Detection of Bacillus cereus and Gram-negative Bacteria Communities in Commercial Sesame in Japan

Abstract

Sesame seeds are used in many traditional Japanese foods for their flavor and taste but commercial sesame can be
highly contaminated with bacteria. We therefore examined the bacterial populations, including Bacillus spp.,
Enterobacteriaceae bacteria and standard plate count bacteria in sesame samples purchased from markets in Japan. A
total of 8 sesame samples were tested, of which 4 (50.0%) harbored 4.3–5.6 log cfu/g standard plate count and 2.7–4.3
log cfu/g Enterobacteriaceae bacilli. Pantoea dispersa, P. septica and P. agglomerans were identified by a MALDI-TOF MSbased test. One (12.5%) sample harbored 3.6 log cfu/g Bacillus cereus, but this strain lacked the gene encoding of the
enzyme responsible for cereulide synthesis and did not produce enterotoxin. B. cereus was also isolated from a heated
sample (98 °C for 20 mins). Metagenome analysis showed that 4 samples were contaminated with bacteria belonging
to the 5 genera Pantoea, Serratia, Pseudomonas, Xanthomonas and Rosenbergiella. Pantoea and Pseudomonas DNA was
detected in all positive samples but the bacterial load varied. Our study revealed that sesame can become contaminated
with Enterobacteriaceae bacteria and B. cereus. Dishes containing contaminated sesame could potentially cause B. cereus
food poisoning, although the B. cereus isolates obtained in this study did not contain the gene encoding the enzyme
responsible for cereulide synthesis and did not produce enterotoxin. To prevent food poisoning caused by bacterial
contamination, it is important to roast sesame seeds at a sufficiently high temperature, do not leave the cooked food
with sesame at room temperature for a long time and avoiding cross-contamination from sesame to ready-to-eat food.