Peptoid Efficacy against Polymicrobial Biofilms Determined by Using Propidium Monoazide-Modified Quantitative PCR

Abstract

Biofilms containing Candida albicans are responsible for a wide variety of clinical infections. The protective effects of the biofilm matrix, the low metabolic activity of microorganisms within a biofilm and their high mutation rate, significantly enhance the resistance of biofilms to conventional antimicrobial treatments. Peptoids are peptide-mimics that share many features of host defence antimicrobial peptides but have increased resistance to proteases and therefore have better stability in vivo. The activity of a library of peptoids was tested against monospecies and polymicrobial bacterial/fungal biofilms. Selected peptoids showed significant bactericidal and fungicidal activity against the polymicrobial biofilms. This coupled with low cytotoxicity suggests that peptoids could offer a new option for the treatment of clinically relevant polymicrobial infections.

Keywords: antibacterial; antibiotics; antiproliferation; cross kingdom; peptoid; quantification.

Figure 1

Representative structures of α‐peptide and α‐peptoid.

Figure 2

Efficacy of a family of 18 peptoids against A) C. albicans, B) S. aureus, and C) E. coli monospecies biofilms determined by a crystal violet assay. Biofilms were treated with peptoid (100 μm) or untreated. The results (mean±SD, n=3) are plotted as percent biomass relative to untreated cells. Statistical analysis was determined by one‐way ANOVA followed by Tukey's post hoc correction for multiple comparisons (ns: p>0.05, * p<0.05, ** p< 0.01, *** p<0.001, **** p<0.0001).

Figure 3

PMA‐qPCR quantification of cell number following peptoid treatment of monospecies biofilms of A) C. albicans, B) S. aureus and C) E. coli treated with 100 μm 5, 7 and 17 (**** p<0.0001; one‐way ANOVA followed by Tukey's post hoc correction for multiple comparisons, mean±SD, n=3).

Figure 4

PMA‐qPCR quantification of cell number following treatment by 100 μm 5, 7 and 17 of polymicrobial biofilms of C. albicans with either S. aureus or E. coli: A) C. albicans and B) S. aureus within the same biofilm, and C) C. albicans and D) E. coli within the same biofilm (one‐way ANOVA followed by Tukey's post hoc correction for multiple comparisons, ** p<0.01, **** p<0.0001; mean±SD, n=3).

Figure 5

Propensity for 5, 7 and 17 to permeabilise the microbial membranes of A) C. albicans, B) E. coli and C) S. aureus, as determined by a SYTOX Green assay. The data were compared with untreated cells, and the results (mean±SD, n=3) were analysed by ANOVA followed by Tukey's post hoc correction for multiple comparisons (**** p<0.0001). Cells permeabilised by heat treatment were used as positive controls.