VPT 421: Veterinary Toxicology (2+0)

TOXICOKINETICS AND MECHANISM OF ACTION OF S. AUREUS AND B. CEREUS

S. aureus

• S. aureus is a facultative anaerobic Gram-positive coccus that may be single, paired or in a grape-like cluster.
• S. aureus does not form spores and thus contamination may be avoided by proper heat treatment of food to kill the bacteria.
• S. aureus is an important infective pathogen as well and can easily be found in the nostrils and on the skin of most mammals.
• Staphylococcal enterotoxins are water soluble, very heat resistant and resist most proteolytic
• enzymes, such as trypsin and pepsin, which make it possible for them to travel through the digestive tract to their site of action.
• They have a direct effect on the intestinal epithelium as well as on the vagus nerve to cause stimulation of the emetic centre as well as increasing peristalsis.

B. cereus

• B. cereus is in the family Bacillaceae which are all Gram positive rod-shaped bacteria which form endospores.
• The family has two main divisions: the anaerobic spore-forming bacteria of the genus Clostridium and the aerobic or facultatively anaerobic spore-forming bacteria of the genus Bacillus.
• B. cereus is a primary inhabitant of soils and contaminates almost all agricultural products and is routinely involved in the contamination and spoilage of food products.
• B. cereus can also be involved in wound, eye or systemic infections.
• B. cereus food poisoning is generally described as having two types of illness caused by different metabolites.
• The diarrheal type of illness is caused by one or several heat-labile high molecular weight proteins, while the vomiting (emetic) type of illness is believed to be caused by a low molecular weight, heat-stable peptide which has been named cereulide.