Mechanisms of hyperproduction of TEM-1 beta-lactamase by clinical isolates of Escherichia coli

J Antimicrob Chemother. 1995 Dec;36(6):927-39. doi: 10.1093/jac/36.6.927.

Abstract

The mechanisms of hyperproduction (defined as > or = 200 nmoles nitrocefin hydrolysed per minute per mg of protein) of TEM-1 beta-lactamase by 38 isolates of Escherichia coli were investigated. The copy numbers of TEM-encoding plasmids were determined for the hyperproducing isolates and for 39 TEM-1-producing isolates that did not hyperproduce the enzyme. Allele-specific PCR was used to determine if the promoter region of the TEM-1 gene was of the TEM-1 or TEM-2 type. Twenty three of the 38 hyperproducers had the TEM-1-type promoter but 15 had the more efficient TEM-2-type promoter; in contrast, 37 of the 39 isolates with lower activities had the TEM-1-type promoter and only two had the TEM-2-type promoter. Many of the TEM-1-hyperproducing isolates possessed small plasmids (< or = 20 MDal) with high copy numbers, in some cases together with large, low copy number plasmids; the average total copy number of TEM-encoding plasmids was 14; if only isolates with the TEM-1-type promoter were included, average total copy number was 22. Hyperproduction was attributed to high copy number (> or = 10) plasmids in 11 isolates; another seven had plasmids with moderately high copy numbers (4-9). The average total copy number for isolates that produced relatively small amounts of TEM-1 beta-lactamase (< or = 100 nmoles/min/mg protein) was 2.2, and for the 12 isolates with TEM-1 activities of 101-200 nmoles/min/mg protein it was 6.8. We conclude that both high copy number plasmids and a more efficient promoter are common causes of hyperproduction of TEM-1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Bacterial Proteins / biosynthesis*
  • Base Sequence
  • DNA Primers
  • DNA, Bacterial / genetics
  • Escherichia coli / enzymology*
  • Escherichia coli / genetics
  • Humans
  • Molecular Sequence Data
  • Plasmids
  • Polymerase Chain Reaction
  • Promoter Regions, Genetic
  • Sensitivity and Specificity
  • beta-Lactamases / biosynthesis*
  • beta-Lactamases / genetics

Substances

  • Bacterial Proteins
  • DNA Primers
  • DNA, Bacterial
  • beta-Lactamases
  • beta-lactamase TEM-1