Seasonal Prevalence and Molecular Characterization of Enterotoxigenic Bacillus cereus in Cooked Rice and Culinary Spices from Indian Public Restaurants

Abstract

Bacillus cereus is a significant agent of foodborne intoxication, often linked to starchy matrices. This study evaluated the role of culinary spices as primary reservoirs for introducing enterotoxigenic endospores into prepared restaurant meals. Twenty samples,10 cooked rice variants and 10 spices were procured from seven dining establishments in Bengaluru, India³. Isolates were recovered on Mannitol Egg Yolk Polymyxin (MYP) agar and confirmed via phenotypic profiling⁴. Molecular characterization targeted the 16S rRNA gene (548 bp) for taxonomic verification and the non-hemolytic enterotoxin (nhe) gene (500 bp) to assess pathogenic potential. Critical microbial titers were identified in raw spices, specifically Saunf (Fennel) at 41.2 x 10⁵ CFU/g and Meat Masala at 37.5 x 10⁵ CFU/g. Cooked rice exhibited significant seasonal escalation (p < 0.05), with loads rising from log10 2.08 CFU/g in February to log10 4.25 CFU/g in April. Genomic screening revealed a 100% prevalence of the nhe gene across isolates, establishing an epidemiological link between raw ingredients and finished products. Spices serve as persistent vectors for enterotoxigenic B. cereus, facilitating survival through standard thermal processing. Effective risk mitigation requires validated spice decontamination and stringent "danger zone" (5°C–60°C) thermal management to disrupt the germination-to-intoxication cycle.