Abstract

MARTINEZ-ARAMBURU, D. et al. Changes in microstructure of Salmonella Typhimurium and Listeria monocytogenes exposed to hydroxycinnamic salts. Rev. Mex. Ing. Quím [online]. 2015, vol.14, n.2, pp.347-354. ISSN 1665-2738.

Bacteria are microorganisms that contain organelles, which have sizes in the nanoscale range. Certain stress conditions may induce morphological changes in bacteria as a strategy to survive. In the present work, the effects of two antimicrobials commonly found in plants were tested to determine the ultrastructure and morphology of Salmonella Typhimurium and Listeria monocytogenes. Kinetics of survival of bacteria were monitored, and ultrastructure changes were observed using scanning and transmission electron microscopy (SEM and TEM, respectively). The results show a bacteriostatic effect on Salmonella at sodium ferulate concentrations between 0.3 and 0.6%, which also caused elongated forms of the bacteria, which were observed by scanning electronic microscopy (SEM). The Feret diameter and surface area of the bacteria were determined using image analysis, where it was shown that these dimensions increased four times on average compared with those of the control cells. These data support the idea of multicellular aggregates. In the case of Listeria monocytogenes, the elongation of the cells occurred after 24 hours of exposure to 0.6% sodium ferulate. The number of cytoplasmic inclusions and the size of vacuoles increased after the first hour of exposure to 0.8% sodium caffeate and corresponded to a bactericidal effect of this antimicrobial. The elongation of the cells that occurred in bacteriostatic concentrations reverted when the bacteria were incubated in media without me antimicrobials, and me kinetics of growth became normal, which suggests a strategy to survive under stress conditions generated by the presence of antibacterial compounds.

Keywords : ultrastructure; Salmonella Typhimurium; Listeria monocytogenes; morphological changes; phenolic acids.