Bacillus cereus is the most prevalent pathogenic Bacillus species found in foods, causing food spoilage and two types of toxin-mediated food poisoning known as the diarrhoeal and emetic syndromes. Other Bacillus species, particularly B. subtilis, B. licheniformis, B. brevis, B. pumilus and B. thuringensis, have also been recognised as food poisoning bacteria of increasing concern, with reports of outbreaks of diarrhoeal or emetic food poisoning. This study involved a systematic ecological investigation of Bacillus species isolated from rice products, commonly associated with Bacillus emetic food poisoning, using cultural and molecular methods. A centrifugation-plating method, more sensitive than the conventional spread plating method, was developed and used to determine the occurrence and biodiversity of Bacillus species in rice, a well known source of B. cereus. Eight different Bacillus species, B. cereus/B. thuringiensis, B. mycoides, B. subtilis/B. mojavensis, B. licheniformis, B. pumilus, B. sphaericus/B. fusiformis and B. megaterium, as well as Paenibacillus species, identified by partial rDNA sequencing, were isolated from raw (uncooked) and cooked rice products. The diversity of the isolates at the subspecies (strain) level was investigated using the RAPD-PCR typing technique, which proved to be useful for differentiating strains of bacilli, revealing broad diversity among the strains. Generally, different genotypes were found in raw and cooked rice, with some isolates of the same RAPD pattern found in both raw and cooked rice. The toxigenic potential of Bacillus isolates were also determined by molecular and immunological analysis as well as an MEKC method, developed in this study for quantitative analysis of the emetic toxin, cereulide. The results revealed that most isolates from the B. cereus group were potentially or actually toxigenic and some isolates were able to produce both diarrhoeal and emetic toxins. Other Bacillus species outside the B. cereus group were also shown to produce cereulide.
| Identifer | oai:union.ndltd.org:ADTP/235006 |
| Date | January 2006 |
| Creators | Oh, Mi Hwa, School of Chemical Engineering & Industrial Chemistry, UNSW |
| Publisher | Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Mi Hwa Oh, http://unsworks.unsw.edu.au/copyright |
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