title: In vitro activity of polymyxin B against carbapenem-resistant Acinetobacter baumannii.
abstract: OBJECTIVE
  To determine in vitro activity of polymyxin B against carbapenem-resistant Acinetobacter baumannii.
  
  
  METHODS
  The activity of polymyxin B was determined against 217 strains of carbapenem-resistant A. baumannii collected from different patients by standard agar dilution method and disk diffusion test using polymyxin B disk (300 units). The control strains were E. coli ATCC 25922 and P. aeruginosa ATCC 27853.
  
  
  RESULTS
  The MIC values and inhibition zone diameters of polymyxin B against the quality control bacteria were within the acceptable range. The MIC50 and MIC90 values of polymyxin B against 217 strains of carbapenem-resistant A. baumannii were 0.5 and 1 mg/l, respectively. If the susceptible MIC breakpoint of polymyxin B was ≤ 2 mg/l, 98.2% of carbapenem-resistant A. baumannii strains were susceptible to polymyxin B. If the susceptible MIC breakpoint of polymyxin B was ≤ 2 mg/l, the sensitivity and the specificity ofthe inhibition zone diameter of > 12 mm were 100% and 75%, respectively. The aforementioned diagnostic parameters gave positive predictive value of 99.5% and negative predictive value of 100% for predicting susceptibility of carbapenem-resistant A. baumannii to polymyxin B by disk diffusion test.
  
  
  CONCLUSIONS
  Polymyxin B was very active against carbapenem-resistant A. baumannii. The inhibition zone diameters of >12 mm was accurate enough to determine susceptibility of carbapenem-resistant A. baumannii topolymyxin B. Polymyxin B can be an alternative to or more preferable than colistin for therapy ofcarbapenem-resistant A. baumannii infections.
authors.forename: Visanu
authors.initials: V
authors.lastname: Thamlikitkul
authors.forename: Surapee
authors.initials: S
authors.lastname: Tiengrim
authors.forename: Chakrapong
authors.initials: C
authors.lastname: Seenama
mesh_terms: D040981:Acinetobacter baumannii / Q000187:drug effects*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015780:Carbapenems / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D006801:Humans; D066298:In Vitro Techniques; D008826:Microbial Sensitivity Tests; D011112:Polymyxin B / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D015780:Carbapenems; D011112:Polymyxin B