Bacillus Testing

Bacillus is a genus of spore-forming, gram-positive, and rod-shaped bacterium. Bacillus cereus which belongs to the Bacillus genus is a foodborne pathogen that produces toxins and causes foodborne illnesses.

Figure 1. Electron micrograph of Bacillus cereus and related contaminated foods

Bacillus cereus is widely found in the natural environment such as soil and a variety of foods including meat, milk, and vegetables as well as raw plant foods such as rice, potatoes and beans. Spores formed by Bacillus cereus are more resistant to the environmental stress than vegetative cells. Spores are able to survive harsh environment conditions, even high temperatures during normal cooking process. Bacillus cereus typically produces two types of toxins (emetic and diarrheal) that cause two kinds of illnesses respectively. The emetic toxin is formed by Bacillus cereus during the growth phase in foods. The diarrheal toxin is produced during the bacteria growth in the small intestine of humans. The growth and survival conditions of Bacillus cereus are related to the strain types. Bacillus cereus generally has optimal cell growth under aerobic conditions, but it can also be facultative anaerobic and grow in the absence of oxygen. The optimal temperature of the cell growth ranges from 30 ℃ to 40 ℃ and the optimal pH ranges from 6.0 to 7.0.

Symptoms caused by Bacillus cereus such as vomiting or diarrhea are generally mild and short period up to 24 hours. The syndrome of vomiting is caused by the ingestion of the toxin that is pre-formed in foods contaminated by Bacillus cereus. These symptoms including vomiting, nausea and abdominal pain usually occur in a couple of hours after the consumption of contaminated foods.

Currently there are no food safety criterions that have been established for Bacillus cereus. There is no available information on human dose response relationship for both two types of toxins produced by Bacillus cereus. The contamination level of Bacillus cereus which has been associated with the majority of outbreaks worldwide caused by Bacillus cereus is typically above 10⁵ CFU/g. Generally, the level of presumptive Bacillus cereus above 10⁵ CFU/g may be considered as a health issue to the public and the level below 10³ CFU/g may be regards as acceptable.

Bacillus Testing of Food at Alfa Chemistry

The standard methods (EN/ISO, AOAC, and FDA BAM) that have been widely used to quantify Bacillus cereus are culture-based methods using general microbiological testing supplies. Selective or differential mediums are used to incubate Bacillus cereus for appropriate time. Then it is followed by the plate counting or most probable number (MPN) technique to determine the contamination level. Plating method for Bacillus cereus uses solid medium of Mannitol-egg yolk-polymyxin (MYP) agar. MPN method is a multi-step assay including presumptive, confirmed, and completed phases based on statistical analysis. Typical colonies grown MYP are confirmed with biochemical testing.

Alfa Chemistry offer accurate and validated testing platforms for the quantification and confirmation of Bacillus cereus in various food samples to meet customers' needs. We also have experience working on different standards and regulations.

Platform: Plate counting or MPN technique

Limit of detection: <10 CFU/g

Sample type: Solid and liquid food samples

Sample size: 50 g