Identifizierung von Bakterien aus positiven Blutkulturen mittels MALDI-TOF Massenspektrometrie

Sepsis is a serious disease with high morbidity and mortality. Fast and adequate antibiotic therapy is of central importance in the treatment of sepsis. It is important to correctly identify the pathogen in order to adapt an empirically initiated antibiotic therapy if necessary. Standard method of pathogen diagnosis in bacterial sepsis is incubation of patient blood in blood culture bottles, which is nowadays carried out in fully automated systems. If the automated system reports a blood culture bottle as "positive", a sample is taken from the corresponding bottle and a culture on an agar plate is then applied overnight. In order to identify the cultivated pathogen, a measurement with MALDI-TOF MS is carried out the following day. The aim of this work was to find out whether it is possible to identify pathogens directly from positive blood culture bottles using MALDI-TOF MS without having to wait for the results of the culture. In future, this saving of time could lead to a faster initiation of an adequate therapy. As main part of this work 206 positive blood culture bottles from the routine diagnostics of the Institute of Medical Microbiology and Hygiene of the University Hospital Marburg were examined. The blood culture bottles had already went through the routine diagnostic procedure. The results of routine diagnostics (culture) were used as the gold standard. Three different methods were tested: on the one hand, a method already described in the literature ("standard method") and two shortened methods ("alternative methods"). In summary, 206 positive blood culture bottles were tested. 161 went through the "standard method", 12 went through the first alternative method and 33 went through the second alternative method. Regarding the first alternative method, a method without use of ethanol, ten of the twelve samples showed a score of less than 1,7 when measured with MALDI-TOF MS and were therefore not conclusive. A total of 33 positive blood culture bottles were examined in the second alternative method, a method using only lysis. Of these, only eight pathogens were correctly identified at the species level. Another five samples were correctly identified at the genus level, which included two samples with enterobacteria. 20 out of 33 blood culture samples showed no evidence of the pathogen. Both alternative (shortened) methods are therefore not suitable for routine diagnostics. A total of 161 positive blood culture bottles were examined using the "standard method". Of these, 151 were positive in the gold standard (culture). Pathogens were correctly identified directly from positive blood culture bottles using MALDI-TOF MS technology in 111 of the 151 samples which were positive in the gold standard. In 40 cases, pathogens could be only detected by culture, but not by MALDI-TOF MS. In two samples, the pathogen identification by MALDI-TOF MS was incorrect, although the score was 1,9. In summary, a pathogen was detected in 73% of the positive blood culture bottles using MALDI-TOF MS. If a pathogen was detected by MALDI-TOF MS, identification was generally correct (in 98% of cases). The breakdown of the results from the "standard method" showed that the identification rate for gram-positive bacteria was slightly lower than for gram-negative bacteria. The detection of fungi directly from blood culture bottles was not possible. The time saved by using the "standard method" was approximately 16-20 hours compared to traditional culture-based methods. In summary, MALDI-TOF MS can be used to directly identify pathogens in positive blood culture bottles.