Identification of cereulide producing Bacillus cereus by MALDI-TOF MS

Abstract

The Bacillus (B.) cereus group is genetically highly homogenous and consists of nine recognized species which are present worldwide. B. cereus sensu stricto play an important role in food-borne diseases by producing different toxins. Yet, only a small percentage of B. cereus strains are able to produce the heat stable depsipeptide cereulide, the causative agent of emetic food poisonings. To minimize the entry of emetic B. cereus into the food chain, food business operators are dependent on efficient and reliable methods enabling the differentiation between emetic and non-emetic strains. Currently, only time-consuming cell bioassays, molecular methods and tandem mass spectrometry are available for this purpose. Thus, the aim of the present study was to establish a fast and reliable method for the differentiation between emetic and non-emetic strains by MALDI-TOF MS. Selected isolates/strains of the B. cereus group (total n=110, i.e. emetic n=45, non-emetic n=65) were cultured on sheep blood agar for 48h.\n\nSubsequently, the cultures were directly analyzed by MALDI-TOF MS without prior extraction steps (direct smear method). The samples were measured in linear positive ionization mode in the mass range of m/z 800 - 1,800 Da. Using ClinProTools 3.0 statistical software and flex analyst, a differentiation between emetic and non-emetic isolates was possible with a rate of correct identification of 99.1 % by means of the evaluation of two specific biomarkers (m/z 1171 and 1187 Da).\n\nImportanceBacillus (B.) cereus plays an important role in food-borne diseases due to the production of different toxins, e.g. the heat stable depsipeptide cereulide. Only a small number of B. cereus strains are able to produce this toxin, the causative agent of emetic food poisonings. To minimize the entry of emetic B. cereus into the food chain, food business operators require efficient and reliable methods enabling the differentiation between emetic and non-emetic strains. The aim of the present study was to develop a fast and reliable method for the differentiation between emetic and non-emetic strains by MALDI-TOF MS. A differentiation between emetic and non-emetic isolates was possible with a rate of correct identification of 99.1 % by means of the evaluation of two specific biomarkers (m/z 1171 and 1187 Da).