Microbiology 27th October 2016 Gram-positive, Aerobic Spore-forming Rods Bacillus cereus and Bacillus anthracis Fermicuties Characteristics They are gram-positive, sporulating rods (gram positive that can only sporulates). They are catalase-positive - protection against hydrogen peroxide. Aerobic - grows in presence of oxygen. The spore is oval and central. There is no distension of sporangium; it does not bulge out the cell. They are motile - peritrichous (apart from Bacillus anthracis). They are metabolically diverse - have a lot of diverse metabolic reactions in the different species of Bacillus. Paenibacillus 'Almost' Bacillus, they are different enough to be diverse from Bacillus. - Reclassified in 1993 Mesophiles Historical Perspective of Bacillus Ferdinand Cohn - good at describing shapes of cells: - 1872 - Work on spores - showed it was a resistant structure and showed the vegetative cycle - Bacillus subtilis Robert Koch - worked on anthrax in mice: - 1876 - Linked Bacillus anthracis to disease - Koch postulates Bacillus genus and nested genera now contain 266 species! Bacillus cereus Ubiquitous in nature, they are typically found in soil and dust- Everywhere! Spore former; able to withstand dry, lack of nutrients, heat ect ... Environmentally persitant, lives in the soil on its own as it does not associate with other bacteria.
27th October 2016 Microbiology Associated with starchy foods like rice, and associated with herbs and spices - food that comes from plants and soil (also animals). Two distinct foodborne intoxications: Emetic and Diarrhoeal Bacillus cereus - Emetic Form Food poisoning has rapid onset, causing nausea and vomiting with an onset of 1 - 6 hours. It has a short incubation form of duration up to 24 hours. Cereulide - Emetic toxin: - Preformed in the food as it is produced in the food by the organism before you eat it. The spores of bacillus withstand the heat of cooking. When you cool it down the spores germinate and the B.cereus produce cereulide, which is then ingested - Heat-stable - reheating doesn't get rid of it - Resistant to proteolytic cleavage - trypsin and pepsin in the stomach will not denature the toxin Activates vagal neural system serotonin receptors, increasing stimulation of enteric nervous system, causing nausea and vomiting - contraction of the stomach. Bacillus cereus - Diarrhoeal Form Less researched - don't know as much Abdominal cramps and diarrhoea with an onset of 8 - 16 hours; it has a long incubation form with duration up to 24 hours (can carry up to 4-5 days). Pore forming complex of three toxins: - Haemolysin BL (Hbl) - Nonhaemolytic Enterotoxin (Nhe) - Cytotoxon K (CytK) The toxins are produced in the intestine and cause beta-barrel conformation, inserting itself into the cell membrane and causing a leak in the cell; resulting in cell death - this leads to loss of structure and function of the gut. It is not able to reabsorb as well; water is left in the lumen of the gut and is expelled as diarrhoea. The toxin itself is heat labile