In Vivo vs. In Vitro: What Does It All Mean?

Below, we’ll explore some definitions in more detail and discuss what each term means in various contexts.

In vivo

In vivo is Latin for “within the living.” It refers to work that’s performed in a whole, living organism.

In vitro

In vitro is Latin for “within the glass.” When something is performed in vitro, it happens outside of a living organism.

In situ

In situ means “in its original place.” It lies somewhere between in vivo and in vitro. Something that’s performed in situ means that it’s observed in its natural context, but outside of a living organism.

Now that we’ve defined these terms, let’s explore some real-life examples of them.

Studies

In vitro, in vivo, or in situ methods are used in scientific studies. In some cases, researchers may use multiple methods to test their hypothesis.

In vitro

In vitro methods used in a laboratory can often include things like studying bacterial, animal, or human cells in culture. Although this can provide a controlled environment for an experiment, it occurs outside of a living organism and results must be considered carefully.

In vivo

When a study is performed in vivo, it can include things like performing experiments in an animal model, or in a clinical trial in the case of humans. In this case, the work is taking place inside a living organism.

In situ

In situ methods can be used to observe things in their natural context, yet outside of a living organism. A good example of this is a technique called in situ hybridization (ISH).

ISH can be used to look for a specific nucleic acid (DNA or RNA) within something like a tissue sample. Specialized probes are used to bind to a specific nucleic acid sequence that the researcher is looking to find.

These probes are tagged with things like radioactivity or fluorescence. This allows the researcher to see where the nucleic acid is located within the tissue sample.

ISH allows the researcher to observe where a nucleic acid is located within its natural context, yet outside of a living organism.

Fertilization

You’ve likely heard of in vitro fertilization (IVF). But what exactly does that mean?

IVF is a type of treatment for infertility. In IVF, one or more eggs are removed from an ovary. The egg is then fertilized in a laboratory and implanted back into the uterus.

Because fertilization occurs within a laboratory environment and not within the body (in vivo), the procedure is referred to as in vitro fertilization.

Antibiotic sensitivity

Antibiotics are medications that work to treat bacterial infections. They do this by disrupting the bacteria’s ability to grow or thrive.

There are many types, or classes, of antibiotics and some bacteria are more sensitive to some classes than others. Additionally, bacteria can evolve to be resistant against antibiotics.

Although bacterial infections occur on or in our bodies, antibiotic sensitivity testing often occurs within a laboratory setting (in vitro).

Now that we’ve gone over the definitions and explored some examples, you may be wondering if there are pros or cons to using one over the other.

There are a few factors to consider when comparing in vitro and in vivo work. These can include:

Context

As a reminder, something that’s in vivo is in the context of a living organism while something that’s in vitro isn’t.

Our bodies and the systems that comprise them are very complex. Because of this, research done in vitro may not accurately replicate conditions that occur inside the body. Therefore, results must be interpreted carefully.

An example of this is in vitro versus in vivo fertilization.

In vivo, very few sperm actually go on to potentially fertilize the egg. In fact, selection of specific sperm populations is mediated in the fallopian tube. During IVF, sperm selection can only be partially mimicked.

However, the dynamics of selection within the fallopian tube as well as the qualities of the sperm populations selected in vivo is an area of increased study. Researchers hope that findings will better inform sperm selection for IVF.

Correlation

In some cases, something you observe in vitro may not correlate with what actually happens in vivo. Let’s use antibiotic sensitivity testing as an example.

As we discussed earlier, antibiotic sensitivity testing can be performed using several in vitro methods. But how do these methods correlate with what actually happens in vivo?

One paper addresses this question. The researchers found some inconsistencies in the results of in vitro testing versus actual clinical outcomes.

In fact, 64 percent of people infected with bacteria reported as resistant to the antibiotic cefotaxime were judged to have responded favorably to treatment with the antibiotic.

Changes

In some cases, an organism can adapt to an in vitro environment. This may in turn affect results or observations. An example of this is how the influenza virus changes in response to laboratory growth substrates.

Influenza, or the flu, is a respiratory infection caused by the influenza virus. In research laboratories, the virus is often grown in chicken eggs.

It’s been observed that clinical isolates of the virus can form particles that are long and filamentous in nature. Continued growth in eggs can sometimes, but not always, change the shape of the virus from filamentous to spherical.

But viral shape isn’t the only thing that can be impacted by adaptation to eggs. Egg-adaptive changes that occur in vaccine strains can impact vaccine effectiveness.

In vitro and in vivo are two terms that you may encounter occasionally, particularly when reading about scientific studies.

In vivo refers to when research or work is done with or within an entire, living organism. Examples can include studies in animal models or human clinical trials.

In vitro is used to describe work that’s performed outside of a living organism. This can include studying cells in culture or methods of testing the antibiotic sensitivity of bacteria.

The two terms are essentially opposites of each other. But can you remember which is which? One way to do this is to note that in vivo sounds like words referring to life, such as live, viable, or vivacious.