Introduction

Klebsiella pneumoniae (K. pneumoniae) is an important opportunistic pathogen in humans and animals that causes pneumonia and urinary tract infections and is capable of biofilm formation. Antimicrobial Peptides (AMPs) are small cationic amphipatic peptides and considered to be a promising alternative for the development of new therapeutic options.The aim of this study is to investigate the effect of different AMPs on the biofilm formation of K. pneumoniae.

Materials & Methods

First, the ability of biofilm formation in vitro of various human and veterinary strains of K. pneumoniae was investigated using a crystal violet assay. The formed biofilms and the kinetics of biofilm formation were visualized using scanning electron microscopy. In the next step, the effect of eight AMPs on biofilm formation of three different strains of K. pneumoniae was analyzed using a serial dilution test followed by a crystal violet assay.

The viability of the formed biofilms was investigated using a resazurin assay. Further the effect of AMPs on mature biofilms was analyzed using the crystal violet assay and scanning electron microscopy.

Results

Biofilm formation of three K. pneumoniae strains was confirmed in vitro in accordance with a calculated cut-off value, which seperates biofilm formers from non-biofilm formers.

Scanning electron micrographs showed that K. pneumoniae is forming a pronounced 3D structure of bacteria adhering to the surface in contrast to the negative control Muribacter muris.

The AMPs human β-defensin 3 and LL-37 showed the greatest effect with a reduction of biofilm formation by more than 75% while planctonic growth was not affected under these conditions. A reduction of biofilm formation by more than 50% for only one of the three tested strains was demonstrated for Onc72 and Onc112. No reduction in biofilm mass was shown for Api137.

Summary

Distinct AMPs such as human β-defensin 3 and LL-37 reduce biofilm formation of K. pneumoniae in vitro, while other AMPs with a described bactericidal effect against planctonic klebsiellae, such as Api137, do not suppress biofilm formation under the chosen experimental conditions.