Contaminated Bacillus cereus in Lao and Thai fermented soybean “Tua Nao”

Abstract

Fermented soybeans without salt (“Tua Nao”) are commonly produced and consumed in northern areas of Lao PDR and Thailand. Contamination of pathogenic Bacillus (B.) cereus during its production may cause toxic food poisoning. To evaluate the practical risk, we purchased 10 Lao and 23 Thai Tua Nao products from local markets in the northern areas of both countries, and then confirmed B. cereus contamination. Nine (90%) of the 10 Lao samples and 18 (78%) of the 23 Thai samples contained B. cereus. Two of the Thai isolates produced diarrheal enterotoxin confirmed by a reversed passive latex agglutination test (an immunological method). Emetic toxin coding gene (crs) was detected from two Lao isolates by the PCR method. These five (potential) toxin-producing B. cereus strains exhibited different random amplified polymorphic DNA (RAPD)-PCR patterns. Improvement of general hygiene control and the use of starter culture are considered necessary to prevent foodborne illnesses caused by B. cereus in fermented soybean produced in these countries.