ZnO nanoparticles induced biofilm formation in Klebsiella pneumoniae and Staphylococcus aureus at sub-inhibitory concentrations

Abstract

Abstract Biofilm formation by pathogenic bacteria generates a serious threat to the public health as it can increase the virulence potential, resistance to drugs and escape from host immune response mechanisms. Among the environmental factors that influence the biofilm formation, there are only limited reports available on the role of antimicrobial agents. During the antimicrobial drug administration or application for any purpose, the microbial population can certainly be exposed to sub-minimum inhibitory concentration (sub-MIC) which will have diverse impact on microbial responses. Hence, the study was conducted to investigate the effects of sub-MIC levels of new-generation antimicrobial agents, the nanoparticles on the biofilm formation of Klebsiella pneumoniae and Staphylococcus aureus by taking zinc oxide nanoparticles (ZnO NPs) as the candidate nanomaterial. Here, the selected bacteria were screened for their ability to form biofilm using the Congo Red Agar method and the antibacterial activity of ZnO NPs was also evaluated. The direct quantification of biofilm formed by selected organisms in the presence of sub-MIC levels of ZnO NPs was further carried out by using the microtiter plate-crystal violet assay. Further, the samples were studied by atomic force microscopy (AFM) to evaluate the properties and pattern of biofilm modulation under different conditions. From these, the organisms treated with sub-MIC levels of ZnO NPs were found to have enhanced biofilm formation when compared with the untreated sample and no growth could be observed for samples treated with the minimum inhibitory concentration (MIC) of ZnO NPs. The results observed in the study provide key insights into the diverse impact of nanomaterials on clinically important microorganisms which demands critical thinking on the antimicrobial use of nanomaterials.