A new class of antimicrobial molecules derived from kefir, effective against Pseudomonas aeruginosa and methicillin resistant Staphylococcus aureus (MRSA) strains

Vaniky Duarte Marques,Tiago Venâncio,Soraia Attie Calil Jorge,Marta De Oliveira Domingos,Roxane Maria Fontes Piazza,Marcia Regina Franzolin,Herbert Guimarães De Sousa Silva,Lucia Mendonça-Previato,Irys Viana Neves,Daniella Dos Santos Courrol,Hugo Vigerelli,Daniel Carvalho Pimenta,Sabri Saeed Sanabani,José Osvaldo Previato

doi:10.1038/s41598-020-73651-7

Abstract

Many studies have linked the antimicrobial properties of kefir with the presence of bacteriocins and organic acids. In the present work, results obtained from bacteriostatic and bactericidal studies, and from RP-HPLC, Mass Spectrometry and proton NMR analysis, show that a sample of milk kefir grains is able to produce an antimicrobial fraction, denoted FK-1000, composed of sugars and amino acids, predominantly polymers of alanine, doublets of tyrosine and phenylalanine. Since this fraction is a lyophilized product whose molecular profile is different from bacteriocins and simple carboxylic acids, its antimicrobial effect cannot be attributed to these molecules, or to alcohols or hydrogen peroxide. The fraction is bactericidal against weak-acid-resistant MRSA and weak-acid resistant P. aeruginosa at pH 5, and is bacteriostatic against both pathogens at pH 7. In combination formulation, the FK-1000 fraction is able to increase fivefold the effect of streptomycin against P. aeruginosa and it is not toxic to human epithelial cells at antimicrobial concentrations. 16 S rRNA microbiota analysis of antimicrobial-producing and non-producing kefir grains demonstrated that they are distinct. In summary, the results indicate that milk kefir grains can produce different classes of molecules with potent antibiotic activity against resistant bacteria.

Highlights

Traditional Kefir is a fermented milk beverage that has been consumed as an aliment for more than 2000 years[1]
The present work has demonstrated that the antibacterial activity of kefir against MRSA and P. aeruginosa strains is strongly associated with the source and the composition of the kefir grains in terms of the microorganisms present, since the antimicrobial-producing and the antimicrobial-nonproducing grains have distinctly different microbiota
Despite the presence of 19 different bacterial families in the antimicrobial nonfunctional grains, 94.43% of all bacterial species encountered belonged to the Lactobacilaceae family, which according to the scientific literature has a high number of bacterial species able to produce antimicrobial peptides such as bacteriocins[7,14,27]

Summary

Introduction

Traditional Kefir is a fermented milk beverage that has been consumed as an aliment for more than 2000 years[1]. The microbiological composition of the grains is the subject of much controversy, the composition differing according to the source, which directly influences the type of the metabolites present in k efir[11]. In recent times, these variations are even greater since fruit juices and molasses have been used as substrates to prepare kefir[12,13]. The results obtained from those studies demonstrated that several isolates were able to produce bacteriocins, which are antimicrobial molecules genetically coded, synthesized through the ribosomal machinery and classified according to their size, structure and resistance to heat[7,15,16]. The results obtained in this study indicate that some batches of kefir grains are able to produce such molecules

Methods

Results

Conclusion