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United States Department of Agriculture

Agricultural Research Service

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What Bad Things Lurk Inside ..... Protozoa????!!

Protozoa are tiny, one-celled creatures that can make a comfortable home out of any place with some moisture in it—the soil, ponds, air vents or even the inside of animals. Although they can only be seen using microscopes, these little critters share a couple of characteristics with much larger mammals: they move about, and they breathe oxygen.

It's true that some of the many types of protozoa in the world can be harmful all by themselves. But many others are helpful. Inside animals, one of the most important things protozoa do is gobble up bacteria that can cause disease.

So imagine the surprise of ARS scientists when they discovered that some protozoa inside cows can actually strengthen bacteria that cause nasty diseases. What's more, the protozoa help the bacteria fight off medicines designed to defeat the bacteria!

That's what researchers Mark Rasmussen and Steven Carlson found at the ARS National Animal Disease Center (NADC) in Ames, Iowa, when they studied protozoa that live in the first stomach—the rumen—of cows.

Did you know that, unlike humans and most other animals, cows have four stomachs? This helps them digest all of that grass that they spend all day munching on.

Cows are a type of animal that is known as a ruminant. Ruminants are even-toed hoofed mammals that eat plants. They include sheep, deer and camels. They have more than one stomach (most ruminants have four), and they chew cud. Actually, the stomachs are more like different parts, or chambers, of one large stomach system. Cows have four of these chambers. They are called the rumen, the reticulum, the omasum and the abomasum.

The rumen is the first "stomach." It's where the large amounts of plants and feed the cattle eat are stored and mushed up. In the rumen live billions and billions of microscopic organisms, such as bacteria and protozoa, that are harmless to the animal and help it digest the food and stay healthy. Once the food goes through the rumen, the cow regurgitates it as cud. "Regurgitate" is a fancy way of saying the mushed-up food goes back up to the cow's mouth, kind of like "throwing up." This may sound yucky, but it's what cows do.

The cow then chews this cud and swallows it down into the other chambers.

The reticulum is a honeycombed stomach that acts as a trap for rocks, nails or other foreign objects that cows could swallow during their day out in the field. The omasum has folds that look like book pages and act as filters for the digesting food. The last compartment, the abomasum, is like a person's stomach, in that it produces acid and enzymes to break down and digest the food.

They Get Stronger While Inside

The NADC scientists were watching a specific type of a dangerous microbe—one that causes an illness called Salmonella poisoning. Not only did this bacterium survive after being taken in by a protozoa, it became especially strong and hard to kill. This was the first time that researchers anywhere had seen bacteria that cause disease get stronger from their interaction with protozoa inside of animals.

“We’ve known for a long time that protozoa are in cattle,” says Rasmussen, a microbiologist. “Protozoa benefit the cow and assist it with digestion." He says protozoa had never before been thought of as organisms in which dangerous microbes could live and multiply.

And there's more bad news! Rasmussen says that the scientists found that there’s something about being inside the protozoa that turns on certain defenses in the Salmonella bacteria that they can use to cause infections later on.

In separate research, Carlson found that protozoa can also play a role in helping disease-causing microbes develop resistance to antibiotics from microbes that already have this resistance.

What are "resistance" and "antibiotics," you ask?

"Resistance" is a living thing's ability to keep other things from harming it. For a person, using a karate chop to fight off an attacker is a form of resistance. For a plant, resistance could be simply tasting nasty to an insect that may want to eat it.

On the other hand, "antibiotics" are medicines that either kill or slow the growth of harmful bacteria. People take them when they have a serious infection.

Anything that helps animals resist antibiotics is important—in a bad way. It means that medicines designed to kill bad bacteria don't work inside the animals. Animals' resistance to antibiotics is one of the biggest worries of ranchers who raise our meat and poultry.

Although the findings by Rasmussen and Carlson are a bit scary, their research is a great thing. First, it's important that scientists study Salmonella, because that bacterium is one of the leading reasons for illness caused by food. Poultry, beef, pork and other foods made from animals and plants have led to people getting sick from Salmonella bacteria.

It's also very helpful to understand how harmful microbes live and multiply. The more we know about them, the easier it will be to find ways to keep them from harming our food animals—and ourselves.

Already, the research at Ames has led to positive things. Rasmussen and Carlson have devised a way to fight the type of Salmonella they found becoming stronger inside the protozoa. They've made a cleansing process that flushes protozoa out of the rumen before the protozoa can help microbes become stronger.

So, take THAT, you nasty microbes!

By Luis Pons, formerly with the ARS Information Staff.

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Last Modified: 4/7/2008
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