gms | German Medical Science

Objective: To evaluate the possibility for time reducing of microbiological examination of blood samples.

Methods: From September 2012 till November 2013 incubation of 336 positive blood cultures from cancer patients with febrile episodes was performed using haemoanalyzer BD BACTEC FX 400. Identification of microorganisms was performed using MALDI-TOF mass spectrometry system (Bruker-Daltonics, Germany, or MALDI-TOF MS). Preparation for rapid identification was conducted with two methods: 1) with MALDI Septityper Kit 50 (SEPTI) (n=336), and 2) using Vacutainer (BD, REF 367954, or BD-TUBE) (44 of 336 positive blood cultures). Both methods were performed in parallel on the same blood cultures for comparison of the methods. Antimicrobial susceptibility testing was performed using automated microbiology system "Microscan WalkAway 96 +" (Siemens, Germany).

Results: The period of time to fixed growth of microorganisms during blood vial incubation ranged from 1 hour and 53 min to 112 hours and 36 min. 99.1% (333/336) of positive blood cultures were identified after preparation with SEPTI set immediately after the detection of microbial growth. 3 strains were identified later, after obtaining a pure culture (Streptococcus agalactiae - 1, Klebsiella pneumoniae - 3, Propionobacterium acne - 1). In 23 of 336 (6.8%) positive blood cultures with a fixed growth after less than 6 hours identification of microorganisms was possible on the day of blood sampling, and final results, including susceptibility testing were given to clinician on the next day. As preparation to MALDI-TOF MS identification with BD-TUBE (n=44), 5 (11.4 %) of positive blood cultures failed to identify microorganisms the same day when growth of microorganisms in the vial was registered (Stenotrophomonas maltophilia - 2; Streptococcus pneumonie, Pseudomonas aeruginosa and K. pneumoniae - 1 for each strain). For both methods the presumed cause of identification failure was insufficient mass of microorganisms. Reduction of time to identification was statistically more often using SEPTI vs BD-TUBE (99.1% vs 88.6% cultures, p <0.02).

Conclusion: The use of MALDI Septityper Kit 50 reduced the time of final results issuing and delivering them to clinicians (often on the day of growth) and is the best way of preparation of positive blood cultures, but more expensive than Vacutainer BD-TUBE, REF 367954. Both methods can be used for reducing the time of obtaining microbiological blood culture results to help to assign rational starting antibiotic therapy in time.