title: TEM-1 β-lactamase as a source of resistance to sulbactam in clinical strains of Acinetobacter baumannii.
abstract: OBJECTIVE
  Sulbactam is well known to have clinically relevant intrinsic activity against Acinetobacter baumannii. Although secondary resistance to this drug has long been reported in acinetobacters, virtually nothing is known about its molecular basis. The aim of this study was to test the hypothesis that β-lactamase TEM-1 is responsible for sulbactam resistance in A. baumannii.
  
  
  METHODS
  Seventeen clinical strains of A. baumannii were selected to represent different combinations of quantitative susceptibilities to sulbactam and molecular typing characteristics. The strains were screened by PCR for the presence of the blaTEM-1 gene and its variants. Amplicons encompassing the blaTEM genes, including their promoters, were sequenced. The expression and copy number of the blaTEM genes were assessed using semi-quantitative real-time PCR. Transfer of the blaTEM-1 gene into a susceptible A. baumannii strain was achieved by electroporation.
  
  
  RESULTS
  Six strains were negative for the blaTEM gene and had sulbactam MICs of 0.5-1.0 mg/L, 10 strains harboured blaTEM-1 and showed MICs ≥ 8.0 mg/L, except for one strain with an MIC of 2 mg/L, while the remaining strain carried blaTEM-19 and had an MIC of 1 mg/L. The level of blaTEM-1 expression positively correlated with the MICs of sulbactam (r = 0.92). Promoter P4 was linked to the blaTEM gene in all strains except for a P3-carrying strain (an MIC of 2 mg/L). Transformation of the susceptible A. baumannii strain with blaTEM-1 resulted in a 64-fold increase in sulbactam MIC and in resistance to ticarcillin and piperacillin, but no change in susceptibility to broad-spectrum generation cephalosporins, aztreonam or carbapenems.
  
  
  CONCLUSIONS
  The results presented suggest that TEM-1 represents a clinically relevant mechanism of sulbactam resistance in A. baumannii.
authors.affiliation: Laboratory of Bacterial Genetics, National Institute of Public Health, Šrobárova 48, 100 42 Prague 10, Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Krizova
authors.forename: Laurent
authors.initials: L
authors.lastname: Poirel
authors.forename: Patrice
authors.initials: P
authors.lastname: Nordmann
authors.forename: Alexandr
authors.initials: A
authors.lastname: Nemec
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000201:enzymology* / Q000302:isolation & purification; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018628:Gene Dosage; D020869:Gene Expression Profiling; D006801:Humans; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013407:Sulbactam / Q000494:pharmacology*; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D004791:Enzyme Inhibitors; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases; C034413:beta-lactamase TEM-1; D013407:Sulbactam
keywords: gene expression; mechanisms of resistance; multidrug resistance; transformation