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The Microbiology of Food

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The Microbiology of Food

The fourth Thursday of November marks the annual tradition in the U.S. called Thanksgiving. Originally, Thanksgiving was a religious holiday that has sinced turned secular and became a national holiday in 1941. Now, for families celebrating Thanskgiving, it is a time to cook a whole lot of food and eat way too much pumpkin pie.

But if you undercook, cross-contaminate, or improperly store your food you can get some pretty interesting microbiology going on, which, unless you have access to microbiology microscopes in your home,  you won’t be able to see. After all, pumpkin pie is full of sugars, protein, and fats- everything that a lovely swarm of bacteria also enjoys as a midnight snack.

So let’s take a seasonal look at what you could be growing in your Thanksgiving dinner, and how you can prevent growing it to ensure the celebrations pass with no ill-effects.

So what are the sources of bacterial contamination in food?

1. The Animal

Microbes are everywhere in our environment and on our bodies so there are many opportunities for bacteria to infect sources of food. In the case of beef and poultry, the microorganisms are often found in the intestines of healthy animals and are spread during slaughter. Fruits and vegetables may become infected when they are washed or irrigated with water contaminated with animal manure. Salmonella can infect the hen egg before it is formed so the egg can be contaminated (which is why you shouldn’t eat raw cookie dough!)

2. Food Handlers

Some types of microbial pathogens can be passed on to your food via the staff working in the kitchen (sorry, Mom. This includes you). Shigella and some viruses (Norwalk and Hepatits A) come from human contact with food. Another source is using cutlery on raw foods and not cleaning them before re-using. Similarly, cutting boards and utensils used for handling raw food need to be cleaned before use. Even if the food was cooked, the contamination can be reintroduced with contact with surfaces or drippings from raw or contaminated food.

Improper Storage

Most likely, mom and her helpers in the kitchen all washed their hands and the utensils after handling the raw turkey and moving on to the mashed potatoes or cranberry sauce. So another source of food poisoning is by simply not storing the cooked food properly once it has cooled down. That’s right- the leftovers!  Make sure to store your leftover food correctly so bacteria that may be present from the environment and the little kids hands isn’t allowed to flourish.

What are the best storage temperatures? According to the Arizona Dept. of Health, food should be stored at 34 to 40°F (1 to 3°C). Above 3°C foods will spoil rapidly. Frozen food should be kept at 0°F (-17°C). The temperature should not reach higher than 5°F (-15°C). Check the temperature with a thermometer, or use this rule of thumb: If the freezer can’t keep ice cream brick-solid, the temperature is above the recommended level. Some additional food storage tips can be found on the website also.

What critters should you watch out for?

Now let’s discuss the bacteria that can cause the post-celebration blues. What are the most typical pathogens that infect foods, both pre and post cooking? Based on statistics collected by the CDC between the years of 1983 and 1997, Campylobacter spp. contamination resulted in the majority of bacterially caused food borne illnesses (2.4 million cases, almost 50%) followed by non-typhoidal Salmonella (1.4 million cases). However, there can be a high degree of under-reporting in bacterial infections because not everyone will go to a hospital when they are sick. The level of under-reporting for Salmonella is estimated at ~38 fold and for E.coli (0157:H7), ~20 fold. However, Norwalk viruses caused far more food-borne illness, approximately 23 million  cases out of a total of 30 million.

Name that Food Pathogen

The following information comes from the Iowa State Food Safety website. The symptoms of all of these are very similar. You can pretty much count on having abdominal cramps and diarrhea if you become infected with any of these microorganisms and for some, add in vomiting:

Bacillus cereus

  • Incubation period: 30 minutes to 15 hours
  • Possible contaminants: meats, milk, vegetables, fish, rice, potatoes, pasta, and cheese
  • Steps for prevention: pay careful attention to food preparation and cooking guidelines.

Campylobacter jejuni

  • Incubation Period: One to seven days
  • Possible Contaminant: Raw milk, eggs, poultry, raw beef, cake icing, water
  • Steps for Prevention: Pasteurize milk; cook foods properly; prevent cross-contamination.

Clostridium botulinum

  • Incubation Period: 12 to 36 hours
  • Possible Contaminant: Low-acid canned foods, meats, sausage, fish
  • Steps for Prevention: Properly can foods following recommended procedures; cook foods properly.

Clostridium perfringens

  • Incubation period: 8 to 22 hours
  • Possible contaminants: meats and gravies
  • Steps for prevention: proper attention to cooking temperatures.

Escherichia coli 0157:H7

  • Incubation Period: Two to four days
  • Possible Contaminant: Ground beef, raw milk
  • Steps for Prevention: Thoroughly cook meat; no cross-contamination.

Hepatitis A

  • Possible contaminants: water, fruits, vegetables, iced drinks, shellfish, and salads
  • Steps for prevention: carefully wash hands with soap and water after using a restroom, changing a diaper, and before preparing food.

Listeria monocytogenes

  • Incubation Period: Two days to three weeks
  • Possible Contaminant: Vegetables, milk, cheese, meat, seafood
  • Steps for Prevention: Purchase pasteurized dairy products; cook foods properly; no cross-contamination; use sanitary practices.

Norwalk, Norwalk-like, or norovirus

  • Incubation Period: Between 12 and 48 hours (average, 36 hours); duration, 12-60 hours
  • Possible Contaminant: raw oysters/shellfish, water and ice, salads, frosting, person-to-person contact
  • Steps for Prevention: Adequate and proper treatment and disposal of sewage, appropriate chlorination of water, restriction of infected food handlers from working with food until they no longer shed virus.


  • Incubation Period: 12 to 24 hours
  • Possible Contaminant: Meat, poultry, egg or milk products
  • Steps for Prevention: Cook thoroughly; avoid cross-contamination; use sanitary practices.


  • Incubation Period: One to six hours
  • Possible Contaminant: Custard- or cream-filled baked goods, ham, tongue, poultry, dressing, gravy, eggs, potato salad, cream sauces, sandwich fillings
  • Steps for Prevention: Refrigerate foods; use sanitary practices.


  • Incubation period: 12 to 50 hours
  • Possible contaminants: salads, raw vegetables, dairy products, and poultry
  • Steps for prevention: practice proper washing and sanitizing techniques.


  • Incubation period: four hours to four days
  • Possible contaminants: fish and shellfish
  • Steps for prevention: cook fish and shellfish thoroughly


  • Incubation Period: One to three days
  • Possible Contaminant: Raw milk, chocolate milk, water, pork, other raw meats
  • Steps for Prevention: Pasteurize milk; cook foods properly; no cross-contamination; use sanitary practices

Make sure the critters don’t get you this year…

As you can see, proper food handling and storage is serious business. But prevention is simple; don’t eat raw chicken,  clean cutlery and counters between handling raw meats, wash your hands after using the bathroom, wash your hands after changing a diaper, don’t sneeze on food and then leave it out on the counter all night, and make sure you have a half-gallon block of ice cream in your freezer that is frozen solid (as a measure of how well your freezer is working).

Joking aside, getting sick on your vacation is not fun or a safe way of losing the extra holiday pounds. So use common sense and enjoy a hot and tasty meal with all the trimmings and the leftovers too.

Thanks for reading and please leave us a comment if you have more  food safety advice or a personal experience involving food-borne pathogens you’d like to share.

~Suzanne (

More information on foodborne illness can be found at the CDC’s website.

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  1. Confidential Scientist on December 1, 2009 at 6:44 am

    It’s funny but the science part of my brain shuts off when I am doing domestic activities, but if I used some aseptic tissue culture/microbiological techniques while cooking, everyone would be a little safer. Of course I have always marveled at how the microbiologists in my department neglect to wash their hands after using the bathroom. Maybe refusing the handshake of a microbiologist should be listed as a prophlyactic measure against food-borne illness.

    Oh and I do not think that Thanksgiving has become a secular holiday. I suspect that Thanksgiving was always regarded as secular to the non-religious, and I can certainly say that Thanksgiving is still a sacred observance to those such as myself that practice Christianity.

  2. Seena on November 29, 2009 at 7:40 am

    I agree with labgrab…the pic ain’t right but the topic was very interesting and particularly the need of the hour.

  3. Ellie on November 27, 2009 at 10:23 pm

    I try to use pasteurized eggs when I’m making cookie dough so I can have an early sample of the finished product without the risk of getting sick.

  4. labgrab on November 26, 2009 at 12:05 am

    That photo “ein’t right” and the post is very thorough and educational but doesn’t make me too hungry! Thanks for sharing the Microbiology wisdom.

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