Molecular mechanisms of biofilm resistance against antibiotics

Abstract

Biofilms are immobile communities of microbes attached to biotic an abiotic surfaces and are embedded inside a self-produced cement-like extracellular polymeric substances. The resistance of biofilms against commonly used drugs has been implicated in the pathogenesis of various bacterial infections under medical and veterinary settings which normally cannot be eradicated by antibiotics. Biofilms are characterized by the ability to evade not only the antibiotic effects but also the host immune system clearance. Currently the most worrisome aspect of global human health is the rise and spread of antimicrobial resistance in bacterial pathogens and this crisis got deepened by the emergence of antimicrobial resistance of bacterial biofilms. Different antibiotic resistance mechanisms, processes by which a target pathogen curtails the interaction between an antimicrobial agent and its intended target molecules, adopted by biofilms have been discussed in this review. Different antibiotic resistance mechanisms are employed by the biofilms depending on the species of the bacteria, growth conditions, and the antibiotic involved. Commonly, the role of biofilm matrix polysaccharides, antibiotic-modifying or degrading enzymes, extracellular DNA, hypoxic conditions, presence of efflux pumps, quorum sensing, horizontal gene transfer, mutation frequency, etc. have been implicated in antibiotic resistance of biofilms. This review also discusses different approaches of overcoming biofilm infections or biofilm resistance. However, it is pertinent to mention that since no new class of antibiotics have been approved in last four decades there is the need of greater understanding of biofilm-associated antibiotic resistance to effectively utilise the therapeutic value of the existing antibiotics. Although a number of anti-biofilm strategies have been put forward as discussed in this review, they are still in nascent stage and need to undergo clinical trials to reach the commercial market.