Phenotype and Genotype Detection of β-Lactamases Encoding Genes in Acinetobacter baumannii: Changes in Antimicrobial Resistance from 1999 to 2003

OBJECTIVE To investigate changes in antimicrobial resistance and the condition of producing β lactamases of Acinetobacter baumannii during the past 5 years and detect their genotype of the β lactamases encoding genes. METHODS Microdilute tests were performed to detect the susceptibility of 23 kinds of antimicrobials against 549 strains of A. baumannii isolated from inpatients between Jan 1999 and Dec 2003. Extended spectrum β lactamases (ESBLs) and AmpC enzyme were tested by three dimensional tests. Genotypes of β lactamases were analyzed by PCR and verificated by DNA sequencing. RESULTS The total susceptibility rates of 549 strains of A. baumannii to imipenem, polymyxin E, meropenem, and piperacillin/tazobactam were 96.4%, 93.0%, 92.9%, and 30.1%, respectively. The susceptibility rate to other antimicrobial agents ranged from 0.0 to 20.9%. The susceptibility rate to imipenem was more than 95.0% and remained unchanged for years. The susceptibility rate to polymyxin E and meropenem were more than 88.0% and 84.0%, respectively. From 1999 to 2003, the antimicrobial agents to whom the resistant rates increased fastest were amoxicillin/clavulanic acid, ceftriaxone, cefotaxime, piperacillin and piperacillin/tazobactam, respectively. The positive rates of ESBLs and AmpC enzyme were 30.0% and 1.7%, respectively, 48.3% of which produced ESBLs and AmpC enzyme simultaneously. The positive rates of the β lactamases encoding genes of TEM and SHV were 100.0% and 29.2%, respectively. The genotypes were TEM 1, SHV 12, SHV 48, and SHV 56, respectively. But the genes