Biology 261

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Brandon47
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120928
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Biology 261
Updated:
2011-12-05 10:35:38
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Chapter 36
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Chapter 36
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  1. What are the difference between perishable, semi
    perishable and non-perishable foods?
    • Food categories:

    – Perishable foods - fresh foods

    – Semiperishable foods - potato and nuts

    – Nonperishable or stable foods - flour, sugar, dry beans, rice
  2. What are the most common techniques for
    prevention of food spoilage? What are their advantages and drawbacks? How does each limit growth of microbes?
    • Temperature (chilling, freezing, heating, heating followed by aseptic packaging)

    • Acidity - pickling and fermentation

    • Drying and lyophilization (freeze-drying)

    • Canning followed by autoclaving.

    • Chemical preservation - sodium propionate, nitrites, sodium benzoate, ethylene oxide.

    • Irradiation, 4.5 to 44 kilo Grays
  3. What are some chemicals that are used to
    preserve food?
    - Sodium or calcium propionate – Bread

    - Sodium benzoate – Carbonated beverages, fruit, fruit juices, pickles, margarine, preserves

    - Sorbic acid – Citrus products, cheese, pickles, salads

    -Sulfur dioxide, sulfites, bisulfites – Dried fruits and vegetables; wine

    -Formaldehyde (from food-smoing process) – Meat, fish

    - Ethylene and propylene oxides – Spices, dried fruits, nuts

    - Sodium nitrite – Smoked ham, bacon
  4. What are the differences between food infections and food
    poisoning?
    • Food poisoning - exotoxin of Clostridium botulinum, enterotoxin of S. aureus.

    • • Food infection - Salmonella
    • enterica, E. coli
  5. How could you test food for the spoilage organisms?
    •Sampling: liquid foods directly, solid foods after homogenization.
  6. How does food poisoning with staphylococcus
    occur and will antibiotics help?
    • • Staphylococcus aureus produces several enterotoxins, which cause nausea, vomiting and diarrhea within 1-6 hr after ingestion. Most common enterotoxin A, which is
    • a superantigen.

    • 185,000 cases in the US annually.

    • ELISA to detect enteroxotins and direct plating to enumerate number of bacteria in foods.
  7. What are three most common microorganisms causing
    food-related infections in the US?
    - Campylobacter jejuni

    - Salmonella spp.

    - Noroviruses
  8. Describe food poisoning caused by Cl. perfringens and Cl.
    botulinum. How are they different?
    •Clostridium perfringens food poisoning

    – Anaerobic, gram-positive, spore-producing soil and gut inhabitant.

    – 248,000 cases in the US each year.

    – Ingestion of large numbers of C. perfringens (>108) leads to poisoning.

    – Diagnosis: isolation of the pathogen from the gut and ELISA for the enterotoxin.

    • Botulism

    – On average 150 cases in the US per year with 25% mortality.

    – Exotoxin is inactivated by the temperature (80oC for 10 min.)

    – Diagnosis: Detection of C. botulinum or toxin in foods

    – Treatment: antitoxin and mechanical ventilation.
  9. What are the infections associated with Salmonella spp.? How might Salmonella contamination be contained?
    • Salmonella enterica (typhimurium)

    • 45,000 documented cases in the US annually. Less than 4% of cases are reported.

    • Most common salmonellosis is enterocolitis. Septicemia and typhoid fever are also possible.

    • Diagnosis: isolation of Salmonella from foods. Antibiotics in case of septicemia and typhoid fever.

    • • Prevention: prevention of contamination during food (meat) processing, thorough cooking and storage at
    • low temperature.
  10. Describe the pathology of E. coli food infection. What are the reservoirs and food sources of pathogenic E. coli strains? How can they be diagnosed, prevented and
    treated?
    • ~200 pathogenic strains

    • Enterohemorrhagic E. coli produce verotoxin, an enterotoxin similar to Shiga-toxin.

    • • Most common enterohemorrhagic strain is E.
    • coli O157:H7.

    • 60,000 infections and 50 death in the US annually.

    • • Most commonly beef (ground beef) is the source of infection. More rarely from swimming in water
    • with fecal contamination.

    • Enterotoxigenic strains cause “traveler’s diarrhea” through the production of two enterotoxins.

    • Infection usually occurs through contaminated water supplies.
  11. What are the sources of pathogenic Campylobacters spp.? What are the reservoir and food sources of pathogenic Campylobacters spp.? How can they be diagnosed, prevented and treated?
    • Several species: C. coli, C jejuni and C. fetus.

    • • C. coli, C jejuni account for 2 million cases of bacterial
    • diarrhea.

    • C. fetus is involved in sterility and spontaneous abortion in cattle and sheep.

    • Transferred to human through contaminated food. C jejuni is a member of normal microflora of poultry.

    • Domestic animals (dogs and cats) may also be reservoirs of Campylobacter spp.

    • Multiplies in small intestine and invades epithelium. Fever is common.

    • Diagnosis: isolation from the stool. Treatment with antibiotics (erythromycin). Prevention: personal hygiene,
    • thorough cooking, preventing contact of uncooked poultry with cooked products
  12. What are the reservoir
    and food sources of pathogenic Listeria monocytogenes? How can they be diagnosed, prevented and treated?
    • • Listeria monocytogenes is psychrotolerant,
    • facultatively anaerobic, salt-tolerant gram-positive bacterium.

    • Widely found in soil and water. Common sources of listeriosis are ready-to-eat processed foods.

    • Intracellular pathogen. Proliferates in phagocytes and then lyses them. AIDS patients are particularly vulnerable.

    • • 2500 cases of acute lesteriosis per year and 32 deaths in the US. Complications – septicemia and
    • meningitis.

    • Diagnosis: culturing from blood or PCR.

    • Treatment with trimethoprime-sulfamethoxazole and penicillin.

    • Prevention: limit contamination during food processing, cooking and irradiation kill Listeria.
  13. How might prion contamination of production animals be
    prevented in the U.S.?
    • Yersinia enterocolitica.

    • Bacillus cereus.

    • Shigella spp.

    • Norwalk-like viruses, rotoviruses, astrovirus, hepatitis A, adenoviruses.

    • • Parasites: Toxoplasma gondii, Giardia lamblia, Cryptosporidium parvum and Cyclospora
    • cayetanensis.

    • Prions
  14. Why does refrigeration help prevent food spoilage? What is a food borne pathogen for which refrigeration is not effective?
    • Listeria monocytogenes is psychrotolerant, facultatively anaerobic, salt-tolerant gram-positive bacterium.

    • Widely found in soil and water. Common sources of listeriosis are ready-to-eat processed foods.

    • Intracellular pathogen. Proliferates in phagocytes and then lyses them. AIDS patients are particularly vulnerable.

    • • 2500 cases of acute lesteriosis per year and 32 deaths in the US. Complications – septicemia and
    • meningitis.

    • Diagnosis: culturing from blood or PCR.

    • Treatment with trimethoprime-sulfamethoxazole and penicillin.

    • Prevention: limit contamination during food processing, cooking and irradiation kill Listeria.

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