title: The resistance mechanisms of b-lactam antimicrobials in clinical isolates of Acinetobacter baumannii.
abstract: BACKGROUND
  Despite increasing importance of Acinetobacter baumannii in nosocomial infections and rapid development of multi-antimicrobial resistance in this strain, the resistance mechanisms of beta-lactam antimicrobials in A. baumannii were not clearly defined. In order to observe the resistance mechanisms against beta-lactams and carbapenem, we characterized the production of beta-lactamases and outermembrane protein (OMP) profiles for the 44 clinical isolates of A. baumannii.
  
  
  METHODS
  The MICs of antimicrobials were determined by agar dilution test. The secondary beta-lactamases were characterized by isoelectric focusing, polymerase chain reactions and nucleotide sequencing, and the production of chromosomal beta-lactamases was quantitated by spectrophotometric method. For two strains with an elevated MIC of carbapenem, outermembrane protein (OMP) profile was analyzed by ultracentrifugation of the sonicated bacteral cells and SDS-PAGE.
  
  
  CONCLUSIONS
  Twenty two or 4 of 44 strains produced TEM-1-like beta-lactamase or PER-1 extended-spectrum beta-lactamase, respectively. However, when we analyzed the MICs of several beta-lactams with the beta-lactamase production, the resistance level of beta-lactam was mainly determined by the production of chromosomal beta-lactamase, not by the secondary beta-lactamases in the clinical isolates of A. baumannii. In two strains with an elevated MIC of imipenem, a decrease or loss of about 35 kDa and 22 kDa proteins in OMP was observed, which suggested that the change of OMP played a role in carbapenem resistance.
authors.affiliation: Dept. of Int. Medicine, Dankook University, College of Medicine, San 29, Anseo-dong, Chonan, Chungnam, Korea 330-715.
authors.forename: Na Young
authors.initials: NY
authors.lastname: Kwon
authors.forename: Jae Deok
authors.initials: JD
authors.lastname: Kim
authors.forename: Hyun Joo
authors.initials: HJ
authors.lastname: Pai
mesh_terms: D000150:Acinetobacter / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D000151:Acinetobacter Infections / Q000188:drug therapy / Q000382:microbiology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis; D015780:Carbapenems / Q000494:pharmacology; D003428:Cross Infection / Q000188:drug therapy / Q000382:microbiology; D024881:Drug Resistance, Bacterial; D006801:Humans; D001618:beta-Lactamases / Q000096:biosynthesis
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D015780:Carbapenems; D001618:beta-Lactamases