Update of Investigation into food poisoning incidents at Pat’s Schoolhouse, The Children’s Place and Learning Vision

Investigation Findings
The investigations have traced the outbreak of food poisoning to the consumption of seafood marinara pasta supplied by the caterer to the pre-schools for lunch on 10 May 2011. The infective agent was Salmonella Enteritidis (a bacteria which can cause food poisoning), found in the stool samples collected from the affected cases. As this organism is not native to seafood but is commonly found in items such as poultry and eggs, there may have been cross-contamination of the pasta with raw food during preparation at the caterer’s premises.

Interviews with the food handlers employed by the caterer indicated that the same trays were used to hold raw and cooked foods, which may be a possible cause of cross-contamination, if the trays were not cleaned properly. Meat, seafood and poultry were also being prepared in the same area, which increases the risk of cross-contamination. 

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Two Catergories of Toxins!

Exotoxins  are soluble, heat-labile, proteins that usually released into the surroundings as the pathogen grows. Often exotoxins may travel from the site of infection to other body tissues or target cells in which they exert their effects. 
 Ø Exotoxins usually are

1.  Synthesized by specific bacteria that often have plasmids or prophages bearing the exotoxin genes

2.  Heat-labile proteins inactivated at 60 to 80°C.

3.  Among the most lethal substances known (toxic in very small doses [microgram per kilogram amounts]; e.g., the botulinum toxin)

Ø   Exotoxins can be divided into four types based on their structure and physiological activities. (1) One type is the AB toxin, which gets its name from the fact that the portion of the toxin (B) that binds to a host cell receptor is separate from the portion (A) that has the enzyme activity that causes the toxicity. (2) A second type, which also may be an AB toxin, consists of those toxins that affect a specific host site (nervous tissue [neurotoxins], the intestines [enterotoxins], general tissues [cytotoxins]) by acting extracellularly or intracellularly on the host cells. (3) A third type does not have separable A and B portions and acts by disorganizing host cell membranes. Examples include the leukocidins, hemolysins, and phospholipases. (4) A fourth type is the superantigen that acts by stimulating T cells to release cytokines.

Endotoxins

Gram-negative bacteria have lipopolysaccharide (LPS) in the outer membrane of their cell wall that, under certain circumstances, is toxic to specific hosts. This LPS

is bound to the bacterium and is released when the microorganism lyses [dissolution or destruction of cells]. Some is also released during bacterial multiplication. The toxic component of the LPS is the lipid portion, called lipid A. Lipid A is not a single macromolecular structure but appears to be a complex array of lipid residues. The lipid A component exhibits all the properties see characteristic 5 on p. 801) associated with endotoxicity and gram-negative bacteremia.

Bacterial endotoxins are:

1. Heat stable

2. Toxic only at high doses (milligram per kilogram amounts)

3. Weakly immunogenic

4. Generally similar, despite source

5. Usually capable of producing general systematic effects: fever (are pyrogenic), shock, blood coagulation, weakness, diarrhea, inflammation, intestinal hemorrhage, and fibrinolysis (enzymatic breakdown of fibrin, the major protein component of blood clots).

 Lansing M. Prescott, John P. Harley, Donald A. Klein (Eds.). (2005) Microbiology. Boston, Mass.: McGraw-Hill Higher Education.

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Detection of toxins by Reserved Passive Agglutination Assay

The Reserved Passive Agglutination Assay requires latex beads covered with a specific antibody, added to the sample and mixes them in a microtiter plate. If the particular antigen is present, agglutination will take place. The latex beads will form a diffuse pattern due to the reaction that take place between antigen and antibody. If the antigen is not present, antigen-antibody reaction will not occur and a tight button or smaller diffuse layer can be seen.

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Detection of Microbial toxin by enzyme-linked immunosorbent assay (ELISA)

The common kits available are, enzyme-linked immunosorbent assay (ELISA). Basically each different species of microorganism or toxin have at least one unique antigen. These antigens could be purified and used to produce specific antibodies.  The antigens and antibodies are useful and precise diagnostic tools. The enzyme-linked immunosorbent assay (ELISA) is a technique commonly used to detect the presence of that particular antigens or antibodies.  The direct ELISA utilizes antibodies to identify the existence of a specific antigen in a sample.
Firstly, a specific antibody will be attached onto the walls of a microtiter plate. Next, the sample will be added into the well to examine the presence of complementary antigen. If the particular antigen is present in the sample, it will attach to the antibodies on the surface of the well. The microtitler plate will be rinsed, and is able to remove any unbound antigen. Next, will be the addition of the monoclonal, modified antibody that is linked to an enzyme (enzyme conjugated antibody). The well will be rinsed again to remove any unbound antibodies. If the particular antigen is not there, the enzyme conjugated antibody will be washed away as it is unable to bind to the antigen. Lastly, the enzyme’s substrate will be added and its purpose is to create a colour change if the enzyme conjugated antibody had reacted with the substrate. No colour change represents a negative result.

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