Catalytic and structural properties of IRT-21 beta-lactamase (TEM-77) from a co-amoxiclav-resistant Proteus mirabilis isolate

FEMS Microbiol Lett. 2001 Dec 18;205(2):185-9. doi: 10.1111/j.1574-6968.2001.tb10945.x.


Proteus mirabilis strain MAG1, a clinical isolate that is resistant to broad-spectrum penicillins and co-amoxiclav, produces inhibitor-resistant TEM (IRT)-21, a novel mutant of TEM beta-lactamase. This enzyme has a pI of 5.2 and is derived from the bla(TEM-1a) gene ancestor. It contains two major amino acid substitutions specific for co-amoxiclav resistance (Leu-69 for Met and Ser-244 for Arg) that have never been found together previously. The dramatic loss of sensitivity to clavulanic acid, the enhancement of K(m) for all beta-lactams and markedly for ticarcillin, and the decrease in the catalytic efficiency makes IRT-21 comparable to the other IRTs with substitutions at position 244 or double substitutions.

Publication types

  • Comparative Study

MeSH terms

  • Amoxicillin-Potassium Clavulanate Combination / pharmacology*
  • Anti-Bacterial Agents / pharmacology*
  • Humans
  • Microbial Sensitivity Tests
  • Molecular Sequence Data
  • Polymorphism, Restriction Fragment Length
  • Proteus mirabilis / drug effects
  • Proteus mirabilis / enzymology*
  • Proteus mirabilis / genetics
  • beta-Lactam Resistance
  • beta-Lactamases / chemistry
  • beta-Lactamases / genetics
  • beta-Lactamases / metabolism*


  • Anti-Bacterial Agents
  • Amoxicillin-Potassium Clavulanate Combination
  • IRT-21 beta-lactamase
  • beta-Lactamases