Isolation and Identification of Probiotics with Antagonistic Effect on Vancomycin Resistant Enterococci

Vancomycin-resistant Enterococci are considered as a serious problem owing to limited selective therapies necessitating alternative antibiotic therapies. The aim of this study was to isolate and identify effective probiotics against vancomycin-resistant Enterococci strains and their biofilms.

In this experimental study, Enterococci samples were isolated from several hospitals in Isfahan and their vancomycin-resistant strains were selected by antibiotic susceptibility testing. The antimicrobial effect of various probiotic bacteria against them was investigated. After selecting the most effective probiotics, various tests including mortality time and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were performed. The inhibitory mechanism of these probiotics and the amount of lactic acid production as the main inhibitory mechanism were studied using high performance chromatography.

On total, 350 Enterococci samples were isolated, 46 of which were vancomycin resistant in which linezolid was among the few effective antibiotic. Two probiotic bacteria, Pediococcus acidilactici and Lactobacillus plantarum, were isolated which were effective against all vancomycin-resistant Enterococci and their biofilms. The lethal time of these two probiotics was 12 hours and the MIC and MBC were at concentrations of 0.5 µg/ml and 1 µg/ml respectively. Various tests on these two probiotics also showed no pathogenicity and no antibiotic resistance. The amount of lactic acid in Lactobacillus plantarum and Pediococcus acidilactici were 2.5 and 1.1 g per 100 ml respectively.

The optimal antimicrobial and antibiofilm properties of these two probiotics alongside producing high levels of lactic acid against all vancomycin resistant strains demonstrate their desirable and potential properties.