Evaluation of the interaction between polymyxin B and Pseudomonas aeruginosa biofilm and planktonic cells: reactive oxygen species induction and zeta potential

Marlucy Rodrigues Lima,Áquila Rodrigues Costa Santos,Ângelo Márcio Leite Denadai,Gabriella Freitas Ferreira,Wallace Ribeiro Nunes Neto,Joveliane De Melo Monteiro,Maria Rosa Quaresma Bomfim,Andrea De Souza Monteiro,Vera Lúcia Dos Santos,Priscila Batista Tavares,Sirlei Garcia Marques

doi:10.1186/s12866-019-1485-8

Abstract

BackgroundAlthough the most widely accepted mechanism of action for polymyxins is related to bacterial lysis via disruption, we hypothesized that this antimicrobial drug class could have other effects on Pseudomonas aeruginosa planktonic and sessile cells. Little is known regarding oxidative burst and zeta potential (ZP) data associated with the interaction between polymyxin B and P. aeruginosa cells. The present study evaluated endogenous reactive oxygen species (ROS) production and changes in the net charges of biofilm and planktonic cells in response to polymyxin B.ResultsPolymyxin B induced concentration-dependent killing at all concentrations tested in planktonic and sessile cells from P. aeruginosa strains. Sublethal concentrations of polymyxin B induced oxidative burst. ROS production was higher in resistant planktonic cells than in biofilm cells but this was not observed for susceptible cells. Moreover, no net surface charge alterations were observed in planktonic cells from a susceptible strain treated with polymyxin B, but a significant increase of ZP was noted in planktonic cells from a resistant strain.ConclusionOxidative burst generated by planktonic and sessile cells from P. aeruginosa strains against polymyxin B indicates that ROS may have an important role in the mechanism of action of this drug. ZP data revealed that electrostatic interactions of the cationic peptide with the anionic surface of the cells are strain-dependent. Therefore, we suggested that the intracellular effects of polymyxin B should be further investigated to understand polymyxin B-induced stress in P. aeruginosa.

Highlights

The most widely accepted mechanism of action for polymyxins is related to bacterial lysis via disruption, we hypothesized that this antimicrobial drug class could have other effects on Pseudomonas aeruginosa planktonic and sessile cells
To evaluate the kinetics of the action of polymyxin B against planktonic and sessile cells, time-kill curves were generated at different times and concentrations using two P. aeruginosa strains
At concentrations of 1 mg/L (2× Minimal inhibitory concentration (MIC)) and 2 mg/L (4× MIC), polymyxin B induced a concentration-dependent killing of susceptible P. aeruginosa planktonic cells, with 100% growth inhibition after 18 h of treatment at 2× MIC and after 6 h of treatment at 4× MIC (Fig. 1a)

Summary

Introduction

The most widely accepted mechanism of action for polymyxins is related to bacterial lysis via disruption, we hypothesized that this antimicrobial drug class could have other effects on Pseudomonas aeruginosa planktonic and sessile cells. Pseudomonas aeruginosa is one of the most important pathogenic bacteria species in the context of hospital infections [1]. It causes high mortality rates in immunocompromised patients, and it is currently classified as a “superbug” because of the limited effectiveness of antimicrobial drugs [2]. The most widely accepted mechanism of action for polymyxins is the interaction with lipopolysaccharide (LPS) in the outer membrane of gram-negative bacteria, disrupting cellular osmotic balance [7] we hypothesized that polymyxins could have other effects on planktonic and sessile gram-negative bacteria. Electrostatic interactions have been observed between cationic agents and Klebsiella pneumoniae, Acinetobacter baumannii, Staphylococcus aureus, and Escherichia coli [8,9,10], and it was suggested that these interactions interfere with cellular net charges and alter cell surface permeability, leading to cell death

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