Application of MALDI-TOF mass spectrometry for the detection of enterotoxins produced by pathogenic strains of the Bacillus cereus group

Enterotoxins produced by different species of the Bacillus cereus group, such as cytotoxin K1 (CytK1) and non-haemolytic enterotoxin (NHE), have been associated with diarrhoeal food poisoning incidents. Detection of CytK1 is not possible with commercial assays while NHE is recognised by an immunological kit (TECRA) that does not specifically target this protein because it is based on polyclonal antibodies. It is evident that the lack of suitable tools for the study of enterotoxins hampers the possibilities for accurate hazard identification and characterisation in microbial food safety risk assessment. We applied matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS) for the detection of CytK1 and NHE produced by pathogenic strains of the B. cereus group using protein digests from 1D gel electrophoresis. Secretion of CytK1 and two of the three components of NHE was confirmed in supernatants of different B. cereus cultures. For each protein, we introduce biomarkers that could be used for the screening of food poisoning or food/environmental isolates that can secrete enterotoxins. For example, tryptic peptides of 2,310.2 and 1,192.5 Da (calculated mass) can be indicators for CytK1 and NheA, respectively, although a simultaneous detection of other enterotoxin-specific peptides is recommended to assure the presence of a toxin in an unknown sample. Comparison of MALDI-TOF/MS with the TECRA kit showed that our methodological strategy performed well and it had the competitive advantage of specifically detecting NheA. Therefore, MALDI-TOF/MS can be successfully incorporated into risk assessment procedures in order to determine the involvement of strains of the B. cereus group in foodborne outbreaks, including the recently described cytK1 producing species, Bacillus cytotoxicus.