Spores from mesophilic Bacillus cereus strains germinate better and grow faster in simulated gastro-intestinal conditions than spores from psychrotrophic strains L.M. Wijnands a, ⁎ , J.B. Dufrenne a , M.H. Zwietering b , F.M. van Leusden a a Microbiological Laboratory for Health Protection, National Institute for Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, The Netherlands b Laboratory for Food Microbiology, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, The Netherlands Received 3 August 2005; received in revised form 23 January 2006; accepted 2 June 2006 Abstract The species Bacillus cereus, known for its ability to cause food borne disease, consists of a large variety of strains. An important property for discrimination of strains is their growth temperature range. Psychrotrophic strains can grow well at refrigerator temperatures but grow at 37 °C with difficulty. Mesophilic strains on the other hand are unable to grow below 10 °C, but grow well at 37 °C. Spores of six psychrotrophic and six mesophilic strains were investigated for their ability to survive and grow in simulated gastro-intestinal fluids, mimicking the conditions in the gastro-intestinal tract. The germination potential of psychrotrophic and mesophilic spores in simulated intestinal fluid does not differ much. Under conditions simulating the gastro-intestinal passage, 5 out of 6 mesophilic strains showed growth, and only 2 out of 6 psychrotrophic strains. Temperature (37 °C) and simulated gastro-intestinal conditions together influenced germination and growth. © 2006 Elsevier B.V. All rights reserved. Keywords: Bacillus cereus; Simulated gastro-intestinal conditions; Psychrotrophic; Mesophilic 1. Introduction Bacillus cereus is a ubiquitous, Gram-positive, spore- forming microorganism capable of causing food borne disease (Kramer and Gilbert, 1989). Two syndromes can be distin- guished, an emetic syndrome and a diarrhoeal syndrome (Granum, 2001). The emetic syndrome is caused by cereulide, a heat- and pH- stable peptide toxin (Agata et al., 1994). Consumption of food contaminated with this toxin may lead to emesis between 30 min and 5 h after ingestion (Drobniewski, 1993). The diarrhoeal syndrome is caused by enterotoxins that are produced during growth of B. cereus in the small intestine. At present three enterotoxins, able to cause the diarrhoeal syndrome, have been described: haemolysin BL (HBL), non- hemolytic enterotoxin (NHE) and cytotoxin K. HBL and NHE are three component proteins, whereas cytotoxin K is a single protein toxin (Beecher and Lee Wong, 1994; Granum et al., 1999; Lund et al., 2000). Symptoms caused by the latter toxin are more severe and may even involve necrosis. In general, the onset of symptoms is within 6 to 24 h after consumption of the incriminated food. Among the strains of B. cereus a great diversity exists, for instance with respect to the presence of enterotoxin genes, with respect to the ability to produce emetic toxin and with respect to the ability to grow at various temperatures. Although many B. cereus strains are able to form enterotoxins, not all of those strains appear to be able to cause disease. The so-called psychrotrophic strains are able to grow at low temperatures as can be encountered in refrigerators. Generally, these do not grow very well at temperatures around 37 °C, like in the human body. Mesophilic strains, on the other hand, easily grow at 37 °C and International Journal of Food Microbiology 112 (2006) 120 – 128 www.elsevier.com/locate/ijfoodmicro ⁎ Corresponding author. Tel.: +31 30 274 2085: fax: +31 30 274 4434. E-mail address: lucas.wijnands@rivm.nl (L.M. Wijnands). 0168-1605/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2006.06.015