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Microscopic Morphology of Bacteria – How Do They Look Under the Microscope?

Last Updated: 06.12.21


If you’re a lot into exploring and your need to quench your curiosity has now taken you to the realm of microorganisms, getting a good microscope to help you with that might not be enough if you want to actually understand what you see when using such a device. You can check out various resources for more info on such instruments yet a bit of biology theory is also needed.

To help you identify the various types of bacteria and do so easily and properly, we have briefly described below some of the characteristics that set each type apart, so check out this post to learn more about bacteria morphology.

Types of bacteria based on morphology

There are many organisms that we cannot see with the naked eye yet, thanks to the latest technological achievements, we can easily discover a new world. Here is where microscopes come into sight.

Many of us tend to get a bit of a shiver when the word bacteria is uttered but these microorganisms are everywhere. It’s true that while some of them are beneficial, others are harmful and, when growing in great numbers, may cause various health issues. That’s why examining them under a microscope is now a common procedure in the medical field.

Still, if you’re interested in learning more about these single-celled organisms as a spare time activity, getting the bacteria under your microscope, after you’ve taken the appropriate steps for a proper observation, might not tell or show you much if you don’t know a few basic things about the various types of bacteria.

You may not want to know everything in minute detail but being able to identify some of the most common bacteria will surely trigger some sort of contentment. Even if these organisms are very small, they come in a variety of shapes and sizes. Based on their shape, bacteria are divided into the following categories.

The most common ones are the Coccus bacteria, known as cocci, that have a spherical or even ovoid shape. This type of microorganisms is further divided into other subclasses including the Diplococcus, Streptococcus, and Staphylococcus.

These bacteria occur in pairs (diplococci), as a long chain (streptococci), in clusters (staphylococci), or even in groups of four (tetrads) thus forming a square structure.

Examining microorganisms under the microscope will also enable you to see rod-like bacteria and when that happens you probably have a Bacillus in front of your eyes. Found in a variety of taxonomic groups of bacteria, bacilli may occur either as single cells, pairs, or chains.

A microscope session can also get you to see the so-called Vibrios, comma-shaped bacteria that got their name from their vibratory motility. They feature a flagellum on one end, which enables them to move around.

Unlike these bacteria, Spirilla have a flagellum on each of their two ends, a feature that helps them move faster in an aquatic environment. As their name suggests, these microorganisms have a spiral shape.

Of course, based on morphology, there are other types of bacteria. You will also find the Spirochetes that have a flexible spiral form with a type of motion that has been associated with a corkscrew motion, the Actinomycetes, which get their name from their resemblance with the sun rays, and the Mycoplasmas.

The latter type comes in different shapes because these microorganisms lack cell walls and thus change their morphology. They can occur as elongated or spherical bodies and even as interlacing filaments.

Types of bacteria based on how they stain

You may have heard of gram-positive and gram-negative bacteria and wondered about the meaning of this. Bacteria can be further divided into these two types based on how they stain. The gram-negative bacteria lose their primary stain during decolorization because their Peptidoglycan layer is thin.

However, when viewing them under the microscope, you will see that they will have a reddish color as a result of the stain used (safranin). This type of bacteria includes Escherichia coli, Salmonella spp, and Enterobacter spp.

The gram-positive bacteria are the opposite and thus retain the primary stain. That’s possible because of the thickness of their Peptidoglycan layer. These microorganisms appear bluish or purple under the microscope. Examples of gram-positive bacteria include Clostridium botulinum and Staphylococcus epidermidis.

How to get your bacteria ready for observation

Now, getting to that part where you actually observe and identify the above-mentioned microorganisms requires a few steps. The first phase is to grow the bacteria in culture media. There are various ways to do that. If, for example, you want to observe Staphylococcus, you can opt for the basal media.

In case you need to grow a specific type of bacteria yet prohibit others from doing so, it is recommended to use selective media such as the Lowenstein-Jensen media. Then you can also employ the enriched media that will help you grow a specific type of bacteria by adding a special component. If you want to grow Streptococci, adding blood will help you with that.

Your specific needs will help you choose the right media to get your bacteria ready for observation. Once you’ve taken care of this step and your bacteria sample is ready, you will have to get the following: distilled water, a Bunsen burner, an inoculating loop, a dropper, a marking pencil, and, of course, a compound microscope and a glass slide.

If you’re all set up, start your lab session by marking a circle on a clean slide in order to have a spot for the smear. This is where you should place the distilled water with the dropper. In case you use the loop, flame it with the Bunsen burner. If you have chosen broth for the media, it is no longer necessary to use distilled water. Also, ensure that the dropper is clean and you use just a drop of water.

Make sure the loop is being passed through the flame and cooled before you scoop the bacteria sample from the Petri dish or the tube you’ve used to grow the microorganisms. If you want to preserve the remaining of the sample and thus avoid contamination, flame the tips of the tube and cover it with the lid only after you’ve done that.

Once you’ve scooped the sample, mix it with the distilled water you’ve placed on the slide and let it air dry completely. To help the stain penetrate the cells better, pass the slide over the flame a few times to fix the smear.

To stain the bacteria sample, you will have to cover it with a gram stain for one minute. You can use safranin, methylene blue, or crystal violet. If there’s too much stain, remove the excess by gently running a bit of water along the slide. Use absorbent paper to remove excess stain or water.

Your sample should now be ready for observation. Make sure you start with low power, though. In case you want to use high power, you should add immersion oil. If you follow these steps, you should be able to observe these microorganisms properly.

There are various staining methods and stain types you can use. They vary since the observation purposes and the specimens used vary. Once you’ve chosen the stain and the method you want to employ, be sure you get all the necessary information to carry out this procedure properly and thus enjoy satisfying results.

A little mistake may affect what you see when you place the sample under the microscope. That’s why utmost attention is required throughout the entire process. Regardless of your observation purposes, the process itself can be a feast for those interested in diving into what cannot be seen without special instruments such as microscopes.



Ioana Moldovan

Ioana’s professional experience in the optics field has helped her understand the value of passing her knowledge forward. Her curious personality helps her gather useful information for her readers and her goal is to make technical information fun and accessible to everyone.

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