Quorum sensing
Quorum sensing is a biological communication process used by bacteria to coordinate their behavior based on population density. Bacteria, which are single-celled prokaryotic organisms, produce signaling molecules that facilitate this communication. When bacteria are sparse, these molecules dissipate, but as their numbers increase, the concentration of these signals builds up, triggering changes within the bacterial community. This process allows bacteria to adapt to their environment, often waiting until their population is sufficient to evade the host's immune system or to enhance their virulence. Different bacterial strains utilize various signaling mechanisms, making inter-strain communication unlikely and promoting cooperation within the same strain. Researchers have developed quorum-sensing inhibitors (QSIs) that disrupt this communication, potentially preventing bacteria from developing harmful traits associated with infections. These QSIs are being explored as treatments, especially in the context of antibiotic-resistant bacterial strains, providing a novel approach to managing bacterial infections.
On this Page
Subject Terms
Quorum sensing
Quorum sensing is a biological process used by bacteria to communicate with one another. Bacteria are single-celled organisms that do not contain a nucleus. Some strains of bacteria are harmful, causing the development of serious illnesses. Other bacteria, such as those that aid with digestion, are necessary for the human body to function.
Many bacteria produce molecular signals, which dissipate when a bacterium is solitary. However, when bacteria are highly concentrated, the molecular signals build up. This triggers changes in the bacteria, allowing them to adapt to their environments. Bacteria commonly use quorum sensing to avoid notice by the immune system until they are numerous enough to overwhelm the immune cells. Other bacteria use quorum sensing to regulate growth or the development of defenses against other microorganisms.
Scientists have developed a series of drugs designed to interfere with quorum sensing. This confuses the bacteria, sometimes stopping them from developing harmful traits associated with bacterial infections. Researchers hope that these medications will be able to assist doctors in treating antibiotic resistant bacterial infections.
Background
Bacteria are microscopic, single-celled organisms. They live in most places throughout the world, including inside the human body. Bacteria are classified as prokaryotes, single-celled, microscopic organisms that lack a nucleus and internal structures surrounded by membranes. Instead of a nucleus, bacteria have other mechanisms for storing DNA and passing it along to future generations. Ribosomes within the cell utilize RNA and amino acids to create proteins. Most bacteria also contain both a cell membrane and a cell wall. Some bacteria lack a cell wall, while other bacteria are encased in a third layer called a capsule.
Bacteria are commonly divided into three shapes. Cylindrical bacteria are called bacilli, spiral bacteria are called spirilla, and round bacteria are called cocci. Though some bacteria occur in other shapes, bacilli, spirilla, and cocci are encountered most often. Most bacteria reproduce through either binary fission or budding. During fission, the bacterium cell copies its DNA, then begins to grow larger. Eventually, the cell splits in two, creating a pair of smaller bacteria. During budding, a child cell begins as a small offshoot of the parent cell. Once the child cell becomes large enough, it breaks off, becoming an independent bacterium.
Some bacteria are hostile to the human body, causing infections. Certain strains of E. coli and Streptococcus bacteria are naturally found within the human body. They are necessary for the body’s digestive tract to properly function. However, other strains of these bacteria can cause serious illness if allowed to enter the body. Often, specialized antibiotic medications are required to treat the illnesses caused by bacterial infections.
Over time, many strains of bacteria have become resistant to antibiotics. This can be caused by the unnecessary use of antibiotics, or by ending antibiotic doses before the entirety of the infection has been destroyed. For this reason, doctors are now more careful when prescribing antibiotics to patients.
Overview
Science has shown that bacteria have developed unique means of communicating with one another, allowing them to act in a social manner and to cooperate with one another. One of the means by which bacteria communicate is through quorum sensing. Quorum sensing is a type of signalling that occurs between bacterial cells. It allows one cell to send signals to another cell, triggering a specific sequence of changes within the cell. Quorum sensing allows this sequence to occur once population levels of the bacteria have reached a specific threshold within a given system.
Many bacteria begin broadcasting a quorum sensing signal when they first enter a new host. As the bacteria increase in number within a given area, the signal grows stronger. Once the signal reaches a specific point, a change is triggered in the bacterial cells. This signal is usually conducted through the creation of signaling molecules, which are produced by the bacteria. While the bacteria are present in a low density, the molecules drift away. At high density, the buildup of signaling molecules triggers changes within the cells. The changes that occur in bacteria once a specific bacterial density has been met are already present within the genetic code of the bacteria. However, expression of those genes is usually restricted until after quorum sensing leads to their activation.
Several methods for quorum sensing are used by different bacterial strains. Different bacteria utilize different types of signaling mechanisms, often producing different types of signaling molecules. For this reason, different strains of bacteria are usually unable to communicate with one another. Scientists believe that this evolved to ensure that bacteria only cooperate with bacteria of the same strain, increasing the cooperation between bacteria of different strains.
The intercellular communication allowed by quorum sensing provides bacteria with a better chance of survival. With quorum sensing, bacteria can change their traits throughout the different stages of an infection. For example, some bacteria utilize quorum sensing to remain relatively harmless during the early stages of the infection. This avoids the host’s notice and helps hide the bacteria from attacks by the host’s immune system. However, once the bacteria have reached a population level where they can easily overwhelm the immune system, quorum sensing may cause bacteria to increase their virulence and activate defenses against attacks. Beneficial bacteria sometimes utilize quorum sensing to trigger increased cell growth, bioluminescence, and many other factors.
Scientists have developed specialized drugs, known as quorum-sensing inhibitors (QSIs), that interfere with bacterial quorum sensing. QSIs confuse the bacteria, reducing the emergence of traits harmful to humans. Such drugs are being tested on their own and in combination with antibiotics as alternative clinical approaches to treating antibiotic-resistant pathogens.
Bibliography
Abisado, Rhea G., et al. “Bacterial Quorum Sensing and Microbial Community Interactions.” American Society for Microbiology, vol. 9, no. 3, 22 May 2018, doi.org/10.1128/mbio.02331-17. Accessed 18 Dec. 2024.
Cella, M.A., Coulson, T., MacEachern, S., et al. “Probiotic Disruption of Quorum Sensing Reduces Virulence and Increases Cefoxitin Sensitivity in Methicillin-Resistant Staphylococcus Aureus.” Sci Rep, vol. 13, 2023, doi.org/10.1038/s41598-023-31474-2. Accessed 18 Dec. 2024.
Hetta, H.F., Ramadan, Y.N., Rashed, Z.I., et al. “Quorum Sensing Inhibitors: An Alternative Strategy to Win the Battle against Multidrug-Resistant (MDR) Bacteria.” Molecules, vol. 29, no. 15, 2024, pp. 3466, doi.org/10.3390/molecules29153466. Accessed 18 Dec. 2024.
LaSarre, Breah, and Michael J. Federle. “Exploiting Quorum Sensing to Confuse Bacterial Pathogens.” Microbiology and Molecular Biology Reviews, vol. 77, no. 1, Mar. 2013, pp. 73–111, doi.org/10.1128/MMBR.00046-12. Accessed 18 Dec. 2024.
Miller, Melissa B., and Bonnie L. Bassler. “Quorum Sensing in Bacteria.” Annual Review of Microbiology, vol. 55, Oct. 2001, pp. 165–199, doi.org/10.1146/annurev.micro.55.1.165. Accessed 18 Dec. 2024.
Naga, N.G., et al. “It Is the Time for Quorum Sensing Inhibition as Alternative Strategy of Antimicrobial Therapy.” Cell Commun Signal, vol. 21, no. 133, 2023, doi.org/10.1186/s12964-023-01154-9. Accessed 18 Dec. 2024.
Rutherford, Steven T., and Bonnie L. Bassler. “Bacterial Quorum Sensing: Its Role in Virulence and Possibilities for Its Control.” Cold Spring Harbor Perspectives in Medicine, vol. 2, no. 11, Nov. 2012, doi.org/10.1101/cshperspect.a012427. Accessed 18 Dec. 2024.
Verbeke, Federick, et al. “Peptides as Quorum Sensing Molecules: Measurement Techniques and Obtained Levels In Vitro and In Vivo.” Frontiers in Neuroscience, 11 Apr. 2017, doi.org/10.3389/fnins.2017.00183. Accessed 18 Dec. 2024.
Vidyasagar, Aparna, and Stephanie Pappas. “What Are Bacteria?” LiveScience, 14 Oct. 2021, www.livescience.com/51641-bacteria.html. Accessed 18 Dec. 2024.
Wang, J., Lu, X., Wang, C., et al. “Research Progress on the Combination of Quorum-Sensing Inhibitors and Antibiotics against Bacterial Resistance.” Molecules, vol. 29, no. 7, 2024, pp. 1674, https://doi.org/10.3390/molecules29071674.