title: In vitro activities of colistin and ampicillin/sulbactam against Acinetobacter baumannii.
abstract: OBJECTIVE
  The aim of the present study was to examine the in vitro antimicrobial activity of colistin, and ampicillin/sulbactam against A. baumannii isolated from pediatric patients and to compare the susceptibility testing using disc diffusion with minimal inhibitory concentration (MIC) E-test method.
  
  
  METHODS
  One hundred strains of A. baumannii from various clinical isolates were included in the present study. Antimicrobial susceptibilities of A. baumannii to colistin, ampicillin/sulbactam were determined by disc diffusion and minimal inhibitory concentration (MIC) using E-test method. The analysis was stratified by carbapenem resistance status. Sensitivity and specificity of the disc diffusion test compared to the MIC E-test were estimated.
  
  
  RESULTS
  Ninety-seven strains of all isolates (97%) were sensitive to colistin using both disc diffusion and E-test methods. In contrast, 41% and 34% of the isolates were sensitive to ampicillin/sulbactam by disc diffusion and MICE-test, respectively. The colistin MIC50 and MIC90 for A. baumannii were 0.38 and 1 microg/mL, respectively. The ampicillin/sulbactam MIC50 and MIC90 were 16 and 89.6 microg/mL, respectively. Based on the results of MIC E-test, ninety-eight (n = 49) and six (n = 3) percent of carbapenem-resistant A. baumannii (n = 50) were susceptible to colistin and ampicillin/sulbactam, respectively. Sensitivity and specificity of disc diffusion test compared to MIC E-test were 99% and 66.7% for colistin and 80.5% and 98.3% for ampicillin/sulbactam, respectively.
  
  
  CONCLUSIONS
  The antimicrobial activities of colistin against A. baumannii isolates remained high for both cabapenem-susceptible and -resistant strains. However, the in vitro activity of ampicillin/sulbactam against A. baumannii was low. Thus, a combination, rather than monotherapy, of ampicillin/sulbactam with other antibiotics is strongly recommended when dealing with A. baumannii infection. In addition, disc diffusion test appeared to be a useful screening method for susceptibility testing for colistin and ampicillin/sulbactam against A. baumanii.
authors: Department of Pediatrics, Queen Sirikit National Institute of Child Health, College of Medicine, Rangsit University, Bangkok, Thailand. warunee@vandepitte.eu
authors: Warunee
authors: W
authors: Punpanich
authors: Anurak
authors: A
authors: Munsrichoom
authors: Suchada
authors: S
authors: Srisarang
authors: Vipa
authors: V
authors: Treeratweeraphong
mesh_terms: D000151:Acinetobacter Infections / Q000188:drug therapy* / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000302:isolation & purification; D000667:Ampicillin / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002648:Child; D003091:Colistin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D005260:Female; D006776:Hospitals, Pediatric; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D012680:Sensitivity and Specificity; D013407:Sulbactam / Q000494:pharmacology*; D013785:Thailand
chemical_list: D000900:Anti-Bacterial Agents; D000667:Ampicillin; D013407:Sulbactam; D003091:Colistin