Presence of extracellular DNA & protein in biofilm formation by gentamicin-resistant Lactobacillus plantarum

Abstract

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.

Keywords: Antibiotic resistance; biofilms; extracellular DNA; lactic acid bacteria; nutrient limitation; persister cells.

Figure

Fluorescent images of Lactobacillus rhamnosus GG (control) and Lactobacillus plantarum MCC3011 (Test) (A) 48 h mature biofilms in phosphate buffered saline, (B) DNase I-treated and incubated for one hour, (C) proteinase K-treated and incubated for one hour. The cells viewed under fluorescent filters (3) with ×100 magnification and scale (2 μ).