Enumeration of Bacillus and Bacillus cereus Spores in Food from Spain

Abstract

The Bacillus and B. cereus spore populations of 102 samples of food (salad dressing, dried soups, sweet desserts, milk and milk products, rice dishes, pasta and flour), 93 collected from retail markets of Madrid and 9 from chinese restaurants have been studied. Bacillus spores were detected in 82.4% of the samples, while the incidence of B. cereus spores was 14.7%. In salad dressing and dried soups the contamination rate by species of Bacillus was 100% and also both showed the highest contamination of B. cereus spores (25% and 50% respectively). No samples of rice dishes and pasta exhibited B. cereus spore contamination although these were contaminated by other Bacillus species. All the samples studies showed less than 10⁴ and 10⁵ c.f.u./g or ml B. cereus and Bacillus spores respectively. Twenty-four strains of B. cereus isolated were characterized by morphology and biochemical properties and showed most of the characteristics of the type strain. Enterotoxin, phospholipase C and hemolysin production were present in 13 of the isolated strains showing different degrees of production. The vascular permeability reaction (VPR) was used for determining enterotoxin activity. The enterotoxigenic strains showed a positive VPR; 6 of them caused necrosis and 12 positive mouse lethal tests.