Harmful Bacteria in Farm Animal Production

Instructor: Stephanie Gorski

Steph has a PhD in Entomology and teaches college biology and ecology.

In this lesson, we'll meet some of the bacteria responsible for food poisoning. We'll also talk about why some people are very concerned about antibiotic-resistant bacteria on farms.

Food Safety

A lot of us like our steak cooked rare. Many of us enjoy the raw fish in sushi. But like many things you do every day, eating undercooked food has risks. One of those risks is that you might ingest bacteria that could make you sick. It's hard to estimate exactly how many people get food poisoning, because not everyone who gets food poisoning goes to the hospital, but there are an estimated 24 to 81 million cases per year in the U.S. alone. Most cases of food poisoning will clear up on their own, if you're lucky enough to live somewhere with clean water and good sanitation. However, a handful of people each year undergo severe complications including paralysis, spontaneous abortion, and death. That doesn't mean you should stop eating sushi. Undercooked chicken, unpasteurized milk, and an unsanitary kitchen are much bigger risks than a well-kept sushi bar. It's just worth taking the time to understand and minimize the risks.

The most important thing you can do is to thoroughly cook meat and eggs. Always keep uncooked meat and eggs separate from other foods, and keep them on lower shelves in your refrigerator than any foods that you might eat raw. Wash your hands thoroughly with warm soap and water for at least 20 seconds after you touch raw meat or eggs. Never drink unpasteurized milk, which is often contaminated with harmful bacteria.

Some people think that the bacteria that causes food poisoning could lead to something akin to a new zombie apocalypse. We'll talk about apocalyptic antibiotic-resistant bacteria later in this lesson. First, let's meet some of the key players in this drama.

Common Food Poisoning Bacteria

Campylobacter jejuni, campylobacter for short, is the most common cause of diarrhea in the US. Healthy humans don't carry campylobacter, but healthy animals often do. Campylobacter can also sometimes be found in water sources. So don't drink untreated water from a stream.


Escherischia coli, or E. coli, exists in your digestive tract and in animals' digestive tracts. It's fine where it is, just doing its job. Problems occur when contamination from sources like animal poop allows E. coli access to places it shouldn't be. The most common source of contamination is from undercooked meats. Sometimes, fresh organic vegetables are responsible for E. coli outbreaks because organic farmers fertilize their fields with animal poop, a rich source of E. coli.

Salmonella enterica, commonly called Salmonella, is dangerous if you handle raw or undercooked meat. Like E. coli, Salmonella is much more common in organic than conventional produce, but it hasn't been shown to be more common on organic meat.


Listeria monocytogenes, commonly called Listeria, is particularly common in raw poultry and unpasteurized milk. Listeria can cause not only gastrointestinal distress, but also serious complications in pregnancy.

Methicillin-resistant Staphylococcus aureus, or MRSA, has also been turning up on raw meat for the last few years. In 2012, researchers found that about 7% of the pork samples they tested had MRSA. Methicillin resistance means that MRSA is able to survive doses of some antibiotics. We'll talk more about antibiotic resistance below.


Why Don't Farmers Just Kill All the Bacteria?

One reason is that some bacteria is good - but that's a subject for another day.

Another reason is antibiotic-resistant bacteria. Antibiotic-resistant bacteria is exactly what it sounds like: bacteria that resists antibiotics. Antibiotic resistance evolves when we use antibiotics to kill bacteria. The vast majority of the bacteria will die, but if even a handful of bacteria survive, those bacteria have whatever it takes to help them withstand the antibiotic. The resistant bacteria will reproduce rapidly, and next time you try to treat the same batch of bacteria with antibiotics, the antibiotic won't work!

There are some people who would have you believe that antibiotic-resistant bacteria from antibiotics used in farm production will lead to a massive epidemic, a sort of zombie apocalypse of chickens. Don't worry; that's a bit alarmist.

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