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Background & Objectives: Bacterial biofilms a multi-layered defence, comprise extracellular DNA (eDNA) and proteins, protect bacteria from harmful environment and nutrient limitation and utilize the mutual benefits within a community. Bacterial biofilms also defend bacteria from harsh environments such as antibiotic treatment. This leads to poor antibiotic penetration, slow growth, adaptive stress responses, and formation of persister cells. This study was done to determine the relation of antibiotic resistance deciphered by the biofilms in Lactobacillus plantarum, a lactic acid bacteria (LAB) with probiotic significance., Methods: The gentamicin-resistant L. plantarum isolates were allowed to form biofilms and subjected to DNase I and proteinase K treatment. The optical density (OD) values were recorded for the biofilm assay and the cell count for the number of viable cells was taken for the control and the test samples. Percentage reduction was calculated based on the difference between the initial and final OD for both the parameters., Results: The biofilm assay revealed that the native L. plantarum isolates which were phenotypically susceptible, possessed the ability to form biofilms. The OD values were significantly decreased in comparison to the biofilm-forming control culture when these were treated with DNase I and proteinase K., Interpretation & Conclusions: The study revealed that the biofilms formed by L. plantarum comprised of eDNA and proteins which was evidenced by the reduction in OD values and percentage in comparison to the control upon DNase I and proteinase K treatment. This indicates that the eDNA and biofilm matrix proteins are vital constituents of biofilms and may carry significant risk when coupled with antibiotic resistance., Competing Interests: None

The study aimed to analyze the effects of sub-inhibitory concentrations of gentamicin on the expressions of high level aminoglycoside resistant (HLAR) bifunctional aac(6')Ie-aph(2″)Ia, biofilm and chaperone genes in Lactobacillus plantarum. The analysis of the biofilm formation in five isolates obtained from chicken sausages indicated their role in exhibiting phenotypic resistance based on the varied MIC values despite carrying the bifunctional gene. The biofilm formation significantly increased when L. plantarum MCC 3011 was grown in sub-inhibitory concentrations of gentamicin (4 μg/ml), kanamycin (8 μg/ml) and streptomycin (2 μg/ml). Thirty day gentamicin selection increased minimum inhibitory concentration (MIC) values from 4 to 64 and 2 to 256 fold for gentamicin and kanamycin, respectively when compared to the parental cultures. Expression studies revealed that constant exposure to gentamicin had induced chaperon [groEL] and the bifunctional gene, aac(6')Ie-aph(2″)Ia upto nine fold. Induction of groEL, groES and lamC genes in gentamicin (4 μg/ml) preincubated MCC 3011 indicated their significant role in aminoglycoside mediated response. Our study indicates that constant exposure to sub inhibitory concentrations of gentamicin allows L. plantarum to adapt against higher doses of aminoglycosides. This highlights the risks and food safety issues associated with the use of aminoglycosides in livestock and consumption of farm oriented fermented food products., (Copyright © 2017 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.)