Brief Outline about Biofilm Resistance to Antimicrobials

Abstract

Background: Antibiotic molecules ought to penetrate throughout the biofilm matrix to impact the covered cells. The extracellular polymeric matrix influences the amount of the molecule, which is transferred to the inner layer of biofilm and interacts with an antibiotic agent, so it provides an anti-spread barrier for an antimicrobial agent. Biofilm EPS confers a physical barrier containing numerous anionic and cationic molecules such as proteins, glycoproteins, and glycolipid that can bind charged antimicrobial agents and provide shelter for microorganisms. For example in Pseudomonas aeruginosa biofilms, Pel exopolysaccharides, an EPS component is able to spread cationic antibiotics such as aminoglycosides and, thus, provides tolerance to these molecules. During growth in biofilm structures, physiological heterogeneity happens due to the occurrence of oxygen and other nutrients gradient in biofilms. This gradient is created because cells that are close to the surface of the biofilm consume obtainable nutrient sources and oxygen before the nutrients disperse into depth of the biofilm. In the biofilm, cells coexist with different genotypes and phenotypes. This leads to expression of distinct metabolic pathways depending on the local environmental conditions in the biofilm. The metabolic activity of bacteria is high in the outer part of the biofilm, while it is low in the inner part. Many antibiotics are directed against processes occurring in growing bacteria e.g. replication, transcription, translation & cell wall synthesis. So, increased antimicrobial tolerance will be found in biofilm bacteria with low metabolic activity located in the inner part of biofilms.