In 2009, a Princeton professor named Bonnie Bassler first presented the science in a presentation titled “How bacteria ‘talk.’” If you are not familiar with quorum sensing, consider this a brief intro to the revolutionary discoveries that paved the way for the innovative technologies helping to improve how we fight pathogenic bacteria.
Bacteria have been formidable opponents of humans since their discovery in 1676 by Dutch scientist Antoni van Leeuwenhoek. For hundreds of centuries, we considered bacteria to be rather simple organisms, living simple existences. We made vast improvements in human health when we realized the benefits of hygiene and importance of handwashing, which was not easily accepted by the scientific community when it was first introduced in 1847. In fact, it took nearly 20 years for this now-common practice to gain widespread acceptance.
It was not until 1928, more than 250 years after we first realized their existence, that humans discovered the power of penicillin to kill bacteria. Again, it took nearly 20 years before penicillin first became available for medical use. Today, antibiotics are used to treat a wide range of bacterial infections in humans and animals, but their efficacy seems to be declining as these bacteria continue to evolve. The phrase “antimicrobial resistance” is becoming more and more common, but how do bacteria become resistant? Are we truly creating super-bugs that cannot be killed, or are they simply outsmarting us in a different way – perhaps through their advanced communication system known as quorum sensing?
The term “quorum sensing” was first introduced by Dr. Steven Winans in 1994 to describe the unique biochemical communication system. Since then, Bassler and her lab at Princeton University have made groundbreaking discoveries into quorum sensing and introduced ideas on different ways we can fight bacteria and help the immune system clear out infections by disrupting this process.
As the unique communication system of bacteria, quorum sensing controls a long list of functions, but today we will focus on three critical functions which are most important to understand. We will walk through each of these functions to understand them in detail and illustrate the benefits of disrupting quorum sensing by comparing a bacterial attack to a military invasion.
Function 1 – Identification
There are thousands of bacteria that exist within the body. We know some bacteria perform helpful functions, such as the microbes in the rumen that help ferment feedstuffs, while other bacteria create harmful disease such as Escherichia coli (E. coli), which cause mastitis. Quorum sensing is how these different species of bacteria identify themselves and count population levels. This is critical because a single bacterium launching an attack on a huge host, such as a cow, would have minimal impact.
Imagine one enemy soldier invading a foreign country – if he immediately started shooting, he would have little chance of taking the region. Instead, he patiently blends in until, and awaits the arrival of, his fellow soldiers to launch an attack that stands a chance of winning. This is how we now understand bacteria to operate. A Staph aureus cell enters the cow from her environment and starts multiplying to build up an army. The army patiently bide their time, utilizing quorum sensing, to know when the time is right to launch an attack.
Function 2 – Coordination
The next critical function quorum sensing enables is coordination. Bacteria synchronize gene expression, and produce toxins in unison, to launch an impactful attack on a host. Scientifically, this is known as virulence – the ability to cause damage to the host. Virulence is controlled by quorum sensing. As we think about our army example, it is the communication function that tells the soldiers which type of weapon to arm themselves with. The type of weapon selected has a significant impact on the success of the attack – are they arming themselves with swords, machine guns or an atomic bomb? Every host’s defense system (immune system) is able to fight at varying levels as well, which impacts the outcome of the battle. While different bacteria have different levels of virulence, what is key is that all bacteria utilize quorum sensing to create virulence.
Function 3 – Protection
Now that the bacteria have armed themselves and coordinated an attack plan, the final step in preparing for battle is to develop their defense system, known as biofilm. A biofilm is a cluster of cells enclosed in a self-produced matrix (mucopolysaccharide layer) or, metaphorically speaking, an armored, camouflaged tank for the enemy soldiers to hide in. Research has shown that a host’s immune system, as well as antibiotics, have been unable to reach bacteria in biofilms. Staphylococcus aureus is one bacteria known to produce biofilm, which can attach in the udder of the cow. This helps explain why these chronic cases of mastitis are so difficult.
It’s easy to see if a host (human or bovine) doesn’t have a strong immune system, it can quickly fall ill to a powerful bacterial attack. Just like if an army does not have a strong defense system in place, this coordinated attack can quickly become overwhelming and weaken the system, especially if the invading army is coming in with guns and the local army only has swords.
Now that we understand how bacteria utilize quorum sensing, and the key functions quorum sensing enables, scientists see new possibilities to fight bacteria differently – to move from hand-to-hand combat and disrupt the entire strategy by shutting down this sophisticated communication system. When we introduce technologies that inhibit quorum sensing, we can better prevent bacteria from forming the army, launching an attack and building up impenetrable biofilm.
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