Isolation of a Lactobacillus strain from aguamiel and preliminary characterization of its antimicrobial components

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.