title: Time-to-positivity, type of culture media and oxidase test performed on positive blood culture vials to predict Pseudomonas aeruginosa in patients with Gram-negative bacilli bacteraemia.
abstract: OBJECTIVE
  The aim of this study was to determine the usefulness of oxidase test and time-to-positivity (TTP) in aerobic and anaerobic blood culture vials to detect the presence of Pseudomonas aeruginosa in patients with Gram-negative bacilli (GNB) bacteraemia.
  
  
  METHODS
  TTP was recorded for each aerobic and anaerobic blood culture vial of monomicrobial bacteraemia due to GNB. Oxidase test was performed in a pellet of the centrifuged content of the positive blood culture. An algorithm was developed in order to perform the oxidase test efficiently taking into account TTP and type of vial.
  
  
  RESULTS
  A total of 341 episodes of GNB bacteraemia were analysed. Sensitivity, specificity, positive predictive value and negative predictive value of the oxidase test performed on positive vials with GNB to predict P. aeruginosa were 95%, 99%, 91%, and 99%, respectively. When growth was first or exclusively detected in anaerobic vials, P. aeruginosa was never identified hence the performance of the oxidase test could be avoided. When growth was only or first detected in aerobic vials, a TTP≥8h predicted P. aeruginosa in 37% or cases (63 of 169), therefore oxidase test is highly recommended.
  
  
  CONCLUSIONS
  Oxidase test performed onto positive blood culture vials previously selected by TTP and type of vials is an easy and inexpensive way to predict P. aeruginosa. In most cases, this can lead to optimization of treatment in less than 24 hours.
authors.affiliation: Nazaret Cobos-Trigueros. Department of Infectious Diseases, Hospital Clínic. Villarroel 170, 08036, Barcelona, Spain. fncobos@clinic.ub.es.
authors.forename: N
authors.initials: N
authors.lastname: Cobos-Triguero
authors.forename: Y
authors.initials: Y
authors.lastname: Zboromyrska
authors.forename: L
authors.initials: L
authors.lastname: Morata
authors.forename: I
authors.initials: I
authors.lastname: Alejo
authors.forename: C
authors.initials: C
authors.lastname: De La Calle
authors.forename: A
authors.initials: A
authors.lastname: Vergara
authors.forename: C
authors.initials: C
authors.lastname: Cardozo
authors.forename: M P
authors.initials: MP
authors.lastname: Arcas
authors.forename: A
authors.initials: A
authors.lastname: Soriano
authors.forename: F
authors.initials: F
authors.lastname: Marco
authors.forename: J
authors.initials: J
authors.lastname: Mensa
authors.forename: M
authors.initials: M
authors.lastname: Almela
authors.forename: J A
authors.initials: JA
authors.lastname: Martínez
mesh_terms: D000328:Adult; D000465:Algorithms; D016470:Bacteremia / Q000382:microbiology*; D000071997:Blood Culture; D003470:Culture Media; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010088:Oxidoreductases / Q000097:blood*; D011237:Predictive Value of Tests; D011550:Pseudomonas aeruginosa
chemical_list: D003470:Culture Media; D010088:Oxidoreductases