Abstract
The aim of the study was to characterize the antimicrobial components of Lactobacillus paracasei KSI. In the study, a L. paracasei KSI strain was isolated and identified from aguamiel using a 16S rRNA, hsp, recA and rpoBgenes sequencing. The antimicrobial capacity of the L. paracasei strain KSI was determined by agar double layer diffusion technique, while the antagonistic activity of the cell-free extract (E-KSI) was evaluated by agar well diffusion method against different bacterial strains; it demonstrated a wide spectrum of inhibition. Likewise, E-KSI showed stability at different temperatures and digestive enzymes; its activity was lost at pH>5. Subsequently, E-KSI was concentrated (10x) by evaporation increasing its antagonistic effect. Antagonism tests by thin-layer chromatography (TLC)–bioautography of the E-KSI 10x showed the presence of more than one active substances different from lactic acid, possibly of the bacteriocin type. Some of these substances were recovered by extractions with ethyl ether, ethyl acetate and n-butanol respectively. Finally, we evaluated them using antagonism tests by minimum inhibitory concentration (MIC) and microdilution. L. paracaseistrain KSI generates substances with antibacterial activity having a wide spectrum of inhibition; it is a promising alternative to future biotechnological applications. The strain of L. paracasei KSI as well as the antimicrobial components that it generates has important antagonistic properties, making them an interesting biotechnological alternative to be used as probiotic or a safe functional food. Key words: Lactobacillus, antimicrobials, probiotics, biotechnology, food safety.
Highlights
The group of lactic acid bacteria (BAL) are microorganisms Gram-positive bacilli, do not form spores, usually immobile, anaerobic, microaerophilic or air tolerant, catalase, oxidase and benzidine negative, withoutAfr
The antimicrobial capacity of the L. paracasei strain KSI was determined by agar double layer diffusion technique, while the antagonistic activity of the cell-free extract (E-KSI) was evaluated by agar well diffusion method against different bacterial strains; it demonstrated a wide spectrum of inhibition
Antimicrobial capacity starts with the production of lactic acid that participates in the progressive decrease of the pH (Erdogrul and Erbilir, 2006); during the fermentation process, the BAL can produce other substances capable of inhibiting the growth of competing bacteria, among which low molecular weight molecules have been found, the most common being: acetic acid, propionic acid, hydrogen peroxide, carbon dioxide, diacetyl, acetaldehyde, ethanol (Piard and Desmazeaud, 1991; Lahtinen et al, 2011); peptides with antimicrobial properties called "bacteriocins" (Chen and Hoover, 2003; Dobson et al, 2012; Shaikh et al, 2012; Ribeiro et al, 2013; Zendo, 2013; Drissi et al, 2014; Yang et al, 2014) biosurfactant compounds (Rodrigues et al, 2006; Saharan et al, 2011; Sharma and Saharan, 2014) and other compounds not yet characterized
Summary
The group of lactic acid bacteria (BAL) are microorganisms Gram-positive bacilli, do not form spores, usually immobile, anaerobic, microaerophilic or air tolerant, catalase, oxidase and benzidine negative, withoutAfr. Cytochromes, nor reduce nitrate to nitrite and produce lactic acid as the only or main product of carbohydrate fermentation (Carr et al, 2002). This group of microorganisms is widely distributed in nature and has been isolated from different foods (Azadnia et al, 2011) (milk and dairy products, wines, fruits, vegetables, fishery products, among others), soil, digestive tract, mouth and vagina of mammalian between other sources (Claesson et al, 2007). The BAL have the category of the generally recognized as safe (GRAS) granted by the food and drug administration (FDA) of the USA (Zacharof and Lovitt, 2012), and due that the substances that produce during their metabolic processes present activity against various pathogens included bacteria, parasites, fungi and yeasts (Papagianni, 2003; Joerger, 2003; Motta and Brandelli, 2008)
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