Eneterotoxigenic Bacillus cereus and Bacillus thuringiensis Spores in U.S. retail Spices
Creators: name: Hariram, Upasana 
Publisher: name: University of Massachusetts Amherst
Year: 2015

description: <em>Bacillus cereus</em> is a ubiquitous organism and a potential foodborne pathogen that can cause two types of gastrointestinal diseases: emesis and diarrhea. The emetic syndrome is caused by a heat and acid stable peptide toxin that is pre-formed in food, while the diarrheal syndrome is associated to two 3-protein, heat labile enterotoxin complexes that are formed in the intestine after ingestion of the organism. There are many reports on the isolation and characterization of <em>Bacillus cereus</em> from various foods, however there are no studies on the levels, toxigenicity and physical characteristics of <em>B</em>. <em>cereus </em>isolated from U.S. retail spices. A huge part of spices sold in the U.S. are imported from developing nations. Developing nations lack hygienic practices during processing and packaging of spices, due to which there is a high chance of imported spices being contaminated with <em>B. cereus</em>. Therefore, the main objective of this thesis work was to characterize <em>B. cereus</em> spores from U.S. retail spices. Levels of aerobic spores and <em>B. cereus </em>spores were determined. <em>B. cereus</em> spores were further analyzed for their enterotoxigenic ability, growth characteristics and physical spore characteristics.
In the 247 spice samples analyzed 77 were found to contain <em>B. cereus</em>, while 11 were positive for <em>B</em>. <em>thuringiensis</em>. Eighty four of the 88 spices tested possessed either one of the enterotoxin genes. None of the isolates tested positive for the emetic toxin (<em>ces</em>) gene. Seventy five of the <em>B. cereus</em> isolates grew at 12 °C, although only two isolates grew well at 9 °C.
Seven selected diarrheal <em>B. cereus</em> spore strains had D<sub>95</sub>-values ranging from 0.64-3.53 min while the two emetic strains had D<sub>95</sub>-values of 7.04 min and 6.64 min. <em>B. cereus</em> grew well in pre-cooked rice. After 48 h, counts of 1.26 X 10<sup>7 </sup>and 3.8 X 10<sup>7 </sup><em>B. cereus</em>/ 10 g were obtained in pre-cooked rice maintained at 17 °C and 20 °C respectively. At 12 °C, counts did not reach 10<sup>4</sup> CFU/ 10g even after 48 h of incubation. The aerobic mesophilic bacterial population and <em>B. cereus</em> population of 0.1% crushed pepper in pre-cooked rice over a period of 48h at temperature 20 °C and 17 °C were also analyzed. Counts of <em>B. cereus</em> in pepper rice samples reached a maximum of 1600 MPN/ 10 g and 1100 MPN/ 10 g at 20 °C and 17 °C respectively while the aerobic mesophilic counts per 10 g were 2.4 X 10<sup>8</sup> and 4.4 X 10<sup>6</sup> at these temperatures. The low <em>B. cereus</em> counts and high aerobic mesophilic population indicates competition of nutrients in cooked rice by background flora other than <em>B. cereus</em>.
The physical spore characteristics of five <em>B. cereus</em> and 3 <em>B. thuringiensis</em> strains were studied using transmission electron microscopy (TEM). Tubular, whip-like appendages were present in four B. <em>cereus</em> and two <em>B.</em> <em>thuringiensis</em>, while all seven isolates possessed exosporia.