Bactec 9240 blood culture system

For each patient, 1–3 mL (for paediatric patients) and 8–10 mL (for adults) of blood cultures injected directly into Bactec^® culture vials (Becton–Dickinson, USA) were submitted for laboratory diagnosis. Blood cultures were processed with Bactec^® 9240 blood culture system (Becton–Dickinson, NJ, USA) according to manufacturer’s instructions. The presence of BSI was defined by at least one set of positive blood culture for bacteria or fungi in patients. When blood cultures yielded positive results, they were evaluated to determine whether it represented true bacteraemia, fungaemia, or simply contamination. For potential skin contaminants (e.g., micrococci, Staphylococcus epidermidis), at least two separate positive blood cultures obtained from different sites had to be isolated for the results to be considered as true infection. A total of 111 blood cultures from cancer patients were positive for various organisms. Aerobic subcultures were made from positive culture vials onto blood, chocolate, MacConkey and Saboraund agar. Identification of bacteria were carried out by Gram-stain microscopy and by conventional biochemical methods. Species identity were confirmed by the BBL crystal identification system (Becton–Dickinson, NJ, USA). Positive blood cultures for yeast and non-yeast fungi were identified on the basis of morphology.

Blood was inoculated into BACTEC culture bottles using the BACTEC 9240 Blood Culture System (Becton Dickinson). All bacterial strains were identified to the species level using conventional methods and were verified using the API-20E System (BioMérieux Vitek) or the Vitek 2 ID-GNB identification card (BioMérieux).

Standard clinical laboratory methods were used to isolate and identify PA from clinical specimens. Briefly, urine was plated on cysteine lactose electrolyte-deficient agar, respiratory samples on blood and chocolate agar, which were incubated at 37 °C for 24 to 48 h. Tissue biopsies were homogenized and incubated in thioglycolate broth at 37 °C for 14 days. Blood, cerebrospinal, pleural and abdominal fluids were processed and monitored with a BACTEC 9240 blood culture system (Becton Dickinson, Sparks, MD, USA). One colony with Pseudomonas-like morphology was identified using classical biochemical tests (catalase and oxidase reactions) and VITEK2 Compact or API tests (bioMérieux, Marcy l’Etoile, France).
Finally, all PA isolates were confirmed by using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (Bruker Daltonics, Bremen, Germany). Only one isolate per patient was included in the final analysis, giving preference to more invasive strains (blood or cerebrospinal fluid).