Lab 10 Flashcards
Describe food-borne illness in Canada.
- Millions of cases every year (estimated) in Canada.
- Most are non-life threatening (diarrhea, vomiting, fever) and not reported to most doctors
- Victims just suffer for a few days and get better, never knowing why they were sick
Why are big outbreaks affecting hundreds to thousands of people is a new phenomenon?
- Due to more centralization of food production in the hands of big companies, more centralized water treatment by municipalities, more centralized eating in restaurants.
- E.g., peanut oil contaminated with Salmonella made by Peanut Corporation of America distributed to 4500 companies in 2008-2009 who in turn used it in their products = massive outbreak. PCA has filed for bankruptcy protection.
Describe how the nature of food borne illness seems to be changing.
- Early 1900s - dairy products
- Now - meat, seafood, vegetables, fruit
- Sometimes caused by bacteria, but viruses are increasingly implicated.
- E.g., Norovius - the cruise ship virus (seems to cause almost all of the epidemic non-bacterial outbreaks of gastroenterititis and may be responsible for half of all foodborne outbreaks in the US)
Define: pasteurization and give an example.
- The process of using precisely controlled heat to reduce the microbial load in heat-sensitive liquids.
- It does not kill all organisms, so it is different than sterilization.
Define: heat sterilization and give an example.
- The most widely used method of controlled microbial growth.
- High temperatures denature macromolecules
- Amount of time required to reduce viability tenfold is called the decimal reduction time (D value)
Define radiation sterilization and give an example.
- Uses microwaves, UV, X-rays, gamma rays, and electrons to reduce microbial growth.
- It causes breaks in DNA of bacteria which makes it difficult for them to grow.
How are endospores killed in food?
Endospore forming cells that carry toxin genes are a concern; if present when packaged, endospores might germinate into vegetative cells and grow during room temperature storage and produce the exotoxin. Many packaged foods are not subsequently cooked.
- Endospores can survive heat that would rapidly kill vegetative cells.
- The autoclave is sealed device that uses steam under pressure.
- Allows temperature of water to get above 100C.
- It is the high temperature that kills things, not the pressure.
Describe irradiation of food products.
- Irradiation does not make foods radioactive, compromise nutritional quality, noticeably change the taste, texture, or appearance of food - it reduces or eliminates microbes and insects.
- Three types of radiation are permitted: gamma rays from cobalt-60, cesium-137, x-rays, or an electron beam
- Irradiation can be used to sterilize foods, which can then be stored for years without refrigeration.
- Useful in hospitals for patients with severely impaired immune systems, such as patients with AIDS or undergoing chemotherapy.
Give some examples of applications of irradiation and examples of foods that have been treated.
Other applications of irradiation:
* Prevention of foodborne illness
* Preservation
* Control of insects
* Delay of sprouting and ripening
Foods that have been treated:
* In US: Beef, pork, poultry, crustaceans, shellfish, fruits, vegetables, eggs, spices.
* In Canada: potatoes, onions, wheat, flour, whole wheat flour, whole and ground spices.
* Treated foods must have the Radura symbol and a statement of “Treated with radiation” or “Treated by irradiation” on the food label or a label next to the sale container.
Describe the basis of how microbes die under heat stress.
- Experiments with populations of pure cultured microbes grown in the lab have shown how microbes die when exposed to lethally high temperatures compatible with food palatability.
- Not all die at the same time. Some organisms are unlucky, accumulating lethal “hits” early and die early.
How is microbial death described as an equation?
- A negative exponential equation
Why does ‘k’ have to be determined for each foodtype?
- Want to calculate how long to heat a food product at a particular temperature (or radiation) to reduce the number of endospores to Nt = 0.
- The term 10-kt/2.303 can never be “0”, therefore, can never truly calculate an accurate Nt.
- “k” – the sensitivity to heat depends on several factors such as cell type (e.g., vegetative vs spore), and environmental conditions (e.g., water, pH, salt content etc. of food)
- Thus, k has to be determined for each food type.
How does the food industry keep food safe if the ‘Nt’ value can never be known? [3]
- Assume endospores are present.
- Use information from basic research using pure cultures of a specific endospore.
- Build a large margin of safety into heating operations.
What does it mean to reduce population size by 12 logs?
Reducing the number of viable endospores by 12 logs means, if there was initially a single endospore in every can of a food product, one would have to eat one trillion (10^12) cans of food to be sure of eating one viable endospore.
What is decimal reduction time?
- The time to reduce population size by 1 log, to 10% of its initial size.
- Can estimate in the lab by using pure cultures.
What is an emerging pathogen?
- Infectious agent whose incidence is increasing following its first introduction into a new host population.
- E.g., New pathogen not previously reported in humans (SARS-CoV2, HIV, Influenza H5N1)
- E.g., Elucidation that a disease can be attributed to infection (cervical cancers (HPV), gastric ulcers (Helicobacter pylori)
Give 4 reasons how and why microbial hazards emerge.
- Increase in population susceptibility
- Pathogens become a greater threat
- New host for an existing pathogen
- Pathogen emerges in a new geographic region
Describe how food is a vector for microbial hazards.
Describe factors that affect food safety. [6]
-
Foodborne exposure
- Consumption of contaminated product
- Consumption of produce contaminated with manure via environmental pathways
-
Non-foodborne exposure
- Contact with live animals or their habitats
- Interaction with environments polluted by nearby animal production facilities
- Consumers’ tastes
- Consumption habits
- Product preferences
- Adoption of new business and agricultural practices.
Describe how microbial hazards may enter the food supply at any point.
Where along milk production do you think pathogens can enter the food supply?
What is the epidemiological triangle?
- Incidence, distribution, and possible control of a disease
- Disease typically emerges from changes in the interplay between host, agent, and environment
Describe factors of the host at the individual level that increases risk of food-borne disease. [4]
- Age
- Immunization
- Health
- Co-morbidities (e.g., HIV/AIDS, diabetes)
Describe factors of the host at the population level that increases risk of food-borne disease. [3]
- Community composition
- Resilience to infection
- Aging population
Describe factors of the agent that increase risk of food-borne disease.
- Changes in the pathogen: becomes more virulent, acquires antimicrobial resistance genes, acquires the ability to infect new hosts.
- Traits that are thought to increase risk of emergence:
- Zoonotic - ability to infect multiple hosts
- Evolve at a high rate - e.g., viruses
- Predisposed to acquiring genetic material
Describe factors of the environment that increase risk of food-borne disease.
- Climactic factors
- Seasonality
- Geographic barriers (e.g., mountains)
- Change in food production
Many strains of E. coli are non-pathogenic, but there are strains that can cause severe gastroenterititis. Describe them.
- Strain 0157:H7 (Enterohemorrhagic E. coli) causes ~60,000 illnesses/year in U.S.
- First emerged in 1982 (in contaminated undercooked meat).
- Over 100 other strains pathogenic E. coli have been identified
- Serologically divided into groups based on types of antigens O: (LPS), H (flagella), K (polysaccharides)
- Diarrheagenic E. coli are categorized by pathogenic features: Entero( ) E. coli
- ETEC (toxigenic)
- EPEC (pathogenic)
- EHEC (hemorrhagic)
- EAEC (aggregative),
- EIEC (invasive)
- Reservoir: Cattle
ETEC is […]
Toxigenic
EPEC is […]
Pathogenic
EHEC is […]
Hemorrhagic
EAEC is […]
aggregative
EIEC is […]
Invasive
Describe the leading cause of foodborne bacterial illness.
-
Salmonella
- Zoonotic; can infect humans and animals
- Resevoirs: poultry, eggs, and meat predominantly
- Potential vehicles of infection: slaughter-house by-products put in animal feeds; aqua-culture (e.g., fish, shellfish (fed meat-scraps))
What are antibiotics?
- Natural or synthetic compounds that inhibit the growth of bacteria or kill bacteria.
- When we take antibiotics to treat an infection, the antibiotics either kill the vast majority of susceptible bacteria leaving a small group that our immune system can clear up easily, or inhibit their growth so that our immune system can catch up.
How does antibiotic resistance occur?
- Antibiotic rich environments like hospitals provide room for antibiotic resistant strains to thrive and spread, leading to the creation of antimicrobial resistant strains.
Describe antibiotic use in factory farms.
- Used to reduce the microbial load and limit disease from arising antibiotics; often continually administered in the animals’ feed.
- Systematic use of antibiotics in livestock creates a strong selective pressure for antibiotic resistant bacteria.
How do antimicrobial resistance traits in emerging pathogens contribute to greater public risk?
- Humans can be exposed to antibiotic resistant bacteria through ingestion of contaminated food and water, using fertilizer, and direct contact with livestock
- Antibiotic resistance genes can be transferred to other human pathogens.
How do foodborne resistant infections develop in humans?
