INHIBITION OF Listeria monocytogenes GROWTH BY A BACTERIOCINOGENIC STRAIN OF Lactobacillus fermentum IN WHOLE MILK

GARCÍA, MARÍA JOSÉ; ASURMENDI, PAULA; PASCUAL, LILIANA; BARBERIS, LUCILA

Congreso; XI Congreso Argentino de Microbiología General; 2015

The objective of this work was to investigate the antimicrobial activity of a bacteriocinogenic strain of Lactobacillus, L. fermentumL23, on Listeria monocytogenes in whole milk. L. fermentum L23 was inoculated in 90 ml of sterilized whole milk at a finalconcentration of 5x106 UFC ml-1 and incubated for 10 h at 30°C. After this period, a suspension of L. monocytogenes LM6 insterilized whole milk was added to lactobacilli culture at a final concentration of 2x104 UFC ml-1 and re-incubated for another 14h at 30°C. Control cultures of L. fermentum and L. monocytogenes inoculated separately in sterilized whole milk were included.Samples were taken at different intervals and bacterial growth was measured by viable cell counts. Samples were seriallydiluted in peptone water and plated on MRS agar for the enumeration of L. fermentum and on Oxford agar for listerial counts.Results were expressed as log UFC ml-1. Maximum specific growth rate (µ max) and generation time (G) were calculated.Furthermore, pH values were measured using a calibrated pH meter. Results showed that L. monocytogenes cultured alone inwhole milk showed an exponential growth with a µ max of 0.25 h-1 and G value of 1.2 h. Listerial counts increased from 4.38 ±0.05 log UFC ml-1 at the beginning of the experiment to a maximum value of 8.75 ± 0.02 log UFC ml-1 reached after 21 h ofincubation at 30°C. In contrast, listerial counts in the assay with L. fermentum varied from 4.36 ± 0.05 to 4.52 ± 0.10 log UFCml-1 along the incubation time. There were no significant differences (p