This work presents a preliminary study on an experimental analysis of the lactobacillus bacterial growth in
liquid medium with and without the presence of silver nanoparticles. The study aims to quantify the
bactericidal effect of nanoparticles. Quantification of bacterial growth at different times was analyzed by
spectroscopy UV/visible and laser reflectometry near the critical angle. From these two techniques the best
results were obtained by spectroscopy, showing that as the concentration of silver nanoparticles increases, it
inhibits the growth of bacteria, it only grows 63% of the population. Regarding Laser Reflectometry, the
variation of reflectance near the critical angle is measured in real time. The observed results at short times are
reasonable, since they indicate a gradual growth of the bacteria and the stabilization stage of the population.
But at long time, the observed results show abrupt changes caused by temperature effects. The bacteria were
isolated from samples taken from commercial yougurth, and cultured in MRS broth at pH 6.5, and controlled
with citric acid and constant temperature of 32 °C. Separately, silver nanoparticles were synthesized at 3 °C
from aqueous solutions of 1.0 mM silver nitrate and chemically reduced with sodium borohydride to 2.0 mM,
with magnetic stirring.