Listeria monocytogenes poisoning

          

           L. monocytogenes was first described by E.G.D.Murray in 1926 based on six cases of sudden death in young rabbits. Murray referred to the organism as Bacterium monocytogenes before J.H. Harvey Pirie changed the genus name to Listeria in 1940. Although clinical descriptions of L. monocytogenes infection in both animals and humans were published in the 1920s, not until 1952 in East Germany was it recognized as a significant cause of neonatal sepsis and meningitis. Listeriosis in adults would later be associated with patients living with compromised immune systems, such as individuals taking immunosuppressant drugs and corticosteroids for malignancies or organ transplants, and those with HIV infection.

          L. monocytogenes has three distinct lineages with differing evolutionary histories and pathogenic potentials. Lineage I strains contain the majority of human clinical isolates and all human epidemic clones, but are underrepresented in animal clinical isolates. Lineage II strains are overrepresented in animal cases and underrepresented in human clinical cases as well as more prevalent in environmental and food samples^. Lineage III isolates are very rare but significantly more common in animal isolates than human.

          Listeriosis is a serious infection caused by eating food contaminated with the bacterium called Listeria monocytogenes. Although there are other types of Listeria, most cases of listeriosis are caused by Listeria monocytogenes.  Listeria is found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin, such as meats and dairy products. Listeria has been found in a variety of raw foods, such as uncooked meats and unpasteurized (raw) milk or foods made from unpasteurized milk. Listeria is killed by pasteurization and cooking; however, in certain ready-to-eat foods, like hot dogs and cold cuts from the deli counter, contamination may occur after cooking but before packaging.

Clostridium botulinum

          

           Clostridium botulinum is a rod-shaped microorganism. It is an obligate anaerobe, meaning that oxygen is poisonous to the cells. However, C. botulinum tolerates traces of oxygen due to the enzyme called superoxide dismutase (SOD) which is an important antioxidant defense in nearly all cells exposed to oxygen.C. botulinum is only able to produce the neurotoxin during sporulation, which can only happen in an anaerobic environment. Other bacterial species produce spores in an unfavorable growth environment to preserve the organism's viability and permit survival in a dormant state until the spores are exposed to favorable conditions.

             In the laboratory Clostridium botulinum is usually isolated in tryptose sulfite cycloserine (TSC) growth media in an anaerobic environment with less than 2% of oxygen. This can be achieved by several commercial kits that use a chemical reaction to replace O₂ with CO₂ (E.J. GasPak System). C. botulinum is a lipase negative microorganism that grows between pH of 4.8 and 7 and it can't use lactose as a primary carbon source, characteristics important during a biochemical identification.

           Clostridium botulinum was first recognized and isolated in 1895 by Emile van Ermengem from home cured ham implicated in a botulism outbreak. The isolate was originally named Bacillus botulinus. However, isolates from subsequent outbreaks were always found to be anaerobic spore formers, so Bengston proposed that the organism be placed into the genus Clostridium as the Bacillus genus was restricted to aerobic spore-forming rods.

             Since 1959 all species producing the botulinum neurotoxins (types A-G) have been designated C. botulinum. Substantial phenotypic and genotypic evidence exists to demonstrate heterogeneity within the species. This has led to the reclassification of C. botulinum type G strains as a new species Clostridium argentinense.

             Clostridium botulinum strains that do not produce a botulin toxin are referred to as Clostridium sporogenes. The complete genome of C. botulinum has been sequenced Sanger.