Multiocus Sequence Typing And Virulence Evaluation Of The Emetic Bacillus Cereus In Rice

Bacillus cereus is an opportunistic pathogen, which is widely presented in the environmentand contaminated food. It can cause two types of diseases: vomit and diarrhea. The35emeticisolates of rice were conducted in this study. The preliminary virulence and molecular typing wereperformed under the following three aspects: which were the toxicity of isolates to Caenorhabditiselegans, biofilm-producing and MLST typing.C. elegans were used as animal model, the35emetic isolates were performed by using NGMbioassays with C.elegans, and we found that there were20emetic isolates having significantinhibition to C.elegans, while the remaining10isolates didn’t have great inhibition to C.elegans.At the same time,120diarrhea isolates were randomly selected for comparative tests. The resultsindicated there were only12diarrheal isolates having great inhibition to C.elegans，the inhibitionof remaining110isolates were very poor to C. elegans. It suggested that C.elegans were moresensitive to emetic isolates than the diarrheal isolates.Almost all the bacteria could form biofilms, the biofim-producing by Bacillus cereus couldcause serious pollution to the food processing equipment, and it was difficult to clean. Thebiofilm-producing capacities of35emetic isolates were measured by using microplates, another35diarrhea isolates were randomly selected for contrastive tests. To our surprise, these resultswere totally opponent to the nematode test results; namely, it was much stronger for diarrheaisolates to form biofilm than emetic isolates.RAPD technique (random amplified polymorphic DNA) was combined with MLST formolecular typing.Fist of all, we choose13emetic isolates which were very different from thestandard isolate by RAPD-PCR; secondly, the13emetic isolates were conducted for MLSTtyping. The results indicated that11isolates were ST26, at the same time, we have found two ne wSTs, one was ST795, and the other one was ST811. This result showed that vomiting strains had aconservative trend to the evolution, and they didn’t have a high level of differentiation...