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The Application of Open Searching-based Approaches for the Identification of Acinetobacter baumannii O-linked Glycopeptides

The Application of Open Searching-based Approaches for the Identification of Acinetobacter baumannii O-linked Glycopeptides

Published on: November 2, 2021

Sub-MIC effects of a proline-rich antibacterial peptide on clinical isolates of Acinetobacter baumannii

Lucilla Dolzani¹, Annalisa Milan¹, Marco Scocchi¹

¹Department of Life Sciences, University of Trieste, Trieste, Italy.

Journal of Medical Microbiology

|June 20, 2019

Abstract

Introduction:

Acinetobacter baumannii is one of the most important nosocomial pathogens, mainly due to its ability to accumulate antibiotic-resistances and to persist in the hospital environment - characteristics related to biofilm production. It is well-known that A. baumannii is inhibited by the proline-rich peptide Bac7(1-35), but its putative effects at sub-MICs were never considered.

Aims:

We examined the sub-MIC effect of Bac7(1-35) on the growth rate, resistance induction and some A. baumannii features linked to virulence.

Methodology:

Growth kinetics in the presence of sub-MICs of Bac7(1-35) were evaluated spectrophotometrically. Peptide uptake was quantified by cytometric analysis. The ability of Bac7(1-35) to interfere with biofilm production was investigated by the crystal violet method and confocal microscopy. Bacterial motility was observed at the interphase between a layer of a semi-solid medium and the polystyrene bottom of a Petri dish. The induction of resistance was evaluated after serial passages with sub-MICs of the peptide.

Results:

Although the MIC of Bac7(1-35) was between 2-4 µM for all tested strains, its effect on the growth rate at sub-MICs was strain-dependent and correlated with the amount of peptide internalized by each strain. Sub-MICs of Bac7(1-35) induced a strongly strain-dependent effect on biofilm formation and reduced motility in almost all strains, but interestingly the peptide did not induce resistance.

Conclusion:

Bac7(1-35) is internalized into A. baumannii and is able to inhibit biofilm formation and bacterial motility, without inducing resistance. This study stresses the importance of considering possible effects that antimicrobials could have at sub-MICs, mimicking a common condition during antibiotic treatment.

Insights

The proline-rich peptide Bac7(1-35) inhibits Acinetobacter baumannii biofilm formation and motility at sub-inhibitory concentrations. Importantly, this peptide does not induce antibiotic resistance in the pathogen.

Area of Science:

Microbiology
Bacterial Pathogenesis
Antimicrobial Peptides

Background:

Acinetobacter baumannii is a significant nosocomial pathogen known for antibiotic resistance and persistence.
Biofilm production is a key characteristic contributing to A. baumannii's virulence and environmental survival.
The proline-rich peptide Bac7(1-35) is known to inhibit A. baumannii, but its effects at sub-inhibitory concentrations (sub-MICs) were unexplored.

Purpose of the Study:

To investigate the effects of sub-MICs of Bac7(1-35) on A. baumannii growth rate.
To assess Bac7(1-35) influence on virulence-linked traits such as biofilm formation and motility.
To determine if sub-MIC Bac7(1-35) exposure induces antibiotic resistance in A. baumannii.

Main Methods:

Growth kinetics were measured spectrophotometrically.
Peptide internalization was quantified using flow cytometry.
Biofilm formation was assessed via crystal violet staining and confocal microscopy.
Bacterial motility was observed on semi-solid interfaces.
Resistance induction was evaluated through serial sub-MIC passages.

Main Results:

Sub-MIC Bac7(1-35) exhibited strain-dependent effects on growth rate, correlating with peptide uptake.
Bac7(1-35) significantly inhibited biofilm formation and reduced motility in most tested A. baumannii strains.
No antibiotic resistance was induced by sub-MIC Bac7(1-35) exposure, even after serial passages.

Conclusions:

Bac7(1-35) is internalized by A. baumannii and effectively inhibits biofilm formation and motility.
The study highlights the significance of evaluating antimicrobial effects at sub-MICs, relevant to clinical treatment scenarios.
Bac7(1-35) presents a potential therapeutic avenue against A. baumannii without the risk of inducing resistance.

Read full analysis

Keywords:

A. baumannii Bac7 antimicrobial peptides biofilm motility proline-rich

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