Morphological alterations in sessile cells of listeria monocytogenes after treatment with cymbopogon sp. essential oils

Abstract

Listeria monocytogenes is a pathogenic bacterium capable of forming biofilms on the surfaces of equipment and utensils, contaminating food products. Essential oils have been used as new alternatives to sanitizing solutions elaboration. The aim of this study was to evaluate, by Scanning Electron Microscopy (SEM), the structural effect of Cymbopogon citratus (D.C.) Stapf. (lemongrass) and Cymbopogon nardus (L.) Rendle (citronella) essential oils, applied isolated and in combinated, against L. monocytogenes sessile cells. The effect was assessed at different stages of biofilm formation on stainless steel surface (3 and 240 hours). For biofilm formation under stainless steel coupons, Tryptic Soy Broth (TSB) was used as substrate and the incubation was performed at 37 °C under agitation at 50 rpm. Sanitizing solutions based on essential oils and a control sanitizing solution were tested at two contact durations (15 and 60 minutes). Then, stainless steel coupons were analyzed by SEM. Several structural alterations were observed in the bacterial cells after the treatment with essential oil solutions: wrinkled surface aspects, acquisition of a curved appearance, reduction of intracellular content and occurrence of long cells. In contrast,scanning electron micrographs of the sessile cells that had been treated with the control sanitizing solution showed no alteration on the bacterial surface. C. citratus and C. nardus essential oils, isolated and in combination, caused morphological alterations in L. monocytogenes sessile cells. SEM is a valid methodology to evaluate the essential oils structural action against biofilm bacterial cells.