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ALGORITHM OF BACTEREMIA DIAGNOSTIC IN CARDIOSURGICAL PATIENTS IN ICU


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Abstract

Objective. to evaluate the results of positive blood cultures identification by MALDI-ToF MS after short-term subcultivation and to develop an optimal algorithm for diagnosis of bacteremia. Material and Methods. A prospective study includes 500 positive blood cultures obtained between January 2015 and November 2016 from 287 cardiosurgical patients (242 adults and 45 children) aged from 1 week up to 83.5 years. Blood samples were taken using standard vials with sorbent for antibiotics and processed in BacT/ALERT 3D 120 incubator (bioMerieux, France). In parallel with the routine method (subcultivation of positive blood cultures during 16-18 h. followed by MALDI-ToF MS-analysis, Vitek MS (bioMérieux, France), the samples were plated on warmed-up blood agar, followed by incubation up to 6 h. at 37°C. When a visually determined growth of microorganisms detecting the samples were identified using the MALDI-ToF MS. Results. Mean blood samples incubation time before growth detection was 18 h. (from 4.3 to 96 h.). The growth of Gram-negative bacteria was registered significantly earlier than Gram-positive cocci and yeasts (13.7 h. (from 4.3 to 68.1 h.) vs. 16.5 h. (from 5 to 86.6 h.), p=0,02 and 32.5 h. (from 12 to 96 h.), p=0.01, respectively. After short-term (up to 6 h.) subcultivation of monocomponent hemocultures (n=475), 437 out of them were identified by the MALDI-ToF MS method (92%). The rate of successful identification was 98% for Gram-negative bacteria, 94% for Gram-positive cocci and 47% for yeasts. There were no identification of 38 microorganisms: C. parapsilosis (n=13), S. epidermidis (n=7), C. albicans (n=4), S. haemolyticus (n=4), S. hominis (n=3), S. marcescens (n=2), S. aureus (n=1), S. sciuri (n=1), E. faecium (n=1), C. tropicalis (n=1) and P. mirabilis (n=1). There were 25 associations of two microorganisms in the studied 500 samples. By MALDI-ToF MS in 21 cases (84%) one microorganism from the association were identified, in another case - both microorganisms (due to testing in two replicates); in 3 cases the results were absent. Conclusion. The method of short-term subcultivation of positive blood cultures with subsequent identification by MALDI-ToF MS allows to quickly and reliably identify the causative agents of bacteremia, which can contribute to the early onset of adequate antibiotic therapy with the use of local microbiological monitoring data.


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