Abstract
Cereulide is a toxic cyclic depsipeptide produced by certain strains of Bacillus cereus found in soil and food products. While some harmless strains of Bacillus are used as probiotic, others can cause nausea and vomiting, and represent an important food safety concern. Current detection methods are time consuming and do not necessarily detect toxic cereulide. Here, we developed a rapid protocol using Matrix Assisted Laser Desorption/Ionization-Time of Flight (MALDI-TOF) mass spectrometry that detects the toxin originating from a colony smear of B. cereus. The distinct molecular feature of the toxin peak at m/z 1,191 was clearly identified from bacterial extracts with a limit of detection (LOD) of 30 ng/mL. Final optimisation of the sample preparation was based on cereulide chelating cations to produce the alkali adduct [M + K]+ without the use of a MALDI matrix, and provided a 1,000-fold improvement of LOD with 30 pg/mL of cereulide. We evaluated the application of this method for the detection of cereulide in rice, milk, and different ready-to-eat meals. The proposed protocol is quick, easy and provides an improvement over conventional methods for the detection of B. cereus toxin.
Highlights
Contamination with soilborne Bacillus cereus is an emerging health safety concern for ready-to-eat foods due to their heat resistant endospores that can survive the cooking and manufacturing processes[1,2]
A colony-smear served as sample and a loop of sample was deposited on the MALDI plate for mass spectrometry (MS) analysis (Fig. 1S)
The spectrum of protein masses was subsequently matched against reference spectra that are stored in the database and had initially been established using well characterized reference strains and defined growth conditions
Summary
Contamination with soilborne Bacillus cereus is an emerging health safety concern for ready-to-eat foods due to their heat resistant endospores that can survive the cooking and manufacturing processes[1,2]. Heat-resistant endospores of some strains from B. cereus produce the toxin cereulide and can cause intoxications shortly after ingestion of contaminated food products, representing a serious health risk to consumers[4]. The prevalence and the health safety concerns related to food contaminated with B. cereus toxins require the development of a sensitive and rapid assay to detect this toxin. Cereulide intoxication may exhibit severe or lethal symptoms in children and elderly people[11,12] This toxin cause nausea, vomiting (emesis) and liver failure in children[13]. Multiple putative biomarkers were identified in the MALDI-TOF mass spectra of emetic B. cereus[18] While both studies examined protein biomarkers of molecular masses ranging from 2,000 to 12,000 Da, they did not report on the application of MALDI-TOF for the detection of lower molecular mass cereulide
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