Can you make bread with the yeast in beer?

Made bread today by replacing the yeast and half the water with hefeweizen beer I brewed recently. I used equal parts beer and water, along with a little sugar, to make a yeast starter, thereby multiplying the amount of yeast present. Works great and provides hints of the distinctive hefeweizen underflavors of clove and banana. My advice is to experiment! Use unfiltered, unpasteurized beer to make a starter, remembering yeast is very sensitive to rapid temperature changes. Gradually warm everything to room temperature before combining!

Depends on the beer.

In Germany we a beer called "Weißbier" or "Hefeweizen" which you can actually use for baking.

The recipe 100ml "Hefeweizen" 15g flour 10g sugar => mix it => after 20h you have the equivalent of 25g yeast

I don't believe you would want to try to leaven bread with beer only, though you could certainly use it as a flavoring.

First, the amount of yeast still present in a brewed batch of beer is very low. Beers that have been bottle carbonated (or bottle conditioned) will have more than others but, particularly with high gravity beers (beers with a lot of alcohol), a lot of the yeast has died due to the alcohol content or been removed by the manufacturer to clarify the brew (yeasts make beer cloudy).

Plus, beer yeast and bread yeast are very different things:

From the info here:

Different strains of Saccharomyces cerevisiae produce different proportions of carbon dioxide and alcohol. Baker's yeast is a blend of several strains of Saccharomyces cerevisiae chosen for their flavor and ability to make carbon dioxide, which causes bread to rise. Brewer's yeast is made of strains chosen for their alcohol-producing ability and tends to have a bitter flavor. Brewer's yeast is considered an inactive yeast while baker's yeast is an active yeast. In an active yeast the yeast cells are still alive, whereas they are killed in the process of making inactive yeasts, like brewer's yeast.

Brewer's yeast is used to brew homemade wines and beers, while baker's yeast makes bread rise. You can't brew alcohol with baker's yeast and you can't leaven bread with brewer's yeast.

As Catija has mentioned, the yeast in beer is dead and typically filtered out.

There does exist a class of recipes that are 'beer breads', in which you add beer or similar bubbly beverage ... but they're quick breads, not yeast breads.

Unlike using sparkling water in tempura, or beer cider in a beer batter, where you rely on the trapped bubbles to give the lift when it's fried, most beer breads also add some baking powder or baking soda to assist on the lifting.

I am not aware of any baked loaf breads that rely on lift solely from beer. You might have some flatbreads flavored with beer, that don't have other lifting agents, but that's not your typical loaf bread.

I've harvested some yeast from bottle conditioned beer and started it off with a small amount of cooled boiled water and sucrose. Not much seemed to happen at first but after a couple of days it's apparent that the yeast is live. Next step is to grow the amount of yeast to a sensible amount for baking. Another teaspoon of sucrose and whirl it around resulted in massive improvement in the froth on top of the culture. Should be ready to bake in a couple of days and I'll be keeping some culture back to use on another bake if the taste is good.