Spore-forming bacteria in dairy products

Various spore forming bacteria belonging to Bacilli and Clostridia classes, which include pathogenic and spoilage associated species, are among the most resistant life forms known. Spores are dormant cellular structures in the life cycle of spore forming bacteria, much more resistant to environmental challenges than vegetative cells of the same species due to a variety of factors related to spore structure and composition. Spore forming bacteria of Bacillus spp. and related genera, and of Clostridium spp., are important contaminants in the dairy industry since they are ubiquitous in nature, can enter the milk chain from different sources (i.e. farm environment, raw milk, dairy plant equipment), can attach to processing equipment and form biofilms, are highly resistant to heat, desiccation or disinfectants, and significantly affect product safety and quality. Certain spore formers like Bacillus cereus, Clostridium botulinum and Clostridium perfringens pose a risk of causing dairy product poisoning by the production of toxins. Moreover, contamination with spore formers can lead to spoilage of milk and dairy products, mainly caused by enzyme deterioration (proteolytic and lipolytic activity by Bacillus species), acid production, (i.e. lactic, butyric and acetic acid), gas production (CO 2 + H 2 gas by Clostridium species) or exceeding number specifications. Diverse preventive and palliative control strategies to prevent poisoning and spoilage of milk and dairy products are adopted by farmers and at the dairy industry (i.e. good farming practices, physically removing of spores, addition of preservatives to avoid spore germination, use of physical, biological and chemical antimicrobial treatments) although the risk of contamination with spores is impossible to eliminate.