Genetic biomarkers of Bacillus cereus sensu stricto cytotoxicity in a CaCo-2 model
Open Access
- Author:
- Prince, Cassidy R
- Area of Honors:
- Microbiology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Jasna Kovac, Thesis Supervisor
Ying Gu, Thesis Honors Advisor - Keywords:
- bacillus cereus
enterotoxins
cytotoxicity
bioinformatics - Abstract:
- Bacillus cereus sensu lato is comprised of multiple species that are genetically similar but differ largely in pathogenicity. Cytotoxicity within this group is highly variable and ranges from non-cytotoxicity in some strains used as bioinsecticides to high cytotoxicity in strains causing foodborne illness and other infections in human. Due to the lack of strong correlation between individual B. cereus group species and pathogenic potential, B. cereus sensu lato isolates need to be characterized at a strain level. However, currently established standard microbiological methods that are based on species identification largely do not consider or measure the variability of individual strains to cause foodborne illness. In this study, we aimed to characterize a collection of closely related B. cereus group isolates belonging to the same genomospecies B. cereus sensu stricto by (i) determining the intraclade variability in cytotoxicity towards colon cell line CaCo-2 and (ii) identifying genetic biomarkers for in vitro cytotoxicity. Growth curves of isolates were characterized to identify the early stationary phase in which supernatants were collected. Cell-free supernatants were then used for cytotoxicity screening in a CaCo-2 model. The cytotoxicity outcome was compared with the phylogenetic placement of individual isolates, the presence of enterotoxin genes and the presence of single nucleotide polymorphisms (SNPs) upstream of enterotoxin genes. The phylogenetic clustering did not explain differences in cytotoxicity among closely related B. cereus s.s. isolates. Furthermore, hbl, nhe, or cytK genes were found to be highly sensitive, but nonspecific biomarkers of cytotoxicity. Several SNPs upstream of the coding regions of hblCDAB, nheABC, and cytK2 were found to be associated with cytotoxicity. These SNPs warrant further investigation as potential genetic markers of B. cereus s.s. cytotoxicity.