Throughout our lives, we encounter millions of microbes that you would never know are there. Most of them are necessary and important for the functioning of our ecosystem and our own health, but a small percentage of these microbes are pathogens that make us ill. Thankfully with modern science, we have access to many vaccinations that can protect us from these pathogens; however, there are always new things to learn about these pathogens that allow us to make vaccines and treatments more effective and safe for use. One such example of these pathogens is Bordetella pertussis or whooping cough.
Figure 1: A microscopic image of Bordetella pertussis. This image shows the microbes under a compound microscope. Source
Each year, there are roughly 24.1 million cases and 160,700 deaths associated with B. pertussis and while the vaccine for it is the most effective method to avoid transmission, you can still become infected with whooping cough after having the vaccine. This is just one example of how science can always improve itself and the best way to do that is to learn more through important research and discoveries, which is exactly what is still happening with B. pertussis.
Originally, B. pertussis was believed to not be motile or possess flagella, which are long external appendages designed to curl into a corkscrew shape and propel the bacteria into motion; however, it has also been recognized that B. pertussis possesses the genetic blueprint to produce flagellum, so Casandra Hoffman and her team began an investigation to see if B. pertussis could actually produce these flagella necessary to move around, which could have huge implications regarding the bacteria’s ability to create and cause infections in humans.
Figure 2: Diagram of a flagellum on a microbe. This image shows the entire microbe and a zoomed-in, simplified image of the flagella structure. Source
B. pertussis exists in states that indicate what internal mechanisms are activated to cause infections, BVG- and BVG+, representing an inability to cause infections and having the ability to cause infection respectively. The state of the bacteria is key to the meaning of the findings because it will determine if flagella are relevant to infection mechanisms. In order to test their hypothesis that B. pertussis can posses flagellum, the research team manipulated the genetic material of the bacteria in the BVG- state to make it signal for the creation of flagella and then grew and compared it to an unmanipulated (wild type) sample. What they found is that the manipulated version of the bacteria had produced flagella and was able to move as a result. Even the wild type sample was observed to have flagella, though this only happened less than 15% of the time, potentially because of a natural mutation or because of a variation in the BVG- strain.
To test why these wild type bacteria were able to create flagella, samples of BVG- wild type bacteria that had flagella were removed from the agar testing plate and moved to a new plate and were allowed to grow. Agar plates are small dishes filled with nutrients that allow bacteria to grow. After growing, the bacteria had grown into groups of BVG- colonies and BVG+ colonies and both produced some motile bacteria, so this indicates that wild type BVG- bacteria can possess a natural mutation to have flagella.
Figure 3: Electron microscope images of B. pertussis and B. bronchiseptica. These images clearly show the flagella attached to the bacteria. Source
The above figure was taken from the original research article by Hoffman and shows the flagella of B. pertussis. These images were taken under an electron microscope in order to show the flagella since the flagella would not be visible otherwise. An electron microscope is a specific type of microscope that allows a picture to be taken of extremely small and detailed objects. You can read more about electron microscopes here. These bacteria were in the Bvg(-) phase and were taken from the edge of a group of bacteria growing on an agar plate. In these images, the flagella of B. pertussis are clearly shown. Each photo shows a different strain or type of bacteria. Some strains come from B. pertussis while other strains come from a bacterium similar to B. pertussis, but it is called B. bronchiseptica, which does have a flagellum. The strains that come from B. pertussis are the ones listed as BP338 and BP347. These names are simply markers for the specific strain of bacteria with its unique genetic code. The titles before those names (WT or BVG(-)) refer to the specific mutation involving the BVG(-) phase. WT stands for wild type while BVG(-) stands for a mutation that brought B. pertussis into the BVG(-) phase.
The results of this experiment clearly show that B. pertussis can produce flagella like structures. This is an important discovery because it allows scientists to gain new insight into the genetic components that make up flagella with regards to unexpressed genetic blueprints. Testing all of these strains and mutations allow scientists to be confident that many types of B. pertussis can produce flagella and that it is not just a fluke with one bacterium. This is part of the scientific method that is used to make sure science is executed in a way that will not favor certain results. This could lead to new discoveries about flagella in other bacteria. It is also important because now that it is known that B. pertussis has the ability to create flagella we can dive deeper into how flagella are or are not utilized during an infection. Knowing more about how bacteria infect the human body and what they use to cause this infection could allow medical scientists to come up with new and innovative ways to fight infections. Whooping cough is a serious and deadly disease that impacts many. If we can find more effective ways of curing this disease through further research, thousands of lives could be saved.
Figure 4: Cartoon of a boy fighting off microbes with a sword. This image is not to scale. Source
An important development made from this specific study is the demonstration that science is constantly growing and expanding. As we saw, these researchers took the preconceived notion that B. pertussis was not able to move or have flagella and questioned it based on the conflicting information that B. pertussis has the blueprints to make flagella. This is an important example of how scientists and researchers must always question things and build upon the work of others in order to help solidify our understanding of how the world, and specifically pathogens like B. pertussis, operate in our lives.
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