Properties of multidrug-resistant, ESBL-producing Proteus mirabilis isolates and possible role of beta-lactam/beta-lactamase inhibitor combinations

Int J Antimicrob Agents. 2001 Feb;17(2):131-5. doi: 10.1016/s0924-8579(00)00325-3.


At our institution, isolation rates of clinical strains of ESBL-producing Proteus mirabilis increased to 8.8% of all P. mirabilis isolates during the period 1997-1999. To evaluate the susceptibility of ESBL-producing P. mirabilis strains against commonly used drugs, we studied 50 non-duplicated isolates selected on the basis of synergy between clavulanate and beta-lactams (ceftazidime, aztreonam, cefotaxime, and ceftriaxone). The presence of ESBL-coding genes was confirmed by colony hybridization with bla(TEM-1) and bla(SHV-1) probes. Minimum inhibitory concentrations of several antimicrobial agents for each isolate were obtained using the Etest method. All strains were encoding for TEM-derived enzymes. Gene sequencing showed that at least three different genes (TEM-15, TEM-20, and TEM-52) were present. These enzymes have not been previously reported in P. mirabilis. Isolates were characterized by: (a) reduced susceptibility or resistance to third- and fourth-generation cephalosporins (MIC > or = 2 mg/l), (b) resistance to piperacillin that was abolished by tazobactam (MIC > or = 256 vs. < or = 2 mg/l, respectively), (c) multiple antibiotic resistance that included gentamicin, fluoroquinolones and co-trimoxazole. Therapeutic failure and lack of eradication of ESBL-positive P. mirabilis by third-generation cephalosporins has been repeatedly observed both at our Institution and elsewhere. Piperacillin-tazobactam, as well as amikacin and meropenem appear to be important therapeutic options for infections due to multidrug-resistant, ESBL-producing P. mirabilis isolates.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Cephalosporins / pharmacology
  • Clavulanic Acid / pharmacology
  • Drug Resistance, Microbial
  • Drug Resistance, Multiple*
  • Enzyme Inhibitors / pharmacology*
  • Genes, Bacterial
  • Humans
  • Microbial Sensitivity Tests
  • Penicillanic Acid / analogs & derivatives*
  • Penicillanic Acid / pharmacology
  • Proteus Infections / drug therapy
  • Proteus Infections / microbiology
  • Proteus mirabilis / drug effects*
  • Proteus mirabilis / enzymology
  • Proteus mirabilis / genetics
  • Tazobactam
  • beta-Lactamase Inhibitors
  • beta-Lactamases / genetics
  • beta-Lactamases / metabolism*


  • Anti-Bacterial Agents
  • Cephalosporins
  • Enzyme Inhibitors
  • beta-Lactamase Inhibitors
  • Clavulanic Acid
  • Penicillanic Acid
  • beta-Lactamases
  • beta-lactamase TEM-1
  • Tazobactam