Abstract
A biofilm is an assemblage of microbial cells attached to a surface and encapsulated in an extracellular polymeric substance (EPS) matrix. The formation of a biofilm is one of the important mechanisms of bacterial resistance, which not only leads to hard-to-control bacterial infections in humans and animals but also enables bacteria to be a major problem in various fields, such as food processing, wastewater treatment and metalworking. Quorum sensing (QS) is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small diffusible signaling molecules called autoinducers (AIs). Bacteria use QS to regulate diverse arrays of functions, including virulence and biofilm formation. Therefore, the interference with QS by using QS inhibiting agents, including QS inhibitors (QSIs) and quorum quenching (QQ) enzymes, to reduce or even completely repress the biofilm formation of pathogenic bacteria appears to be a promising approach to control bacterial infections. In this review, we summarize the mechanisms of QS-regulating biofilm formation and QS-inhibiting agents that control bacterial biofilm formation, strategies for the discovery of new QS inhibiting agents, and the current applications of QS-inhibiting agents in several fields to provide insight into the development of effective drugs to control pathogenic bacteria.
Highlights
A biofilm is a large number of bacterial cell aggregates coated in an extracellular mucous comprised of a polysaccharide matrix, lipids, and proteins, which they secrete (Sutherland, 2001; Branda et al, 2005)
Kim et al (2011) immobilized a quorum quenching (QQ) enzyme onto a nano-filtration membrane, and found the acylase-immobilized membrane prohibits the formation of the mushroom-shaped mature biofilm and prevents more than 90% of the initial flux after 38 h operation, while the unimmobilized raw membrane dropped to 60% accompanied by severe biofouling
Conventional antibiotics and bactericides cannot penetrate the extracellular matrix of biofilms, resulting in decreased bacterial sensitivity, and biofilm-related pollution poses serious problems in many fields, including the environment, food, and human diseases
Summary
A biofilm is a large number of bacterial cell aggregates coated in an extracellular mucous comprised of a polysaccharide matrix, lipids, and proteins, which they secrete (Sutherland, 2001; Branda et al, 2005). Bacteria tend to form biofilms when exposed to external environmental pressure, such as extreme nutrient deficiency or excess, high osmotic pressure, low pH, oxidative stress, antibiotics and antimicrobial agents (Costerton et al, 1994). It is a state of self-protection formed when bacteria grow on the surfaces of objects under natural conditions. More than 60% of all bacterial infections are caused by biofilm formation, according to a public announcement from the National Institutes of Health (NIH) (Lewis, 2001). The formation of biofilms leads to common bacterial infections, such as infections of the urinary tract, catheters, children’s middleear, common dental plaque formation, and gingivitis, and to hard-to-treat or relapsing infections and severe infections that cause serious morbidity and mortality (Lewis, 2001)
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