Direct Identification of Microorganisms from Positive Blood Cultures by MALDI-TOF MS Using an in-House Tween® 80 Method: Experimental and Clinical Study

It has been reported that direct identification from blood culture bottles with positive signals and reporting the results to the clinics earlier has positive effects on mortality and morbidity. Extraction methods especially using detergents are used for the direct identification from the bottles which give positive signal. For this purpose, in-house methods developed based on the usage of saponin are widely available in the literature. In this study, it was aimed to develop a simple, easy-to-apply and reliable protocol for identifying the agent directly from the blood culture bottle that gives positive signal with the use of detergent Tween (R) 80, and to study the obtained protocol in clinical samples in a routine microbiology laboratory and to evaluate the results. The study was carried out in two stages, the experimental stage where the method was developed and the clinical stage where the method was applied. In the experimental stage, blood culture bottles were created with standard strains and isolates previously diagnosed with the 16S rRNA method. 10% solution of Tween (R) 80 was prepared with distilled water. 1 mu l sample was transferred from the bottle that gave positive signal to the microcentrifuge tube, 100 mu l of 10% solution of Tween (R) 80 was added, vortexed for 10 seconds and then incubated for 5 minutes at room temperature. The tubes were centrifuged for 5 min at 14.000 rpm, the supernatant was discarded and the pellet was washed with 1 mu l of distilled water and centrifuged at 14.000 rpm for 5 minutes in three times. Samples taken from the pellets were rubbed on the slide and dried on air. Firstly, 1 mu l of 70% formic acid, then 1 mu l, of matrix solution was added and it was used after drying. In the second stage of the study, the method was applied to the 502 vials giving positive signal in the Microbiology Laboratory of Ankara University Faculty of Medicine Ibni Sina Hospital between 17 April 2018-31 August 2018 and the results were compared with the subculture results. The results obtained at the end of extraction in the experimental stage were compared with the subculture results and no statistical difference was found. In 383 (82.9%) bottles among 462 (92.1%) bottles with monomicrobial positive cultures, compatible results with the subculture results were obtained. Of the microorganisms correctly identified, 350 (91.3%) were bacteria and 33 (8.7%) were fungi. On the other hand, 216 (56.4%) of the bacteria were gram positive and 134 (34.9%) of them were gram negative bacteria. At least one microorganism was correctly identified in 19 (47.5%) of 40 (7.9%) bottles with polymicrobial blood cultures. Their distribution was gram negative (n= 10) and gram positive (n= 8) and yeast (n= 1). No microorganisms were identified in six bottles with polymicrobial cultures. According to the results, we believe that this in-house method developed using Tween (R) 80 will be a routinely applicable method for blood culture bottles that give positive signal in microbiology laboratories and it will contribute to the early diagnosis.