Question

The Case:

There is a suspected outbreak of food poisoning with at least 90 confirmed cases. All of the individuals attended a summer picnic and have had the following symptoms: bloody diarrhea (100% of all individuals), abdominal pain (92% of all individuals), moderate fever (80%), and nausea (48%). All of the infected individuals ate a picnic lunch of hamburgers, grilled chicken, potato salad, fruit salad, chips, and cake. The patient’s symptoms started about days after the field trip and have lasted approximately 7 days.

1. Is this infection an example of food borne intoxication or food borne infection? Why?

2. You are asked to determine which organism is likely causing this infection. Propose two possible organisms that could be causing the infection. Give reasons to support why you chose these two organisms.

3. The microbiology lab identifies a gram-negative rod that is non-motile and also a facultative anaerobe. Based on the information provided, which organism do you suspect to be responsible for this outbreak? Explain why you chose the organisms as a possible suspect and give specific evidence to support your answer.

4. Explain the mechanisms of pathogenesis of this organism. (How does this organism cause disease?)

Answer 1

Answer-

1- food infection - because the patients developed symptoms within few days . As in food infection ,food contaminated with bacteria is consumed which invades the gut epithelium and produces toxin to cause symptoms .

In case of food intoxication ,the food consumed will have the toxin meaning the bacteria propagates on the food and releases toxin so the food will be spoiled and the onset of symptoms will within few hours.

2- Ecoli and shigella . Both cause food poisoning , and manifest as abdominal pain , fever , diarrhea ,nausea . The incubation period for both is 1-7 days after exposure via contaminated food .

3- shigella , because 100% patients had bloody diarrhea . Bloody diarrhea is charecteristic of shigella and E coli infection . Also E coli i and shigella both are gram negative bacilli , an aerobe and facultative anaerobe . But shigella is non motile while most strains of E coli is motile and peritrichous.

4- pathogenesis

Man is natural host of shigella . Type 1 shigella dysentriae causes most severe form of dysentry along with toxemia. The type 1 causes toxemia because of production of exotoxin called shiga toxin which is both an enterotoxin and neurotoxin . When the food and drinks are contaminated by feces of cases ,the bacteria remains localisedin gut wall and produces toxin . This toxin accumulates fluid leading to severe diarrhea and other complications like joint pain , polyneuritis,inflammation of conjunctiva ,parotitis etc .This toxin is a verocytotoxin which halts protein synthesis causing cell death and since endothelium exfoliates and forms new cells continuously to replace old ones the lining breaks down due to dead cells and cayses hemirrhage with appears along with stool .

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