In this video, we're going to focus on the bacilli bacterial cell arrangements. Bacilli is the plural form of bacillus, which, recall from some of our previous lesson videos, is one of the 3 main types of bacterial cell morphologies where bacteria take on a rod shape. Bacilli, recall, are rod-shaped bacterial cells. They can only divide across their short axis; they cannot divide along their long axis. For example, if we're looking at a bacilli cell like what you see down here, it can only divide along its short axis. So it can only divide this way; it cannot divide along the long axis. Because bacilli can only divide in one plane, they have fewer possible arrangements than the cocci, which can divide in many different planes. Let's take a look at some of these arrangements for the bacilli.
First, we have a single bacillus, which is actually a single cell, and this is the most common arrangement for bacilli bacteria. You can see that here we have a single cell that has this rod shape, this bacillus morphology. An example of this is E. coli or Escherichia coli. The next arrangement that we have over here is diplobacilli. The root di means 2, and so this arrangement occurs when there are 2 cells that remain attached after division. Notice that this cell divided along its short axis to create 2 cells here, resulting in a chain of 2; that's why it's called diplobacilli. An example of this is Bacillus megaterium, which you can see has a chain of 2 cells in that arrangement.
The next arrangement that we have is streptobacilli. The root strepto refers to a chain, and so this involves bacilli in a chain-like pattern of multiple cells. You can see here there's a chain of multiple bacilli all linked up in a long chain here, and that's why it is streptobacilli. An example of this is Anthracis. You can see the images here, and it has all of these bacterial cells linked in a chain.
Last but not least, what we have over here on the far right is coccobacilli, which is really just a mixture of coccus and bacillus in a diplo format. These are going to be short rod-shaped ovals, or short ovals, that can appear as diplococci. They look a lot like diplococci, and it's very difficult to tell the difference between them unless you're an expert. However, they are slightly different, and they have somewhat of a merge between the coccus and the bacillus. An example of this is Coxiella burnetii, whose arrangement is somewhat of a diplo, but the morphology is a mixture between coccus and bacillus. We refer to these as coccobacilli.
This here concludes our brief introduction to bacilli cell arrangements. We'll be able to get some practice and learn more about arrangements as we move forward in our course. See you all in our next video.