA) expression and beta-lactamase activity were measured following imipenem induction.
  • In vitro susceptibility testing was performed using the beta-lactamase inhibitor R0481220 and cefepime.

Main Results:

  • The ampC structural gene was detected in 51 out of 55 (92.7%) Enterobacter cloacae strains via PCR and DNA sequencing.
  • All PCR products yielded 666- and 328-bp fragments after Kpn1 digestion.
  • Imipenem demonstrated potent induction of both ampC gene mRNA expression and beta-lactamase activity.
  • The beta-lactamase inhibitor R0481220 exhibited strong inhibition of AmpC beta-lactamases.
  • A high proportion of AmpC-producing strains (96.4%, 53/55) were susceptible to cefepime.

Conclusions:

  • The majority of Enterobacter cloacae strains examined harbor the ampC gene, contributing to beta-lactam resistance.
  • Imipenem is a potent inducer of AmpC expression and activity in these bacteria.
  • The beta-lactamase inhibitor R0481220 shows promise in combating AmpC-mediated resistance.
  • Cefepime remains an effective therapeutic option against a significant percentage of AmpC-producing Enterobacter cloacae.

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