Identificación y cuantificación de compuestos antimicrobianos producidos por bacterias ácido lácticas aisladas de alimentos artesanales mexicanos

The increasing tendencies of consumption of healthy foods are producing a lot of research in the field of food sciences with a focus on new biopreservation technologies. Some lactic acid bacteria (LAB) are capable of producing antimicrobial substances, so they are being used empirically in the artisanal food preservation done in Mexico. The study of foodassociated LAB in artisanal Mexican products could lead us to understand the antimicrobial potential and its appropriate use to enhance food safety. The aim of this study was to identify and quantify antimicrobial substances produced by indigenous LAB isolated from traditional Mexican foods, in order to use in food biopreservation. We worked with four LAB strains isolated from unlabeled artisan Mexican products: Leuconostoc (Lc.) mesenteroides CH210 (chorizo), Lc. mesenteroides PT8 (pulque), Lactobacillus (Lb.) plantarum CC10 (mother of vinegar) and Enterococcus (E.) faecium QPI1 (panela cheese). These strains showed inhibitory activity against pathogenic bacteria from food origin. The extract produced by Le. mesenteroides CH210 and PT8 reduced the UFC/mL of enteropatogenic E. coli more than 5 log and Lb. plantarum CC10 showed high capability to inhibit the growth of S. aureus and V. cholerae. E. faecium QPI1 had high antimicrobial activity against S. aureus and L. monocytogenes. The antimicrobial activity of Le. mesenteroides CH210, Le. mesenteroides PT8 and Lb. plantarum CC10 was attributed to acetic and lactic acids produced. Only E. faecium QPI1 showed capability to produce bacteriocins with a wide spectrum of antimicrobial activity against L. monocytogenes. Using the fermentation broth produced by E. faecium QPI1 and after ammonium sulfate precipitation (EPS), three fractions with antimicrobial activity were obtained. The purification strategy included a step of adsorption-desorption in cells, solid phase extraction, cationic interchange chromatography, and reverse phase chromatography. The IC45 fraction showed antimicrobial activity by itself. Another two fractions SP40 and FR75, that showed the typical mechanism of action of bacteriocins class IIb, with synergistic activity that reduce when each fraction were tested separately. The molecular weight of active peptides calculated by electrophoretic mobility were ranged between 2.0 to 3.0 kDa. The molecular techniques allowed us to find the genes that codify the enterocins A, L50A and L50B into the genetic material of E. faecium QPI1 strains. The organic acids produced by LAB isolated from artisanal Mexican foods Le. mesenteroides CH210, PT8 and Lb. plantarum CC, showed an important inhibitory activity against pathogenic strains form food origin. The bacteriocins produced by E. faecium QPI1 showed wide antimicrobial activity in different model systems, representing an alternative with good potential in food preservation. Antimicrobial effect was shown both by using the producing LAB strains or using the free cells extract, diversifying the type of use in food products.