Quinolones Sensitize Gram-Negative Bacteria to Antimicrobial Peptides

Abstract

The treatment of infections caused by bacteria resistant to the vast majority of antibiotics is a challenge worldwide. Antimicrobial peptides (APs) make up the front line of defense in those areas exposed to microorganisms, and there is intensive research to explore their use as new antibacterial agents. On the other hand, it is known that subinhibitory concentrations of antibiotics affect the expression of numerous bacterial traits. In this work we evaluated whether treatment of bacteria with subinhibitory concentrations of quinolones may alter the sensitivity to APs. A 1-h treatment of Klebsiella pneumoniae with 0.25؋ the MIC of ciprofloxacin rendered bacteria more sensitive to polymyxins B and E, human neutrophil defensin 1, and ␤-defensin 1. Levofloxacin and nalidixic acid at 0.25؋ the MICs also increased the sensitivity of K. pneumoniae to polymyxin B, whereas gentamicin and ceftazidime at 0.25؋ the MICs did not have such an effect. Ciprofloxacin also increased the sensitivities of K. pneumoniae ciprofloxacin-resistant strains to polymyxin B. Two other pathogens, Pseudomonas aeruginosa and Haemophilus influenzae, also became more sensitive to polymyxins B and E after treatment with 0.25؋ the MIC of ciprofloxacin. Incubation with ciprofloxacin did not alter the expression of the K. pneumoniae loci involved in resistance to APs. A 1-N-phenyl-naphthylamine assay showed that ciprofloxacin and levofloxacin increased the permeabilities of the K. pneumoniae and P. aeruginosa outer membranes, while divalent cations antagonized this action. Finally, we demonstrated that ciprofloxacin and levofloxacin increased the binding of APs to the outer membrane by using dansylated polymyxin B.

Capsule polysaccharide is a bacterial decoy for antimicrobial peptides

“…The dansylated peptide exhibits low fluorescent yield when diluted into aqueous buffer; however, the fluorescent yield increases, with the maximum fluorescence shifting to a lower wavelength, in a hydrophobic environment (Moore et al, 1986;Newton, 1955). Therefore there is a correlation between fluorescence and the amount of dansyl-polymyxin B bound (Bengoechea et al, 1998;Campos et al, 2006;Moore et al, 1986). The results shown in Fig.…”

“…Secondly, we evaluated the binding of dansyl-polymyxin B to CPSs. This compound has been extensively used to study the binding of APs to polysaccharides, proteins and intact bacteria (Bengoechea et al, 1998;Campos et al, 2006;Moore et al, 1986). The dansylated peptide exhibits low fluorescent yield when diluted into aqueous buffer; however, the fluorescent yield increases, with the maximum fluorescence shifting to a lower wavelength, in a hydrophobic environment (Moore et al, 1986;Newton, 1955).…”

Efficacy of Cryptdin-2 as an Adjunct to Antibiotics from Various Generations Against Salmonella

“…It could be attributed to the fact that besides acting directly on bacterial cell, quinolones have also been reported to sensitize Gram-negative bacteria to cationic AMPs by displacement of divalent cations from their LPSbinding sites thereby increases the binding of AMPs to outer membrane [25]. These two mechanisms might have acted mutually leading to make this very combination to be the most effective amongst all the combinations tested.…”

Characterization and Biological Role of the O-Polysaccharide Gene Cluster ofYersinia enterocoliticaSerotype O:9

“…The results were expressed as survival percentages, taking the colony counts of bacteria not exposed to antibacterial agents as 100%. The 50% inhibitory concentration of antimicrobial peptides (IC 50 ) was defined as the concentrations showing a 50% reduction in the colony count compared with bacteria not exposed to the antibacterial agent (21). All experiments were done in duplicate and on four independent occasions.…”