Rapid detection of salmonella from clinical specimen by MALDI-TOF MS

Abstract

Salmonella infections cause severe diarrhoea. Detection of positive specimen employing standard procedures takes at least 2 days. Faster approaches are necessary to start respective therapies earlier. Aim The aim of our work was the development of a rapid approach for the detection of Salmonella. Methods A small piece of the stool sample was incubated in selective media, e.g., selenit bouillon, for 20 h at 37°C. Subsequently, 150 μL from the top of the culture supernatant was taken and directly applied to 1 mL pure water. Bacteria were collected by centrifugation. Pellets were re-suspended in 1 mL water and centrifuged again. This washing step was repeated once. After air drying, bacteria were transferred onto a MALDI target, overlaid with HCCA matrix and subjected to MALDI-TOF MS analysis. Spectra were evaluated by MALDI Biotyper software. Experiments employing spiked stool samples were performed to establish the method. Subsequently, this approach was applied to routine samples and compared to the standard procedure. Results Over a time frame of 3 months, 1220 samples were analysed in parallel to the standard routine procedure. In total, 33 positive samples were identified. Fifteen of these were already positive after the direct streak of the stool sample and could be identified from the plate by MALDI Biotyper. Eighteen specimens were positive the same day by MALDI Biotyper analysis after the selective enrichment. No positive sample was missed by the novel approach which allowed detection of Salmonella after just one day of incubation.