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Aerobic Gram-Positive Bacilli: Characteristics, Types & Examples

Aerobic Gram-Positive Bacilli: Characteristics, Types & Examples
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  • 0:04 Different Bacteria
  • 0:33 Characteristics & Examples
  • 1:48 Lab Tests
  • 4:49 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson is going to define and characterize the major aspects of aerobic Gram-positive bacilli. You'll learn numerous examples of such bacteria as well as the many ways by which they can be identified. A case example is presented as well.

Different Bacteria

Bacteria come in all shapes and sizes, and they even differ in the ways they live inside and infect us. Some of them are circular in shape, and others are rod-shaped. Most are extremely tiny, but some can actually be seen with the naked eye. Some love oxygen, and others despise it.

This lesson is going to go over some types and examples of something called aerobic Gram-positive bacilli, including some of their characteristics and lab methods that can be utilized to identify them.

Characteristics & Examples

Aerobic Gram-positive bacilli will have the following characteristics:

  • They're bacteria that have a rod-like shape, hence the term bacilli.
  • They're microorganisms that grow in the presence of oxygen. In one word, they are aerobic. This lesson also includes examples of bacteria that can either grow in the presence of oxygen or, at the very least, tolerate its presence.
  • They have a thick cell wall, ergo they are Gram-positive bacteria.

Some examples of such Gram-positive bacilli include the following:

  • Bacillus. This includes Bacillus cereus and Bacillus anthracis, among others.
  • Clostridium, including Clostridium botulinum, Clostridium tetani, Clostridium difficile, and Clostridium perfringens.
  • Corynebacterium, such as Corynebacterium diphtheriae and Corynebacterium jeikeium.
  • Listeria, such as Listeria monocytogenes.
  • Erysipelothrix, like Erysipelothrix rhusiopathiae.
  • Lactobacillus, as per Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus acidophilus.
  • Gardnerella, as per Gardnerella vaginalis.

Lab Tests

So how can these bacteria be identified in the lab? There's actually more than one method to help you do this.

Laboratory examination of any microscopic organism involves the examination of stained and fresh unstained materials as well as the culture of the organism that's most likely to have caused the person's illness based on clinical evidence. For example, when you receive a specimen from a person suspected of having some kind of bacterial infection, you should smear the specimen on a glass slide and Gram-stain the slide. Place it on a microscope and look for tell-tale signs of Gram-positive reaction (a purple color to the microorganism) and for its shape (like a rod). With respect to culturing the organism, many aerobic and facultatively anaerobic bacteria will grow on what is known as blood agar. This is a standard culture medium made with 5% sheep blood. The presence of various bacteria can also be detected with ELISA, or enzyme-linked immunosorbent assays, western blot immunoassays, polymerase chain reactions, mass spectrometry, and many other types of laboratory tests.

Let's go over a specific example of how this may be utilized. Let's say that someone is suspected of contracting anthrax. In this case, specimens should be collected from blood, pleural fluid, cerebrospinal fluid, or pus (or other fluid) from a lesion. When you stain a smear of such a specimen, you'll visually see chains of relatively large Gram-positive bacilli.

B. anthracis under the microscope
B. anthracis under the microscope

You're right on track! When you grow these bacteria on blood agar media, the organisms will produce colonies with several key features you should recognize as those of B. anthracis. Check out the image on your screen. The red circular area near the top represents an area where bacteriophages were applied to the colonies to destroy them, and thus confirm the presence of B. anthracis in the colonies

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