Rapid detection of Salmonella sp. by means of a combination of selective enrichment broth and MALDI-TOF MS

Abstract

The identification of Salmonella sp. in stool samples usually takes 2 days when employing routine procedures. Fast approaches are necessary in order to shorten the analysis time. The aim of this work was the development of a rapid procedure for the detection of Salmonella sp. from clinical stool samples. Spiked stool samples were cultured in selective selenite enrichment broth. Identifications were directly performed from the liquid broth by the MALDI Biotyper. After the evaluation of this method, the same procedure was applied to clinical samples. Coevally, the samples were streaked on Hektoen agar and single colonies were analyzed by the MALDI Biotyper. For comparison, the liquid broth was plated according to the standard laboratory procedure. A total of 4,847 samples were analyzed for Salmonella sp. In total, 108 Salmonella sp.-positive samples were identified; 66 of these were identified after the streaking of stool samples on Hektoen agar and subsequent MALDI Biotyper analysis of Salmonella sp. suspicious colonies. These and a further 34 samples were detected as Salmonella sp.-positive directly from the selenite enrichment broth on day one. Eight Salmonella sp.-positive samples were not detected before plating of the selenite broth and subsequent MALDI Biotyper analysis on day two. The combination of MALDI Biotyper analysis and selective selenite enrichment broth identification delivers positive results for the majority of the samples already after one day.

Beyond the Matrix-Assisted Laser Desorption Ionization (MALDI) Biotyping Workflow: in Search of Microorganism-Specific Tryptic Peptides Enabling Discrimination of Subspecies

“…Identification of Salmonella on the genus level by classical MALDI biotyping was reported earlier by Sparbier and colleagues (26). In the present study, the identification was correct on the species level; however, the results were inconsistent on the subspecies level, the spectra being too similar to consistently distinguish the three S. enterica subspecies (Fig.…”

“…Protein extraction was performed in accordance with a procedure previously described (18) and lately applied by many research groups (19)(20)(21)(22)(23)(24)(25)(26). For classical biotyping, which uses undigested cell extracts, Salmonella enterica subsp.…”

Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry: a Fundamental Shift in the Routine Practice of Clinical Microbiology

“…An examination of this enrichment method followed by MALDI-TOF MS on 4,847 routine clinical specimens found that of the 108 Salmonella-positive specimens identified by traditional biochemical analysis, MALDI-TOF MS identified 100 of them correctly 24 h earlier. The 8 specimens missed by MALDI-TOF MS could be identified as Salmonella positive only after plating of the enrichment medium, indicating that the bacterial concentration was likely too low to be detected by MALDI-TOF MS (165).…”

How MALDI-TOF mass spectrometry can aid diagnosis of hard-to-identify pathogenic bacteria

“…The broad coverage of bacterial species enables such early identification not only for the frequently occurring but also rare pathogens. To combine growth in selective enrichment broth and MALDI-TOF MS identification may help rapid identification of epidemiologically important carriage of Salmonella [18].…”