Evaluación de la actividad probiótica de bacterias ácido lácticas aisladas en muestras de leche cruda de la parroquia San Luis-Riobamba

Abstract

The main objective of this research study was to determine the probiotic activity of lactic acid bacteria isolated in raw milk samples obtained in the San Luis parish of the city of Riobamba. The samples were collected through a convenience sampling method from milk producers, 3 samples were collected and each of these samples was a mixture of milk from different producers. Once the samples were collected, dilutions were made up to 10-7 and the last two dilutions were sown on M17 and MRS agar, respectively. Once the growth was evident, successive sowings were made in order to isolate colonies of both lactobacilli and lactococci. The bacteria were analyzed employing biochemical and characterization tests to select the strains that complied with phenotypic characteristics typical of lactic acid bacteria (gram-positive cocci and bacilli, resistant to environmental changes such as temperature, salinity, and pH). As a result, when testing probiotic capacity, 8 of the 35 isolated strains had useful characteristics for their implementation as probiotic agents, such as survival to gastric juices and bile salts, Gamma hemolysis, and resistance to antibiotics. Of these 8 strains of lactic acid bacteria, 6 were subjected to a PCR test for identification, resulting in 5 colonies identified as Lactococcus lactis; 1 colony as Lactococcus cremoris. As a last test, the antagonistic effect of the identified strains was evaluated against Staphylococcus aureus; Escherichia coli; Pseudomona aeruginosa; Citrobacter freundii, and Klebsiella pneumoniae. It was concluded that none of the six isolated colonies presented antagonism against the five pathogens analyzed. It is recommended to encourage the continuity of the research by carrying out subsequent studies of further in vitro evaluation, as these bacteria are candidates for probiotics.