Antagonistic Activities of Cell-Free Supernatants of Lactobacilli Against Extended-Spectrum β-Lactamase Producing Klebsiella pneumoniae and Pseudomonas aeruginosa

This study aimed to describe the inhibitory activity of cell-free supernatants (CFS) of lactobacilli against extended-spectrum β-lactamase (ESBL)-producing ( ) and . Pathogenic clinical strains of and were isolated from urine samples and selected for investigation. Anti-bacterial activities of the CFS of lactobacilli were assessed by agar well diffusion, MTT assay, as well as time-kill tests. In addition, the antibiofilm characteristics were analyzed by the microplate method against fresh and 24 h-old biofilms. The ability of CFS to interfere with bacterial invasion was analyzed by flow cytometry. Although all tested strains were ESBL producers and showed a multidrug-resistant phenotype, the CFS displayed a high anti-ESBL activity with inhibition zone diameters greater than 13 mm in the agar well diffusion assays against both pathogens. The growth kinetics of and were dramatically decreased in the presence of the CFS. The CFS not only inhibited the biofilm formation by these pathogens but also was able to remove the 24-h formed biofilms. The invasion abilities of FITC-labelled decreased from 30.3%±7 to 15.4%±5 and invasion of FITC-labelled was reduced from 36.9%±7 to 25.2%±5. CFS of lactobacilli exhibit anti-ESBL activities, which suggests its potential application for controlling or preventing colonization of infections caused by ESBL-producing bacteria.