ANTAGONIC EFFECT OF LACTIC ACID BACTERIA ISOLATED FROM MINIMALLY PROCESSED FRUITS AGAINST Salmonella typhimurim

LUCIANA DEL VALLE RIVERO, MARÍA JOSÉ RODRÍGUEZ VAQUERO, FABIANA MARÍA SAGUIR.

Tucumán

Congreso; XII CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL (SAMIGE); 2017

SAMIGE

Demand for fresh fruits and minimally processed products (MP) is constantly growing among the world's population. The use of bio-preservation is a promising technique to ensure the microbial safety of MP fruits. Lactic bacteria (LAB) could prevent the development of pathogenic microorganisms present in these foods. However, information about this is scare yet. LAB strains with antimicrobial activity against various pathogens including Salmonella typhimurim in culture medium (BHI) isolated from fruits were selected in a previous study. The aim of this study was to determine the antimicrobial activity of three selected strains of LAB against S. typhimurium when cultivated in a commercial fruit juice stored at 30 ºC. Flasks containing 30 mL of commercial juice were co-inoculated with S. typhimurium (3% v/v) previously grown in BHI medium and with each LAB strain (Lactobacillus plantarum N4 from orange and Lactobacillus sp. FEV3 or JES1 from salad fruits) grown in MRS medium, pH 6.5 and incubated at 30°C for 72 h. Before inoculation fruit juice was clarified by centrifugation (7000 rmp, 15 min) and separated in two group: without or with adjustment of pH (3.43 and 6.5 respectively). At the same time uninoculated juice was tested at both pH. Bacterial growth was determined by measuring cfu/mL in BHI medium (S. tiphymurium) and MRS ( LAB strains). The initial concentration of pathogen and LAB strains was in order of 106 cfu/ mL for all treatments (single and co-inoculated cultures). In juice, pH 3.43 no growth of S. typhimurium was observed regardless LAB presence. At pH 6.5, S. typhimurium alone grew 2.49 log units at 24 h, then decreased of about 4 units until 72 h inoculation. The S. typhimurim growth was totally and almost 50% inhibited in co-cultures with FEV3 and N4 strain while no effect was observed for JES1 at 24 h. Moreover, no growth was detected at 48 h for N4 and FEV3 while this fact was observed later for strain JES1 (72 h). In this condition, the initial pH of 6.5 decreased to final values of 4.95 (in 24 h) and ̴ 3.40 (in 48 h) in presence of pathogen alone and co-cultures with each LAB respectively. Thus, result demonstrated that S. thyphimurim was totally inactivated in commercial fruit juice at 24 h at 30 ºC due to acid pH, as it rapidly grew in juice adjusted to pH 6.5. In this condition, the LAB strains tested significantly reduced counts of S. typhimurium until levels below detection limit. However, the effectiveness of their effect antagonist significantly varied among them, being FEV3 the most effective. This difference appears have no relation with the fruit from which was isolated as well as with its acidification rate which was similar respect to other test bacteria