Detection of Emetic Toxin Genes in Bacillus cereus Isolated from Food and their Production of Cereulide in Liquid Culture

Abstract

Bacillus cereus is a Gram‐positive that is ubiquitous in foods and the wider environment. The B. cereus emetic toxin, cereulide, synthesized by nonribosomal peptide synthetase (NRPS), can cause either gastrointestinal disorders and/or emetic form of food poisoning. In this study, 108 B. cereus isolates from foods were tested for a correlation between the presence of emetic toxin genes and cereulide production. Based on 16S rRNA sequence analysis, 107 isolates were identical to B. cereus spp. Further experiments showed that fourteen isolates exhibited 1,271, 2,200 and 188‐bp bands, corresponding to amplification of the ces1, ces2 and NRPS gene, respectively. However, only 7 out of 13 strains possessing the NRPS, ces1, and ces2 genes produced cereulide in liquid culture. Strain number 93, isolated from fresh vegetables, produced the highest levels of cereulide (11.17 μg/mL); maximum cereulide levels were observed after 4 days of cultivation at 30C in LB broth. The amount of cereulide produced differed between each isolate. Practical Applications The incident of Bacillus cereus in food could cause food poisoning. The results of our study on the presence of B. cereus in spoiled foods demonstrated that not all the food poisoning B. cereus spp. have the ability to synthesize the emetic toxin, cereulide. Nonribosomal peptide synthetase and cereulide synthetase genes could be used as biological markers for differentiation of cereulide producing and nonproducing B. cereus. Estimation of cereulide level reveals that the amounts of cereulide produced by some strains were very high and could be a threat to human health if consumed in contaminated foods. This study presents proper methods to select cereulide producing food‐poisoning B. cereus spp. and gives more information on the condition of cereulide production to prevent future cases of emetic food poisoning.

An outbreak of Bacillus cereus toxin-mediated emetic and diarrhoeal syndromes at a restaurant in Canberra, Australia 2018

“…17 It is well accepted that the emetic toxin is difficult to isolate in food and stool samples which emphasises the importance of epidemiological evidence. 18 Limitations of this investigation included no stool samples being received; however, nearly all the ill patrons had recovered by the time they were contacted. Steps to minimise this bias included a standard detailed questionnaire.…”

Development of a selective and differential media for the isolation and enumeration of Bacillus cereus from food samples

“…Bacillus cereus is endospore forming, gram positive rods that inhabits soil and contaminates a wide range of food products such as rice, spices, dried food, vegetables, eggs, meat products and milk and its derivatives (Stenfors Arnesen et al ; Phat et al ).…”

Toxins of Foodborne Pathogen Bacillus cereus and the Regulatory Factors Controlling the Biosynthesis of Its Toxins

“…eMeTIC ToXIn oF B. cereus and ITS RegulaToRY FaCToRS eMeTIC ToXIn emetic toxin is also known as cereulide, which is a small, hydrophobic and cyclic dodecadepsipeptide (d-o-leu-d-ala-l-o-val-l-val) 3 (ehling-Schulz et al 2005;Phat et al 2016) with a molecular weight of approximately 1.2 kda (Kranzler et al 2016). emetic toxin and its chemical structure (Figure 1) were first described by Agata et al (1994).…”

“…emetic toxin and its chemical structure (Figure 1) were first described by Agata et al (1994). This toxin is a very stable molecule as it is resistant towards heat, ph and proteases (lücking et al 2015;Phat et al 2016). The chemical structure of cereulide which is homologous to potassium ionophore valinomycin, indicates that it is synthesised nonribosomally by peptide synthetases, specifically by cereulide synthetase (ces) gene (Kranzler et al 2016).…”